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使用叔丁基锂(t-BuLi)与乙二胺(EDA)的混合溶液活化聚四氟乙烯(PTFE),并在活化的PTFE上接枝甲基丙烯酸缩水甘油酯(GMA)。使用傅立叶红外吸收光谱(FTIR)对活化与接枝后的PTFE进行了分析,结果表明:本工艺成功将GMA接枝到PTFE上。通过扫描电子显微镜(SEM)观察了接枝表面,使用TGA法测定接枝聚合物的接枝率达到5.83%。最后研究了接枝反应时间和温度对PTFE-g-GMA接枝率的影响。结果表明,接枝率随着反应时间的延长逐渐增加,反应时间超过8h后基本恒定;在70℃反应时接枝率出现最大值。 相似文献
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李玉莹%刘祖黎%潘华锦%姚凯伦 《宇航材料工艺》2000,30(1):46-49
利用空间测量方法对不同浓度手性旋波介质的吸波性能进行了测量。实验表明,手性螺旋的浓度可以做为调节旋波介质吸波性能的一个灵敏参量。在非手性基体中加入适当浓度的螺旋体可有效提高手性介质的吸波性能。手性螺旋体的基体中的浓度有一最佳浓度匹配点,该浓度点在3.2%和4.0%之间。在设计高吸收宽频段的手征性吸波材料时,应考虑螺旋体在手性介质中的浓度匹配。 相似文献
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Cheng Pan Zengke Li Jingxiang Gao Fangchao Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(6):1859-1869
In the application of precise point positioning (PPP), especially in the dynamic mode, the classical Kalman filter (KF) usually produces a large number of estimation errors or diverges when there are gross errors in the observation data or unexpected turbulences occur in target motion state or both of them. For such problem, a variational Bayesian (VB)-based robust adaptive Kalman filtering (VB-RAKF) is proposed in this paper. This filter introduces a classification robust equivalent weight function to resist observation gross error and the inverse Wishart prior to model inaccurate process noise covariance matrix (PNCM). To improve the instantaneous accuracy of state estimation, the VB approach is used to obtain better estimations of inaccurate PNCM. Several sets of observation data collected by IGS reference stations and vehicles are employed to check the robustness and positioning accuracy of the VB-RAKF model. The results show that the VB-RAKF algorithm is more robust than the KF, and can effectively resist the gross error in observation data and control state disturbance. In the IGS reference station tests, when compared to the KF, the static positioning accuracies of the VB-RAKF in the north, east and up directions are improved by 13%, 8% and 22%, respectively, and the simulated dynamic positioning accuracies of the VB-RAKF in the north, east and up directions are improved by 19%, 9% and 21%, respectively. The in-vehicle dynamic test verifies that the VB-RAKF outperforms the KF, and shows that the VB-RAKF has better performance than the KF when dealing with observation data which has obvious gross errors, and similar performance as the KF when gross errors are small. 相似文献
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为了解决人在遥操作回路中,人与操作目标时空隔离、缺乏环境信息和天地回路大时延等实际问题,以及减少空间机器人缺乏自主智能性和操作者手抖颤等不利因素,针对空间在轨服务操作交互问题,提出一种基于增强虚拟安全通道(AVSC)的分层辅助遥操作(LAT)方法。首先,设计组合体增强虚拟安全通道,通过给主端操作者施加虚拟引导力辅助完成操作任务,与徒手操作相比,操作时间短、操作平稳;其次,设计分层辅助遥操作系统,通过获取空间机器人末端与期望轨迹上最近点之间的距离,在安全通道内划分不同的虚拟力场,辅助操作者更加灵活地操作。演示实验表明,该方法利用力触觉和视觉信息,引导操作者控制空间机器人末端运动至期望位置,可以有效地提高操作精度、减轻操作者心理压力和减少操作时间。 相似文献
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Lin Pan Xiao Gao Jiahuan Hu Fujian Ma Zhiyu Zhang Weiwang Wu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):234-252
For precise position services, the real-time precise point positioning (PPP) is a promising technology. The real-time PPP performance is expected to be improved by multi-system combination. The performance of real-time multi-system PPP needs to be periodically investigated, with the increasing number of available satellites and the continuously improved quality of real-time precise products of satellite clocks and orbits. In this study, a comprehensive performance assessment is conducted for the four-system integrated real-time PPP (FSIRT-PPP) with GPS, BDS, Galileo and GLONASS in both static and kinematic modes. The datasets from 118 stations spanning approximately a month are used for analysis, and the real-time stream CLK93 is employed. The superior performance of FSIRT-PPP is validated by comparing with the results of GPS/BDS, GPS/Galileo, GPS/GLONASS, GPS-only, BDS-only, Galileo-only and GLONASS-only cases. The FSIRT-PPP using ionospheric-free (IF) combined observables can achieve a convergence time of 10.9, 4.8 and 11.8 min and a positioning accuracy of 0.4, 0.5 and 0.7 cm in the static mode in the east, north and up directions, respectively, while the derived statistic is 15.4, 7.0 and 16.4 min, and 1.6, 1.2 and 3.4 cm in the kinematic mode in the three directions, respectively. Moreover, we also compare the position solutions of real-time PPP adopting IF combined and uncombined (UC) observables, and prove the mathematical equivalence between the two PPP models in the converged stage, provided that there are no external ionospheric corrections or constraints given to the estimated ionospheric delays in the UC model. The difference between the fully converged positioning accuracy of IF-based and UC-based real-time PPP is marginal, but the UC-based real-time PPP has longer convergence time due to the influence of the significant unmodeled time-varying errors in the real-time precise products as well as the different parameterization between them. For completeness, the real-time kinematic PPP results in harsh environments and the post-processed PPP results are also presented. 相似文献