全文获取类型
收费全文 | 496篇 |
免费 | 107篇 |
国内免费 | 106篇 |
专业分类
航空 | 389篇 |
航天技术 | 100篇 |
综合类 | 41篇 |
航天 | 179篇 |
出版年
2024年 | 2篇 |
2023年 | 15篇 |
2022年 | 21篇 |
2021年 | 14篇 |
2020年 | 31篇 |
2019年 | 31篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 38篇 |
2015年 | 29篇 |
2014年 | 34篇 |
2013年 | 28篇 |
2012年 | 32篇 |
2011年 | 45篇 |
2010年 | 33篇 |
2009年 | 29篇 |
2008年 | 42篇 |
2007年 | 27篇 |
2006年 | 23篇 |
2005年 | 22篇 |
2004年 | 24篇 |
2003年 | 17篇 |
2002年 | 20篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 17篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1985年 | 3篇 |
排序方式: 共有709条查询结果,搜索用时 906 毫秒
701.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(5):2509-2520
This work develops a tension control strategy for deploying an underactuated spin-stable tethered satellite formation in the hub-spoke configuration. First, the Lagrange equation is used to model the spin-deployment dynamics of the tethered satellite formation. The central spacecraft is modeled as a rigid body, and the tethered subsatellites are simplified as lumped masses. Second, a pure tension controller has been proposed to suppress the tether libration motion in the deployment without thrusting at the subsatellites. A nonlinear sliding mode control is introduced in the tension controller for the underactuated system to suppress the periodic gravitational perturbations caused by the spinning hub-spoke tethered satellite formation. The unknown upper bounds of the perturbations are estimated by adaptive control law. The bounded stability of the closed-loop tension controller has been proved by the Lyapunov theory. Finally, numerical simulations validate the effectiveness and robustness of the proposed controller, i.e., tethers are fully deployed stably to the desired hub-spoke configuration. 相似文献
702.
《中国航空学报》2023,36(5):582-594
The Large-size Conical Cylinders with Inner Transverse High Ribs (LCCWITHR) can reduce the weight of the parts while maintaining high rigidity and strength. Radially Loading Rotary Extrusion (RLRE) forming technology can achieve integral forming of LCCWITHR through the synergy of radial and rotary movements of dies. The flow law of the material during the forming process is the key to forming large-size inner ribs. At present, there is no unified understanding of the metal flow law of RLRE forming technology. An analytical expression was derived to predict the Radial Direction (RD) deformation loads. The FE simulation and process experiment were carried out to investigate the effects of the inclination angle, thickness factor and transition arc radius of the split top dies on the spacing of the metal diversion plane, the metal flow velocity of the rib area and the final radius of the inner rib. The influence of the split top dies loading distance and the bottom die rotation angle of each pass on the inner radius of the inner rib was verified. And the optimal combination of dies shape parameters and loading paths which can make the metal flow orderly was obtained: the inclination angle is 140°, the thickness factor is 3.64, the transition arc radius is 16 mm; the top dies loading distance is 15 mm, the bottom die rotation angle is 45°. The FE simulation results have been found to be in close agreement with physics experiment. The research results reveal the metal flow law of rib growth in the RLRE of LCCWITHR, which lays a theoretical foundation for subsequent thorough research and process optimization. 相似文献
703.
The minimum-time path for intercepting a moving target with a prescribed impact angle is studied in the paper. The candidate paths from Pontryagin’s maximum principle are synthesized,so that each candidate is related to a zero of a real-valued function. It is found that the real-valued functions or their first-order derivatives can be converted to polynomials of at most fourth degree.As a result, each candidate path can be computed within a constant time by embedding a standard polynomial solver... 相似文献
704.
705.
This paper deals with the problem of intercepting maneuvering targets with terminal angle constraints for missiles subjected to three-dimensional non-decoupling engagement geometry.To achieve the finite-time interception and satisfactory overload characteristics, a time varying sliding mode control methodology is developed based on a time base generator function. The main feature of the proposed guidance law guarantees the Line-of-Sight(LOS) angles to converge to small neighborhoods of the desir... 相似文献
706.
707.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(1):654-675
Space law education has an essential role in the space capacity building of a country because of its importance for human resources development in space law. Comparisons between Canada and China, the European Union and China and the United States of America (USA) and China in space law degree education, course, teaching methodology, institute and practice and communication platform are provided in an attempt to review some issues which exist within the Chinese space law educational system and to seek a better choice for China’s space law education reform. Chinese space law education has achieved noticeable progress over the past two decades. However, it is still limited in comparison to its counterparts in Europe and Northern America. The range of the space law degree education programmes and space-law-related courses is comparatively limited. A gap remains between space law education and practice in China. Chinese space law classes are still dominated by the teacher-centred teaching methodology, although several universities have some new teaching practices. The establishment of seven space law-related research institutes plays an increasingly important role in Chinese space law education, space law and policy research and legal advisory services for the Chinese government and non-governmental sectors. However, these institutes still have a long way to go in comparison with their counterparts in Europe and Northern America. While China has established domestic research platforms for space law communication through international cooperation, it does not provide space law practice platforms for space law education. While international space law does not provide a direct legal foundation for space law education in China, Chinese educational laws can lay a profound legal foundation for Chinese space law education. To promote its national expertise and capacity in space law, based on the three-pillar model and the experiences of its counterparts in North America and Europe, China should adopt a systematic and sustainable regime for its space law education. 相似文献
708.
针对一类含不确定参数的严格反馈型极值搜索系统的控制问题,将极值搜索方法和反演(Backstepping)控制方法相结合,设计出系统状态的极值参考轨迹,利用 Backstepping控制方法逐步递推选取适当的 Lyapunov函数设计控制器和不确定参数自适应估计律,实现目标函数的极值搜索。仿真表明所提出控制器设计方法的有效性。 相似文献
709.