We empirically assess the impact of the EU roaming regulation on mobile operators’ average revenues per user (ARPU) and retail prices. Using a differences-in-difference approach, hedonic price regressions and detailed operator and plan-level data we find that the regulation decreased mobile operator’s revenues per user, while it had no impact on tariffs during the latest phase of the regulation.
{"title":"Impact of Roaming Regulation on Revenues and Prices of Mobile Operators in the EU","authors":"L. Grzybowski, Ángela Muñoz-Acevedo","doi":"10.2139/ssrn.3904537","DOIUrl":"https://doi.org/10.2139/ssrn.3904537","url":null,"abstract":"We empirically assess the impact of the EU roaming regulation on mobile operators’ average revenues per user (ARPU) and retail prices. Using a differences-in-difference approach, hedonic price regressions and detailed operator and plan-level data we find that the regulation decreased mobile operator’s revenues per user, while it had no impact on tariffs during the latest phase of the regulation.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115137202","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We develop a model of strategic geoblocking, where two competing multi-channel retailers, located in different countries, can decide to block access to their online store from foreign consumers. We characterize the equilibrium when firms decide unilaterally whether to introduce geoblocking restrictions. We show that geoblocking results in a “puppy dog” strategy (Fudenberg and Tirole, 1984) for firms, which allows them to soften competition, but that it comes at the cost of lower demand. In the short term, a ban on geoblocking leads to lower prices, both offline and online. However, in the longer term, when firms can invest in increasing the demand from online shoppers, the ban may have adverse effects on investment and social welfare. We extend our analysis to account for price discrimination and investigate the role of shipping costs.
我们开发了一种战略地理封锁模型，即位于不同国家的两家竞争多渠道零售商可以决定阻止外国消费者进入他们的在线商店。我们描述了当企业单方面决定是否引入地理封锁限制时的均衡。我们表明，地理封锁导致了企业的“小狗”战略(Fudenberg and Tirole, 1984)，这使它们能够软化竞争，但其代价是需求降低。在短期内，禁止地理屏蔽会降低线下和线上的价格。然而，从长远来看，当企业可以投资增加网上购物者的需求时，这项禁令可能会对投资和社会福利产生不利影响。我们将分析扩展到考虑价格歧视，并调查运输成本的作用。
{"title":"Selling Cross-Border in Online Markets: The Impact of the Ban on Geoblocking Strategies","authors":"M. Bourreau, Fabio M. Manenti","doi":"10.2139/ssrn.3731987","DOIUrl":"https://doi.org/10.2139/ssrn.3731987","url":null,"abstract":"We develop a model of strategic geoblocking, where two competing multi-channel retailers, located in different countries, can decide to block access to their online store from foreign consumers. We characterize the equilibrium when firms decide unilaterally whether to introduce geoblocking restrictions. We show that geoblocking results in a “puppy dog” strategy (Fudenberg and Tirole, 1984) for firms, which allows them to soften competition, but that it comes at the cost of lower demand. In the short term, a ban on geoblocking leads to lower prices, both offline and online. However, in the longer term, when firms can invest in increasing the demand from online shoppers, the ban may have adverse effects on investment and social welfare. We extend our analysis to account for price discrimination and investigate the role of shipping costs.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131997347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The long-term trend toward more work from home due to digitization has found a strong new driver, the Covid-19 pandemic. The profound change in urban mobility patterns supports the often-held view that reducing the number of commuting trips can lower carbon emissions to a certain degree. We investigate this optimistic view from a long-run perspective in a monocentric urban model with household-level vehicle choice based on fuel efficiency. In the medium run, fewer trips lead to the choice of less fuel-efficient vehicles. In addition, with lower annual driving costs to the city center, households change their location in the long run toward longer commuting trips, but cheaper housing, implying an adjustment in the real-estate market. These changes in vehicle choice and the urban form largely eliminate the initial environmental benefits. Binding fuel economy standards completely prevent the medium-run drop in fuel efficiency, but slightly exacerbate the long-term increase in commuting trip length.
{"title":"Does Telecommuting Reduce Commuting Emissions?","authors":"Waldemar Marz, Suphi Şen","doi":"10.2139/ssrn.3945279","DOIUrl":"https://doi.org/10.2139/ssrn.3945279","url":null,"abstract":"The long-term trend toward more work from home due to digitization has found a strong new driver, the Covid-19 pandemic. The profound change in urban mobility patterns supports the often-held view that reducing the number of commuting trips can lower carbon emissions to a certain degree. We investigate this optimistic view from a long-run perspective in a monocentric urban model with household-level vehicle choice based on fuel efficiency. In the medium run, fewer trips lead to the choice of less fuel-efficient vehicles. In addition, with lower annual driving costs to the city center, households change their location in the long run toward longer commuting trips, but cheaper housing, implying an adjustment in the real-estate market. These changes in vehicle choice and the urban form largely eliminate the initial environmental benefits. Binding fuel economy standards completely prevent the medium-run drop in fuel efficiency, but slightly exacerbate the long-term increase in commuting trip length.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123204438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The German DEAL agreements between German universities and research institutions on the one side and Springer Nature and Wiley on the other side facilitate easy open access publishing for researchers located in Germany. We use a dataset of all publications in chemistry from 2016 to 2020 and apply a difference-in-differences approach to estimate the impact on eligible scientists’ choice of publication outlet. We find that even in the short period following the conclusion of these DEAL agreements, publication patterns in the field of chemistry have changed, as eligible researchers have increased their publications in Wiley and Springer Nature journals at the cost of other journals. From that two related competition concerns emerge: First, academic libraries may be, at least in the long run, left with fewer funds and incentives to subscribe to non-DEAL journals published by smaller publishers or to fund open access publications in these journals. Secondly, eligible authors may prefer to publish in journals included in the DEAL agreements, thereby giving DEAL journals a competitive advantage over non-DEAL journals in attracting good papers. Given the two-sided market nature of the academic journal market, these effects may both further spur the concentration process in this market.
{"title":"The Impact of the German 'DEAL' on Competition in the Academic Publishing Market","authors":"Justus Haucap, Nima Moshgbar, W. Schmal","doi":"10.2139/ssrn.3815451","DOIUrl":"https://doi.org/10.2139/ssrn.3815451","url":null,"abstract":"The German DEAL agreements between German universities and research institutions on the one side and Springer Nature and Wiley on the other side facilitate easy open access publishing for researchers located in Germany. We use a dataset of all publications in chemistry from 2016 to 2020 and apply a difference-in-differences approach to estimate the impact on eligible scientists’ choice of publication outlet. We find that even in the short period following the conclusion of these DEAL agreements, publication patterns in the field of chemistry have changed, as eligible researchers have increased their publications in Wiley and Springer Nature journals at the cost of other journals. From that two related competition concerns emerge: First, academic libraries may be, at least in the long run, left with fewer funds and incentives to subscribe to non-DEAL journals published by smaller publishers or to fund open access publications in these journals. Secondly, eligible authors may prefer to publish in journals included in the DEAL agreements, thereby giving DEAL journals a competitive advantage over non-DEAL journals in attracting good papers. Given the two-sided market nature of the academic journal market, these effects may both further spur the concentration process in this market.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126865132","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In a recent paper Juodis and Reese (2021) (JR) show that the application of the CD test proposed by Pesaran (2004) to residuals from panels with latent factors results in over-rejection and propose a randomized test statistic to correct for over-rejection, and add a screening component to achieve power. This paper considers the same problem but from a different perspective and shows that the standard CD test remains valid if the latent factors are weak, and proposes a simple bias-corrected CD test, labelled CD*, which is shown to be asymptotically normal, irrespective of whether the latent factors are weak or strong. This result is shown to hold for pure latent factor models as well as for panel regressions with latent factors. Small sample properties of the CD* test are investigated by Monte Carlo experiments and are shown to have the correct size and satisfactory power for both Gaussian and non-Gaussian errors. In contrast, it is found that JR's test tends to over-reject in the case of panels with non-Gaussian errors, and have low power against spatial network alternatives. The use of the CD* test is illustrated with two empirical applications from the literature.
{"title":"A Bias-Corrected CD Test for Error Cross-Sectional Dependence in Panel Data Models with Latent Factors","authors":"M. Pesaran, Yimeng Xie","doi":"10.2139/ssrn.3904536","DOIUrl":"https://doi.org/10.2139/ssrn.3904536","url":null,"abstract":"In a recent paper Juodis and Reese (2021) (JR) show that the application of the CD test proposed by Pesaran (2004) to residuals from panels with latent factors results in over-rejection and propose a randomized test statistic to correct for over-rejection, and add a screening component to achieve power. This paper considers the same problem but from a different perspective and shows that the standard CD test remains valid if the latent factors are weak, and proposes a simple bias-corrected CD test, labelled CD*, which is shown to be asymptotically normal, irrespective of whether the latent factors are weak or strong. This result is shown to hold for pure latent factor models as well as for panel regressions with latent factors. Small sample properties of the CD* test are investigated by Monte Carlo experiments and are shown to have the correct size and satisfactory power for both Gaussian and non-Gaussian errors. In contrast, it is found that JR's test tends to over-reject in the case of panels with non-Gaussian errors, and have low power against spatial network alternatives. The use of the CD* test is illustrated with two empirical applications from the literature.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128112073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tracking is widespread in U.S. education. In post-secondary education alone, at least 71% of colleges use a test to track students. However, there are concerns that the most frequently used college placement exams lack validity and reliability, and unnecessarily place students from under-represented groups into remedial courses. While recent research has shown that tracking can have positive effects on student learning, inaccurate placement has consequences: students face misaligned curricula and must pay tuition for remedial courses that do not bear credits toward graduation. We develop an alternative system to place students that uses predictive analytics to combine multiple measures into a placement instrument. Compared to colleges’ existing placement tests, the algorithm is more predictive of future performance. We then conduct an experiment across seven colleges to evaluate the algorithm’s effects on students. Placement rates into college-level courses increased substantially without reducing pass rates. Adjusting for multiple testing, algorithmic placement generally, though not always, narrowed gaps in college placement rates and remedial course taking across demographic groups. A detailed cost analysis shows that the algorithmic placement system is socially efficient: it saves costs for students while increasing college credits earned, which more than offsets increased costs for colleges. Costs could be reduced with improved data digitization as opposed to entering data by hand.
{"title":"Using Predictive Analytics to Track Students: Evidence from a Seven-College Experiment","authors":"Peter Bergman, E. Kopko, Julio Rodriguez","doi":"10.1257/rct.7827","DOIUrl":"https://doi.org/10.1257/rct.7827","url":null,"abstract":"Tracking is widespread in U.S. education. In post-secondary education alone, at least 71% of colleges use a test to track students. However, there are concerns that the most frequently used college placement exams lack validity and reliability, and unnecessarily place students from under-represented groups into remedial courses. While recent research has shown that tracking can have positive effects on student learning, inaccurate placement has consequences: students face misaligned curricula and must pay tuition for remedial courses that do not bear credits toward graduation. We develop an alternative system to place students that uses predictive analytics to combine multiple measures into a placement instrument. Compared to colleges’ existing placement tests, the algorithm is more predictive of future performance. We then conduct an experiment across seven colleges to evaluate the algorithm’s effects on students. Placement rates into college-level courses increased substantially without reducing pass rates. Adjusting for multiple testing, algorithmic placement generally, though not always, narrowed gaps in college placement rates and remedial course taking across demographic groups. A detailed cost analysis shows that the algorithmic placement system is socially efficient: it saves costs for students while increasing college credits earned, which more than offsets increased costs for colleges. Costs could be reduced with improved data digitization as opposed to entering data by hand.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124576303","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Feedback scores in an online marketplace have risen sharply over time, leading to substantial top-censoring. Some of the increase is explained by more satisfied raters, but at least 35-45% is attributable to raters applying lower standards. We show that this “reputation inflation” is the equilibrium outcome of a model in which (a) inferences made by future trading partners determine what constitutes “bad” feedback and (b) giving “bad” feedback is costly to raters. The introduction of a new feedback system confirms our model predictions: raters were candid when feedback was private, but when feedback suddenly became public, reputations began inflating.
{"title":"Reputation in the Long-Run","authors":"Apostolos Filippas, J. Horton, Joseph M. Golden","doi":"10.2139/ssrn.3103688","DOIUrl":"https://doi.org/10.2139/ssrn.3103688","url":null,"abstract":"Feedback scores in an online marketplace have risen sharply over time, leading to substantial top-censoring. Some of the increase is explained by more satisfied raters, but at least 35-45% is attributable to raters applying lower standards. We show that this “reputation inflation” is the equilibrium outcome of a model in which (a) inferences made by future trading partners determine what constitutes “bad” feedback and (b) giving “bad” feedback is costly to raters. The introduction of a new feedback system confirms our model predictions: raters were candid when feedback was private, but when feedback suddenly became public, reputations began inflating.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114900126","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Envelopment is an effective form of market entry that facilitates competition among platforms. Nevertheless, many commentators have focused on the anticompetitive potential of envelopment, and some have argued for regulation of platforms because of that concern. These calls for regulation are not supported by robust formal analysis or comprehensive empirical evidence. We analyze a visible recent contribution by Condorelli and Padilla (2020a,b) and explain why the model that they put forward is not ripe for policy advice in relation to concerns with envelopment.
{"title":"Does Envelopment Through Data Advantage Call for New Regulation?","authors":"Gregor Langus, V. Lipatov","doi":"10.2139/ssrn.3805458","DOIUrl":"https://doi.org/10.2139/ssrn.3805458","url":null,"abstract":"Envelopment is an effective form of market entry that facilitates competition among platforms. Nevertheless, many commentators have focused on the anticompetitive potential of envelopment, and some have argued for regulation of platforms because of that concern. These calls for regulation are not supported by robust formal analysis or comprehensive empirical evidence. We analyze a visible recent contribution by Condorelli and Padilla (2020a,b) and explain why the model that they put forward is not ripe for policy advice in relation to concerns with envelopment.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128260905","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Boca, Noemi Oggero, P. Profeta, Mariachristina Rossi
The COVID-19 pandemic has had a dramatic impact on families' lives, with parents all over the world struggling to meet the increased demands of housework, childcare and home-schooling. Much of the additional burden has been shouldered by women, particularly in countries with a traditionally uneven division of household labor. Yet the dramatic increase in remote work from home since the pandemic also has the potential to increase paternal involvement in family life and thus to redress persistent domestic gender role inequalities. This effect depends on the working arrangements of each partner, whether working remotely, working at their usual workplace or ceasing work altogether. We examine the role of working arrangements during the pandemic on the traditional division of household labor in Italy using survey data from interviews with a representative sample of working women conducted during the two waves of COVID-19 (April and November 2020). Our data show that the gender gap in household care related activities was widest during the first wave of the pandemic, and although it was less pronounced during the second wave, it was still higher than pre-COVID-19. The time spent by women on housework, childcare, and assisting their children with distance learning did not depend on their partners' working arrangements. Conversely, men spent fewer hours helping with the housework and distance learning when their partners were at home. It is interesting, however, that although men who worked remotely or not at all did devote more time to domestic chores and child care, the increased time they spent at home did not seem to lead to a reallocation of couples' roles in housework and child care. Finally, we find that working arrangements are linked to women's feelings of uncertainty, with heterogeneous effects by level of education.
{"title":"Did COVID-19 Affect the Division of Labor within the Household? Evidence from Two Waves of the Pandemic in Italy","authors":"D. Boca, Noemi Oggero, P. Profeta, Mariachristina Rossi","doi":"10.2139/ssrn.3863828","DOIUrl":"https://doi.org/10.2139/ssrn.3863828","url":null,"abstract":"The COVID-19 pandemic has had a dramatic impact on families' lives, with parents all over the world struggling to meet the increased demands of housework, childcare and home-schooling. Much of the additional burden has been shouldered by women, particularly in countries with a traditionally uneven division of household labor. Yet the dramatic increase in remote work from home since the pandemic also has the potential to increase paternal involvement in family life and thus to redress persistent domestic gender role inequalities. This effect depends on the working arrangements of each partner, whether working remotely, working at their usual workplace or ceasing work altogether. We examine the role of working arrangements during the pandemic on the traditional division of household labor in Italy using survey data from interviews with a representative sample of working women conducted during the two waves of COVID-19 (April and November 2020). Our data show that the gender gap in household care related activities was widest during the first wave of the pandemic, and although it was less pronounced during the second wave, it was still higher than pre-COVID-19. The time spent by women on housework, childcare, and assisting their children with distance learning did not depend on their partners' working arrangements. Conversely, men spent fewer hours helping with the housework and distance learning when their partners were at home. It is interesting, however, that although men who worked remotely or not at all did devote more time to domestic chores and child care, the increased time they spent at home did not seem to lead to a reallocation of couples' roles in housework and child care. Finally, we find that working arrangements are linked to women's feelings of uncertainty, with heterogeneous effects by level of education.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132945599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The arrival of the cloud has enabled a shift in the nature of ICT use, from investment in sunk capital to a pay-on-demand service that allows firms to rapidly scale up. This paper uses new firm-level data to examine the impact of cloud on firm growth in the UK, using zipcode-level instruments of the timing of high-speed fibre availability and expected speeds. We find cloud leads to the growth of young firms in terms of employment and productivity, but they become more concentrated in fewer plants. For older firms we find no scale or productivity growth, but instead disperse activity by closing plants and moving employment further from the headquarters. In addition, the plants that close tend to be those without access to fibre broadband.
{"title":"Cloud Computing and Firm Growth","authors":"Timothy DeStefano, R. Kneller, Jon Timmis","doi":"10.2139/ssrn.3618829","DOIUrl":"https://doi.org/10.2139/ssrn.3618829","url":null,"abstract":"The arrival of the cloud has enabled a shift in the nature of ICT use, from investment in sunk capital to a pay-on-demand service that allows firms to rapidly scale up. This paper uses new firm-level data to examine the impact of cloud on firm growth in the UK, using zipcode-level instruments of the timing of high-speed fibre availability and expected speeds. We find cloud leads to the growth of young firms in terms of employment and productivity, but they become more concentrated in fewer plants. For older firms we find no scale or productivity growth, but instead disperse activity by closing plants and moving employment further from the headquarters. In addition, the plants that close tend to be those without access to fibre broadband.","PeriodicalId":217784,"journal":{"name":"CESifo: Economics of Digitization (Topic)","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132592767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：