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   18580篇
  免费   57篇
  国内免费   123篇
航空   10059篇
航天技术   5501篇
综合类   246篇
航天   2954篇
  2021年   157篇
  2018年   242篇
  2016年   173篇
  2014年   434篇
  2013年   513篇
  2012年   436篇
  2011年   618篇
  2010年   435篇
  2009年   784篇
  2008年   829篇
  2007年   403篇
  2006年   432篇
  2005年   414篇
  2004年   449篇
  2003年   555篇
  2002年   483篇
  2001年   603篇
  2000年   365篇
  1999年   467篇
  1998年   449篇
  1997年   328篇
  1996年   394篇
  1995年   457篇
  1994年   451篇
  1993年   359篇
  1992年   337篇
  1991年   250篇
  1990年   235篇
  1989年   407篇
  1988年   207篇
  1987年   244篇
  1986年   231篇
  1985年   636篇
  1984年   517篇
  1983年   414篇
  1982年   485篇
  1981年   614篇
  1980年   244篇
  1979年   190篇
  1978年   189篇
  1977年   146篇
  1976年   156篇
  1975年   191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 312 毫秒
991.
The techniques of recursive estimation and Kalman filtering are applied to the problem of estimation of space vehicle orbits and trajectories using only measurements of the Doppler shifts in radio signals transmitted by or reflected from the target. Two approaches are described. One is a global fit technique in which the parameters of an assumed trajectory model are estimated. The second is a pointwise mapping technique in which the trajectory estimate is extrapolated as the target tracking data is received. The paper provides a tutorial illustration of the direct application of recursive optimization techniques to a class of engineering problems.  相似文献   
992.
993.
Position-Location Solutions by Taylor-Series Estimation   总被引:12,自引:0,他引:12  
Taylor-series estimation gives a least-sum-squared-error solution to a set of simultaneous linearized algebraic equations. This method is useful in solving multimeasurement mixed-mode position-location problems typical of many navigational applications. While convergence is not proved, examples show that most problems do converge to the correct solution from reasonable initial guesses. The method also provides the statistical spread of the solution errors.  相似文献   
994.
995.
Results of the study of the influence of Martian soil analogues, both as described by American scientists and as prepared by us, and of hydrogen peroxide on the viability of microorganisms are presented. The experiments were carried out using mixtures of soil analogues with desert soil and black earth (chernozem) samples, and pure cultures of microorganism. Microorganisms capable of withstanding a concentration of hydrogen peroxide in the medium as high as 1.5–2.0% were isolated. None of the 40 strains of microorganisms studied, all belonging to different systematic and physiological groups, exhibited growth inhibition on solid media in the presence of Martian soil analogues. In view of the fact that Martian soil cannot contain microorganisms in great quantities, we suggest using electroadsorption for their concentration, to make detection reliable. A device was designed for this purpose, using the principle of electroadsorption on a polarisable carrier (sterile cotton wool or cheesecloth). The concentrated suspension of microorganisms thus obtained was then characterized by various physicochemical methods.  相似文献   
996.
This paper describes two rocket experiments “Aelita” with high power lithium plasma injection. The results of onboard magnetometer, massspectrometer, photometer, plasma, corpuscular and ground radar measurements are given. Dynamics and structure of plasma formation are discussed.  相似文献   
997.
"I can't get that stupid kite in the air! I can't! I can't!" "Oh, come on now, Charlie Brown ... that's no way to talk. The whole trouble with you is that you don't believe in yourself! You don't believe in your own abilities. You've got to say to yourself, 'I believe that I can fly this kite.' Now, go ahead, say to yourself, ' I believe that I can fly this kite.'" "I believe that I can fly this kite." "All right, now say it out loud. Say it over and over." "I believe that I can fly this kite! I believe that I can fly this kite! I actually believe I can fly this kite!" "You do? I'll bet you ten-to-one you're wrong!"  相似文献   
998.
The scattering effect of structures on Instrument Landing System localizer signals is analyzed in this paper. A generalized computer program results which can be used to determine the reflection from surfaces of most materials and orientations for which the radius of curvature is large compared with the wavelength. For most reflecting walls, a closed form solution is used and the computation time is short. The program will enable users to determine the placement of hangars, towers, etc., in airports and to find ways to reduce their effect on localizer facilities.  相似文献   
999.
A space diversity method of receiving and processing ILS localizer information has been developed and flight tested. Multiple lateral ly separated antennas are used which sense the ILS signal on and around the approach path. Combining these signals suppresses ILS beam distortion produced by multipath signal interference and provides much improved guidance information to the landing aircraft control system.  相似文献   
1000.
The literature on the dynamics of Jupiter's atmosphere is reviewed and used as a basis for suggesting what observations would yield useful information about Jovian Dynamics. The atmospheres of Saturn, Uranus and Neptune are discussed from the same point of view.This is one of the publications by the Science Advisory Group.  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