全文获取类型
收费全文 | 7678篇 |
免费 | 13篇 |
国内免费 | 40篇 |
专业分类
航空 | 3669篇 |
航天技术 | 2763篇 |
综合类 | 27篇 |
航天 | 1272篇 |
出版年
2021年 | 59篇 |
2019年 | 50篇 |
2018年 | 133篇 |
2017年 | 84篇 |
2016年 | 73篇 |
2014年 | 154篇 |
2013年 | 210篇 |
2012年 | 195篇 |
2011年 | 285篇 |
2010年 | 187篇 |
2009年 | 317篇 |
2008年 | 395篇 |
2007年 | 212篇 |
2006年 | 177篇 |
2005年 | 229篇 |
2004年 | 213篇 |
2003年 | 258篇 |
2002年 | 158篇 |
2001年 | 237篇 |
2000年 | 154篇 |
1999年 | 193篇 |
1998年 | 224篇 |
1997年 | 166篇 |
1996年 | 213篇 |
1995年 | 275篇 |
1994年 | 242篇 |
1993年 | 141篇 |
1992年 | 207篇 |
1991年 | 85篇 |
1990年 | 74篇 |
1989年 | 186篇 |
1988年 | 64篇 |
1987年 | 64篇 |
1986年 | 78篇 |
1985年 | 234篇 |
1984年 | 192篇 |
1983年 | 149篇 |
1982年 | 188篇 |
1981年 | 208篇 |
1980年 | 73篇 |
1979年 | 66篇 |
1978年 | 59篇 |
1977年 | 50篇 |
1976年 | 46篇 |
1975年 | 56篇 |
1974年 | 57篇 |
1973年 | 41篇 |
1972年 | 45篇 |
1970年 | 38篇 |
1969年 | 38篇 |
排序方式: 共有7731条查询结果,搜索用时 15 毫秒
991.
A Gaussian sum estimation algorithm has previously been developed to deal with noise processes that are non-Gaussian. Inherent in this algorithm is a serious growing memory problem that causes the number of terms in the Gaussian sum to increase exponentially at each iteration. A modified Gaussian sum estimation algorithm using an adaptive filter is developed that avoids the growing memory problem of the previous algorithm while providing effective state estimation. The adaptive filter is comprised of a fixed set of estimators operating in parallel with each individual estimate possessing its own corresponding weighting term. A simulation example illustrates the new non-Gaussian estimation technique 相似文献
992.
A data path consists of memory elements (i.e., registers), data operators (i.e. ALUs) and interconnection units (i.e. buses) to control the data transfers in the digital system. Many approaches to hardware allocation for data path synthesis have been proposed in the literature; however, only single-port memory is considered for register allocation and no efficient synthesis approach for multiport memory synthesis. A novel design methodology for data path synthesis using multiport memories is proposed which can be applied to hardware allocation algorithms or to already synthesized data path as a postprocessor to achieve a better design. Illustrations of applying this method to different synthesis examples are presented. Results and improvements over previous techniques are demonstrated. Experiments on benchmarks show very promising results 相似文献
993.
Morgan C.J. Moyer L.R. Wilson R.S. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(3):41-43
A technique is presented for determining the ideal detection threshold when Gaussian noise and Weibull distributed clutter returns are present on a radar receiver and neither is dominant. Quantitative data is presented for several clutter types and false alarm probabilities 相似文献
994.
The performance of multiple signal classification (MUSIC) algorithm using three different inputs over a wideband of frequencies is considered. These inputs are: 1) ideal voltages, 2) actual voltages which include coupling effects and are obtained with the method or moments, and 3) corrected voltages which are obtained from the actual voltages so that the mutual coupling effects are removed. Linear arrays of dipoles, sleeve dipoles, and spiral antennas are considered over 200 MHz to 400 MHz band 相似文献
995.
The author outlines several rules for starting electrical engineers that he developed during his career. The rules are divided into general rules, rules for career growth, and job-related rules 相似文献
996.
Haimovich A.M. Yosko J. Greenberg R.J. Parisi M.A. Becker D. 《IEEE transactions on aerospace and electronic systems》1993,29(1):245-250
The case of data fusion of sensors dissimilar in their measurement/tracking errors is considered. It is shown that the fused track performance is similar whether the sensor data are fused at the track level or at the measurement level. The case of a cluster of targets, resolved by one sensor but not the other, is also considered. Under certain conditions the fused track may perform worse than the worst of the sensors. A remedy to this problem through modifications of the association algorithm is presented 相似文献
997.
J C Guillemin S El Chaouch A Bouayad T Janati 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(2):245-253
The photolysis of mixtures of gases containing NH3 or PH3 presents important differences mainly due to the strength of the X-H bond. On some examples, these differences are evidenced and the consequences for mixtures of gases containing these two compounds are shown: the photolysis of ammonia and ethylene mainly gives ethyl-, butyl- and hexylamine whereas the photolysis of phosphine and ethylene leads to ethyl- and vinylphosphine. When gaseous mixtures of NH3, PH3 and ethylene are photolyzed together, the presence of phosphine dramatically decreases the formation of nitrogen derivatives. The relevance of such lab studies to the atmospheres of Jupiter and Saturn is discussed. 相似文献
998.
A.I. Podgorny I.M. Podgorny 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(12):1929-1932
The patterns of reconnection in the Earth magnetotail and in the solar corona above the active region are presented. The electric field and field-aligned currents (FAC) generation in the current sheet are discussed. 相似文献
999.
D. Odstrcil M. Karlicky 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(12):1895-1898
Interaction of shocks with a current sheet is investigated within a 2D MHD model based on an improved FCT numerical scheme. Basic parameters of the problem are chosen to correspond to situations in the solar corona with low plasma β and moderate shock strength. Slow and fast MHD shocks are introduced with shock normal parallel to magnetic field lines. The interaction with the current sheet causes distortion of the shock front and this distorts the magnetic field lines and generates electric current. Large current densities are generated especially when the fast MHD shock becomes the intermediate MHD shock at the current sheet. Then peak values of the current density are about 3–4 times larger than the initial undisturbed values in the current sheet. 相似文献
1000.
V. Formisano V.I. Moroz H. Hirsch P. Orleanski G. Michel J. Lopez-Moreno E. Amata G. Bellucci G. Piccioni G. Chionchio A. Carusi A. Coradini P. Cerroni M.T. Capria F. Capaccioni A. Adriani M. Vitterbini F. Angrilli G. Bianchini B. Saggin S. Fonti E. Bussoletti D. Mancini L. Colangeli A. Grigoriev B. Moshkin V. Gnedykh I.A. Matsygorin D. Patsaev Yu.V. Nikolsky D.V. Titov L.V. Zasova I. Khatuntsev A. Kiselev G. Arnold H. Driesher M.I. Blecka R. Rodrigo J. Rodriguez-Gomez 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(12):61-64
Thin films containing a mixture of aliphatic (glycine) and aromatic (tryptophan or tyrosine) amino acids were exposed to a vacuum ultraviolet radiation (VUV) with wavelenghts 100–200 nm. Dipeptides (glycyl-tryptophan and glycyl-tyrosine) were synthesized in these conditions. We compared the actions of VUV and γ-radiation. Polymerization is an essential step in prebiological evolution and we have shown that this stage probably occured over an early Solar system history. 相似文献