全文获取类型
收费全文 | 8543篇 |
免费 | 18篇 |
国内免费 | 24篇 |
专业分类
航空 | 4234篇 |
航天技术 | 2994篇 |
综合类 | 38篇 |
航天 | 1319篇 |
出版年
2021年 | 65篇 |
2019年 | 52篇 |
2018年 | 144篇 |
2017年 | 89篇 |
2016年 | 86篇 |
2014年 | 181篇 |
2013年 | 227篇 |
2012年 | 206篇 |
2011年 | 290篇 |
2010年 | 204篇 |
2009年 | 339篇 |
2008年 | 428篇 |
2007年 | 223篇 |
2006年 | 210篇 |
2005年 | 236篇 |
2004年 | 190篇 |
2003年 | 274篇 |
2002年 | 169篇 |
2001年 | 290篇 |
2000年 | 156篇 |
1999年 | 203篇 |
1998年 | 237篇 |
1997年 | 180篇 |
1996年 | 220篇 |
1995年 | 278篇 |
1994年 | 259篇 |
1993年 | 160篇 |
1992年 | 192篇 |
1991年 | 113篇 |
1990年 | 84篇 |
1989年 | 199篇 |
1988年 | 99篇 |
1987年 | 105篇 |
1986年 | 85篇 |
1985年 | 263篇 |
1984年 | 210篇 |
1983年 | 181篇 |
1982年 | 201篇 |
1981年 | 262篇 |
1980年 | 92篇 |
1979年 | 72篇 |
1978年 | 74篇 |
1977年 | 66篇 |
1976年 | 63篇 |
1975年 | 75篇 |
1974年 | 56篇 |
1973年 | 58篇 |
1972年 | 69篇 |
1971年 | 59篇 |
1970年 | 59篇 |
排序方式: 共有8585条查询结果,搜索用时 796 毫秒
551.
E. H. B. M. Gronenschild R. Mewe N. J. Westergaard J. Heise F. D. Seward T. Chlebowski N. P. M. Kuin A. C. Brinkman J. H. Dijkstra H. W. Schnopper 《Space Science Reviews》1981,30(1-4):185-189
The binary system Capella (G6 III + F9 III) has been observed on 1979 March 15 and on 1980 March 15–17 with the Objective Grating Spectrometer (OGS) onboard theEinstein Observatory. The spectrum measured with the 1000 l/mm grating covers the range 5–30 Å with a resolution < 1 Å. The spectra show evidence for a bimodal temperature distribution of emission measure in an optically thin plasma with one component 5 million degrees and the other one 10 million degrees. Spectral features can be identified with line emissions from O VIII, Fe XVII, Fe XVIII, Fe XXIV, and Ne X ions. Good spectral fits have been obtained assuming standard cosmic abundances. The data are interpreted in terms of emission from hot static coronal loops rather similar to the magnetic arch structures found on the Sun. It is shown that the conditions required by this model exist on Capella. Mean values of loop parameters are derived for both temperature components. 相似文献
552.
553.
B. Aschenbach H. Bräuninger U. Briel W. Brinkmann H. Fink N. Heinecke H. Hippmann G. Kettenring G. Metzner A. Ondrusch E. Pfeffermann P. Predehl G. Reger K. -H. Stephan J. Trümper H. U. Zimmermann 《Space Science Reviews》1981,30(1-4):569-573
The primary scientific objective of the ROSAT mission is to perform the first all sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. Consequently a large number of new sources (> 105) will be discovered and located with an accuracy of 1 arcmin. After completion of the survey which will take about half a year the instrument will be used for detailed observations of selected targets.The X-ray telescope consists of a fourfold nested Wolter type I mirror system with 80 cm aperture and 240 cm focal length, and three focal plane detectors. In the baseline version these will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 20 × 20. 相似文献
554.
555.
An Exact Trajectory Solution from Doppler Shift Measurements 总被引:2,自引:0,他引:2
Three radar Doppler shift measurements are sufficient to determine the range and velocity, and the angle between them, of a target in uniform rectilinear motion. A solution using derivative approximations has recently appeared. An exact solution in terms of the original measurements is presented here. 相似文献
556.
It is shown that the common series resonant power converter is subject to a low frequency oscillation that can lead to the loss of cyclic stability. This oscillation is caused by a low frequency resonant circuit formed by the normal L and C components in series with the magnetizing inductance of the output transformer. Three methods for eliminating this oscillation are presented and analyzed. One of these methods requires a change in the circuit topology during the resonance cycle. This requires a new set of steady state equations which are derived and presented in a normalized form. Experimental results are included which demonstrate the nature of the low frequency oscillation before cyclic stability is lost. 相似文献
557.
558.
R. H. D. Corbet A. P. Smale J. W. Menzies G. Branduardi-Raymont P. A. Charles K. O. Mason 《Space Science Reviews》1985,40(3-4):415-419
We present optical spectroscopy and photometry of 4U 1258-61 obtained over the course of six years. Evidence for the evolution of a circumstellar envelope throughout the course of the observations is presented. 相似文献
559.
M. Pakull H. Brunner W. Pietsch A. Staubert K. Beuermann M. van der Klis J. M. Bonnet-Bidaud 《Space Science Reviews》1985,40(3-4):379-382
Repeated observations of LMC X-4 with EXOSAT were carried out in 1983/84 in order to study its 30.5 day cycle and to cover the expected outbursts of the recurrent LMC transient A0538-66. The latter source was inactive during our campaign although a variable circumstellar envelope was still present around the optical counterpart.At least ten further X-ray sources are detected in the CMA field of view around LMC X-4 including the SNR N49 which is the possible site for the March 5, 1979 -ray burster and N63A which appears to be variable in X-ray luminosity. We furthermore discuss the strongest sources that were not present in a previous EINSTEIN survey of the LMC. 相似文献
560.
Her X-1 has been observed with EXOSAT for one 35d cycle between March 1 and April 5, 1984 at about 4 day intervals. During three observations, absorption dips were encountered showing fluctuations with time scales in the several hundred seconds range. The data are interpreted with a model where random superposition of absorbing blobs or inhomogeneous structures within the accretion disk, in the line of sight, cause these intensity variations. The calculations give a measure of the extent of the disk both in vertical and radial directions. 相似文献