全文获取类型
收费全文 | 4292篇 |
免费 | 939篇 |
国内免费 | 947篇 |
专业分类
航空 | 2978篇 |
航天技术 | 1224篇 |
综合类 | 602篇 |
航天 | 1374篇 |
出版年
2024年 | 26篇 |
2023年 | 52篇 |
2022年 | 128篇 |
2021年 | 171篇 |
2020年 | 165篇 |
2019年 | 113篇 |
2018年 | 136篇 |
2017年 | 148篇 |
2016年 | 132篇 |
2015年 | 184篇 |
2014年 | 277篇 |
2013年 | 271篇 |
2012年 | 309篇 |
2011年 | 329篇 |
2010年 | 374篇 |
2009年 | 325篇 |
2008年 | 317篇 |
2007年 | 258篇 |
2006年 | 223篇 |
2005年 | 179篇 |
2004年 | 146篇 |
2003年 | 129篇 |
2002年 | 119篇 |
2001年 | 120篇 |
2000年 | 158篇 |
1999年 | 172篇 |
1998年 | 209篇 |
1997年 | 151篇 |
1996年 | 139篇 |
1995年 | 120篇 |
1994年 | 105篇 |
1993年 | 102篇 |
1992年 | 78篇 |
1991年 | 72篇 |
1990年 | 57篇 |
1989年 | 48篇 |
1988年 | 51篇 |
1987年 | 36篇 |
1986年 | 18篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1965年 | 3篇 |
排序方式: 共有6178条查询结果,搜索用时 15 毫秒
871.
872.
杨光 《沈阳航空工业学院学报》1997,(4)
本文研究了P1─—多面体与其对偶图形的对偶图形边长之间的关系问题.设P1─—多面体的边长为a,其对偶图形的对偶图形的边长为C,则其中θ1为多面体A的过顶点的相邻两校之间的夹角,θ2为多面体B的过顶点的相邻两校之间的夹角,取θ=max{θ1,θ1} 相似文献
873.
874.
杨继松 《中国空间科学技术》1997,17(4):1-8
通过对几个具体实例的计算,证实了在电磁场边值问题的矩量法求解过程中,选用不同的基函数其解的数值稳定性会有很大的差别。从而有可能选择一种数值稳定性比较好的基函数来进行矩量法求解。另一方面,提出了选用多尺度子域基函数,并通过多次迭代来提高矩量法解的精度的算法。实例计算表明,该算法不仅可以有效地降低系数矩阵的条件数,而且还降低了对计算机内存容量的要求,是一种有效的、稳定的算法 相似文献
875.
Alberto Buzzoni Giuseppe Altavilla Siwei Fan Carolin Frueh Italo Foppiani Marco Micheli Jaime Nomen Noelia Sánchez-Ortiz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):371-393
We report on extensive photometry and low-resolution () spectroscopy of the deep-space debris WT1190F, which impacted Earth offshore from Sri Lanka, on 2015 November 13. In spite of its likely artificial origin (as a relic of some past lunar mission), the case offered important points of discussion for its suggestive connection with the envisaged scenario for a (potentially far more dangerous) natural impactor, like an asteroid or a comet.Our observations indicate for WT1190F an absolute magnitude , with a flat dependence of reflectance on the phase angle, such as ?mag?deg?1. The detected short-timescale variability suggests that the body was likely spinning with a period twice the nominal figure of , as from the observed lightcurve. In the color domain, WT1190F closely resembled the Planck deep-space probe. This match, together with a depressed reflectance around 4000 and 8500 Å may be suggestive of a “grey” (aluminized) surface texture.The spinning pattern remained in place also along the object fiery entry in the atmosphere, a feature that may have partly shielded the body along its fireball phase perhaps leading a large fraction of its mass to survive intact, now lying underwater along a tight (?km) strip of sea, at a depth of 1500?m or less.Under the assumption of Lambertian scatter, an inferred size of ?cm is obtained for WT1190F. By accounting for non-gravitational dynamical perturbations, the Area-to-Mass ratio of the body was in the range ?m2?kg?1.Both these figures resulted compatible with the two prevailing candidates to WT1190F’s identity, namely the Athena II Trans-Lunar Injection Stage of the Lunar Prospector mission, and the ascent stage of the Apollo 10 lunar module, callsign “Snoopy”. Both candidates have been analyzed in some detail here through accurate 3D CAD design mockup modelling and BRDF reflectance rendering to derive the inherent photometric properties to be compared with the observations. 相似文献
876.
877.
878.
879.
在5G快速发展的时代背景下,为解决林业资源管理中网络覆盖有限、即时通信困难和遥感数据利用不充分等问题,本文探讨了融合通信、导航、遥感卫星系统与地面移动通信网络,实现即时通信、精准定位、遥感数据按需服务的可行性,提出了“云+端”的5G通导遥融合应用模式,推动新一代航天技术赋能智慧林业建设。 相似文献
880.
Rui Zhang Rui Tu Pengfei Zhang Lihong Fan Junqiang Han Xiaochun Lu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(12):4011-4024
The BeiDou global navigation satellite system (BDS-3) has established the Ka-band inter-satellite link (ISL) to realize a two-way ranging function between satellites, which provides a new observation technology for the orbit determination of BDS-3 satellites. Therefore, this study presents a BDS satellite orbit determination model based on ground tracking station (GTS) observations and ISL ranging observations firstly to analyze the impact of the ISL ranging observations on the orbit determination of BDS-3 satellites. Subsequently, considering the data fusion processing, the variance component estimation (VCE) algorithm is applied to the parameter estimation process of the satellite orbit determination. Finally, using the measured data from China’s regional GTS observations and BDS-3 ISL ranging observations, the effects of ISL ranging observations on the orbit determination accuracy of BDS-3 satellites are analyzed. Moreover, the impact of the VCE algorithm on the fusion data processing is evaluated from the aspects of orbit determination accuracy, Ka-band hardware delay parameter stability, and ISL ranging observation residuals. The results show that for China’s regional GTSs, the addition of BDS-3 ISL ranging observations can significantly improve the orbit determination accuracy of BDS-3 satellites. The observed orbit determination accuracy of satellite radial component is improved from 48 cm to 4.1 cm. In addition, when the initial weight ratio between GTS observations and ISL ranging observations is not appropriate, the various indicators which include orbit determination accuracy, ISL hardware delay, and ISL observation residuals were observed to have improved after the adjustment of the VCE algorithm. These results validate the effectiveness of the VCE algorithm for the fusion data processing of the GTS observations and ISL ranging observations. 相似文献