首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   19234篇
  免费   43篇
  国内免费   124篇
航空   10256篇
航天技术   5693篇
综合类   246篇
航天   3206篇
  2021年   155篇
  2018年   274篇
  2017年   157篇
  2016年   180篇
  2014年   434篇
  2013年   514篇
  2012年   448篇
  2011年   660篇
  2010年   487篇
  2009年   839篇
  2008年   868篇
  2007年   450篇
  2006年   439篇
  2005年   438篇
  2004年   472篇
  2003年   564篇
  2002年   498篇
  2001年   628篇
  2000年   368篇
  1999年   467篇
  1998年   474篇
  1997年   339篇
  1996年   419篇
  1995年   481篇
  1994年   480篇
  1993年   366篇
  1992年   358篇
  1991年   252篇
  1990年   243篇
  1989年   422篇
  1988年   211篇
  1987年   244篇
  1986年   241篇
  1985年   642篇
  1984年   522篇
  1983年   419篇
  1982年   490篇
  1981年   624篇
  1980年   246篇
  1979年   194篇
  1978年   189篇
  1977年   147篇
  1976年   156篇
  1975年   193篇
  1974年   181篇
  1973年   161篇
  1972年   188篇
  1971年   148篇
  1970年   143篇
  1969年   147篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
111.
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   
112.
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   
113.
With the mathematical basis for the precise analysis of developmental processes in plants, the patterns of growth in phototropic and gravitropic responses have become better understood. A detailed temporal and spatial quantification of a growth process is an important tool for evaluating hypotheses about the underlying physiological mechanisms. Studies of growth rates and curvature show that the original Cholodny-Went hypothesis cannot explain the complex growth patterns during tropic responses of shoots and roots. In addition, regulating factors other than the lateral redistribution of hormones must be taken into account. Electrophysiological studies on roots led to a modification of the Cholodny-Went hypothesis in that redistributions of bioelectrical activities are observed.  相似文献   
114.
115.
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   
116.
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   
117.
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   
118.
119.
120.
In this review the IR emission from circumstellar material is discussed, both of ionized gas and dust grains, and the astrophysical information that can be extracted from such observations. Some emphasis is placed on the possibilities of stellar IR astronomy using a large space-borne telescope, especially with respect to the much better spatial and spectral resolution of such a telescope compared to the current generation of ground-based and space IR telescopes.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号