全文获取类型
收费全文 | 5698篇 |
免费 | 9篇 |
国内免费 | 29篇 |
专业分类
航空 | 2574篇 |
航天技术 | 2167篇 |
综合类 | 19篇 |
航天 | 976篇 |
出版年
2021年 | 54篇 |
2019年 | 40篇 |
2018年 | 119篇 |
2017年 | 81篇 |
2016年 | 71篇 |
2015年 | 25篇 |
2014年 | 126篇 |
2013年 | 163篇 |
2012年 | 155篇 |
2011年 | 228篇 |
2010年 | 147篇 |
2009年 | 257篇 |
2008年 | 314篇 |
2007年 | 168篇 |
2006年 | 145篇 |
2005年 | 174篇 |
2004年 | 177篇 |
2003年 | 198篇 |
2002年 | 123篇 |
2001年 | 183篇 |
2000年 | 128篇 |
1999年 | 139篇 |
1998年 | 158篇 |
1997年 | 125篇 |
1996年 | 153篇 |
1995年 | 197篇 |
1994年 | 178篇 |
1993年 | 93篇 |
1992年 | 145篇 |
1991年 | 49篇 |
1990年 | 51篇 |
1989年 | 127篇 |
1988年 | 40篇 |
1987年 | 40篇 |
1986年 | 58篇 |
1985年 | 172篇 |
1984年 | 131篇 |
1983年 | 105篇 |
1982年 | 132篇 |
1981年 | 155篇 |
1980年 | 45篇 |
1979年 | 30篇 |
1978年 | 37篇 |
1977年 | 36篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 34篇 |
1973年 | 25篇 |
1970年 | 27篇 |
1969年 | 24篇 |
排序方式: 共有5736条查询结果,搜索用时 31 毫秒
171.
Calculation of optimum gain for minimum distortion due to A/D (analog-to-digital) conversion requires the estimation of the input signal strength. To use a common AGC (automatic gain control) for both the I/Q (in-phase and quadrature) signals, it is efficient to estimate the input signal strength using the quantized A/D output from both channels. Assuming a Gaussian input, the relationship between σ of the input of the A/D converter and E (|x |+|y |) and E (max(|x |,|y |)+1/2 min (|x |,|y |)) for t quantized I/Q output x and y is derived. Numerical results obtained using the derived expression and the statistical data obtained through simulation show excellent agreement. It is concluded that, because of its simplicity, the cubic equation obtained by fitting the numerical results should be useful 相似文献
172.
P.L. Boglar (see ibid., vol.AES-23, no.3, p.298-310, May 1987) developed a recursive formulation of the Chan, Hu, and Plant (CHP) algorithm, and the results of the simulation verified the performance improvements. The commenter claims that Bogler obtained an incorrect recursive formulation of input estimation because he incorrectly used the formulation of the Kalman filter. The commenter presents calculations that aim to demonstrate this claim 相似文献
173.
This correspondence considers the problem of optimal regulator design for discrete time linear systems subjected to white state-dependent and control-dependent noise in addition to additive white noise in the input and the observations. A pseudo-deterministic problem is first defined in which multiplicative and additive input disturbances are present, but noise-free measurements of the complete state vector are available. This problem is solved via discrete dynamic programing. Next is formulated the problem in which the number of measurements is less than that of the state variables and the measurements are contaminated with state-dependent noise. The inseparability of control and estimation is brought into focus, and an "enforced separation" solution is obtained via heuristic reasoning in which the control gains are shown to be the same as those in the pseudo-deterministic problem. An optimal linear state estimator is given in order to implement the controller. 相似文献
174.
175.
176.
Krishna M. V. Apparao 《Space Science Reviews》1994,69(3-4):255-329
Observations of X-ray emission from Be star/X-ray binaries are reviewed. Some optical characteristics of these binaries are also presented. Theoretical aspects pertaining to the X-ray emissions are given. 相似文献
177.
Jovanovic M.M. Lee F.C. Chen D.Y. 《IEEE transactions on aerospace and electronic systems》1986,(2):138-145
Reverse-bias safe operating area (RBSOA) of high-power Darlington transistors is characterized using a 120 A/1000 V nondestructive reverse-bias second breakdown tester designed and fabricated at Virginia Polytechnic Institute and State University. Elaborate RBSOA characteristics are generated with different forward/reverse base drives and collector current levels. The effects of elevated case temperature and second-base drive on RBSOA of four-terminal Darlington devices are also discussed. 相似文献
178.
Radar Target Detection and Map-Matching Algorithm Studies 总被引:1,自引:0,他引:1
Results of a study of adaptive threshold target detection and map-matching algorithms are presented. Log threshold processing is shown to be preferred over linear threshold processing when the clutter data surrounding the target cell is contaminated by other targets, decoy corner reflectors, or bright clutter cells. Whereas previous studies have resorted to extensive Monte-Carlo simulations of log threshold algorithms, the results were obtained using a novel analytical approach based upon Parseval's theorem. 相似文献
179.
An improved moving target detector (MTD) (a digital signal processor) has been designed, constructed, and tested which successfully rejects all forms of radar clutter while providing reliable detection of all aircraft within the coverage of the radar. The MTD is being tested on both terminal and enroute surveillance radars for the FAA. This processor has been integrated with automatic tracking algorithms to give complete rejection of ground clutter, heavy precipitation, and angels (birds). 相似文献
180.