Pub Date : 1992-03-23DOI: 10.1109/PLANS.1992.185875
M. Wei, M. Cannon, K. Schwarz
A series of airborne GPS (Global Positioning System) tests using the Ashtech XII receivers was used to demonstrate the effect of cycle slips and erroneous data on the positioning accuracy. The overall achievable accuracy is in the order 20 cm; however, errors of several decimeters were detected in some instances. Traverse closures and residual analysis are used to assess the occurrence and magnitude of these errors. The addition of an inertial navigation system in the aircraft, which provides accurate relative positions, is also used to detect cycle slips and outliers in the GPS data. Strategies to achieve consistent accuracies are discussed, and results for different alternatives are presented.<>
{"title":"Maintaining high accuracy GPS positioning 'on the fly'","authors":"M. Wei, M. Cannon, K. Schwarz","doi":"10.1109/PLANS.1992.185875","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185875","url":null,"abstract":"A series of airborne GPS (Global Positioning System) tests using the Ashtech XII receivers was used to demonstrate the effect of cycle slips and erroneous data on the positioning accuracy. The overall achievable accuracy is in the order 20 cm; however, errors of several decimeters were detected in some instances. Traverse closures and residual analysis are used to assess the occurrence and magnitude of these errors. The addition of an inertial navigation system in the aircraft, which provides accurate relative positions, is also used to detect cycle slips and outliers in the GPS data. Strategies to achieve consistent accuracies are discussed, and results for different alternatives are presented.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121909836","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185879
D. T. Knight
Addresses a problem of GPS/INS (Global Positioning System/inertial navigation system) integration wherein the conflicting goals of modularity and tight coupling are both sought. The advantages to be gained from modularity are described. The performance advantages of tight coupling are reviewed, and it is explained why it is so difficult to achieve both modularity and tight coupling in the same architecture. A candidate is then presented and evaluated relative to the stated goals. Key aspects of its operation and timing structure are described, including difficulties the architecture overcomes such as discontinuous INS aiding of receiver tracking loops as the system transitions through various modes. Computational requirements and throughput or the integration processor are discussed. The problem of testing individual components is considered where those components are normally expected to operate only when fully integrated. The author deals primarily with low-cost applications such as remotely piloted vehicles and tactical munitions where tight coupling and modularity are especially valuable.<>
{"title":"Achieving modularity with tightly-coupled GPS/INS","authors":"D. T. Knight","doi":"10.1109/PLANS.1992.185879","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185879","url":null,"abstract":"Addresses a problem of GPS/INS (Global Positioning System/inertial navigation system) integration wherein the conflicting goals of modularity and tight coupling are both sought. The advantages to be gained from modularity are described. The performance advantages of tight coupling are reviewed, and it is explained why it is so difficult to achieve both modularity and tight coupling in the same architecture. A candidate is then presented and evaluated relative to the stated goals. Key aspects of its operation and timing structure are described, including difficulties the architecture overcomes such as discontinuous INS aiding of receiver tracking loops as the system transitions through various modes. Computational requirements and throughput or the integration processor are discussed. The problem of testing individual components is considered where those components are normally expected to operate only when fully integrated. The author deals primarily with low-cost applications such as remotely piloted vehicles and tactical munitions where tight coupling and modularity are especially valuable.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129841544","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185876
H. Abidin
It is noted that resolving the carrier phase cycle ambiguity on the fly is the key to precise (centimeter-level accuracy) real-time differential GPS (Global Positioning System) kinematic positioning. The resolution requires on the fly isolation of the correct ambiguity from the geometric range and the errors and biases in the observations, and therefore it is not an easy task to accomplish. The performance of the ambiguity resolution, however, can be improved by using more than one monitor station along with a reliable on the fly ambiguity resolution technique. The advantages of multimonitor station on the fly ambiguity resolution are described. The impacts of satellite geometry and monitor station geometry on the ambiguity resolution are analyzed, and some results are presented to highlight the important issues. The effects of the geometry of satellites and monitor stations on the on the fly ambiguity resolution were investigated by considering only the observation noises, assuming that all the biases in the observations have been eliminated by applying the corrections derived by the primary monitor stations.<>
{"title":"Multi-monitor station 'on the fly' ambiguity resolution: the impacts of satellite geometry and monitor station geometry","authors":"H. Abidin","doi":"10.1109/PLANS.1992.185876","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185876","url":null,"abstract":"It is noted that resolving the carrier phase cycle ambiguity on the fly is the key to precise (centimeter-level accuracy) real-time differential GPS (Global Positioning System) kinematic positioning. The resolution requires on the fly isolation of the correct ambiguity from the geometric range and the errors and biases in the observations, and therefore it is not an easy task to accomplish. The performance of the ambiguity resolution, however, can be improved by using more than one monitor station along with a reliable on the fly ambiguity resolution technique. The advantages of multimonitor station on the fly ambiguity resolution are described. The impacts of satellite geometry and monitor station geometry on the ambiguity resolution are analyzed, and some results are presented to highlight the important issues. The effects of the geometry of satellites and monitor stations on the on the fly ambiguity resolution were investigated by considering only the observation noises, assuming that all the biases in the observations have been eliminated by applying the corrections derived by the primary monitor stations.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125302277","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185889
J. R. Gibson, K. Schwarz, M. Wei, M. Cannon
Summary form only given, as follows. Flight tests have been performed for the purpose of assessing the use of post-mission integrated data from GPS (Global Positioning System) and INS (inertial navigation system) systems for remote sensing applications. While GPS data alone are sufficient for aircraft guidance, they do not currently satisfy the requirement for position and attitude information at high data rates, with typical sampling times between 5 and 40 ms. This information is needed for image processing applications where data discontinuities greater than a few centimeters in the positions must be avoided. The authors describe the test design which provided for multiple GPS stations on the ground from which the GPS receiver in the aircraft was monitored. The airborne GPS receiver was precisely synchronized with the stable platform INS. The accuracy of position, velocity, and attitude was analyzed using different approaches to post-mission data integration. These results were then used to georeference the imagery from the Multiple-Detector Electro-Optical Imaging Scanner and to compare it to independent ground truth.<>
{"title":"GPS-INS data integration for remote sensing","authors":"J. R. Gibson, K. Schwarz, M. Wei, M. Cannon","doi":"10.1109/PLANS.1992.185889","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185889","url":null,"abstract":"Summary form only given, as follows. Flight tests have been performed for the purpose of assessing the use of post-mission integrated data from GPS (Global Positioning System) and INS (inertial navigation system) systems for remote sensing applications. While GPS data alone are sufficient for aircraft guidance, they do not currently satisfy the requirement for position and attitude information at high data rates, with typical sampling times between 5 and 40 ms. This information is needed for image processing applications where data discontinuities greater than a few centimeters in the positions must be avoided. The authors describe the test design which provided for multiple GPS stations on the ground from which the GPS receiver in the aircraft was monitored. The airborne GPS receiver was precisely synchronized with the stable platform INS. The accuracy of position, velocity, and attitude was analyzed using different approaches to post-mission data integration. These results were then used to georeference the imagery from the Multiple-Detector Electro-Optical Imaging Scanner and to compare it to independent ground truth.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"59 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130152725","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185870
M. Celenk, M. Mylvaganam
The authors describe a time-efficient implementation of the baseline microwave landing system (BMLS) computer model on 16- and 64-node hypercube processors. First the sequential execution of the model was improved by eliminating the receiver input data file which logically connects the transmitter (BMLST) and receiver (BMLSR) units of the BMLS. The combined code was then mapped onto the nodes of parallel processors (AMETEK S-14/16 and 64) by creating a child program to run the combined BMLST and BMLSR routines in S-14 and a parent program to handle all the I/O and disk operations in the host (VAX 11/750). Parallel decomposition of the 95 percent PFE (path following error) contour generation task was achieved by dividing the search grid points into 16 or 64 groups, each of which was assigned to a particular node of the system S-14. Each processing element executed the same combined code for a different set of gridpoints of an airport scenario. This resulted in 15- and 60-fold speedups for 16- and 64-node implementations.<>
{"title":"Implementation of BMLS computer model on hypercube systems","authors":"M. Celenk, M. Mylvaganam","doi":"10.1109/PLANS.1992.185870","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185870","url":null,"abstract":"The authors describe a time-efficient implementation of the baseline microwave landing system (BMLS) computer model on 16- and 64-node hypercube processors. First the sequential execution of the model was improved by eliminating the receiver input data file which logically connects the transmitter (BMLST) and receiver (BMLSR) units of the BMLS. The combined code was then mapped onto the nodes of parallel processors (AMETEK S-14/16 and 64) by creating a child program to run the combined BMLST and BMLSR routines in S-14 and a parent program to handle all the I/O and disk operations in the host (VAX 11/750). Parallel decomposition of the 95 percent PFE (path following error) contour generation task was achieved by dividing the search grid points into 16 or 64 groups, each of which was assigned to a particular node of the system S-14. Each processing element executed the same combined code for a different set of gridpoints of an airport scenario. This resulted in 15- and 60-fold speedups for 16- and 64-node implementations.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128078337","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185896
A. Brown
A low-cost GPS (Global Positioning System) tracking system which provides a highly accurate service suitable for operation worldwide is described. The system includes a low-cost vehicle sensor, the TIDGET, developed by NAVSYS, and a PC-based workstation which is located at the customer's facility. The workstation includes aiding software that allows the vehicle's location to be computed even when only two GPS satellites are visible. This provides reliable GPS service even in an urban environment. The vehicle location is computed and displayed on a PC workstation at the customer's dispatch facility. The low cost of the TIDGET sensor combined with the performance of the PC-based workstation provides a highly accurate yet inexpensive vehicle tracking system that is capable of operating anywhere in the world. The system is designed to be integrated with a variety of alternative communication links for any vehicle tracking application.<>
{"title":"A low cost vehicle location and tracking system","authors":"A. Brown","doi":"10.1109/PLANS.1992.185896","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185896","url":null,"abstract":"A low-cost GPS (Global Positioning System) tracking system which provides a highly accurate service suitable for operation worldwide is described. The system includes a low-cost vehicle sensor, the TIDGET, developed by NAVSYS, and a PC-based workstation which is located at the customer's facility. The workstation includes aiding software that allows the vehicle's location to be computed even when only two GPS satellites are visible. This provides reliable GPS service even in an urban environment. The vehicle location is computed and displayed on a PC workstation at the customer's dispatch facility. The low cost of the TIDGET sensor combined with the performance of the PC-based workstation provides a highly accurate yet inexpensive vehicle tracking system that is capable of operating anywhere in the world. The system is designed to be integrated with a variety of alternative communication links for any vehicle tracking application.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125601340","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185823
F. D. Mackenzie, F. Coyne
In November 1993 NFOLDS's (National Field Office for Loran Data Support) work-but not its expert staff-will move to the Federal Aviation Administration in Oklahoma City. To recreate NFOLDS's skills in detecting data anomalies, a merger of artificial intelligence and propagation technology has been designed into the system. The authors describe the use of a neural network acting on Loran data to classify anomalies. They also describe an expert system for Loran area monitors to aid operators in managing data collection. It is concluded that the use of artificial intelligence will preserve the quality of Loran data and enhance its value to the scientific community.<>
{"title":"Merger and acquisition: enhancing Loran propagation technology with artificial intelligence","authors":"F. D. Mackenzie, F. Coyne","doi":"10.1109/PLANS.1992.185823","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185823","url":null,"abstract":"In November 1993 NFOLDS's (National Field Office for Loran Data Support) work-but not its expert staff-will move to the Federal Aviation Administration in Oklahoma City. To recreate NFOLDS's skills in detecting data anomalies, a merger of artificial intelligence and propagation technology has been designed into the system. The authors describe the use of a neural network acting on Loran data to classify anomalies. They also describe an expert system for Loran area monitors to aid operators in managing data collection. It is concluded that the use of artificial intelligence will preserve the quality of Loran data and enhance its value to the scientific community.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134273202","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185838
T. Allison, D. Farmer, G. R. Lennen, Kreg A. Martin
Summary form only given. A novel commercial geodetic survey receiver which uses advanced tracking and postprocessing techniques to produce a high-performance, high-quality, robust survey tool has been developed. The receiver makes use of the P code modulation, and its operation in the event of P code being encrypted into the secret Y code must be considered. The tracking mechanisms and measurements and postprocessing techniques with Y code on or off have been examined, and results demonstrating receiver performance in the surveying environment have been obtained.<>
{"title":"An advanced GPS geodetic survey receiver","authors":"T. Allison, D. Farmer, G. R. Lennen, Kreg A. Martin","doi":"10.1109/PLANS.1992.185838","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185838","url":null,"abstract":"Summary form only given. A novel commercial geodetic survey receiver which uses advanced tracking and postprocessing techniques to produce a high-performance, high-quality, robust survey tool has been developed. The receiver makes use of the P code modulation, and its operation in the event of P code being encrypted into the secret Y code must be considered. The tracking mechanisms and measurements and postprocessing techniques with Y code on or off have been examined, and results demonstrating receiver performance in the surveying environment have been obtained.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131660714","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185816
J.I. Lahham, J. Brazell
Sperry Marine has devised a passive structure-borne noise isolation system that reduces the noise generated by dithered ring laser gyroscopes to levels below the requirements of MIL-STD-740-2. Descriptions of some of the analytical and experimental processes required to develop this system are presented, together with structure-borne noise test results. Results show that a 47-dB structure-borne noise reduction has been achieved with a noise isolation system that is compatible with the stability and repeatability required by navigation systems. The noise reduction techniques presented have enabled Sperry Marine to develop a dithered ring laser gyroscope navigator feasible for naval applications, the MK 49.<>
{"title":"Acoustic noise reduction in the MK 49 ship's inertial navigation system (SINS)","authors":"J.I. Lahham, J. Brazell","doi":"10.1109/PLANS.1992.185816","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185816","url":null,"abstract":"Sperry Marine has devised a passive structure-borne noise isolation system that reduces the noise generated by dithered ring laser gyroscopes to levels below the requirements of MIL-STD-740-2. Descriptions of some of the analytical and experimental processes required to develop this system are presented, together with structure-borne noise test results. Results show that a 47-dB structure-borne noise reduction has been achieved with a noise isolation system that is compatible with the stability and repeatability required by navigation systems. The noise reduction techniques presented have enabled Sperry Marine to develop a dithered ring laser gyroscope navigator feasible for naval applications, the MK 49.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"146 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116452100","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 : 1992-03-23DOI: 10.1109/PLANS.1992.185822
H. Shirer
The author presents an overview of the 1990 Federal Radionavigation Plan policy and a discussion of the status of GPS (Global Positioning System), Loran-C, Omega, VOR/DME (VHF omnidirectional range/distance measuring equipment), VORTAC (combined VOR and TACAN stations), TACAN, (tactical air navigation), MLS (microwave landing system), ILS (instrument landing systems), Transit, and radiobeacons. The 1990 FRP contains significant changes regarding several of the radionavigation systems. It is concluded that it is difficult at best to ascertain the post-GPS final systems mix of federally provided radionavigation systems. The phase-out dates of other systems in favor of GPS still remain soft. Many uncertainties remain until the capabilities of GPS are verified for all classes of users. The federal radionavigation planning process accommodates such uncertainties, keeping pace with the constantly changing radionavigation user profile and rapid advancements in system technology.<>
{"title":"The US Federal Radionavigation Plan","authors":"H. Shirer","doi":"10.1109/PLANS.1992.185822","DOIUrl":"https://doi.org/10.1109/PLANS.1992.185822","url":null,"abstract":"The author presents an overview of the 1990 Federal Radionavigation Plan policy and a discussion of the status of GPS (Global Positioning System), Loran-C, Omega, VOR/DME (VHF omnidirectional range/distance measuring equipment), VORTAC (combined VOR and TACAN stations), TACAN, (tactical air navigation), MLS (microwave landing system), ILS (instrument landing systems), Transit, and radiobeacons. The 1990 FRP contains significant changes regarding several of the radionavigation systems. It is concluded that it is difficult at best to ascertain the post-GPS final systems mix of federally provided radionavigation systems. The phase-out dates of other systems in favor of GPS still remain soft. Many uncertainties remain until the capabilities of GPS are verified for all classes of users. The federal radionavigation planning process accommodates such uncertainties, keeping pace with the constantly changing radionavigation user profile and rapid advancements in system technology.<<ETX>>","PeriodicalId":422101,"journal":{"name":"IEEE PLANS 92 Position Location and Navigation Symposium Record","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123403228","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：