全文获取类型
收费全文 | 8543篇 |
免费 | 18篇 |
国内免费 | 24篇 |
专业分类
航空 | 4234篇 |
航天技术 | 2994篇 |
综合类 | 38篇 |
航天 | 1319篇 |
出版年
2021年 | 65篇 |
2019年 | 52篇 |
2018年 | 144篇 |
2017年 | 89篇 |
2016年 | 86篇 |
2014年 | 181篇 |
2013年 | 227篇 |
2012年 | 206篇 |
2011年 | 290篇 |
2010年 | 204篇 |
2009年 | 339篇 |
2008年 | 428篇 |
2007年 | 223篇 |
2006年 | 210篇 |
2005年 | 236篇 |
2004年 | 190篇 |
2003年 | 274篇 |
2002年 | 169篇 |
2001年 | 290篇 |
2000年 | 156篇 |
1999年 | 203篇 |
1998年 | 237篇 |
1997年 | 180篇 |
1996年 | 220篇 |
1995年 | 278篇 |
1994年 | 259篇 |
1993年 | 160篇 |
1992年 | 192篇 |
1991年 | 113篇 |
1990年 | 84篇 |
1989年 | 199篇 |
1988年 | 99篇 |
1987年 | 105篇 |
1986年 | 85篇 |
1985年 | 263篇 |
1984年 | 210篇 |
1983年 | 181篇 |
1982年 | 201篇 |
1981年 | 262篇 |
1980年 | 92篇 |
1979年 | 72篇 |
1978年 | 74篇 |
1977年 | 66篇 |
1976年 | 63篇 |
1975年 | 75篇 |
1974年 | 56篇 |
1973年 | 58篇 |
1972年 | 69篇 |
1971年 | 59篇 |
1970年 | 59篇 |
排序方式: 共有8585条查询结果,搜索用时 62 毫秒
961.
The approach of the Year 2000 (Y2K) has called into question the condition of readiness of computer systems upon which organizations depend. Will these systems operate reliably after midnight, January 1, 2000, or will problems associated with date calculations cause failures that adversely affect users? This question has caused organizations to identify their critical systems, test these systems for Y2K problems, and take corrective action where necessary to ensure Y2K readiness. This paper examines various technical and management issues that Southwest Research Institute has dealt with in solving these problems 相似文献
962.
963.
964.
The effects of frequency multiplication circuits on the short-term stability of an oscillator system are analyzed. The short-term stability of real components such as varactor multipliers are compared to the short-term stability of an ?ideal? frequency multiplier which maintains the stability of the basic oscillator. In addition, it is shown that positive feedback like that used in a synchronized oscillator, while useful for tracking, degrades short-term stability. 相似文献
965.
A technique is presented which simplifies the analysis of sampled-data control systems. The use of a finite-term approximation to the Poisson summation rule, in conjunction with digital computer evaluation, is presented as a good alternative to use of the Z transform whenever frequency-domain analysis is required. The Poisson summation rule is reviewed and its application to sampled-data system analysis is discussed. The form of the computer program used in the analysis is presented, along with a design criterion to evaluate the accuracy of the technique. A detailed example of a typical application is presented. 相似文献
966.
The factors which affect the target-handling capacity of an agile-beamelectronically scanned multitarget-tracking radar are reviewed and analyze.Consideration is given to the choice of strategy for dwell allocation amongtargets, the choice of trajectory extrapolation algorithms for target tracking, and the determination of saturation target acquisition rates. Emphasisis placed upon radar systems with control computers having limited speed and memory, and recommendations are made for allocation strategy and targetytracking algorithms, based on uniform sampling, to be used in maximizing thetarget-handling capacity in this situation. 相似文献
967.
S M Kochubey O I Volovik L V Porubleva V V Shevchenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1127-1130
The photosynthetic membrane composition and low temperature fluorescence spectra were analyzed for pea chloroplasts from control and clinostated plants. Clinorotation induces a decrease in the amount of the oligomeric form of the light-harvesting chlorophyll a/b complex (LHCII) and an increase of its monomeric form. Some changes in organization of photosystem 1 (PS1) complex were revealed as well. These changes are in accordance with the variations of fluorescence characteristics and photochemical activity. 相似文献
968.
Jao J.K. Lee C.F. Ayasli S. Haywiser E.J. 《Aerospace and Electronic Systems Magazine, IEEE》1999,14(6):5-9
In July and October 1995, a large-scale airborne SAR experiment was conducted in the Yuma Proving Ground, Yuma, Arizona, to investigate ground penetration radar phenomenology and buried target detection. This paper describes the Yuma experiment and measurement results for many tactical, utility, and environmental targets deployed in the test 相似文献
969.
The performances of the importance sampling (IS) techniques are improved by using multiparametric distortions of the input random processes. The analysis of different constant false-alarm rate (CFAR) algorithms confirms the usefulness of this method. The potential of this new approach is fully exploited if optimization techniques are used to obtain the optimum distortions and to avoid bias in the estimates 相似文献
970.