全文获取类型
收费全文 | 6948篇 |
免费 | 9篇 |
国内免费 | 23篇 |
专业分类
航空 | 3561篇 |
航天技术 | 2528篇 |
综合类 | 28篇 |
航天 | 863篇 |
出版年
2019年 | 41篇 |
2018年 | 81篇 |
2017年 | 54篇 |
2016年 | 39篇 |
2014年 | 114篇 |
2013年 | 171篇 |
2012年 | 137篇 |
2011年 | 207篇 |
2010年 | 151篇 |
2009年 | 251篇 |
2008年 | 309篇 |
2007年 | 170篇 |
2006年 | 167篇 |
2005年 | 179篇 |
2004年 | 162篇 |
2003年 | 238篇 |
2002年 | 135篇 |
2001年 | 233篇 |
2000年 | 140篇 |
1999年 | 203篇 |
1998年 | 220篇 |
1997年 | 163篇 |
1996年 | 207篇 |
1995年 | 250篇 |
1994年 | 242篇 |
1993年 | 141篇 |
1992年 | 159篇 |
1991年 | 91篇 |
1990年 | 86篇 |
1989年 | 177篇 |
1988年 | 75篇 |
1987年 | 90篇 |
1986年 | 70篇 |
1985年 | 236篇 |
1984年 | 173篇 |
1983年 | 152篇 |
1982年 | 170篇 |
1981年 | 226篇 |
1980年 | 76篇 |
1979年 | 60篇 |
1978年 | 65篇 |
1977年 | 63篇 |
1976年 | 48篇 |
1975年 | 73篇 |
1974年 | 48篇 |
1973年 | 49篇 |
1972年 | 59篇 |
1971年 | 45篇 |
1970年 | 50篇 |
1969年 | 45篇 |
排序方式: 共有6980条查询结果,搜索用时 31 毫秒
91.
When a micro-debris or a micrometeoroid impacts a spacecraft surface, a large number of secondary particles, called ejecta, are produced. These particles can contribute to a modification of the debris environment: either locally by the occurrence of secondary impacts on the components of complex and large space structures, or at great distance by the formation of a population of small orbital debris. This paper describes firstly, the ejecta overall production, and secondly, the lifetime and the orbital evolution of the particles. Finally the repartition of ejecta in LEO is computed. Some results describing the population as a function of size and altitude are presented. 相似文献
92.
Robert J. HaydukWalter S. ScottGerald D. WalbergJames J. ButtsRichard D. Starr 《Acta Astronautica》1996,39(9-12):677-686
The Small Satellite Technology Initiative (SSTI) is a National Aeronautics and Space Administration (NASA) program to demonstrate smaller, high technology satellites constructed rapidly and less expensively. Under SSTI, NASA funded the development of “Clark,” a high technology demonstration satellite to provide 3-m resolution panchromatic and 15-m resolution multispectral images, as well as collect atmospheric constituent and cosmic x-ray data. The 690-Ib. satellite, to be launched in early 1997, will be in a 476 km, circular, sun-synchronous polar orbit. This paper describes the program objectives, the technical characteristics of the sensors and satellite, image processing, archiving and distribution. Data archiving and distribution will be performed by NASA Stennis Space Center and by the EROS Data Center, Sioux Falls, South Dakota, USA. 相似文献
93.
94.
Hwu S.U. Loh Y.C. Dobbins J.A. Kroll Q.D. Sham C.C. 《Aerospace and Electronic Systems Magazine, IEEE》2005,20(10):9-14
Computational investigations and experimental measurements were performed to evaluate the Space Shuttle UHF communication system performance for payload bay antenna at the proposed new location. To insure adequate communication coverage at relocated new location, the link margin for the Extravehicular Activity (EVA) astronauts and between Space Shuttle Orbiter and International Space Station (SSO-ISS) during rendezvous were analyzed. The multipath effects from the vehicle structures surrounding the antenna were investigated. The Radio Frequency (RF) electromagnetic radiation to the Orbiter Docking System (ODS) pyrotechnics was also analyzed to ensure the EMC/EMI compliances. 相似文献
95.
96.
Ruoskanen J. Eskelinen P. Heikkila H. 《Aerospace and Electronic Systems Magazine, IEEE》2003,18(10):19-23
A portable millimeter wave test radar system, also suitable for battery operation, gives interesting possibilities for clutter recordings at hard-to-reach sites. The designed system covers all common radar frequencies from the Ka- to V-bands and enables spatial detection of targets or clutter elements within an adjustable time gate, whereby spatial clutter profiles of rain can be analyzed. The construction allows full operation with non-scanning antennas as well. This is advantageous when measuring temporal RCS variations of selected targets or surface clutter from snow dunes. 相似文献
97.
98.
The fine structure of the Auroral Kilometric Radiation (AKR) is studied using multicomponent measurements of the electric component of the electromagnetic field in the frequency band 4 kHz–1 MHz (the POLRAD experiment onboard the INTERBALL-2 satellite). Special attention is paid to the measurements near the source of the AKR: under conditions when the lower boundary of the emission range descended sufficiently low, down to the local gyrofrequency of electrons. From the analysis of the electric field structure the conclusion is drawn that the bulk of the AKR power is carried by the signal component fast variable in time and frequency (flickering component). The power of a constant component (continuum) is lower by at least an order of magnitude. During strong bursts of the AKR, the relative contribution of the flickering component increases. The spatial structure of the zone of generation has at least three characteristic scales along and across the magnetic field. 相似文献
99.
Kuroki F. Wagatsuma Y. Yoneyama T. 《Aerospace and Electronic Systems Magazine, IEEE》2006,21(5):26-29
An FM-CW radar front-end was fabricated in an integrated manner at 60 GHz by using the NRD guide. Main emphasis was placed on compactness in size and high-precise operation in performance. The fabricated radar consists of an FM Gunn oscillator, a balanced mixer, and a planar antenna fed by leaky NRD guide with a mechanically beam-scanning performance. All circuit components and the antenna were contained in a compact housing of 170 /spl times/ 140 mm in area and 25 mm in thickness, and thus, a thin type of millimeter-wave radar front-end was successfully developed. Moreover, an error of distance estimation was measured to be less than a distance of 0.7 m. 相似文献
100.
Valve regulated lead acid (VRLA) batteries provide electrical performance that is virtually identical to sintered plate nickel-cadmium battery systems. In addition, the VRLA batteries offer the user a no-maintenance battery and other enhanced features that make this a very desirable battery for aircraft applications. In field trials, where VRLA batteries were substituted for nickel-cadmium batteries, the VRLA provided the user with a high reliability turbine engine starting battery under a wide variety of climatic conditions 相似文献