全文获取类型
收费全文 | 633篇 |
免费 | 128篇 |
国内免费 | 246篇 |
专业分类
航空 | 599篇 |
航天技术 | 166篇 |
综合类 | 85篇 |
航天 | 157篇 |
出版年
2024年 | 2篇 |
2023年 | 28篇 |
2022年 | 45篇 |
2021年 | 46篇 |
2020年 | 61篇 |
2019年 | 42篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 44篇 |
2015年 | 52篇 |
2014年 | 65篇 |
2013年 | 56篇 |
2012年 | 49篇 |
2011年 | 68篇 |
2010年 | 53篇 |
2009年 | 63篇 |
2008年 | 40篇 |
2007年 | 38篇 |
2006年 | 33篇 |
2005年 | 34篇 |
2004年 | 25篇 |
2003年 | 17篇 |
2002年 | 16篇 |
2001年 | 17篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
排序方式: 共有1007条查询结果,搜索用时 15 毫秒
1.
《中国航空学报》2020,33(2):407-417
Multi-faults detection is a challenge for rolling bearings due to the mode mixture and coupling of multiple fault features, as well as its easy burying in the complex, non-stationary structural vibrations and strong background noises. In this paper, a method based on the flexible analytical wavelet transform (FAWT) possessing fractional scaling and translation factors is proposed to identify multiple faults occurred in different components of rolling bearings. During the route of the proposed method, the proper FAWT bases are constructed via genetic optimization algorithm (GA) based on maximizing the spectral correlated kurtosis (SCK) which is firstly presented and proved to be efficient and effective in indicating interested fault mode. Via using the customized FAWT bases for each interested fault mode, the original vibration measurements are decomposed into fine frequency subbands, and the sensitive subband which enhances the signal-to-noise ratio (SNR) is selected to exhibit the fault signature on its envelope spectrum. The proposed method is tested via simulated signals, and applied to analyze the experimental vibration measurements from the running roller bearings subjected to outrace, inner-race and roller defects. The analysis results validate the effectiveness of the proposed method in identifying multi-faults occurred in different components of rolling bearings. 相似文献
2.
《中国航空学报》2020,33(12):3206-3219
Topology optimization is an effective method to obtain a lightweight structure that meets the requirements of structural strength. Whether the optimization results meet the actual needs mainly depends on the accuracy of the material properties and the boundary conditions, especially for a tiny Flapping-wing Micro Aerial Vehicle (FMAV) transmission system manufactured by 3D printing. In this paper, experimental and numerical computation efforts were undertaken to gain a reliable topology optimization method for the bottom of the transmission system. First, the constitutive behavior of the ultraviolet (UV) curable resin used in fabrication was evaluated. Second, a numerical computation model describing further verified via experiments. Topology optimization modeling considering nonlinear factors, e.g. contact, friction and collision, was presented, and the optimization results were verified by both dynamic simulation and experiments. Finally, detailed discussions on different load cases and constraints were presented to clarify their effect on the optimization. Our methods and results presented in this paper may shed light on the lightweight design of a FMAV. 相似文献
3.
4.
5.
6.
In 1994-1995 Lavochkin Association (Russia) together with the other enterprises in accordance with technical requirements of the Russian Space agency, developed a new Russian communication satellite of a small class that will operate in both the geostationary (GSO) and high-elliptical (HEO) orbits. This satellite may be injected into operational orbits using a SOYUZ-2 launch vehicle (LV) and a FREGAT upper stage (US) from Plesetsk and Baykonur space launch sites (SLS).The main reason for creating such a satellite was to decrease the cost of the support and development of the Russian communication geostationary satellites group.Russian satellites Horizont, Express, Ekran and Gals, which operate in GSO, are the basis of the space segment for communications, radio and TV broadcasting. All of these satellites are injected into GSO by the PROTON LV. PROTON is a launch vehicle of a heavy class. The use of a middle class LV instead of a heavy class will allow to reduce considerably the launch cost. The change of a heavy class LV to a LV of middle class determined one economic reason for this project. Besides, the opportunity to launch S/C into GSO from Russian Plesetsk SLS increases the independence of Russia in the domain of space communications, despite the presence of the contract with Kazachstan about the rent of Baykonur SLS. Finally, use of small satellites with a rather small number of transponders is more effective than the use of big satellites. It will allow also to increase a satellite group (by the launch of additional satellites) precisely in accordance to the development of the ground segment. 相似文献
7.
根据气动布局的基本原理,结合低RCS要求,设计了一种鸭式布局、带边条的翼身融合无人飞行器外形,实验结果表明,该外形不仅具有低RCS特征,而且具有良好的气动特性,升阻比达到8左右。 相似文献
8.
9.
10.
对机动再入飞行器弧段的复合制导方案进行了研究,首先提出了通过高低空复合制导控制再入飞行器的终端速度和弹道倾角的思路;然后分别给出了高空最优制导律和大气厚再入最优制导律;最后对此复合制导方案进行了数字仿真。仿真结果表明此方案在理论上是可行的。 相似文献