This is the first comprehensive study of the SABR (Stochastic Alpha-Beta-Rho) model (Hagan et. al (2002)) on the pricing and hedging of interest rate caps. We implement several versions of the SABR interest rate model and analyze their respective pricing and hedging performance using two years of daily data with seven different strikes and ten different tenors on each trading day. In-sample and out-of-sample tests show that in addition to having stochastic volatility for the forward rate, it is essential to recalibrate daily either the “vol of vol” or the correlation between forward rate and its volatility, although recalibrating both further improves pricing performance. The fully stochastic version of the SABR model exhibits excellent pricing accuracy and more importantly, captures the dynamics of the volatility smile over time very well. This is further demonstrated through examining delta hedging performance based on the SABR model. Our hedging result indicates that the SABR model produces accurate hedge ratios that outperform those implied by the Black model.
{"title":"Pricing and Hedging the Smile with SABR: Evidence from the Interest Rate Caps Market","authors":"Tao Wu","doi":"10.2139/ssrn.1989261","DOIUrl":"https://doi.org/10.2139/ssrn.1989261","url":null,"abstract":"This is the first comprehensive study of the SABR (Stochastic Alpha-Beta-Rho) model (Hagan et. al (2002)) on the pricing and hedging of interest rate caps. We implement several versions of the SABR interest rate model and analyze their respective pricing and hedging performance using two years of daily data with seven different strikes and ten different tenors on each trading day. In-sample and out-of-sample tests show that in addition to having stochastic volatility for the forward rate, it is essential to recalibrate daily either the “vol of vol” or the correlation between forward rate and its volatility, although recalibrating both further improves pricing performance. The fully stochastic version of the SABR model exhibits excellent pricing accuracy and more importantly, captures the dynamics of the volatility smile over time very well. This is further demonstrated through examining delta hedging performance based on the SABR model. Our hedging result indicates that the SABR model produces accurate hedge ratios that outperform those implied by the Black model.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124874741","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 extend the widely used SABR model (Hagan et al (2002)) to include a general volatility function and a CEV power on the stochastic volatility process itself. Using a short time expansion we derive results for the Dupire local volatility which in turn is inserted into a single time step finite difference scheme to generate arbitrage free option prices. Our approach has a number of advantages over the standard SABR model: a. it eliminates arbitrage for low and high strikes, b. it allows for an exact fit to a set of discrete option quotes, and c. it gives more explicit control over the wings, both for low (and potentially negative) strikes and for very high strikes. All of this without sacrificing speed in the implementation.
{"title":"ZABR -- Expansions for the Masses","authors":"J. Andreasen, B. Huge","doi":"10.2139/ssrn.1980726","DOIUrl":"https://doi.org/10.2139/ssrn.1980726","url":null,"abstract":"We extend the widely used SABR model (Hagan et al (2002)) to include a general volatility function and a CEV power on the stochastic volatility process itself. Using a short time expansion we derive results for the Dupire local volatility which in turn is inserted into a single time step finite difference scheme to generate arbitrage free option prices. Our approach has a number of advantages over the standard SABR model: a. it eliminates arbitrage for low and high strikes, b. it allows for an exact fit to a set of discrete option quotes, and c. it gives more explicit control over the wings, both for low (and potentially negative) strikes and for very high strikes. All of this without sacrificing speed in the implementation.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115675972","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}
A bank's stock price is modeled as a call option on the spread of random assets over random liabilities. The logarithm of assets and liabilities are jointly modeled as driven by four variance gamma processes and this model is estimated by calibrating to quoted equity options seen as compound spread options. On defining risk-weighted assets as asset value less the bid price plus the ask price of liabilities less the liability value we endogenize capital adequacy ratios following the methods of conic finance for the bid and ask prices. All computations are illustrated on CSGN.VX, ADRed into USD on March 29, 2011.
{"title":"On the Pricing of Contingent Capital Notes","authors":"D. Madan","doi":"10.2139/ssrn.1971811","DOIUrl":"https://doi.org/10.2139/ssrn.1971811","url":null,"abstract":"A bank's stock price is modeled as a call option on the spread of random assets over random liabilities. The logarithm of assets and liabilities are jointly modeled as driven by four variance gamma processes and this model is estimated by calibrating to quoted equity options seen as compound spread options. On defining risk-weighted assets as asset value less the bid price plus the ask price of liabilities less the liability value we endogenize capital adequacy ratios following the methods of conic finance for the bid and ask prices. All computations are illustrated on CSGN.VX, ADRed into USD on March 29, 2011.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131267552","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}
This paper studies the time series predictability of currency carry trades, constructed by selecting currencies to be bought or sold against the US dollar, based on forward discounts. Changes in a commodity index, currency volatility and, to a lesser extent, a measure of liquidity predict in-sample the payoffs of dynamically re-balanced carry trades, as evidenced by individual and joint p-values in monthly predictive regressions at horizons up to six months. Predictability is further supported through out-of-sample metrics, and a predictability-based decision rule produces sizable improvements in the Sharpe ratios and skewness profile of carry trade payoffs. Our evidence also indicates that predictability can be traced to the long legs of the carry trades and their currency components. We test the theoretical restrictions that an asset pricing model, with average currency returns and the mimicking portfolio for the innovations in currency volatility as risk factors, imposes on the coefficients in predictive regressions.
{"title":"Predictability of Currency Carry Trades and Asset Pricing Implications","authors":"G. Bakshi, George Panayotov","doi":"10.2139/ssrn.1977642","DOIUrl":"https://doi.org/10.2139/ssrn.1977642","url":null,"abstract":"This paper studies the time series predictability of currency carry trades, constructed by selecting currencies to be bought or sold against the US dollar, based on forward discounts. Changes in a commodity index, currency volatility and, to a lesser extent, a measure of liquidity predict in-sample the payoffs of dynamically re-balanced carry trades, as evidenced by individual and joint p-values in monthly predictive regressions at horizons up to six months. Predictability is further supported through out-of-sample metrics, and a predictability-based decision rule produces sizable improvements in the Sharpe ratios and skewness profile of carry trade payoffs. Our evidence also indicates that predictability can be traced to the long legs of the carry trades and their currency components. We test the theoretical restrictions that an asset pricing model, with average currency returns and the mimicking portfolio for the innovations in currency volatility as risk factors, imposes on the coefficients in predictive regressions.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132110979","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}
Recent studies add to the evidence against Miller’s (1977) overvaluation theory, further dwarfing the already sparse evidence for the theory. In this paper, we identify several issues untouched so far. Addressing these issues simultaneously, we conceive a novel empirical identification strategy which (1) looks at short-sale bans rather than short-sale constraints; (2) treats a short-sale ban (or no ban) as a regime rather than as an event; (3) probes the same stock that traverses the ban and no-ban regimes rather than different stocks concurrently under different regimes or the same regime; and (4) allows for possible endogeneity in regulators’ decision to change the short-selling regime for a stock. Employing data from the Hong Kong market, we find robust and strong evidence for Miller’s theory. Stocks earn significantly higher abnormal returns in the ban regime than in the no-ban regime. The ban regime and wider dispersion of investor opinions reinforce each other in further increasing current, while further reducing subsequent, returns to individual stocks. The tick rule acts as a short-sale constraint to impair the negative price effects of the no-ban regime.
{"title":"Traversing the Short-Sale-Ban and the No-Ban Regime: A New Tale of the Old Overvaluation Story","authors":"Xiaoming Li, M. Bai","doi":"10.2139/ssrn.1929123","DOIUrl":"https://doi.org/10.2139/ssrn.1929123","url":null,"abstract":"Recent studies add to the evidence against Miller’s (1977) overvaluation theory, further dwarfing the already sparse evidence for the theory. In this paper, we identify several issues untouched so far. Addressing these issues simultaneously, we conceive a novel empirical identification strategy which (1) looks at short-sale bans rather than short-sale constraints; (2) treats a short-sale ban (or no ban) as a regime rather than as an event; (3) probes the same stock that traverses the ban and no-ban regimes rather than different stocks concurrently under different regimes or the same regime; and (4) allows for possible endogeneity in regulators’ decision to change the short-selling regime for a stock. Employing data from the Hong Kong market, we find robust and strong evidence for Miller’s theory. Stocks earn significantly higher abnormal returns in the ban regime than in the no-ban regime. The ban regime and wider dispersion of investor opinions reinforce each other in further increasing current, while further reducing subsequent, returns to individual stocks. The tick rule acts as a short-sale constraint to impair the negative price effects of the no-ban regime.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114656898","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}
Pub Date : 2011-09-01DOI: 10.1111/j.1540-6296.2011.01206.x
R. Derrig, Sharon Tennyson
The article tests the hypothesis that insurance price subsidies created by rate regulation lead to higher insurance cost growth. The article makes use of data from the Massachusetts private passenger automobile insurance market, where cross‐subsidies were explicitly built into the rate structure through rules that limit rate differentials and differences in rate increases across driver rating categories. Two approaches are taken to study the potential loss cost reaction to the Massachusetts cross‐subsidies. The first approach compares Massachusetts with all other states while controlling for demographic, regulatory, and liability coverage levels. Loss cost levels that were about 29 percent above the expected level are found for Massachusetts during years 1978–1998, when premiums charged were those fixed by the state and included explicit subsidies for high‐risk drivers. A second approach considers changing cost levels across Massachusetts by studying loss cost changes by town and relating those changes to subsidy providers and subsidy receivers. Subsidy data based on accident year data for 1993–2004 show a significant and positive (relative) growth in loss costs and an increasing proportion of high‐risk drivers for towns that were subsidy receivers, in line with the theory of underlying incentives for adverse selection and moral hazard.
{"title":"The Impact of Rate Regulation on Claims: Evidence from Massachusetts Automobile Insurance","authors":"R. Derrig, Sharon Tennyson","doi":"10.1111/j.1540-6296.2011.01206.x","DOIUrl":"https://doi.org/10.1111/j.1540-6296.2011.01206.x","url":null,"abstract":"The article tests the hypothesis that insurance price subsidies created by rate regulation lead to higher insurance cost growth. The article makes use of data from the Massachusetts private passenger automobile insurance market, where cross‐subsidies were explicitly built into the rate structure through rules that limit rate differentials and differences in rate increases across driver rating categories. Two approaches are taken to study the potential loss cost reaction to the Massachusetts cross‐subsidies. The first approach compares Massachusetts with all other states while controlling for demographic, regulatory, and liability coverage levels. Loss cost levels that were about 29 percent above the expected level are found for Massachusetts during years 1978–1998, when premiums charged were those fixed by the state and included explicit subsidies for high‐risk drivers. A second approach considers changing cost levels across Massachusetts by studying loss cost changes by town and relating those changes to subsidy providers and subsidy receivers. Subsidy data based on accident year data for 1993–2004 show a significant and positive (relative) growth in loss costs and an increasing proportion of high‐risk drivers for towns that were subsidy receivers, in line with the theory of underlying incentives for adverse selection and moral hazard.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"94 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130070816","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}
Factorial moments are convenient tools in particle physics to characterize the multiplicity distributions when phase-space resolution ($Delta$) becomes small. They include all correlations within the system of particles and represent integral characteristics of any correlation between these particles. In this letter, we show a direct comparison between high energy physics and quantitative finance results. Both for physics and finance, we illustrate that correlations between particles lead to a broadening of the multiplicity distribution and to dynamical fluctuations when the resolution becomes small enough. From the generating function of factorial moments, we make a prediction on the gap probability for sequences of returns of positive or negative signs. The gap is defined as the number of consecutive positive returns after a negative return, thus this is a gap in negative return. Inversely for a gap in positive return. Then, the gap probability is shown to be exponentially suppressed within the gap size. We confirm this prediction with data.
{"title":"Factorial Moments in Complex Systems","authors":"Laurent Schoeffel","doi":"10.2139/ssrn.1955253","DOIUrl":"https://doi.org/10.2139/ssrn.1955253","url":null,"abstract":"Factorial moments are convenient tools in particle physics to characterize the multiplicity distributions when phase-space resolution ($Delta$) becomes small. They include all correlations within the system of particles and represent integral characteristics of any correlation between these particles. In this letter, we show a direct comparison between high energy physics and quantitative finance results. Both for physics and finance, we illustrate that correlations between particles lead to a broadening of the multiplicity distribution and to dynamical fluctuations when the resolution becomes small enough. From the generating function of factorial moments, we make a prediction on the gap probability for sequences of returns of positive or negative signs. The gap is defined as the number of consecutive positive returns after a negative return, thus this is a gap in negative return. Inversely for a gap in positive return. Then, the gap probability is shown to be exponentially suppressed within the gap size. We confirm this prediction with data.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127811386","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}
This papers addresses the stock option pricing problem in a continuous time market model where there are two stochastic tradable assets, and one of them is selected as a num'eraire. It is shown that the presence of arbitrarily small stochastic deviations in the evolution of the num'eraire process causes significant changes in the market properties. In particular, an equivalent martingale measure is not unique for this market, and there are non-replicable claims. The martingale prices and the hedging error can vary significantly and take extreme values, for some extreme choices of the equivalent martingale measures. Some rational choices of the equivalent martingale measures are suggested and discussed, including implied measures calculated from observed bond prices. This allows to calculate the implied market price of risk process.
{"title":"On Martingale Measures and Pricing for Continuous Bond-Stock Market with Stochastic Bond","authors":"N. Dokuchaev","doi":"10.2139/ssrn.1903852","DOIUrl":"https://doi.org/10.2139/ssrn.1903852","url":null,"abstract":"This papers addresses the stock option pricing problem in a continuous time market model where there are two stochastic tradable assets, and one of them is selected as a num'eraire. It is shown that the presence of arbitrarily small stochastic deviations in the evolution of the num'eraire process causes significant changes in the market properties. In particular, an equivalent martingale measure is not unique for this market, and there are non-replicable claims. The martingale prices and the hedging error can vary significantly and take extreme values, for some extreme choices of the equivalent martingale measures. Some rational choices of the equivalent martingale measures are suggested and discussed, including implied measures calculated from observed bond prices. This allows to calculate the implied market price of risk process.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114767814","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}
After Lehman default (credit crisis which started in 2007), practitioners considered the default risk as a major risk. The Industry began to charge for the default risk of any derivatives. In this article we try to extend the work of V.Piterbarg who established the fundamental of a new world in the pricing of derivatives. Our main focus will be on the Equity CVA but can be extended to any asset class. In this article we established the default risky price of particular space of derivatives based on vanilla CVA then we introduced the CVA implied Volatility and described a new pricing methodology.
{"title":"CVA Implied Vol and Netting Arbitrage","authors":"Christian Kamtchueng","doi":"10.2139/ssrn.1941327","DOIUrl":"https://doi.org/10.2139/ssrn.1941327","url":null,"abstract":"After Lehman default (credit crisis which started in 2007), practitioners considered the default risk as a major risk. The Industry began to charge for the default risk of any derivatives. In this article we try to extend the work of V.Piterbarg who established the fundamental of a new world in the pricing of derivatives. Our main focus will be on the Equity CVA but can be extended to any asset class. In this article we established the default risky price of particular space of derivatives based on vanilla CVA then we introduced the CVA implied Volatility and described a new pricing methodology.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132996307","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}
This article establishes that most yield curve models within the popular Nelson and Siegel (1987, hereafter NS) class may be obtained as a formal Taylor approximation to the dynamic component of the generic Gaussian affine term structure model outlined in Dai and Singleton (2002). That fundamental theoretical foundation provides an assurance to users of NS models that they correspond to a well-accepted set of principles and assumptions for modeling the yield curve and its dynamics. Indeed, arbitrage-free NS models will parsimoniously and reliably represent the data generated by any Gaussian affine term structure model regardless of its true number of underlying factors and specification, and even non-arbitrage-free NS models will adequately capture the dynamics of the state variables. Combined with the well-established practical benefits of applying NS models, the theoretical foundation provides a compelling case for applying NS models as standard tools for yield curve modeling and analysis in economics and finance. As an illustration, this article develops a two-factor arbitrage-free NS model and applies it to testing for changes in United States yield curve dynamics. The results confirm those of Rudebusch and Wu (2007) based on a latent two-factor essentially affine term structure model: there was a material change in the behavior of the yield curve between the sample prior to 1988 and the sample from 1988 onwards.
{"title":"A Theoretical Foundation for the Nelson and Siegel Class of Yield Curve Models","authors":"Leo Krippner","doi":"10.2139/ssrn.1921045","DOIUrl":"https://doi.org/10.2139/ssrn.1921045","url":null,"abstract":"This article establishes that most yield curve models within the popular Nelson and Siegel (1987, hereafter NS) class may be obtained as a formal Taylor approximation to the dynamic component of the generic Gaussian affine term structure model outlined in Dai and Singleton (2002). That fundamental theoretical foundation provides an assurance to users of NS models that they correspond to a well-accepted set of principles and assumptions for modeling the yield curve and its dynamics. Indeed, arbitrage-free NS models will parsimoniously and reliably represent the data generated by any Gaussian affine term structure model regardless of its true number of underlying factors and specification, and even non-arbitrage-free NS models will adequately capture the dynamics of the state variables. Combined with the well-established practical benefits of applying NS models, the theoretical foundation provides a compelling case for applying NS models as standard tools for yield curve modeling and analysis in economics and finance. As an illustration, this article develops a two-factor arbitrage-free NS model and applies it to testing for changes in United States yield curve dynamics. The results confirm those of Rudebusch and Wu (2007) based on a latent two-factor essentially affine term structure model: there was a material change in the behavior of the yield curve between the sample prior to 1988 and the sample from 1988 onwards.","PeriodicalId":366327,"journal":{"name":"ERN: Other Econometrics: Applied Econometric Modeling in Financial Economics (Topic)","volume":"78 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126313053","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：