全文获取类型
收费全文 | 3307篇 |
免费 | 89篇 |
国内免费 | 124篇 |
专业分类
航空 | 1737篇 |
航天技术 | 1192篇 |
综合类 | 81篇 |
航天 | 510篇 |
出版年
2021年 | 21篇 |
2019年 | 24篇 |
2018年 | 38篇 |
2017年 | 27篇 |
2016年 | 27篇 |
2015年 | 30篇 |
2014年 | 81篇 |
2013年 | 93篇 |
2012年 | 89篇 |
2011年 | 130篇 |
2010年 | 104篇 |
2009年 | 135篇 |
2008年 | 194篇 |
2007年 | 115篇 |
2006年 | 93篇 |
2005年 | 108篇 |
2004年 | 92篇 |
2003年 | 95篇 |
2002年 | 59篇 |
2001年 | 100篇 |
2000年 | 86篇 |
1999年 | 103篇 |
1998年 | 111篇 |
1997年 | 75篇 |
1996年 | 76篇 |
1995年 | 90篇 |
1994年 | 92篇 |
1993年 | 62篇 |
1992年 | 72篇 |
1991年 | 49篇 |
1990年 | 38篇 |
1989年 | 76篇 |
1988年 | 34篇 |
1987年 | 30篇 |
1986年 | 33篇 |
1985年 | 131篇 |
1984年 | 76篇 |
1983年 | 60篇 |
1982年 | 62篇 |
1981年 | 110篇 |
1980年 | 34篇 |
1979年 | 26篇 |
1978年 | 25篇 |
1977年 | 28篇 |
1975年 | 32篇 |
1974年 | 19篇 |
1973年 | 26篇 |
1972年 | 21篇 |
1970年 | 24篇 |
1969年 | 27篇 |
排序方式: 共有3520条查询结果,搜索用时 15 毫秒
61.
62.
An optimum filter for direct A/D conversion 总被引:1,自引:0,他引:1
The author describes a design procedure to find the optimum finite-impulse-response (FIR) filter coefficients when the characteristics of the bandpass filter preceding the analog-to-digital (A/D) converter are known. A simulation of direct A/D conversion performance shows the improvement over the filter coefficients designed to minimize the maximum error over a specified band of frequencies. DC cancellation may be added to the process with very little change in the coefficients of the optimum FIR filter or its performance.<> 相似文献
63.
Lee M.H. Kolodziej W.J. Mohler R.R. 《IEEE transactions on aerospace and electronic systems》1985,(5):594-600
The control of a linear system with random coefficients is studied here. The cost function is of a quadratic form and the random coefficients are assumed to be partially observable by the controller. By means of the stochastic Bellman equation, the optimal control of stochastic dynamic models with partially observable coefficients is derived. The optimal control is shown to be a linear function of the observable states and a nonlinear function of random parameters. The theory is applied to an optimal control design of an aircraft landing in wind gust. 相似文献
64.
Alabaster C.M. Hughes E.J. Matthew J.H. 《IEEE transactions on aerospace and electronic systems》2003,39(3):990-1001
Evolutionary algorithms are applied to the optimization of pulse repetition frequency (PRF), for both eight-and nine PRFs, in medium PRF radar while considering the detailed effects of sidelobe clutter and many other technical factors. The algorithm presented also ensures that all the solutions produced are fully decodable and have no blind velocities. The evolutionary algorithm was able to identify near-optimum PRF sets for a realistic radar system with only a modest computational effort. 相似文献
65.
Multiposition alignment of strapdown inertial navigation system 总被引:3,自引:0,他引:3
Lee J.G. Park C.G. Park H.W. 《IEEE transactions on aerospace and electronic systems》1993,29(4):1323-1328
The authors demonstrate that the stationary alignment of strapdown inertial navigation system (SDINS) can be improved by employing the multiposition/technique. Using an observability analysis, it is shown that an optimal two-position alignment not only satisfies complete observability conditions but also minimizes alignment errors. This is done by analytic rank testing of the stripped observability matrix and numerical calculation of the error covariance. It is also shown that an optimal three-position alignment accelerates the convergence of the alignment error compared with two-position alignment 相似文献
66.
A two-pole filter is proposed as a detector for a scanning radar. The optimum values of the filter coefficients are found and are approximated by a simple expression. The optimum two-pole filter requires a 0.15-dB increase in signal-to-noise ratio in order to provide the same detection capability as the optimum detector, and yields azimuth estimates whose standard deviation are within 15 percent of the Cramér-Rao lower bound. The estimator is simple to implement, avoiding the storage requirements of the moving window detector and the bias complications of the feedback integrator. 相似文献
67.
68.
H. Borg L. -A. Holmgren B. Hultovist F. Cambou H. Rème A. Bahnsen G. Kremser 《Space Science Reviews》1978,22(5):511-535
Some preliminary new results are presented of the keV plasma experiment on GEOS-1. Electrons and ions have been observed to stream along the magnetic field lines in the dayside magnetosphere from the ionospheric side of the satellite towards the equatorial plane during magnetic storms, with streaming velocities corresponding to a kinetic energy of the order of a keV. The opposite streaming velocity has also been seen, but primarily in the ions only and with a smaller flux ratio for the two opposite directions along the field lines. The transition between the two opposite streaming directions, as seen by the satellite, has been found to occur even in a fraction of a second.In magnetic storm conditions azimuthal asymmetries in ion fluxes corresponding to electric field intensities of several tens of millivolts per meter have been observed. 相似文献
69.
Gawron T.E. Klembowski W. Pikielny J. Jakubiak A. Wojtkiewicz A. Czyz Z.H. Tuszynski M. Centkowski G. 《IEEE transactions on aerospace and electronic systems》1991,27(5):748-783
Polish radar research and development since 1953 is reviewed, covering the development and production of surveillance radars, height finders, tracking radars, air traffic control (ATC) radars and systems, and marine and Doppler radars. Some current work, including an L-band ATC radar for enroute control, a weather channel for primary surveillance radar, signal detection in non-Gaussian clutter, adaptive MTI filters and postdetection filtering, and a basic approach to radar polarimetry, is examined.<> 相似文献
70.
A. L. Broadfoot B. R. Sandel D. E. Shemansky S. K. Atreya T. M. Donahue H. W. Moos J. L. Bertaux J. E. Blamont J. M. Ajello D. F. Strobel J. C. McConnell A. Dalgarno R. Goody M. B. McElroy Y. L. Yung 《Space Science Reviews》1977,21(2):183-205
The Voyager Ultraviolet Spectrometer (UVS) is an objective grating spectrometer covering the wavelength range of 500–1700 Å with 10 Å resolution. Its primary goal is the determination of the composition and structure of the atmospheres of Jupiter, Saturn, Uranus and several of their satellites. The capability for two very different observational modes have been combined in a single instrument. Observations in the airglow mode measure radiation from the atmosphere due to resonant scattering of the solar flux or energetic particle bombardment, and the occultation mode provides measurements of the atmospheric extinction of solar or stellar radiation as the spacecraft enters the shadow zone behind the target. In addition to the primary goal of the solar system atmospheric measurements, the UVS is expected to make valuable contributions to stellar astronomy at wavelengths below 1000 Å. 相似文献