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   18575篇
  免费   35篇
  国内免费   122篇
航空   9897篇
航天技术   5612篇
综合类   258篇
航天   2965篇
  2021年   156篇
  2018年   211篇
  2016年   150篇
  2014年   443篇
  2013年   529篇
  2012年   421篇
  2011年   596篇
  2010年   405篇
  2009年   747篇
  2008年   803篇
  2007年   369篇
  2006年   441篇
  2005年   408篇
  2004年   447篇
  2003年   563篇
  2002年   486篇
  2001年   589篇
  2000年   381篇
  1999年   465篇
  1998年   450篇
  1997年   337篇
  1996年   413篇
  1995年   499篇
  1994年   485篇
  1993年   362篇
  1992年   356篇
  1991年   252篇
  1990年   246篇
  1989年   432篇
  1988年   208篇
  1987年   242篇
  1986年   240篇
  1985年   656篇
  1984年   529篇
  1983年   415篇
  1982年   489篇
  1981年   616篇
  1980年   248篇
  1979年   193篇
  1978年   189篇
  1977年   146篇
  1976年   155篇
  1975年   197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 46 毫秒
991.
992.
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   
993.
994.
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   
995.
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   
996.
"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   
997.
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   
998.
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   
999.
The facts presented represent, for convenience, a composite clinical picture of the three crewmen aboard Skylab II as observed by me.  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