全文获取类型
收费全文 | 18419篇 |
免费 | 41篇 |
国内免费 | 124篇 |
专业分类
航空 | 9956篇 |
航天技术 | 5540篇 |
综合类 | 247篇 |
航天 | 2841篇 |
出版年
2021年 | 158篇 |
2018年 | 228篇 |
2016年 | 158篇 |
2014年 | 433篇 |
2013年 | 517篇 |
2012年 | 421篇 |
2011年 | 608篇 |
2010年 | 425篇 |
2009年 | 777篇 |
2008年 | 810篇 |
2007年 | 403篇 |
2006年 | 429篇 |
2005年 | 401篇 |
2004年 | 457篇 |
2003年 | 535篇 |
2002年 | 478篇 |
2001年 | 577篇 |
2000年 | 370篇 |
1999年 | 459篇 |
1998年 | 441篇 |
1997年 | 331篇 |
1996年 | 397篇 |
1995年 | 460篇 |
1994年 | 446篇 |
1993年 | 357篇 |
1992年 | 342篇 |
1991年 | 250篇 |
1990年 | 238篇 |
1989年 | 405篇 |
1988年 | 207篇 |
1987年 | 240篇 |
1986年 | 238篇 |
1985年 | 645篇 |
1984年 | 521篇 |
1983年 | 408篇 |
1982年 | 488篇 |
1981年 | 614篇 |
1980年 | 245篇 |
1979年 | 184篇 |
1978年 | 189篇 |
1977年 | 146篇 |
1976年 | 156篇 |
1975年 | 185篇 |
1974年 | 180篇 |
1973年 | 161篇 |
1972年 | 188篇 |
1971年 | 148篇 |
1970年 | 143篇 |
1969年 | 147篇 |
1967年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Manufacturers are increasingly offering Ethernet connectivity on their test instruments. An additional benefit of this connection method is the ease of conversion to wireless connectivity. This paper describes the Ethernet interface used in the remote control of a RF power amplifier and describes the conversion to wireless connection. 相似文献
62.
The problem of the optimal number of phased array faces for performing 360/spl deg/ horizon surveillance is considered. Assuming the detection performance is the same in all beam positions and the total number of T/R modules is constant, it is shown that the optimal number of array faces is three. This is true whether the arrays are operating simultaneously or sequentially. A parametric analysis is performed between the number of array faces operating simultaneously and the associated cost of simultaneous operation in terms of the size of the array. 相似文献
63.
64.
The robustness of a moving-bank multiple model adaptive estimator/controller to order reduction in the controller design model is examined. It is shown that the adaptive mechanism and bank-moving logic are not confounded by the effects of unmodeled higher order modes of a large flexible spacestructure. Control characteristics are achieved that are essentially equivalent to those of an artificially informed benchmark controller 相似文献
65.
Design for validation 总被引:2,自引:0,他引:2
An approach is outlined for the development of ultrareliable avionics for civil air transports using a design-for-validation philosophy that includes rigorous application of formal methods. The basic concept of the methodology is introduced, and the role of formal methods is explored. The impact of the design-for-validation philosophy on the system design process is then demonstrated by two simple examples. More details about the design-for-validation methodology are then given 相似文献
66.
This paper discusses and evaluates two innovative SETI education programs conducted at the University of Western Sydney, viz: the SETI Pathways Program and the Life in the Universe Curriculum Project. 相似文献
67.
The problem of optimal data fusion in multiple detection systems is studied in the case where training examples are available, but no a priori information is available about the probability distributions of errors committed by the individual detectors. Earlier solutions to this problem require some knowledge of the error distributions of the detectors, for example, either in a parametric form or in a closed analytical form. Here we show that, given a sufficiently large training sample, an optimal fusion rule can be implemented with an arbitrary level of confidence. We first consider the classical cases of Bayesian rule and Neyman-Pearson test for a system of independent detectors. Then we show a general result that any test function with a suitable Lipschitz property can be implemented with arbitrary precision, based on a training sample whose size is a function of the Lipschitz constant, number of parameters, and empirical measures. The general case subsumes the cases of nonindependent and correlated detectors. 相似文献
68.
69.
An experimental investigation of three eigen DF techniques 总被引:1,自引:0,他引:1
The comparative direction-finding (DF) performance of multiple signal classification (MUSIC), ROOT-MUSIC, and estimation of signal parameters via rotational invariance techniques (ESPRIT) is considered. Data were collected from two target transmitters operating simultaneously. The objective of the experiment was to evaluate multipath resolution capability using measurement precision equivalent to that found in modern radio direction-finding systems 相似文献
70.
Bucci N.J. Nespor J.D. Urkowitz H. Mokry D. Brown R. Baldygo W. 《Aerospace and Electronic Systems Magazine, IEEE》1995,10(8):37-43
A major technology barrier to the application of pulse compression for the meteorological functions required by a next generation ATC radar is range/time sidelobes which mask and corrupt observations of weak phenomena occurring near areas of strong extended meteorological scatterers. Techniques for suppressing range sidelobes are well known but without prior knowledge of the scattering medium's velocity distribution their performance degrades rapidly in the presence of Doppler. Recent investigations have presented a “doppler tolerant” range sidelobe suppression technique. The thrust of the work described herein is the extension of previous simulations to actual transmitted dispersed/coded waveforms using the S-band surveillance radar located at Rome Laboratory Surveillance Facility. The objectives of the experiment are: 1) to extend the verification of the simulation of the Doppler tolerant technique; and 2) to demonstrate that the radar transmitter, waveform generator, and receiver imperfections do not significantly degrade resolution, performance or reliability of meteorological spectral moment estimates 相似文献