全文获取类型
收费全文 | 1798篇 |
免费 | 309篇 |
国内免费 | 255篇 |
专业分类
航空 | 429篇 |
航天技术 | 749篇 |
综合类 | 59篇 |
航天 | 1125篇 |
出版年
2024年 | 21篇 |
2023年 | 76篇 |
2022年 | 77篇 |
2021年 | 91篇 |
2020年 | 87篇 |
2019年 | 74篇 |
2018年 | 112篇 |
2017年 | 57篇 |
2016年 | 71篇 |
2015年 | 104篇 |
2014年 | 145篇 |
2013年 | 98篇 |
2012年 | 141篇 |
2011年 | 153篇 |
2010年 | 106篇 |
2009年 | 108篇 |
2008年 | 103篇 |
2007年 | 106篇 |
2006年 | 78篇 |
2005年 | 72篇 |
2004年 | 56篇 |
2003年 | 52篇 |
2002年 | 36篇 |
2001年 | 62篇 |
2000年 | 37篇 |
1999年 | 24篇 |
1998年 | 32篇 |
1997年 | 22篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 29篇 |
1989年 | 8篇 |
1988年 | 14篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有2362条查询结果,搜索用时 31 毫秒
991.
美国FIA光学成像卫星项目失败的启示 总被引:1,自引:1,他引:1
“未来成像体系”(FIA)是美国政府大胆创新发展的新一代间谍卫星项目。此项目的取消或许是美国50年间谍卫星发展历史中最为惨痛的失败。文章介绍了FIA项目的发展背景、先进能力以及整个研制过程,并介绍了美国采取的一些补救措施。最后总结了FIA项目失败所揭示的一些经验教训。 相似文献
992.
993.
994.
卫星和地面之间的交流通过它们之间的数据通讯来实现。为了实现星地通讯,必须选定双方都要遵守的协议。考虑到星地通信的可靠性和效率,在选择通讯协议时需遵循实用且最简单的原则。参考CCSDS的相关建议和Ax.25协议,开发了一种星地链路层通信协议。纳星一号飞行试验的运行结果表明,该协议具有较高的数据传榆效率和良好的可靠性,可以满足微小卫星的实际通信要求。 相似文献
995.
996.
Chang'E-1, the first lunar mission in China, was successfully launched on October 24,2007, which opened the prelude of China's Lunar Exploration Program. Later on, the Chang'E-2 and Chang'E-3 satellites were successfully launched in 2010 and 2013, respectively. In order to achieve the science objectives, various payloads boarded the spacecraft. The scientific data from these instruments were received by Beijing and Kunming ground stations simultaneously. Up to now, about 5.628 Terabytes of raw data were received totally. A series of research results has been achieved. This paper presents a brief introduction to the main scientific results and latest progress from Chang'E-3 mission. 相似文献
997.
Atanas Marinov Atanassov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Computer simulation is a very helpful approach for improving results from space born experiments. Initial-value problems (IVPs) can be applied for modeling dynamics of different objects – artificial Earth satellites, charged particles in magnetic and electric fields, charged or non-charged dust particles, space debris. An ordinary differential equations systems (ODESs) integrator based on applying different order embedded Runge–Kutta–Fehlberg methods is developed. These methods enable evaluation of the local error. Instead of step-size control based on local error evaluation, an optimal integration method is selected. Integration while meeting the required local error proceeds with constant-sized steps. This optimal scheme selection reduces the amount of calculation needed for solving the IVPs. In addition, for an implementation on a multi core processor and parallelization based on threads application, we describe how to solve multiple systems of IVPs efficiently in parallel. 相似文献
998.
Guanwen Huang Bobin Cui Qin Zhang Pingli Li Wei Xie 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(5):1681-1696
The information of the satellite clock switching and performance variations on-orbit of Chinese BeiDou-2 Navigation System (BDS) is not available for the public. In order to detect the BDS satellite clock switching and performances variation, we analyzed the precise clock offset products with a total duration of 5?years every BDS satellite equipped four atomic clocks from four different manufactures from January 2013 to October 2017. Three important contributions are concluded as follows. (1) It is found that the average time of on-orbit operation for BDS satellite clocks is about 1–2?years. There have been 22 times of clock switching for BDS satellites, of which the C05 and C08 satellites have been switched to the fourth (last) atomic clock. (2) There are frequent phase adjustments for BDS on-orbit satellite clocks, and the frequency series is relatively stable. Furthermore, there are semi-annual sinusoid cycles in the frequency drift series of C06 and C09 satellites. (3) The performances of MEO satellite clocks perform better than the IGSO and GEO satellite clocks. The average ten-thousand frequency stability of BDS satellite clocks is about 1E-13, which is worse than that of GPS and Galileo but better than that of GLONASS. 相似文献
999.
为提高中继卫星系统的应用效能及数传任务的完成率,在中继卫星调度中考虑了断点续传这一应用模式,即对单个数传任务进行合理拆分,使其在多个时间窗口内完成。首先构建面向断点续传的中继卫星单址天线的调度模型,然后提出一种基于冲突风险评估的冲突度量化方法,并设计考虑断点续传的两阶段调度算法。最后开展大量的仿真实验将该算法与贪婪算法、基于最小冲突度的启发式算法和基于任务优先级的启发式算法这3个不考虑断点续传的算法进行对比。实验结果表明,所提出的算法在任务完成率方面分别提高了7.67%、6.34%和8.67%。 相似文献
1000.
Arun Kumar Singh Haris Haralambous Christina Oikonomou Theodoros Leontiou 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):739-748
We examine the systematic differences between topside electron density measurements recorded by different techniques over the low-middle latitude operating European station in Nicosia, Cyprus (geographical coordinates: 35.14oN, 33.2oE), (magnetic coordinates 31.86oN, 111.83 oE). These techniques include space-based in-situ data by Langmuir probes on board.European Space Agency (ESA) Swarm satellites, radio occultation measurements on board low Earth orbit (LEO) satellites from the COSMIC/FORMOSAT-3 mission and ground-based extrapolated topside electron density profiles from manually scaled ionograms. The measurements are also compared with International Reference Ionosphere Model (IRI-2016) topside estimations and IRI-corrected NeQuick topside formulation (method proposed by Pezzopane and Pignalberi (2019)). The comparison of Swarm and COSMIC observations with digisonde and IRI estimations verifies that in the majority of cases digisonde underestimates while IRI overestimates Swarm observations but in general, IRI provides a better topside representation than the digisonde. For COSMIC and digisonde profiles matched at the F layer peak the digisonde systematically underestimates topside COSMIC electron density values and the relative difference between COSMIC and digisonde increases with altitude (above hmF2), while IRI overestimates the topside COSMIC electron density but after a certain altitude (~150 km above hmF2) this overestimation starts to decrease with altitude. The IRI-corrected NeQuick underestimates the majority of topside COSMIC electron density profiles and relative difference is lower up to approximately 100 km (above the hmF2) and then it increases. The overall performance of IRI-corrected NeQuick improves with respect to IRI and digisonde. 相似文献