全文获取类型
收费全文 | 764篇 |
免费 | 104篇 |
国内免费 | 104篇 |
专业分类
航空 | 467篇 |
航天技术 | 163篇 |
综合类 | 143篇 |
航天 | 199篇 |
出版年
2024年 | 3篇 |
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 11篇 |
2017年 | 19篇 |
2016年 | 23篇 |
2015年 | 12篇 |
2014年 | 36篇 |
2013年 | 30篇 |
2012年 | 33篇 |
2011年 | 34篇 |
2010年 | 48篇 |
2009年 | 41篇 |
2008年 | 38篇 |
2007年 | 43篇 |
2006年 | 48篇 |
2005年 | 39篇 |
2004年 | 45篇 |
2003年 | 34篇 |
2002年 | 31篇 |
2001年 | 23篇 |
2000年 | 22篇 |
1999年 | 38篇 |
1998年 | 37篇 |
1997年 | 32篇 |
1996年 | 36篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 23篇 |
1992年 | 20篇 |
1991年 | 20篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 11篇 |
1987年 | 8篇 |
排序方式: 共有972条查询结果,搜索用时 31 毫秒
941.
942.
943.
索穹顶结构的气动阻尼识别 总被引:1,自引:0,他引:1
索穹顶是一种具有很强风振敏感性的大跨柔性结构,风振问题在设计中应予以高度重视,这其中气动阻尼有至关重要的影响,而如何有效地识别气动阻尼则是问题的关键.利用肋环型索穹顶结构气弹模型风洞实验的数据,先由经验模态分解法提取信号的低频分量,并在此基础上采用改进的随机减量法及Hilbert变换得到结构的气动阻尼,结果证明该方法是稳定而有效的.最后在计算分析的基础上总结了索穹顶结构中气动阻尼随风速及风向角的变化规律. 相似文献
944.
945.
采用伴随技术,得到了确定性误差条件下反舰导弹末端机动突防的稳态脱靶量解析解。利用该解析解,得到了各种末端机动的脱靶量曲线。结果表明,两种非平面机动方式比平面机动方式有更大的脱靶量,从而有更好的突防效果。 相似文献
946.
Modeling of LEO orbital debris populations for ORDEM2008 总被引:2,自引:0,他引:2
Y.-L. Xu M. Horstman P.H. Krisko J.-C. Liou M. Matney E.G. Stansbery C.L. Stokely D. Whitlock 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The NASA Orbital Debris Engineering Model, ORDEM2000, is in the process of being updated to a new version: ORDEM2008. The data-driven ORDEM covers a spectrum of object size from 10 μm to greater than 1 m, and ranging from LEO (low Earth orbit) to GEO (geosynchronous orbit) altitude regimes. ORDEM2008 centimeter-sized populations are statistically derived from Haystack and HAX (the Haystack Auxiliary) radar data, while micron-sized populations are estimated from shuttle impact records. Each of the model populations consists of a large number of orbits with specified orbital elements, the number of objects on each orbit (with corresponding uncertainty), and the size, type, and material assignment for each object. This paper describes the general methodology and procedure commonly used in the statistical inference of the ORDEM2008 LEO debris populations. Major steps in the population derivations include data analysis, reference-population construction, definition of model parameters in terms of reference populations, linking model parameters with data, seeking best estimates for the model parameters, uncertainty analysis, and assessment of the outcomes. To demonstrate the population-derivation process and to validate the Bayesian statistical model applied in the population derivations throughout, this paper uses illustrative examples for the special cases of large-size (>1 m, >32 cm, and >10 cm) populations that are tracked by SSN (the Space Surveillance Network) and also monitored by Haystack and HAX radars operating in a staring mode. 相似文献
947.
介绍了CV技术的基本原理和罗兰C系统原子频标资源的使用状况,并通过引入系统融合和CV技术,对比对数据进行检测校验,最终实现了罗兰C导航系统原子频标与UTC时间基准同步。 相似文献
948.
949.
Jae-Ik Park Han-Earl ParkSang-Young Park Kyu-Hong Choi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
A relative navigation and formation control algorithm for satellite formation flying was developed, and a hardware-in-the-loop (HIL) simulation testbed was established and configured to evaluate this algorithm. The algorithm presented is a relative navigation estimation algorithm using double-difference carrier-phase and single-difference code measurements based on the extended Kalman filter (EKF). In addition, a state-dependent Riccati equation (SDRE) technique is utilized as a nonlinear controller for the formation control problem. The state-dependent coefficient (SDC) form is formulated to include nonlinearities in the relative dynamics. To evaluate the relative navigation and control algorithms developed, a closed-loop HIL testbed is configured. To demonstrate the performance of the testbed, a test formation flying scenario comprising formation acquisition and keeping in a low earth orbit (LEO) has been established. The relative navigation results from the closed-loop simulations show that a 3D RMS of 0.07 m can be achieved for position accuracy. The targeted leader–follower formation flying in the along-track separation of 100 m was maintained with a mean position error of approximately 0.2 m and a standard deviation of 0.9 m. The simulation results show that the HIL testbed is capable of successful demonstration of the GPS-based satellite autonomous formation flying mission. 相似文献
950.
微吹减阻技术影响因素的数值模拟 总被引:1,自引:0,他引:1
以NASA格伦中心的PN3和PN23型微孔壁板为原形建立"1排微孔"、"4排微孔"、"8排微孔"和"16排微孔"4种计算模型,针对不同的几何、物理参数进行了微吹技术MBT(Micro-Blowing Technique)降低平板摩擦阻力的数值模拟参数研究.结果显示:微量吹气使主流边界层近壁面流动减速,从而改变了壁面局部摩擦力的分布;不同几何、物理参数对MBT技术减阻能力的影响满足一定的规律.参数研究的结果可为该技术的减阻应用提供一定的指导. 相似文献