全文获取类型
收费全文 | 2712篇 |
免费 | 28篇 |
国内免费 | 14篇 |
专业分类
航空 | 1102篇 |
航天技术 | 1011篇 |
综合类 | 16篇 |
航天 | 625篇 |
出版年
2022年 | 13篇 |
2021年 | 28篇 |
2019年 | 24篇 |
2018年 | 80篇 |
2017年 | 62篇 |
2016年 | 51篇 |
2015年 | 20篇 |
2014年 | 86篇 |
2013年 | 101篇 |
2012年 | 73篇 |
2011年 | 147篇 |
2010年 | 106篇 |
2009年 | 154篇 |
2008年 | 165篇 |
2007年 | 85篇 |
2006年 | 73篇 |
2005年 | 82篇 |
2004年 | 82篇 |
2003年 | 96篇 |
2002年 | 59篇 |
2001年 | 83篇 |
2000年 | 47篇 |
1999年 | 54篇 |
1998年 | 58篇 |
1997年 | 52篇 |
1996年 | 47篇 |
1995年 | 59篇 |
1994年 | 41篇 |
1993年 | 43篇 |
1992年 | 56篇 |
1991年 | 13篇 |
1990年 | 19篇 |
1989年 | 47篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 65篇 |
1984年 | 60篇 |
1983年 | 42篇 |
1982年 | 48篇 |
1981年 | 67篇 |
1980年 | 35篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 11篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1974年 | 13篇 |
1972年 | 11篇 |
1970年 | 9篇 |
排序方式: 共有2754条查询结果,搜索用时 351 毫秒
961.
The systems of gyrodynes installed on a spacecraft body on the one-axis controlled platform are considered. An algorithm to determine the special states and the special surfaces corresponding to them in the region of variation of the total angular momentum is obtained, as well as an algorithm to study the permeability of special surfaces. The results of calculation of the special surfaces for two types of gyro systems are presented. 相似文献
962.
The coplanar problem of minimizing propellant consumption in impulsive transfer between circular boundary orbits is investigated. The launch time and the initial configuration of objects on the boundary orbits are specified arbitrarily. The qualitative properties of optimal two-impulse trajectories and their optimality in the class of multi-impulse transfers are studied. 相似文献
963.
The concept of radar satellite constellations, or clusters, for synthetic aperture radar (SAR), moving target indicator (MTI), and other radar modes has been proposed and is currently under research. These constellations form an array that is sparsely populated and irregularly spaced; therefore, traditional matched filtering is inadequate for dealing with the constellation's radiation pattern. To aid in the design, analysis, and signal processing of radar satellite constellations and sparse arrays in general, the characterization of the resolution and ambiguity functions of such systems is investigated. We project the radar's received phase history versus five sensor parameters: time, frequency, and three-dimensional position, into a phase history in terms of two eigensensors that can be interpreted as the dimensions of a two-dimensional synthetic aperture. Then, the synthetic aperture expression is used to derive resolution and the ambiguity function. Simulations are presented to verify the theory. 相似文献
964.
Variations in fluxes of quasi-trapped energetic protons were studied on the basis of the data of the CORONAS-I satellite. These variations are characterized by an increase in the proton fluxes with E P ≥ 1 MeV both in the vicinity of the geomagnetic equator and in the high-latitude region of the magnetosphere. The analysis of structural features of the proton distributions in the regions at L ~ 1–1.1; 3 < L < 4; and L > 4, was performed and made it possible to detect reliably the type of the proton flux increase in this region. The mechanisms of particle scattering leading to the precipitation of energetic protons under conditions of various types of geomagnetic disturbances are considered. 相似文献
965.
A time-stepping coupled finite element-state space approach was developed for synchronous machine unbalanced impedance load and balanced/unbalanced rectifier load operation, in the natural time-domain ABC frame of reference. Synergism between the space and time harmonics was inherently included in the simulated results by use of this approach. It offers an effective and powerful tool for synchronous machine design before prototype construction. 相似文献
966.
N. V. Emelyanov J. -E. Arlot M. I. Varfolomeev S. N. Vashkov’yak A. A. Kanter S. M. Kudryavtsev L. P. Nasonova V. S. Ural’skaya 《Cosmic Research》2006,44(2):128-136
A knowledge base for natural satellites of planets is created. On the basis of observations, new numerical models of motion are constructed for all 96 outer satellites of Jupiter, Saturn, Uranus, and Neptune. A special database is compiled from all available observational data for natural satellites of planets, as well as a bibliographical database and information system of physical and orbital parameters of planets and satellites. The tools for calculations of ephemerides of all natural satellites (except for the Moon) of planets are developed. They represent the final result of studies and actually incorporate the entire knowledge about dynamics of the satellites of planets. Also developed are special ephemerides in order to observe singular phenomena in the apparent motion of the satellites of planets. A computer environment and the Internet allowed us to concentrate all above-listed options in a single toolkit easily available to any user in the world. 相似文献
967.
R. F. Wimmer-Schweingruber N. U. Crooker A. Balogh V. Bothmer R. J. Forsyth P. Gazis J. T. Gosling T. Horbury A. Kilchenmann I. G. Richardson J. D. Richardson P. Riley L. Rodriguez R. von Steiger P. Wurz T. H. Zurbuchen 《Space Science Reviews》2006,123(1-3):177-216
While interplanetary coronal mass ejections (ICMEs) are understood to be the heliospheric counterparts of CMEs, with signatures
undeniably linked to the CME process, the variability of these signatures and questions about mapping to observed CME features
raise issues that remain on the cutting edge of ICME research. These issues are discussed in the context of traditional understanding,
and recent results using innovative analysis techniques are reviewed. 相似文献
968.
M.C. Ramadevi S. Seetha V.C. Babu B.N. Ashoka P. Sreekumar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):3002-3004
The Scanning Sky Monitor (SSM) on ASTROSAT is a position-sensitive gas-filled proportional counter with a wide field of view. The scientific objective of SSM is to scan the sky within few hours to detect and locate transient X-ray sources in the outburst phase. Once detected, this information will be provided for studies in all energy bands. The energy range of operation of SSM is 2–10 keV. The optimisation of the parameters of the proportional counter such as the cell size, the gas mixture and the gas pressure for the SSM are discussed here. 相似文献
969.
970.
Bozzi S. Capigatti U. Cappellini V. Re E.D. Margheri M. Saltini I. 《IEEE transactions on aerospace and electronic systems》1982,(5):704-708
The design and implementation of a second-order nonrecursive moving target indication (MTI) radar filter using commercially available charge-transfer devices as delay lines are described. A simple technique is included to compensate for the device charge-transfer in-efficiency and its sensitivity is analyzed. Experimental laboratory tests and results in an operating radar system are reported showing the good performance of the realized MTI radar filter. 相似文献