全文获取类型
收费全文 | 5169篇 |
免费 | 29篇 |
国内免费 | 10篇 |
专业分类
航空 | 2663篇 |
航天技术 | 1813篇 |
综合类 | 23篇 |
航天 | 709篇 |
出版年
2021年 | 37篇 |
2019年 | 32篇 |
2018年 | 80篇 |
2017年 | 60篇 |
2016年 | 51篇 |
2014年 | 86篇 |
2013年 | 112篇 |
2012年 | 104篇 |
2011年 | 158篇 |
2010年 | 117篇 |
2009年 | 180篇 |
2008年 | 264篇 |
2007年 | 113篇 |
2006年 | 101篇 |
2005年 | 128篇 |
2004年 | 131篇 |
2003年 | 168篇 |
2002年 | 96篇 |
2001年 | 163篇 |
2000年 | 111篇 |
1999年 | 101篇 |
1998年 | 149篇 |
1997年 | 108篇 |
1996年 | 139篇 |
1995年 | 177篇 |
1994年 | 168篇 |
1993年 | 101篇 |
1992年 | 136篇 |
1991年 | 60篇 |
1990年 | 65篇 |
1989年 | 143篇 |
1988年 | 59篇 |
1987年 | 62篇 |
1986年 | 84篇 |
1985年 | 166篇 |
1984年 | 133篇 |
1983年 | 122篇 |
1982年 | 124篇 |
1981年 | 144篇 |
1980年 | 56篇 |
1979年 | 46篇 |
1978年 | 52篇 |
1977年 | 44篇 |
1975年 | 53篇 |
1974年 | 45篇 |
1973年 | 39篇 |
1972年 | 51篇 |
1971年 | 45篇 |
1969年 | 35篇 |
1967年 | 30篇 |
排序方式: 共有5208条查询结果,搜索用时 31 毫秒
751.
The authors provide an overview of expert systems and how they may effect the development of future defense applications. Military uses of computers are outlined, and expert-systems fundamentals are described. Artificial research and development efforts by the military are examined, and potential military applications are discussed. Expert systems efforts at NASA, by the US Air Force, and for the Strategic Defence Initiative are considered 相似文献
752.
S.S. Gaigerov M.Ya. Kalikhman V.V. Fedorov E.D. Zhorova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(1):29-32
Circulation and thermal structure for the 90–95 km region is described on the basis of the joint analysis of direct and indirect sounding data. Mean season charts of the 0.001 mb surface were compiled using data from meteor trials, ionospheric drifts, rocket launchings and data of the rotational temperature of hydroxyl emission. 相似文献
753.
Gordon D. Holman 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(11):181-183
Theoretical work on the interpretation of high brightness temperature microwave spike emission is reviewed, with emphasis upon recent contributions from the University of Maryland. Recent work on the interpretation of the spike emission as gyrosynchrotron masering is reviewed. Two alternative radiation mechanisms, stimulated plasma emission from the coherent intraction of electrostatic upper hybrid waves and from the interaction of electron plasma waves, are also discussed. 相似文献
754.
D. Wonnacott 《Space Science Reviews》1989,50(1-2):375-375
Simulations of the Algol-like binary CX Draconis, combined with IUE observations of the stream of material escaping the system can place limits on the inclination of the system and give estimates, via line profile synthesis, of the mass-loss rate at the L1 point. 相似文献
755.
756.
757.
Ernest W. Lichfield 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(6):87-96
Long duration balloon flights require more electrical power than can be carried in primary batteries. This paper provides design information for selecting rechargeable batteries and charging systems. Solar panels for recharging batteries are discussed, with particular emphasis on cells mounting suitable for balloon flights and panel orientation for maximum power collection. Since efficient utilization of power is so important, modern DC to DC power conversion techniques are presented.On short flights of 1 day or less, system designers have not been greatly concerned with battery weight. But, with the advent of long duration balloon flights using superpressure balloons, anchor balloon systems, and RACOON balloon techniques, power supplies and their weight become of prime importance. The criteria for evaluating power systems for long duration balloon flights is performance per unit weight. Instrumented balloon systems have flown 44 days. For these very long duration flights, batteries recharged from solar cells are the only solution. For intermediate flight duration, say less than 10 days, the system designer should seriously consider using primary cells. 相似文献
758.
G Horneck H Bucker K Dose K D Martens A Bieger H D Mennigmann G Reitz H Requardt P Weber 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(10):19-27
Bacterial spores are proper test organisms for studying problems of space biology and exobiology. During the Spacelab 1 mission, studies on the limiting factors for survival of Bacillus subtilis spores in free space have been performed. An exposure tray on the pallet of Spacelab 1 accomodated 316 samples of dry spores for treatment with space vacuum and/or the following selected wavelengths of solar UV: > 170 nm, 220 nm, 240nm, 260nm and 280 nm. After recovery, inactivation, mutation induction, reparability, and photochemical damages in DNA and protein have been studied. The results contribute to the understanding of the mechanisms of increased UV sensitivity of bacterial spores in vacuo and to a better assessment of the chance of survival of resistant forms in space and of interplanetary transfer of life. 相似文献
759.
J.W. Harvey 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(11):31-37
The decaying solar active region that crossed the central meridian on May 20, 1980 at latitude S13° produced a major flare (2B/X1) at 2054 on May 21. This region was a target of the international Flare Buildup Study and was well observed. The buildup was characterized by little flare activity during two days prior to the major flare but a great deal of activity in the filament that separated the opposite magnetic polarities of the active region. Large proper motions of sunspots and magnetic fields suggest that the magnetic field was stressed prior to the flare. The immediate trigger of the flare appears to have been an eruption of new magnetic flux in the center of the active region. The new flux erupted in a configuration that decreased the net flux of the active region and contributed to the decay of the region. 相似文献
760.
M. A. Azouni W. Kalita 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1988,8(12):219-224
The interaction of inert foreign particles and a solid-liquid interface during solidification is considered. The viscous drag on the particle which produces a force on the interface is calculated under general assumptions as well as the disjoining force for small particles and the buoyancy force for large ones. 相似文献