全文获取类型
收费全文 | 2224篇 |
免费 | 642篇 |
国内免费 | 381篇 |
专业分类
航空 | 1690篇 |
航天技术 | 440篇 |
综合类 | 332篇 |
航天 | 785篇 |
出版年
2024年 | 3篇 |
2023年 | 38篇 |
2022年 | 100篇 |
2021年 | 107篇 |
2020年 | 135篇 |
2019年 | 109篇 |
2018年 | 124篇 |
2017年 | 118篇 |
2016年 | 106篇 |
2015年 | 134篇 |
2014年 | 148篇 |
2013年 | 142篇 |
2012年 | 162篇 |
2011年 | 166篇 |
2010年 | 138篇 |
2009年 | 185篇 |
2008年 | 175篇 |
2007年 | 140篇 |
2006年 | 125篇 |
2005年 | 112篇 |
2004年 | 85篇 |
2003年 | 93篇 |
2002年 | 118篇 |
2001年 | 100篇 |
2000年 | 46篇 |
1999年 | 68篇 |
1998年 | 54篇 |
1997年 | 36篇 |
1996年 | 35篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1986年 | 10篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1966年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有3247条查询结果,搜索用时 15 毫秒
141.
Jin-xing Yao Xing-feng Yu A. Tlamicha Feng-si Wei 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(12):2351-2354
This paper analyzes a Type U burst at 1.0 – 2.8 GHz which occurred between 12:36:26 – 12:36:32 UT on 1992 August 22, observed by Ond
ejov Observatory, Czech Republic. This may be the first example of Type U bursts in the decimetric range, as far as we know. From analysis we came to the following conclusion: (1) The frequency drift rates of the ascending and descending branches are 1.25 and 0.225 GHz/s, respectively, and the velocities of the electron beam are 0.38 c and 0.26 c, respectively; (2) The burst decay of the ascending branch is larger than that of the descending branch; (3) The variations of the maximum frequencies of instantaneous spectra with time appear as from the highest (1.92 GHz) to the lowest (1.0 GHz), then toward higher frequency (1.53 GHz) (this is consistent with that predicted by plasma emission theory); (4) The bandwidths of the ascending branch are about twice that of the descending branch (this may be caused by the larger drift rates of the ascending branch); (5) The temperature of the coronal loop apex is 6.3 × 106 K; (6) The magnetic field at the top of the loop is greater than 9.2 G; (7) This U burst emission is plasma radiation at the second harmonic. 相似文献
142.
以中国空间技术研究院电子元器件可靠性中心1987~1990四个年度数百份失效分析报告为依据,得到卫星用半导体器件解剖前失效模式分布:逻辑失控占36.3%,开路占22.2%等;失效机理分布:铝腐蚀占1 6.3%,使用不当占14.6%等。该项研究以第一手数据首次全面、系统指出卫星用器件失效模式和机理。为卫星可靠性设计、优选器件厂及器件厂采取措施提供重要依据。 相似文献
143.
电离层延迟是全球卫星导航系统(GNSS)的主要误差源之一。对于装配GNSS单频接收机的航空器,选择简单有效的Klobuchar广播电离层模型来改正电离层延迟误差,其修正率为50%~60%。针对45°(N)纬度带,提出了更高电离层修正需求。考虑到季节因素对中高纬度地区电离层的显著影响,利用GIMs(Global Ionospheric Maps)分析了昼夜中TEC(Total Electron Content)的峰值和谷值随季节(年积日)的变化,建立了一种适用于45°(N)纬度带的Klobuchar like电离层模型。该模型不增加广播模型系数,新模型的夜间和VTEC高峰时电离层修正率分别达到了82%和80%,表明在穿刺点集中的45°(N)纬度地区使用该模型可以更精确地描述该地区的电离层,帮助航空器实现更高精度的定位。 相似文献
144.
145.
146.
147.
148.
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
149.
150.