全文获取类型
收费全文 | 2008篇 |
免费 | 242篇 |
国内免费 | 601篇 |
专业分类
航空 | 1099篇 |
航天技术 | 379篇 |
综合类 | 410篇 |
航天 | 963篇 |
出版年
2024年 | 5篇 |
2023年 | 18篇 |
2022年 | 29篇 |
2021年 | 36篇 |
2020年 | 39篇 |
2019年 | 40篇 |
2018年 | 34篇 |
2017年 | 29篇 |
2016年 | 33篇 |
2015年 | 53篇 |
2014年 | 58篇 |
2013年 | 91篇 |
2012年 | 113篇 |
2011年 | 112篇 |
2010年 | 66篇 |
2009年 | 92篇 |
2008年 | 74篇 |
2007年 | 64篇 |
2006年 | 58篇 |
2005年 | 69篇 |
2004年 | 195篇 |
2003年 | 137篇 |
2002年 | 204篇 |
2001年 | 238篇 |
2000年 | 97篇 |
1999年 | 95篇 |
1998年 | 62篇 |
1997年 | 40篇 |
1996年 | 32篇 |
1995年 | 24篇 |
1994年 | 22篇 |
1993年 | 59篇 |
1992年 | 65篇 |
1991年 | 164篇 |
1990年 | 135篇 |
1989年 | 125篇 |
1988年 | 25篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1966年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有2851条查询结果,搜索用时 770 毫秒
491.
492.
Xuemin Zhang Shufan Zhao Rui Song Dulin Zhai 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(11):3536-3544
The artificial low frequency (LF) signals recorded at topside ionosphere from DEMETER satellite were analyzed in this paper, and the typical diurnal and seasonal variations were illustrated around 162?kHz in electric field spectra. The larger power spectrum density (PSD) values in electric field at local nighttime and in winter season all demonstrate the correlation feature of lower plasma content to higher penetration of LF waves into ionosphere. Around Wenchuan earthquake, the comparison of signal-noise-ratio (SNR) values in electric field with each half month during January to May in 2008 and the same half month in May from 2005 to 2007 revealed their lowest values and small covering area around the preparation region of Wenchuan earthquake in 2008. Combined with other researches in VLF radio waves and geochemical observations from satellite, the interaction of ion accumulation and upward movement from gas-water release at surface might be a key factor to disturb the ionospheric plasma density, and then possibly leading to the decrease of low energy penetration of LF radio waves from the artificial transmitted source at ground. 相似文献
493.
Fen Cao XuHai Yang ZhiGang Li BaoQi Sun Yao Kong Liang Chen Chugang Feng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
In order to establish a continuous GEO satellite orbit during repositioning maneuvers, a suitable maneuver force model has been established associated with an optimal orbit determination method and strategy. A continuous increasing acceleration is established by constructing a constant force that is equivalent to the pulse force, with the mass of the satellite decreasing throughout maneuver. This acceleration can be added to other accelerations, such as solar radiation, to obtain the continuous acceleration of the satellite. The orbit determination method and strategy are illuminated, with subsequent assessment of the orbit being determined and predicted accordingly. The orbit of the GEO satellite during repositioning maneuver can be determined and predicted by using C-Band pseudo-range observations of the BeiDou GEO satellite with COSPAR ID 2010-001A in 2011 and 2012. The results indicate that observations before maneuver do affect orbit determination and prediction, and should therefore be selected appropriately. A more precise orbit and prediction can be obtained compared to common short arc methods when observations starting 1 day prior the maneuver and 2 h after the maneuver are adopted in POD (Precise Orbit Determination). The achieved URE (User Range Error) under non-consideration of satellite clock errors is better than 2 m within the first 2 h after maneuver, and less than 3 m for further 2 h of orbit prediction. 相似文献
494.
一类非线性系统的变结构控制问题 总被引:1,自引:0,他引:1
本文研究了简约型非线性控制系统的变结构控制问题,针对变结构控制切换函数的确定问题进行了深入研究,给出了一类非线性系统切换函数的确定方法。研究结果表明,该方法适用于一类难于或不能可控正则化和线性化的非线性控制系统的综合。最后通过仿真证实了该方法的有效性。 相似文献
495.
496.
戚发轫 《中国空间科学技术》1990,10(1):1-7
通信卫星是空间技术和通信技术相结合,并在应用中效益最显著的成果之一。本文就通信卫星的历史、现状作了一些回顾和阐述;对我国通信卫星发展方向提出了一些看法和建议。 相似文献
497.
498.
499.
500.