全文获取类型
收费全文 | 7034篇 |
免费 | 13篇 |
国内免费 | 21篇 |
专业分类
航空 | 3144篇 |
航天技术 | 2441篇 |
综合类 | 23篇 |
航天 | 1460篇 |
出版年
2021年 | 76篇 |
2019年 | 49篇 |
2018年 | 164篇 |
2017年 | 109篇 |
2016年 | 113篇 |
2015年 | 53篇 |
2014年 | 183篇 |
2013年 | 231篇 |
2012年 | 219篇 |
2011年 | 333篇 |
2010年 | 235篇 |
2009年 | 341篇 |
2008年 | 370篇 |
2007年 | 231篇 |
2006年 | 159篇 |
2005年 | 190篇 |
2004年 | 188篇 |
2003年 | 211篇 |
2002年 | 148篇 |
2001年 | 223篇 |
2000年 | 130篇 |
1999年 | 163篇 |
1998年 | 194篇 |
1997年 | 110篇 |
1996年 | 175篇 |
1995年 | 206篇 |
1994年 | 189篇 |
1993年 | 122篇 |
1992年 | 152篇 |
1991年 | 48篇 |
1990年 | 48篇 |
1989年 | 139篇 |
1988年 | 59篇 |
1987年 | 59篇 |
1986年 | 63篇 |
1985年 | 187篇 |
1984年 | 145篇 |
1983年 | 110篇 |
1982年 | 118篇 |
1981年 | 218篇 |
1980年 | 51篇 |
1979年 | 46篇 |
1978年 | 50篇 |
1977年 | 43篇 |
1975年 | 51篇 |
1974年 | 39篇 |
1972年 | 36篇 |
1971年 | 35篇 |
1970年 | 38篇 |
1967年 | 33篇 |
排序方式: 共有7068条查询结果,搜索用时 31 毫秒
991.
Z.I. Tsvetanov S.A. Zhekov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
The kinematics of gas clouds in broad-line region of active galactic nuclei and quasars is considered. The motion of the clouds is governed by three forces — gravitational influence from the central supermassive body, radiational pressure from the continuum radiation, and resistance of the intercloud medium. Clouds moves radial but only outward motion gives a velocity field, which is in accordance with the observational data. The profiles of the permited lines are obtained in some simplify assumptions for the emissive capacity of the gas in clouds, and are in good agreement with the observational data. In the framework of the model under consideration there is a possibility to estimate some physical parameters of the nuclei such as mass of the central body and density of the intercloud medium. 相似文献
992.
N.A. Savich 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(9):17-25
A comparison of the Venusian ionosphere electron density profiles obtained by the dual-frequency radio occultation method for the satellites Venera-9,10 (1975) and the Pioneer-Venus orbiter (1978–1979) has been carried out. It is shown that the general nature of the profiles, the main maximum heights and electron densities, the ionopause height positions determined with the satellites Venera-9, 10 on the one hand and Pioneer-Venus orbiter on the other hand are in good agreement. This fact testifies to the reliability of the experimental dual-frequency radio occultation data. An attempt to compare the radio occultation data with the direct measurements points out the essential contradictions between them, which need detailed analysis and discussion. 相似文献
993.
P Rambaut A Nicogossian 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(10):277-283
Plans for the various missions in which men and women are expected to participate during the next 10 years are outlined. Such missions include flights of up to three months duration in low earth orbit as well as possible short excursions to geosynchronous orbit. Research activities are described which cover the full spectrum of physiological and psychological responses to space flight. These activities are shown to contribute to the ongoing Shuttle program and the future Space Station. The paper includes a summary of the major technical thrusts needed to support extended habitation in space. 相似文献
994.
995.
Recent developments in the physics input for iron core collapse models of type II supernovae are reviewed. The effect of these developments on collapse calculations is also discussed. The inner core collapses homologously, with little change in specific entropy, bounces in the neighborhood of nuclear density, and sets up an outward moving shock. In adiabatic models an explosion may result. The Inclusion of neutrino effects may produce substantial shock damping. Current results indicate that core collapse, bounce and shock propagation does not produce an explosion when neutrino effects are included. 相似文献
996.
Mohamed A. Ayyad 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(8):19-29
The western Mediterranean desert of Egypt has a long history of land-use. With recent development activities, land transformation is progressing at a high rate. Monitoring of changes to allow for predictions of long-term effects of these activities is viewed at three levels: (a) quantities of ecosystem components; (b) detailed distribution of patterns of land-use, vegetation and physiography; and (c) general distribution of the salient features of land. This study provides estimates at the first (a) and second (b) levels of changes in this region due to the main land-use types: grazing rain-fed farming, and irrigated farming.Grazing had little effects on soil characters, but it resulted in lower soil stability and abundance of plants and above-soil invertebrates. Irrigation resulted in water-logging and salinization, formation of calcic horizons, decrease in soil organic matter and soluble nitrogen, and in increase of above-and below-soil biota.A comparison of the distribution of vegetation and land-use in one of the sectors in 1964 and 1981, using maps based on aerial photographs and ground-truth data, indicated remarkable changes in areas of rain-fed farming, and in vegetation composition due to over-grazing. 相似文献
997.
G. Branduardi-Raymont R. Corbet A. N. Parmar P. G. Murdin K. O. Mason 《Space Science Reviews》1981,30(1-4):279-286
We report photometric observations of the optical counterpart of the X-ray source 2S0921-630. The data, obtained at the South African Astronomical Observatory during 3 weeks in 1980 and 1981, are consistent with a 17.9 day periodic modulation of the flux in the B band. Correlated variability of the (B-V) and (U-B) colour indices with the B mag. is demonstrated and quantified. The observed B mag. and colours at maximum and minimum light are used to compute some of the system parameters. A model of 2S0921-630 is proposed in terms of a binary system in which the variable inclination of a luminous accretion disc produces the long-term modulation of the optical flux. 相似文献
998.
Equations are derived to predict the electrical behavior of a three-phase superconducting alternator connected to a full-wave bridge rectifier. This is accomplished by expanding a previous analysis for conventional rectified alternators and adding computational impovements. The significance of the work is that it provides a means of calculating certain critical variables such as the ac current in the superconducting field winding and the ac voltage harmonics at the rectified output. A numerical example based on a machine designed for airborne applications is included. 相似文献
999.
1000.
The planetary radio astronomy experiment will measure radio spectra of planetary emissions in the range 1.2 kHz to 40.5 MHz. These emissions result from wave-particle-plasma interactions in the magnetospheres and ionospheres of the planets. At Jupiter, they are strongly modulated by the Galilean satellite Io.As the spacecraft leave the Earth's vicinity, we will observe terrestrial kilometric radiation, and for the first time, determine its polarization (RH and LH power separately). At the giant planets, the source of radio emission at low frequencies is not understood, but will be defined through comparison of the radio emission data with other particles and fields experiments aboard Voyager, as well as with optical data. Since, for Jupiter, as for the Earth, the radio data quite probably relate to particle precipitation, and to magnetic field strength and orientation in the polar ionosphere, we hope to be able to elucidate some characteristics of Jupiter auroras.Together with the plasma wave experiment, and possibly several optical experiments, our data can demonstrate the existence of lightning on the giant planets and on the satellite Titan, should it exist. Finally, the Voyager missions occur near maximum of the sunspot cycle. Solar outburst types can be identified through the radio measurements; when the spacecraft are on the opposite side of the Sun from the Earth we can identify solar flare-related events otherwise invisible on the Earth. 相似文献