全文获取类型
收费全文 | 2771篇 |
免费 | 30篇 |
国内免费 | 15篇 |
专业分类
航空 | 1245篇 |
航天技术 | 915篇 |
综合类 | 12篇 |
航天 | 644篇 |
出版年
2022年 | 15篇 |
2021年 | 32篇 |
2019年 | 26篇 |
2018年 | 146篇 |
2017年 | 102篇 |
2016年 | 65篇 |
2015年 | 32篇 |
2014年 | 85篇 |
2013年 | 112篇 |
2012年 | 91篇 |
2011年 | 159篇 |
2010年 | 118篇 |
2009年 | 158篇 |
2008年 | 166篇 |
2007年 | 98篇 |
2006年 | 64篇 |
2005年 | 84篇 |
2004年 | 81篇 |
2003年 | 81篇 |
2002年 | 56篇 |
2001年 | 81篇 |
2000年 | 39篇 |
1999年 | 47篇 |
1998年 | 52篇 |
1997年 | 49篇 |
1996年 | 41篇 |
1995年 | 56篇 |
1994年 | 35篇 |
1993年 | 41篇 |
1992年 | 52篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 41篇 |
1988年 | 19篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 60篇 |
1984年 | 51篇 |
1983年 | 41篇 |
1982年 | 41篇 |
1981年 | 56篇 |
1980年 | 34篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1976年 | 16篇 |
1975年 | 15篇 |
1974年 | 12篇 |
1971年 | 7篇 |
1969年 | 7篇 |
排序方式: 共有2816条查询结果,搜索用时 265 毫秒
421.
S. Cazes J. Charra N. Coron B. Cougrand J.-F. Crifo J. Crovisier C. Emerich R. Gispert B. Gondet G. Guyot D. Harduin J.-M. Lamarre G. Levanti C. Maurel D. Parisot F. Rocard P. Salvetat A. Soufflot T. Encrenaz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):273-276
The IKS infrared spectro-photometer will fly on board the VEGA platforms. It is designed to characterize the size, temperature and emissivity of the Comet Halley nucleus, to identify the major gaseous components of the inner coma and to detect the emission of the cometary grains. This paper presents the “calibration” experiments required to reduce the raw data: (i) absolute wavelength calibration of the filter wheels; (ii) modeling of the internal signal, as a function of the temperature of the different sub-systems; (iii) absolute and spectral responsivities of each of the spectrometric and photometric channels, as a function of the wavelength and position of the source in the field of view. Finally, we shall indicate the expected S/N ratios. 相似文献
422.
K.Ya. Kondratyev N.I. Moskalenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(8):53-58
The models of chemical composition and structure of the Earth-type planetary atmospheres are offered. The optical properties of gaseous and disperse phases of the atmospheres are investigated. 相似文献
423.
A computationally efficient scheme for estimating the digital instantaneous frequencies of narrowband inputs is introduced. The frequency estimates are obtained by searching for minima of the inverse input power spectrum. This spectrum is estimated at each input sample from the weights of an adaptive linear predictor which uses the LMS (least mean square) algorithm to update its weights. The related minima are sought via an iterative search algorithm, referred to as the iterative frequency estimator. This algorithm is computationally more efficient than available methods, and also provides a higher resolution. Simulation results are included; these include tracking of random message sequences in FM signals, and the formant frequency estimation of speech. 相似文献
424.
The structural features of the germanium-silicon solid solution crystals obtained under microgravity
V.S. Zemskov I.N. Belokurova I.L. Shulpina A.N. Titkov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(5):11-14
Structural features of germanium-silicon solid solution crystals have been investigated and silicon distribution in the crystals has been studied. All the crystals obtained under microgravity had, in spite of good external shape and facetting, a poorer internal structure than those obtained on Earth. The distribution of silicon have been shown to be non-uniform. High dislocation densities were observed. 相似文献
425.
N.H. Stone U. Samir 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):361-372
A brief review of early laboratory investigations of bodies in flowing, rarefied plasmas is given together with a discussion of more recent parametric studies carried out at NASA/Marshall Space Flight Center (MSFC), which include the effects of the ion acoustic Mach number and the normalized test body potential. Good agreement is found between the experimental results and theoretical calculations which omit ion thermal motion. The relation between laboratory investigations and the results of satellite-borne measurements is addressed. This relationship has led to an appreciation for the benefits of applying the methods and techniques of laboratory plasma physics to investigations in space, where several limitations inherent to the laboratory can be circumvented. These types of investigations, conducted in Earth orbit, can enhance our understanding of space plasma physics and have direct application to certain types of solar system phenomena. 相似文献
426.
Oka I. Kabasawa S. Morinaga N. Namekawa T. 《IEEE transactions on aerospace and electronic systems》1981,(1):93-100
Transmission characteristics are described for M-ary coherent phase-shift keyed (CPSK) systems with N-stage hard-limiting transponders where noise and multiple continuous wave (CW) interference sources are additively combined in each link. A general expression for the probability density function of the composite phase at the final link is derived; the overall error probability is then obtained from this general expression. Comparisons with N-cascaded linear amplifier systems clearly show the noise and interference immunity that result from the use of bandpass hard limiters (BPHLs). The BPHL system's error probability improvement versus interference sources is shown to be much larger than the improvement versus noise. 相似文献
427.
428.
Kim N.P. Stanbery B.J. Burgess R.M. Mickelsen R.A. McClelland R.W. King B.D. Gale R.P. 《Aerospace and Electronic Systems Magazine, IEEE》1989,4(11):23-32
Mechanically stacked tandem cells consisting of GaAs thin-film upper cells and CuInSe2 thin-film lower cells have been developed to meet the increasing power needs projected for future spacecraft. The authors report the fabrication of the first highly efficient lightweight GaAs/CuInSe2 tandem cell on a 2-mil thick substrate, update recent performance improvements in thin-film GaAs/CuInSe2 tandem cells, and discuss their application to space power systems. The efficiency of 4-cm2 cells has improved to 21.6% AM0, the highest ever reported for a thin-film photovoltaic cell. Lightweight 4-cm2 tandem cells have been successfully fabricated with efficiencies as high as 20.8%. These cells weighed about 180 mg without optimized substrate trimming. Radiation and operating temperature effects on GaAs/CuInSe2 tandem cells are also discussed, and an interconnect scheme to form a voltage-matched string is described 相似文献
429.
Severns J.G. Hobbs R.M. Elliott N.P. Towsley R.H. Conway R.W. Virshup G.F. 《Aerospace and Electronic Systems Magazine, IEEE》1989,4(12):8-12
The LIPS III satellite, which was launched into a 1100-km circular orbit of 60° inclination in the spring of 1987, is discussed. LIPS III is a member of the living-plume-shield class of spacecraft, all of which were built around a simple sheet metal plume deflector. The purpose of LIPS III was to provide a testbed for space power sources. An overview of the LIPS III system is given, and the experiments submitted for it, all but one of which were photovoltaic in nature, are described 相似文献
430.
A. DasGupta D.N. Anderson J.A. Klobuchar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(10):199-202
Ionospheric total electron content and the F-region maximum electron density at a number of stations in the equatorial region, during the recent solar activity maximum period 1979 to 1980, show significant differences between the two equinoctial periods. Ionization during the month of March is higher than in September, irrespective of the station location both in northern and southern hemispheres, and in different longitude sectors. The observed pattern is compared with those predicted by different models, in particular with one of the authors which includes processes such as ionization production, loss, electrodynamic drifts, winds and global composition changes involved in the equatorial ionosphere. It is found that a change in the neutral composition is primarily responsible for the observed F-region density differences between March and September. 相似文献