全文获取类型
收费全文 | 9068篇 |
免费 | 22篇 |
国内免费 | 24篇 |
专业分类
航空 | 4115篇 |
航天技术 | 3115篇 |
综合类 | 198篇 |
航天 | 1686篇 |
出版年
2021年 | 86篇 |
2019年 | 57篇 |
2018年 | 229篇 |
2017年 | 144篇 |
2016年 | 124篇 |
2015年 | 64篇 |
2014年 | 214篇 |
2013年 | 266篇 |
2012年 | 260篇 |
2011年 | 389篇 |
2010年 | 275篇 |
2009年 | 408篇 |
2008年 | 460篇 |
2007年 | 263篇 |
2006年 | 200篇 |
2005年 | 237篇 |
2004年 | 232篇 |
2003年 | 272篇 |
2002年 | 279篇 |
2001年 | 355篇 |
2000年 | 155篇 |
1999年 | 221篇 |
1998年 | 246篇 |
1997年 | 158篇 |
1996年 | 241篇 |
1995年 | 270篇 |
1994年 | 251篇 |
1993年 | 148篇 |
1992年 | 194篇 |
1991年 | 72篇 |
1990年 | 71篇 |
1989年 | 179篇 |
1988年 | 79篇 |
1987年 | 74篇 |
1986年 | 88篇 |
1985年 | 252篇 |
1984年 | 208篇 |
1983年 | 151篇 |
1982年 | 175篇 |
1981年 | 273篇 |
1980年 | 68篇 |
1979年 | 57篇 |
1978年 | 65篇 |
1977年 | 55篇 |
1975年 | 64篇 |
1974年 | 60篇 |
1972年 | 49篇 |
1971年 | 52篇 |
1970年 | 49篇 |
1969年 | 47篇 |
排序方式: 共有9114条查询结果,搜索用时 0 毫秒
61.
The design of fault-tolerant distributed control systems is discussed. The application described is a generic flight control system (FCS) for a fighter aircraft. The system is designed for high redundancy and expandability to meet various requirements. The communication network is based on the fiber distributed data interface (FDDI), which provides a high level of electromagnetic interference resistance and reliability. The choice of fiber optic media also provides an extremely high bandwidth and tremendous growth capability for future communications needs. This study is not specific to FDDI or flight control systems. The methods and configurations presented should be applicable to many real-time control implementations 相似文献
62.
63.
G Horneck R Facius G Reitz P Rettberg C Baumstark-Khan R Gerzer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(1):87-95
Human missions to Mars are planned to happen within this century. Activities associated therewith will interact with the environment of Mars in two reciprocal ways: (i) the mission needs to be protected from the natural environmental elements that can be harmful to human health, the equipment or to their operations; (ii) the specific natural environment of Mars should be protected so that it retains its value for scientific and other purposes. The following environmental elements need to be considered in order to protect humans and the equipment on the planetary surface: (i) cosmic ionizing radiation, (ii) solar particle events; (iii) solar ultraviolet radiation; (iv) reduced gravity; (v) thin atmosphere; (vi) extremes in temperatures and their fluctuations; and (vii) surface dust. In order to protect the planetary environment, the requirements for planetary protection as adopted by COSPAR for lander missions need to be revised in view of human presence on the planet. Landers carrying equipment for exobiological investigations require special consideration to reduce contamination by terrestrial microorganisms and organic matter to the greatest feasible extent. Records of human activities on the planet's surface should be maintained in sufficient detail that future scientific experimenters can determine whether environmental modifications have resulted from explorations. 相似文献
64.
A. Sh. Dzhabrailov Yu. V. Klochkov S. S. Marchenko A. P. Nikolaev 《Russian Aeronautics (Iz VUZ)》2007,50(2):115-120
We demonstrate that it is possible to express each component of the displacement vector for the interior point of the finite element (FE) through all components of nodal unknowns in curvilinear coordinates. The effectiveness of the valid technique of vector approximation for displacement fields has been verified on an example. 相似文献
65.
The characteristics of the insulator wear process in the discharge chamber of a stationary plasma thruster (SPT) are analyzed. The results of studying the erosion resistance to ionic spraying of different ceramic compositions are presented. It is shown experimentally that the integral characteristics (the value of thrust and thrust efficiency) as well as the SPT lifetime can be improved in changing from the conventional hot-pressed boron silicate (BN + SiO2) ceramics to the BN + Si3N4 ceramic compositions. 相似文献
66.
V. A. Ovchinnikov 《Russian Aeronautics (Iz VUZ)》2007,50(2):146-149
We analyze the effect of injection both of uniformly distributed over the entire cylinder surface and of the optimal one on the velocity distribution at the outer border of the boundary layer and, as a result, on friction. 相似文献
67.
The results of studying an incompressible gas flow field in a periodic element of the porous structure made up of the same radius spheres are presented; the studies were based on the solution of the Navier-Stokes equations using FLUENT software. The possibilities to accelerate the solution process with the use of parallel calculations are investigated and the calculation results under changes of pressure differential in the periodic element are given. 相似文献
68.
介绍了NIST开展的微波散射参数(S参数)及功率测量业务。包括在这两项业务中的各自的测量内容,系统的校准技术,对系统及所用的标准件的描述和对于不同测量所考虑的测量不确定度。此外还介绍了在S参数测量及功率测量的未来工作方向。 相似文献
69.
A. I. Belousov S. V. Falaleev A. S. Vinogradov P. V. Bondarchuk 《Russian Aeronautics (Iz VUZ)》2007,50(4):390-394
Problems arising in introduction of gasodynamic seals in aircraft engines are considered. The operation of a face gasodynamic seal as part of a natural gas pump is analyzed and its efficiency in the presence of oil is shown. 相似文献
70.
A system for measuring the altitude-airspeed parameters of rotorcraft and very light flight vehicles
In this paper, a problem on measuring the altitude-airspeed parameters (AAPs) of rotorcraft and very light flight vehicles is considered. Some ways of improving systems used to measure the parameters of FV elements and units have been determined. Also suggested and substantiated are the principles and designs of the basic variants of these measuring systems as well as the algorithms of their operation. 相似文献