全文获取类型
收费全文 | 17651篇 |
免费 | 33篇 |
国内免费 | 123篇 |
专业分类
航空 | 9822篇 |
航天技术 | 5187篇 |
综合类 | 245篇 |
航天 | 2553篇 |
出版年
2021年 | 154篇 |
2018年 | 193篇 |
2016年 | 154篇 |
2014年 | 434篇 |
2013年 | 515篇 |
2012年 | 404篇 |
2011年 | 558篇 |
2010年 | 394篇 |
2009年 | 757篇 |
2008年 | 790篇 |
2007年 | 365篇 |
2006年 | 422篇 |
2005年 | 368篇 |
2004年 | 419篇 |
2003年 | 497篇 |
2002年 | 468篇 |
2001年 | 540篇 |
2000年 | 356篇 |
1999年 | 441篇 |
1998年 | 406篇 |
1997年 | 306篇 |
1996年 | 360篇 |
1995年 | 429篇 |
1994年 | 398篇 |
1993年 | 352篇 |
1992年 | 296篇 |
1991年 | 250篇 |
1990年 | 232篇 |
1989年 | 374篇 |
1988年 | 203篇 |
1987年 | 240篇 |
1986年 | 232篇 |
1985年 | 640篇 |
1984年 | 511篇 |
1983年 | 402篇 |
1982年 | 488篇 |
1981年 | 607篇 |
1980年 | 243篇 |
1979年 | 183篇 |
1978年 | 189篇 |
1977年 | 144篇 |
1976年 | 155篇 |
1975年 | 182篇 |
1974年 | 180篇 |
1973年 | 161篇 |
1972年 | 188篇 |
1971年 | 148篇 |
1970年 | 143篇 |
1969年 | 147篇 |
1967年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The microwave landing system (MLS) transmits angle, data, andrange information for use by airborne receivers. In this paper, theintegrity of the data functions is analyzed in terms of the probabilityof undetected errors remaining in the data. The data format andintegrity requirements were derived from the MLS standards andguidance material defined by the International Civil Aviation Organization (ICAO). Results show that the performancerequirements can be met by: 1) averaging the received data bits ofseveral samples of the same word using a majority voting;2) reducing the bit error rate at the output of the receiver'sdecoder; and 3) a combination of the above techniques. 相似文献
102.
Stevens J. Componation P.I. 《IEEE transactions on aerospace and electronic systems》2004,40(2):478-490
The ability to model and analyze system performance is a key enabler when you are extending the operational life of complex systems. This is especially true when the system is operating in a hostile environment, such as space. This paper discusses a change made to the Space Shuttle main engines (SSMES) that affected the solid rocket booster (SRB) performance, and illustrates how databases maintained by the different subsystem contractors can be integrated, correlated, and evaluated to improve a subsystem component performance model. The enhanced model can be used not only for better prediction of component performance on the existing system, but can be used on upgrades to the system, or the next generation space shuttle solid rocket. motor. 相似文献
103.
104.
Steven D. Howe 《Space Policy》2001,17(4):275-283
The potential benefits to humankind of space exploration are tremendous. Space is not only the final frontier but is also the next marketplace. The orbital space above Earth offers tremendous opportunities for both strategic assets and commercial development. The critical obstacle retarding the use of the space around the Earth is the lack of low cost access to orbit. Further out, the next giant leap for mankind will be the human exploration of Mars. Almost certainly within the next 30 years, a human crew will brave the isolation, the radiation, and the lack of gravity to walk on and explore the Red planet. Both of these missions will change the outlook and perspective of every human being on the planet. However, these missions are expensive and extremely difficult. Chemical propulsion has demonstrated an inability to achieve orbit cheaply and is a very high-risk option to accomplish the Mars mission. An alternative solution is to develop a high performance propulsion system. Nuclear propulsion has the potential to be such a system. The question will be whether humanity is willing to take on the challenge. 相似文献
105.
通过对电阻应变式称重传感器在各种加载卸载情况下的滞后特性的分析 ,建立了其相应的数学模型 ,并初步探讨了一种可以通过程序在仪表中对传感器的重要指标—滞后进行补偿从而提高整个传感器的精度的方法。最后 ,对以上方法进行了验证性试验 ,证明了补偿方法的可行性。 相似文献
106.
107.
介绍自行研制的VKM—5型立式捏合机的构造及工作原理,详述了该机采用液压传动和气动元件进行位置检测以及气、电、液安全联锁的特点,并说明与卧式捏合机对比试验情况。 相似文献
108.
Guerci J.R. Goetz R.A. DiModica J. 《IEEE transactions on aerospace and electronic systems》1994,30(4):1090-1093
A relatively simple method is presented which eliminates previously reported (Oct. 1985) erratic estimation performance associated with Cartesian formulations of the extended Kalman filter (EKF) for the 2D angle-only emitter location problem. The technique is based on an initialization procedure which combines a priori probability density function (pdf) information with single measurement a posteriori pdf information in a manner which is more efficient than the EKF. Simulation results are presented which demonstrate the utility of the technique as compared with a previously offered modified gain EKF 相似文献
109.
G. Paschmann M. Boehm H. Höfner R. Frenzel P. Parigger F. Melzner G. Haerendel C. A. Kletzing R. B. Torbert G. Sartori 《Space Science Reviews》1994,70(3-4):447-463
The Electron Beam Instrument (F6) onFreja is the first attempt to apply the electron drift technique in a region of large ambient magnetic fields. The paper describes the operational principles, the technical realization, and the difficulties encountered in the derivation of the electric fields. 相似文献
110.