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   8989篇
  免费   12篇
  国内免费   38篇
航空   4317篇
航天技术   3081篇
综合类   200篇
航天   1441篇
  2021年   78篇
  2019年   54篇
  2018年   157篇
  2017年   95篇
  2016年   86篇
  2014年   168篇
  2013年   221篇
  2012年   222篇
  2011年   326篇
  2010年   213篇
  2009年   372篇
  2008年   403篇
  2007年   235篇
  2006年   193篇
  2005年   236篇
  2004年   236篇
  2003年   292篇
  2002年   277篇
  2001年   331篇
  2000年   183篇
  1999年   223篇
  1998年   264篇
  1997年   188篇
  1996年   247篇
  1995年   302篇
  1994年   267篇
  1993年   148篇
  1992年   225篇
  1991年   97篇
  1990年   98篇
  1989年   223篇
  1988年   88篇
  1987年   89篇
  1986年   102篇
  1985年   272篇
  1984年   208篇
  1983年   184篇
  1982年   216篇
  1981年   259篇
  1980年   91篇
  1979年   66篇
  1978年   79篇
  1977年   61篇
  1976年   63篇
  1975年   70篇
  1974年   68篇
  1972年   65篇
  1971年   60篇
  1970年   54篇
  1969年   54篇
排序方式: 共有9039条查询结果,搜索用时 78 毫秒
781.
A new type of synthetic radar, the circular synthetic radar, uses a simple interferometer whose elements are mounted at the ends of a horizontal boom rotating about a vertical mast. Pulses are radiated alternately ?in-phase? and in ?phase-quadrature.? The returning echoes are also detected incoherently, both ?in-phase? and in ?phase-quadrature.? The four distinct outputs are fed into an on-line computer which, after a Fourier analysis, synthesizes a mapping function of the azimuthal distribution of targets.  相似文献   
782.
A recursive method of computing values of the generalized Q function is described. The Q function is also interpreted in terms of noncentral chi-square distributed random variables, and in terms of the difference between Poisson random variables.  相似文献   
783.
784.
The need to acquire a better knowledge of the main biological problems induced by microgravity implies--in addition to human experimentation--the use of animal models, and primates seem to be particularly well adapted to this type of research. The major areas of investigation to be considered are the phospho-calcium metabolism and the metabolism of supporting tissues, the hydroelectrolytic metabolism, the cardiovascular function, awakeness, sleep-awakeness cycles, the physiology of equilibrium and the pathophysiology of space sickness. Considering this program, the Centre d'Etudes et de Recherches de Medecine Aerospatiale, under the sponsorship of the Centre National d'Etudes Spatiales, developed both a program of research on restrained primates for the French-U.S. space cooperation (Spacelab program) and for the French-Soviet space cooperation (Bio-cosmos program), and simulation of the effects of microgravity by head-down bedrest. Its major characteristics are discussed in the study.  相似文献   
785.
The imaging capabilities of the Exosat and Einstein satellites at soft X-ray wavelengths have begun to show that suitable Galactic X-ray sources have extended ( 10 arcmin) haloes due to scattering of soft X-rays by interstellar dust. A simple argument suggests that similar haloes, due to scattering by intergalactic dust, should exist around distant (z 1) quasars and detailed analysis confirms this conclusion. A search for such haloes around suitable X-ray quasars could provide valuable, model-independent, constraints on the amount and origin of intergalactic dust.  相似文献   
786.
This paper presents an overview of the identification and selection process of experiments and payloads for manned space flight missions, emphasizing the scope and magnitude of the problem of doing activity planning and the need for a methodology to assure timely flight and appropriate spacecraft design. Conclusions and results derived from the past several years are presented together with an analysis of the current procedure for defining activity for the space station.  相似文献   
787.
788.
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   
789.
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   
790.
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   
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