全文获取类型
收费全文 | 1628篇 |
免费 | 253篇 |
国内免费 | 84篇 |
专业分类
航空 | 251篇 |
航天技术 | 939篇 |
综合类 | 10篇 |
航天 | 765篇 |
出版年
2023年 | 30篇 |
2022年 | 35篇 |
2021年 | 67篇 |
2020年 | 73篇 |
2019年 | 50篇 |
2018年 | 74篇 |
2017年 | 16篇 |
2016年 | 44篇 |
2015年 | 49篇 |
2014年 | 170篇 |
2013年 | 104篇 |
2012年 | 66篇 |
2011年 | 156篇 |
2010年 | 111篇 |
2009年 | 105篇 |
2008年 | 96篇 |
2007年 | 71篇 |
2006年 | 68篇 |
2005年 | 91篇 |
2004年 | 55篇 |
2003年 | 33篇 |
2002年 | 49篇 |
2001年 | 40篇 |
2000年 | 48篇 |
1999年 | 56篇 |
1998年 | 32篇 |
1997年 | 23篇 |
1996年 | 24篇 |
1995年 | 22篇 |
1994年 | 7篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 22篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1984年 | 2篇 |
排序方式: 共有1965条查询结果,搜索用时 0 毫秒
11.
12.
A numerical procedure for the calculation of the transonic dip of airfoils in the time domain is presented. A viscous-inviscid aerodynamic interaction method is taken to calculate the unsteady aerodynamic loads. In the present case the integral boundary layer equations are coupled with the Transonic Small Disturbance (TSD) Potential Equation. The coupling between structural motion and aerodynamic loads is carried out using State Space equation. It is solved by State Transition Matrix technique. Results are presented for NACA 64A010 and NLR 7301 airfoils with structural data from Isogai and DLR, respectively. Comparisons show good agreement with other numerical results. Certain deviations of experimental data taken from literature need more insight in the detailed test conditions. 相似文献
13.
14.
15.
16.
Various plants have the ability to follow the sun with their flowers or leaves during the course of a day via a mechanism known as heliotropism. This mechanism is characterised by the introduction of pressure gradients between neighbouring motor cells in the plant?s stem, enabling the stem to bend. By adapting this bio-inspired mechanism to mechanical systems, a new class of smart structures can be created. The developed overall structure is made up of a number of cellular colonies, each consisting of a central pressure source surrounded by multiple cells. After launch, the cellular arrays are deployed in space and are either preassembled or alternatively are attached together during their release or afterwards. A central pressure source is provided by a high-pressure storage unit with an integrated valve, which provides ingress gas flow to the system; the gas is then routed through the system via a sequence of valve operations and cellular actuations, allowing for any desired shape to be achieved within the constraints of the deployed array geometry. This smart structure consists of a three dimensional adaptable cellular array with fluid controlling Micro Electromechanical Systems (MEMS) components enabling the structure to change its global shape. The proposed MEMS components include microvalves, pressure sensors, mechanical interconnect structures, and electrical routing. This paper will also give an overview of the system architecture and shows the feasibility and shape changing capabilities of the proposed design with multibody dynamic simulations. Example applications of this lightweight shape changing structure include concentrators, mirrors, and communications antennas that are able to dynamically change their focal point, as well as substructures for solar sails that are capable of steering through solar winds by altering the sails? subjected area. 相似文献
17.
18.
Zhendong XU Yingchun ZHANG Pengfei LI Yongsheng WANG Limin DONG Guodong XU 《中国航空学报》2022,35(10):247-253
High precision and stable clock is extremely important in communication and navigation. The miniaturization of the clocks is considered to be the trend to satisfy the demand for5G and the next generation communications. Based on the concept of meter bar and the principle of the constancy of light velocity, we designed a micro clock, Space Time Clock(STC), with the size smaller than 1 mm × 1 mm and the power dissipation less than 2 m W. Designed in integrated circuit of 0.18 μm technology, the in... 相似文献
19.
Timothy G. Hawarden Robert Crane Harley A. Thronson Jr. Alan J. Penny Anna H. Orlowska Thomas W. Bradshaw 《Space Science Reviews》1995,74(1-2):45-56
The designs of cold space telescopes, cryogenic and radiatively cooled, are similar in most elements and both benefit from orbits distant from the Earth. In particular such orbits allow the anti-sunward side of radiatively-cooled spacecraft to be used to provide large cooling radiators for the individual radiation shields. Designs incorporating these features have predictedT
tel near 20 K. The attainability of such temperatures is supported by limited practical experience (IRAS, COBE). Supplementary cooling systems (cryogens, mechanical coolers) can be advantageously combined with radiative cooling in hybrid designs to provide robustness against deterioration and yet lower temperatures for detectors, instruments, and even the whole telescope. The possibility of such major additional gains is illustrated by the Very Cold Telescope option under study forEdison, which should offerT
tel5 K for a little extra mechanical cooling capacity. 相似文献
20.