全文获取类型
收费全文 | 2534篇 |
免费 | 496篇 |
国内免费 | 344篇 |
专业分类
航空 | 1834篇 |
航天技术 | 430篇 |
综合类 | 341篇 |
航天 | 769篇 |
出版年
2024年 | 27篇 |
2023年 | 50篇 |
2022年 | 78篇 |
2021年 | 115篇 |
2020年 | 121篇 |
2019年 | 120篇 |
2018年 | 109篇 |
2017年 | 143篇 |
2016年 | 167篇 |
2015年 | 115篇 |
2014年 | 198篇 |
2013年 | 130篇 |
2012年 | 184篇 |
2011年 | 202篇 |
2010年 | 116篇 |
2009年 | 141篇 |
2008年 | 153篇 |
2007年 | 129篇 |
2006年 | 137篇 |
2005年 | 143篇 |
2004年 | 125篇 |
2003年 | 102篇 |
2002年 | 80篇 |
2001年 | 67篇 |
2000年 | 51篇 |
1999年 | 49篇 |
1998年 | 66篇 |
1997年 | 50篇 |
1996年 | 29篇 |
1995年 | 33篇 |
1994年 | 29篇 |
1993年 | 23篇 |
1992年 | 17篇 |
1991年 | 18篇 |
1990年 | 21篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 10篇 |
1984年 | 1篇 |
排序方式: 共有3374条查询结果,搜索用时 0 毫秒
711.
Arc fault detection is desperately required in Solid State Power Controllers (SSPC) in addition to their fundamental functions because arcs will provoke growing harm and threat to aircraft safety. Experimental study has been done to obtain the faulted current data. In order to improve the detection speed and accuracy, two fast arc fault detection methods have been proposed in this paper with the analysis of only half cycle data. Both Fast Fourier Transform (FFT) and Wavelet Packets Decomposition (WPD) have been adopted to distinguish arc fault currents from normal operation currents. Analysis results show that Alternating Current (AC) arcs can be effectively and accurately detected with the proposed half cycle data based methods. Moreover, experimental verification results have also been provided. 相似文献
712.
LEAP—X发动机是CFM国际公司研发的新一代发动机,采用了许多先进技术。本文就LEAP-X发动机的先进技术创新做一概括性分析。供相关人士参考。 相似文献
713.
Tech-X发动机是GE公司研发的用于超大航程公务机的新一代高涵道比涡扇发动机.本文就Tech-X发动机的性能指标和先进技术创新进行了概括性分析,供相关人士参考. 相似文献
714.
715.
《北京航空航天大学学报》2012,38(2)
以机载泵源系统的恒功率控制为目标,针对作业任务中系统负载随时间变化的情况,采用使液压系统输出功率保持恒定的控制方式来达到充分利用发动机功率的目的,对于机载泵源控制系统的主要被控对象——轴向柱塞式变量泵,建立了其状态方程和流量输出方程,采用H。鲁棒镇定控制策略实时调节泵的排量,仿真结果表明:当负载变化时,系统能根据压力的变化快速转换到恒功率工作曲线下对应的流量状态,所设计的H。控制器能够减小干扰和模型参数不确定对系统稳定性的影响,具有良好的鲁棒性,表明该方法用于机载液压系统可以改善系统工作性能,提高系统功率的利用率。 相似文献
716.
717.
A new type of plasma rocket engine, the Kabila rocket, using a radioisotope heated thermionic heating chamber instead of a conventional combustion chamber or catalyst bed is introduced and it achieves specific impulses similar to the ones of conventional solid and bipropellant rockets. Curium-244 is chosen as a radioisotope heat source and a thermal reductive layer is also used to obtain precise thermionic emissions. The self-sufficiency principle is applied by simultaneously heating up the emitting material with the radioisotope decay heat and by powering the different valves of the plasma rocket engine with the same radioisotope decay heat using a radioisotope thermoelectric generator. This rocket engine is then benchmarked against a 1 N hydrazine thruster configuration operated on one of the Pleiades-HR-1 constellation spacecraft. A maximal specific impulse and power saving of respectively 529 s and 32% are achieved with helium as propellant.Its advantages are its power saving capability, high specific impulses and simultaneous ease of storage and restart. It can however be extremely voluminous and potentially hazardous. The Kabila rocket is found to bring great benefits to the existing spacecraft and further research should optimize its geometric characteristics and investigate the physical principals of its operation. 相似文献
718.
719.
S. Gadimova H.J. Haubold 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1863-1865
Based on resolutions of the United Nations General Assembly, Regional Centres for Space Science and Technology Education were established in India, Morocco, Nigeria, Brazil and Mexico. Simultaneously, education curricula were developed for the core disciplines of remote sensing, satellite communications, satellite meteorology, and space and atmospheric science. This paper provides a brief summary on the status of the operation of the regional centres with a view to use them as information centres of the International Committee on Global Navigation Satellite Systems (ICG), and draws attention to their educational activities. 相似文献