全文获取类型
收费全文 | 5105篇 |
免费 | 6篇 |
国内免费 | 16篇 |
专业分类
航空 | 2530篇 |
航天技术 | 1798篇 |
综合类 | 18篇 |
航天 | 781篇 |
出版年
2021年 | 28篇 |
2019年 | 28篇 |
2018年 | 77篇 |
2017年 | 44篇 |
2016年 | 45篇 |
2014年 | 100篇 |
2013年 | 140篇 |
2012年 | 106篇 |
2011年 | 176篇 |
2010年 | 137篇 |
2009年 | 207篇 |
2008年 | 269篇 |
2007年 | 126篇 |
2006年 | 110篇 |
2005年 | 131篇 |
2004年 | 129篇 |
2003年 | 168篇 |
2002年 | 86篇 |
2001年 | 170篇 |
2000年 | 84篇 |
1999年 | 132篇 |
1998年 | 149篇 |
1997年 | 122篇 |
1996年 | 138篇 |
1995年 | 184篇 |
1994年 | 164篇 |
1993年 | 100篇 |
1992年 | 135篇 |
1991年 | 52篇 |
1990年 | 57篇 |
1989年 | 129篇 |
1988年 | 58篇 |
1987年 | 46篇 |
1986年 | 57篇 |
1985年 | 145篇 |
1984年 | 148篇 |
1983年 | 91篇 |
1982年 | 138篇 |
1981年 | 145篇 |
1980年 | 48篇 |
1979年 | 48篇 |
1978年 | 56篇 |
1977年 | 28篇 |
1976年 | 27篇 |
1975年 | 58篇 |
1974年 | 39篇 |
1973年 | 32篇 |
1972年 | 39篇 |
1969年 | 27篇 |
1967年 | 25篇 |
排序方式: 共有5127条查询结果,搜索用时 281 毫秒
861.
McCormick W.S. Tsui J.B.Y. Bakkie V.L. 《IEEE transactions on aerospace and electronic systems》1989,25(5):729-732
The instantaneous frequency measurement (IFM) receiver is capable of measuring the center frequency of single frequency pulses over a wide range (bandwidth) of center frequencies. Because of various constraints, the frequency resolution requirement results in long correlator delay times that reduce the single correlator bandwidth. A large bandwidth can be achieved only if two or more correlators are used. The problem of estimating frequency is then reduced to the simultaneous congruence problem of number theory. A design procedure is presented for solving the congruence problem for a given amount of noise protection, a stated frequency resolution, a minimum bandwidth, and a fixed level of precision (bits) in the IFM receiver 相似文献
862.
Buongiorno C. Vallerani E. Borriello G. 《Aerospace and Electronic Systems Magazine, IEEE》1989,4(5):17-25
The authors present the plan under discussion in Italy between the government entities and Aeritalia, the leading Italian aerospace company, for the technology development needed to support advanced transportation systems. The plan centers around the following areas: thermal protection and control; advanced structures and materials; guidance, navigation, and control; and tests and computation methods. Experimental activities needed to support the development of such systems and the difficulties involved are examined 相似文献
863.
This paper is devoted to an experimental study of swept wing leading edge contamination by the turbulence emanating from the wing-wall junction. The main objective is to delay the contamination onset by applying surface suction along the attachment line. Two series of experiments are described; the first one was performed in a small wind tunnel at CERT ONERA, the second one was carried out in the F2 wind tunnel at Le Fauga Mauzac centre. Hot film measurements showed that leading edge contamination could be delayed up to very large Reynolds numbers. We also studied the behaviour of the relaminarized boundary layer downstream of the sucked region, along the span as well as in the chordwise direction. 相似文献
864.
J.C. Legros 《Acta Astronautica》1986,13(11-12)
Generally, the tension at a liquid/gas interface is decreasing with temperature. For aqueous solution of alcohol, alkylammonium chloride in water, some binary metallic alloys and nematic liquid crystals the surface tension presents an extremum as a function of temperature. The influence of this property on the hydrodynamic stability and on the surface tension induced flows is studied as well theoretically as experimentally. 相似文献
865.
C. -G. Fälthammar 《Space Science Reviews》1974,15(6):803-825
Space-related laboratory experiments can play an important role as a complement to observations and active experiments in the magnetosphere. Excluding laboratory experiments for mere developing or testing of techniques for space experiments, we may distinguish between two major types: (1) partial scale model experiments and (2) experiments for clarifying basic plasma physical processes known or expected to be important in the magnetosphere (but without the ambition to simulate actual space configurations). The limitations and potentialities of both types are discussed and examples of experiments are given. It is concluded that there should be an increasing need for the experiments of the second type. In particular, they are needed for the clarification of the response of a thin plasma to electric fields and its ability to carry electric currents. This encompasses such key questions as the nature and role of anomalous resistivity (and electron runaway in its presence), the possible formation of double layers (and the acceleration processes associated with them) and rapid dissipation of magnetic-field energy. 相似文献
866.
An approach to the problem of achieving frame synchronization in the presence of jamming or other large disturbances is presented. It is assumed that the disturbance can be detected at the receiver, which then erases the corresponding bits and passes this information to the synchronizer. A synchronization algorithm designed to operate in the presence of both erasures and background errors is described and evaluated for a representative set of system parameters. This algorithm is shown to have a significant advantage over an algorithm which does not use the location information inherent in the erasure model. 相似文献
867.
M.M. Gogoshev B.P. Komitov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(8):155-160
In this paper the latest neutral and ionospheric models of the upper Martian atmosphere, created on the Viking data are used. For the calculations of the photoelectron spectra the Hinteregger's measurements of the solar flux together with the theoretical photoelectron distribution are also used. 相似文献
868.
T.C. Forbes 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):53-56
The resistive MHD equations are numerically solved in two dimensions for an initial-boundary-value problem which simulates reconnection between an emerging magnetic flux region and an overlying coronal magnetic field. The solution involves both ideal-MHD and resistive-MHD processes, and the solution shows an evolution which is remarkably suggestive of the preflare, impulsive, and main phases of the flare-cycle. 相似文献
869.
870.
B. Valníček F. Fárník B. Sylwester J. Sylwester 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):121-123
X-ray data obtained by the Prognoz 5,6,7 and 8 hard X-ray photometers are compared with the measurements carried out by similar instruments aboard the Solrad 11, ISEE 3, SMM and Hinotori satellites. Using the method of relative amplitude analysis, the apparent disagreement in the energy discrimination level calibration between the instruments is pointed out. The results of the comparison and the possible sources of disagreement are given. We suggest an international effort be made to develop a system of uniform pre-launch calibration of photometers based on a reference calibration source. 相似文献