全文获取类型
收费全文 | 2666篇 |
免费 | 2篇 |
国内免费 | 19篇 |
专业分类
航空 | 1317篇 |
航天技术 | 1052篇 |
综合类 | 10篇 |
航天 | 308篇 |
出版年
2019年 | 18篇 |
2018年 | 24篇 |
2017年 | 18篇 |
2016年 | 17篇 |
2014年 | 48篇 |
2013年 | 58篇 |
2012年 | 51篇 |
2011年 | 82篇 |
2010年 | 60篇 |
2009年 | 104篇 |
2008年 | 158篇 |
2007年 | 63篇 |
2006年 | 66篇 |
2005年 | 69篇 |
2004年 | 79篇 |
2003年 | 80篇 |
2002年 | 51篇 |
2001年 | 75篇 |
2000年 | 49篇 |
1999年 | 63篇 |
1998年 | 80篇 |
1997年 | 49篇 |
1996年 | 61篇 |
1995年 | 78篇 |
1994年 | 76篇 |
1993年 | 49篇 |
1992年 | 61篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 70篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 30篇 |
1985年 | 120篇 |
1984年 | 68篇 |
1983年 | 57篇 |
1982年 | 58篇 |
1981年 | 103篇 |
1980年 | 34篇 |
1979年 | 26篇 |
1978年 | 24篇 |
1977年 | 28篇 |
1976年 | 18篇 |
1975年 | 31篇 |
1974年 | 19篇 |
1973年 | 25篇 |
1972年 | 20篇 |
1971年 | 16篇 |
1970年 | 24篇 |
1969年 | 26篇 |
排序方式: 共有2687条查询结果,搜索用时 0 毫秒
961.
A computer simulation model capable of predicting the performance nce of a high-dta-rate end-to-end communication system with adaptive equalization is described in this paper. The model is used to characterize the behavior of NASA's proposed tracking and data relay satellite system (TDRSS), while accounting for signal distortion effects due to operational conditions and the required hardware are components necessary to fulfill mission objectives. Specifically, the performance of the TDRSS high-dta-rate lik (300 Mbps) is defined, both with and without adaptive equalization. 相似文献
962.
Dynamics of the satellite angular momenta is modeled by ordinary differential equations with additive white noise. A feedback controller er is desired to maintain tolerable satellite momenta and to economize ze the fuel consumption. The stochastic optimal control problem is transformed into an equivalent deterministic optimization problem involving a parabolic partial differential equation. Necessary optimality y conditions are used to develop a computation algorithm. Results regarding optimal controls, expected costs, and confinement probabilities in different noisy environments are presented. 相似文献
963.
964.
The cell averaging LOG/CFAR receiver is a special implementation of a constant-false-alarm-rate (CFAR) receiver in which the noise level estimate is derived from a set of contiguous time samples of the output of a logarithmic (LOG) detector as obtained from a tapped delay line. This CFAR receiver is capable of operating over a larger dynamic range of noise levels than a conventional cell averaging CFAR receiver, but with somewhat poorer detectability. The performance in stationary Gaussian noise of the cell averaging LOG/CFAR receiver with no post-detection integration is determined in this paper. For a small number of reference noise samples, results were obtained by a Monte Carlo simulation using the technique of importance sampling. For a large number of reference noise samples, a second moment analysis gave the desired results. Both these results can be summarized in the following simple formula, NLOG = 1.65NLIN - 0.65, which relates the number of reference samples required by each of the two receivers for equivalent performance. Thus, for the cell averaging LOG/CFAR receiver to give the same detection performance as the conventional cell averaging CFAR receiver, the number of reference noise samples has to be increased by up to 65 percent. 相似文献
965.
966.
M.C. Zolcinski D.J. Forrest J.M. Ryan E.L. Chupp G. Kanbach C. Reppin E. Rieger G.H. Share 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(11):193-196
We have searched for anisotropic X-ray bremsstrahlung photon production from relativistic electrons by studying the heliocentric angular dependence of 53 flares detected at energies above 300 keV. We have found no evidence for a higher rate of detectable flares near the limb at the 80% confidence level. This result implies that the X-ray directivity as defined by the ratio of photon intensity at 75° and 0° of heliocentric angle is less than 1.5 above 300 keV and strongly rejects any flare model predicting X-ray production from a radial “beam” of energetic electrons. 相似文献
967.
968.
Kaplan L.J. Ormsby J.F.A. Fowle E.N. Johnson K.R. Bates R.H.T. Bickel S.H. 《IEEE transactions on aerospace and electronic systems》1969,(4):654-660
A satellite has been designed for application to radar calibration. Electromagnetic and mechanical characteristics of the satellite and their influence on the selection of shape and other parameters are discussed. Theoretical and experimental scattering data are included. 相似文献
969.
970.
The modern digital computer is rapidly permeating all areas of our highly industrialized society-from agriculture to education-from process control to zoology. Printing and publishing and allied fields involved in graphic communications have been changing rapidly in this decade as the digital computer and associated peripheral devices have made rapid inroads in the graphic communications process. This paper describes the nature of the impact which the digital computer has had, and is making, upon today's graphic communications, particularly upon the editing and composition functions. A prediction of future impact is also presented. 相似文献