全文获取类型
收费全文 | 6391篇 |
免费 | 26篇 |
国内免费 | 16篇 |
专业分类
航空 | 3062篇 |
航天技术 | 2242篇 |
综合类 | 20篇 |
航天 | 1109篇 |
出版年
2021年 | 50篇 |
2019年 | 41篇 |
2018年 | 101篇 |
2017年 | 79篇 |
2016年 | 76篇 |
2015年 | 38篇 |
2014年 | 118篇 |
2013年 | 157篇 |
2012年 | 156篇 |
2011年 | 236篇 |
2010年 | 167篇 |
2009年 | 245篇 |
2008年 | 320篇 |
2007年 | 171篇 |
2006年 | 138篇 |
2005年 | 184篇 |
2004年 | 177篇 |
2003年 | 202篇 |
2002年 | 131篇 |
2001年 | 215篇 |
2000年 | 114篇 |
1999年 | 147篇 |
1998年 | 182篇 |
1997年 | 125篇 |
1996年 | 145篇 |
1995年 | 203篇 |
1994年 | 201篇 |
1993年 | 114篇 |
1992年 | 145篇 |
1991年 | 61篇 |
1990年 | 68篇 |
1989年 | 140篇 |
1988年 | 65篇 |
1987年 | 57篇 |
1986年 | 66篇 |
1985年 | 200篇 |
1984年 | 182篇 |
1983年 | 161篇 |
1982年 | 140篇 |
1981年 | 211篇 |
1980年 | 56篇 |
1979年 | 55篇 |
1978年 | 58篇 |
1977年 | 56篇 |
1976年 | 47篇 |
1975年 | 63篇 |
1974年 | 50篇 |
1973年 | 45篇 |
1972年 | 68篇 |
1971年 | 39篇 |
排序方式: 共有6433条查询结果,搜索用时 31 毫秒
531.
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
532.
533.
A.A. Imshenetsky B.G. Murzakov M.D. Evdokimova I.K. Dorofeyeva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(14):21-26
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
534.
R.Z. Sagdeev G.G. Managadze A.A. Martinson Yu.A. Romanovsky R.I. Moisya W.K. Riedler M.F. Friedrich T.G. Adeishvily S.B. Lyakhov L.S. Novikov N.A. Leonov T.I. Gagua I.I. Slyusarenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):129-140
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
535.
"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
536.
537.
Musal H.M. Thomas P.D. Vinokur M. 《IEEE transactions on aerospace and electronic systems》1970,(2):252-254
The evaluation of the double convolution integrat involved in the expression of the radar response to scattering from a turbulent ionized wake is simplified by the approximation technique presented here, so that the Doppler spectrum parameters can be explicitly expressed in terms of the wake characteristics. 相似文献
538.
The influence of sudden increases of electron content on the accurate determination of the position of a satellite is investigated based on a spherically stratified ionospheric model. Using the total electron content information from Faraday rotation measurements, a procedure is presented whereby the corrections of satellite position due to the unpredicted electron increase can be accounted for without the need to know the spatial distribution of the additional electrons. 相似文献
539.
Smith G.H. Cunningham D.R. Ziemer R.E. 《IEEE transactions on aerospace and electronic systems》1973,(4):548-555
Plots of performance degradation are used to compare the effects of fading and intersymbol interference in a two- component specular multipath digital communications channel. Similar plots are then used to compare two practical receivers designed to combat the interference. Degradation plots are shown to allow easy identification of each receiver's range of usefulness, as well as identification of variance bounds demanded of channel parameter estimates which the receivers require. 相似文献
540.
Kau S. Kumar K.S.P. Granley G.B. 《IEEE transactions on aerospace and electronic systems》1969,(6):906-911
The theory of nonlinear filtering has been applied to the problem of the attitude determination of a satellite. Two approximation methods have been studied with a view to practical implementation. Computer simulation results are included. 相似文献