全文获取类型
收费全文 | 6479篇 |
免费 | 665篇 |
国内免费 | 503篇 |
专业分类
航空 | 3660篇 |
航天技术 | 1670篇 |
综合类 | 436篇 |
航天 | 1881篇 |
出版年
2024年 | 17篇 |
2023年 | 52篇 |
2022年 | 113篇 |
2021年 | 172篇 |
2020年 | 137篇 |
2019年 | 126篇 |
2018年 | 287篇 |
2017年 | 269篇 |
2016年 | 186篇 |
2015年 | 187篇 |
2014年 | 240篇 |
2013年 | 264篇 |
2012年 | 280篇 |
2011年 | 399篇 |
2010年 | 425篇 |
2009年 | 474篇 |
2008年 | 397篇 |
2007年 | 347篇 |
2006年 | 214篇 |
2005年 | 252篇 |
2004年 | 162篇 |
2003年 | 195篇 |
2002年 | 195篇 |
2001年 | 197篇 |
2000年 | 152篇 |
1999年 | 164篇 |
1998年 | 136篇 |
1997年 | 143篇 |
1996年 | 125篇 |
1995年 | 158篇 |
1994年 | 139篇 |
1993年 | 82篇 |
1992年 | 96篇 |
1991年 | 50篇 |
1990年 | 50篇 |
1989年 | 68篇 |
1988年 | 50篇 |
1987年 | 28篇 |
1986年 | 39篇 |
1985年 | 86篇 |
1984年 | 77篇 |
1983年 | 44篇 |
1982年 | 75篇 |
1981年 | 79篇 |
1980年 | 18篇 |
1978年 | 34篇 |
1975年 | 24篇 |
1974年 | 19篇 |
1973年 | 17篇 |
1972年 | 17篇 |
排序方式: 共有7647条查询结果,搜索用时 78 毫秒
991.
The influence of zonal and meridional components of the neutral wind under anthropogenic impacts of water molecules on the ionospheres electron concentration distributed along a magnetic field tube is considered. Computer simulation method based on a mathematical model of the F2 region along a field tube is used.Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 1, 2005, pp. 76–80.Original Russian Text Copyright © 2005 by Medvedev, Ishanov, Zenkin. 相似文献
992.
The COSAC (Cometary Sampling and Composition Experiment) onboard the Rosetta mission is a combined gas chromatograph (GC)-mass spectrometer (MS). It is situated on Philae, the lander of the mission, which is intended to land on the nucleus of comet 67P/Churyumov- Gerasimenko. The purpose of the experiment is to analyze the volatile fraction of soil samples retrieved by a drill. For investigation, the samples will be pyrolysed, and the emanating gases fed into a GC, into an MS, or the combination of both. In the first part of this paper, the bioastronomical relevance of such measurements is outlined. In the second part the details of the hardware and its performance are described. 相似文献
993.
It is thought that the chiral molecules of living material can induce circular polarization in light at levels much higher than expected from abiotic processes. We therefore obtained high quality imaging circular polarimetry of the martian surface during the favorable opposition of 2003 to seek evidence of anomalous optical activity. We used two narrow-band filters covering 43% of the martian surface, 15% of it in-depth. With polarization noise levels <0.1% (4.3 upper limits 0.2-0.3%) and spatial resolution 210 km, we did not find any regions of circular polarization. When data were averaged over the observed face of the planet, we did see a small non-zero circular polarization 0.02%, which may be due to effects associated with the opposition configuration though it is at the limit of the instrumental capability. Our observations covered only a small fraction of parameter space, so although we obtained a null result, we cannot exclude the presence of optical activity at other wavelengths, in other locations, or at higher spatial resolution. 相似文献
994.
Yu.V. Kushnerevsky S.A. Pulinets 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):97-101
Experimental results of the Wave measurements over frequency range 0.1–5.0 MHz during the second launch of the ARAKS Experiment (15.02.75) are reported. The differences between the results of the first and the second launches are discussed. 相似文献
995.
996.
This paper reports on the objectives of the German space processing programme with sounding rockets and the scientific results obtained thus far. 相似文献
997.
Miles R.B. Kimball R.B. Frey W.H. 《IEEE transactions on aerospace and electronic systems》1971,(4):578-584
Outdated and rigorous curricula are not only producing engineers unsuited to the challenges of the 1970's, but they are scaring off many of the most creative and intelligent students. Engineering education has become an endurance test; the excitement has been lost. Most students strive only to get out. Engineering schools have not yet realized the importance of the involvement of engineers in current environmental problems. They continue to present only the dry technical courses and seem unconcerned about the student's sense of social perspective or his motivation. This paper proposes a freshman awareness seminar plus project oriented learning in the following years as a remedy for this sad situation. 相似文献
998.
Cantrell B.H. Gordon W.B. Trunk G.V. 《IEEE transactions on aerospace and electronic systems》1981,(2):213-221
The maximum likelihood estimates of the elevation angles of two closely spaced targets within the beamwidth is considered. For an array divided into three subapertures, a simple, closed form solution is found whose accuracy compares favorably to the maximum likelihood estimate which uses all the individual elements. Simulation results are presented for the case of a radar target located over a smooth reflecting surface. 相似文献
999.
Space radiation dosimetry with active detections for the scientific program of the second Bulgarian cosmonaut on board the Mir space station. 总被引:1,自引:0,他引:1
J V Dachev TsPMatviichuk YuN Semkova R T Koleva B Boichev P Baynov N A Kanchev P Lakov P T Ivanov YaJTomo V M Petrov V I Redko V I Kojarinov R Tykva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):247-251
A dosimetry-radiometry system has been developed at the Space Research Institute of the Bulgarian Academy of Science to measure the fluxes and dose rates on the flight of the second Bulgarian cosmonaut. The dosimetry system is designed for monitoring the different space radiations, such as solar cosmic rays, galactic cosmic rays and trapped particles in the earth radiation belts. The system consists of a battery operated small size detector unit and a "read-write" and telemetry microcomputer unit. The sensitivity of the instrument (3.67 x 10(-8) rad/pulse) permits high resolution measurements of the flux and dose rate along the track of the Mir space station. We report our initial results for the period of the flight between the 7th and 17th June 1988. 相似文献
1000.