全文获取类型
收费全文 | 4370篇 |
免费 | 5篇 |
国内免费 | 13篇 |
专业分类
航空 | 2382篇 |
航天技术 | 1122篇 |
综合类 | 9篇 |
航天 | 875篇 |
出版年
2019年 | 20篇 |
2018年 | 190篇 |
2017年 | 155篇 |
2016年 | 59篇 |
2015年 | 41篇 |
2014年 | 60篇 |
2013年 | 87篇 |
2012年 | 106篇 |
2011年 | 242篇 |
2010年 | 215篇 |
2009年 | 245篇 |
2008年 | 271篇 |
2007年 | 234篇 |
2006年 | 65篇 |
2005年 | 134篇 |
2004年 | 94篇 |
2003年 | 100篇 |
2002年 | 54篇 |
2001年 | 109篇 |
2000年 | 49篇 |
1999年 | 82篇 |
1998年 | 97篇 |
1997年 | 74篇 |
1996年 | 92篇 |
1995年 | 131篇 |
1994年 | 98篇 |
1993年 | 71篇 |
1992年 | 103篇 |
1991年 | 44篇 |
1990年 | 36篇 |
1989年 | 89篇 |
1988年 | 32篇 |
1987年 | 30篇 |
1986年 | 33篇 |
1985年 | 92篇 |
1984年 | 96篇 |
1983年 | 61篇 |
1982年 | 92篇 |
1981年 | 97篇 |
1980年 | 36篇 |
1979年 | 42篇 |
1978年 | 32篇 |
1977年 | 22篇 |
1976年 | 21篇 |
1975年 | 38篇 |
1974年 | 24篇 |
1973年 | 18篇 |
1972年 | 29篇 |
1969年 | 17篇 |
1967年 | 20篇 |
排序方式: 共有4388条查询结果,搜索用时 500 毫秒
991.
The paper is devoted to studies and a quantitative estimation of the influence of scattering of direct solar radiation by particles of tropospheric aerosols in the period of light twilight, close to sunrise and sunset. Polarization measurements of the twilight sky in two broad spectral bands lying near the standard bands V and R form the basis of these studies. The measurements were carried out in 2002 and 2003 at the Southern Laboratory (Crimea) of the Sternberg Astronomical Institute. The twilight period during which the single aerosol scattering becomes significant is isolated. The character of its influence on the intensity and polarization of the twilight sky is demonstrated. A method is suggested to evaluate polarization of the single aerosol scattering and its contribution to the general brightness of the twilight sky background. The method is based on differential characteristics of the background near the zenith and on their correlations with each other. 相似文献
992.
993.
Comets with a high content of organics and light molecules are expected under cosmic radiation to gain a relatively unreactive crust and less volatile material to some ten metres deep. Interstellar dust impacts act to loosen and turn over 1 cm of the surface. We discuss how far this accords with observations of cometary dust halos and new versus old comets. Two key material properties have emerged from recent studies. Firstly, the source of cometary volatiles is not ice in the sense of material with a single sublimation energy. Secondly, the particulates are not simply mineral dust but include much organic material, some of which undergoes chemical processing and exchanges with the gaseous environment. Consistent with these properties, a coherent crust rather than a mantle of loose grains would build up to cover much of the nucleus of periodic comets. It would consolidate by cooking in the solar radiation, especially at peak temperatures around perihelion. There are two disjoint surface phases: one of volatile material, the other the refractory crust, the former deepening into crater-like hollows over successive apparitions. The transition to non-volatile crust is unstable, subject to competing consolidation and disruption processes, and sensitive to seasonal changes. A comet dims and becomes asteroidal as the inert crust extends over the erosion craters, and may only be rejuvenated via collision with a boulder-sized impactor or perturbation of the orbit to smaller perihelion distance. 相似文献
994.
The human exploration of Mars has the potential to return a rich harvest of scientific information about that planet, its possible past biological history and the prospects for future habitation by Earthly life. The realization of that potential will require new approaches and new technologies--a whole new paradigm in space exploration. Picture yourself exploring the surface of Mars, where your task involves conducting a detailed investigation of features larger than the United States in order to uncover a record of planetary history spanning over four billion years. 相似文献
995.
We discuss the use of multilayered annular-plate dampers as rotor supports in turbopumps of the RD-0120 and RD-0146 rocket engines. We present a technique of calculating the elastic and damping characteristics of multilayer corrugated annular supports in the case of the conical precession of the rotor. 相似文献
996.
V. T. Grumondz E. I. Karpezhnikov M. A. Polishchuk M. V. Polishchuk 《Russian Aeronautics (Iz VUZ)》2017,60(4):534-541
The algorithms of controlled descent for unmanned winged gliders are designed taking into account the requirements to the flight trajectory. The calculation results are represented to show the efficiency of the algorithms. 相似文献
997.
Features of fuel atomization and propagation in the flow behind a gas-dynamic stabilizer are considered. Estimations of the influence of transverse jets impulse magnitude on characteristics of mixing behind the stabilizer are obtained by numerical and experimental methods. 相似文献
998.
R.A. Gowen A. Smith A.D. Fortes S. Barber P. Brown P. Church G. Collinson A.J. Coates G. Collins I.A. Crawford V. Dehant J. Chela-Flores A.D. Griffiths P.M. Grindrod L.I. Gurvits A. Hagermann H. Hussmann R. Jaumann A.P. Jones K.H. Joy O. Karatekin K. Miljkovic E. Palomba W.T. Pike O. Prieto-Ballesteros F. Raulin M.A. Sephton S. Sheridan M. Sims M.C. Storrie-Lombardi R. Ambrosi J. Fielding G. Fraser Y. Gao G.H. Jones G. Kargl W.J. Karl A. Macagnano A. Mukherjee J.P. Muller A. Phipps D. Pullan L. Richter F. Sohl J. Snape J. Sykes N. Wells 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
999.
An approach to the analysis of electric arc process stability in plasma systems of ignition is considered depending on the
ignition system power circuit parameters, speed of plasma-generating air, and combustion chamber inlet pressure. Also solved
is the problem on determination of the calculated value of the maximum admissible speed of plasma-generating air that corresponds
to the critical regime of stable arcing in plasma spark plug at the GTE start. 相似文献
1000.
A technique of evaluating the micromechanical characteristics (namely, microhardness, microdurability, microbrittleness and
static crack resistance coefficient) using microindentation as applied to plasma zirconia-based thermal barrier coatings is
presented. 相似文献