全文获取类型
收费全文 | 2169篇 |
免费 | 4篇 |
国内免费 | 6篇 |
专业分类
航空 | 752篇 |
航天技术 | 762篇 |
综合类 | 8篇 |
航天 | 657篇 |
出版年
2022年 | 6篇 |
2021年 | 22篇 |
2019年 | 7篇 |
2018年 | 73篇 |
2017年 | 58篇 |
2016年 | 56篇 |
2015年 | 20篇 |
2014年 | 69篇 |
2013年 | 68篇 |
2012年 | 66篇 |
2011年 | 109篇 |
2010年 | 80篇 |
2009年 | 125篇 |
2008年 | 144篇 |
2007年 | 81篇 |
2006年 | 51篇 |
2005年 | 66篇 |
2004年 | 70篇 |
2003年 | 83篇 |
2002年 | 53篇 |
2001年 | 90篇 |
2000年 | 38篇 |
1999年 | 41篇 |
1998年 | 43篇 |
1997年 | 34篇 |
1996年 | 49篇 |
1995年 | 40篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 35篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 34篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 67篇 |
1984年 | 35篇 |
1983年 | 25篇 |
1982年 | 37篇 |
1981年 | 66篇 |
1980年 | 16篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1974年 | 15篇 |
1973年 | 8篇 |
1970年 | 4篇 |
排序方式: 共有2179条查询结果,搜索用时 125 毫秒
671.
Evaluation of built-in test 总被引:1,自引:0,他引:1
Pecht M. Dube M. Natishan M. Williams R. Banner J. Knowles I. 《IEEE transactions on aerospace and electronic systems》2001,37(1):266-271
Built-in test (BIT) provides fault finding as a means to aid in system assembly, test, and maintenance. An investigation to evaluate BIT of a particular electronics board used in the in-flight entertainment system for Boeing 777s is described. We found BIT proved useful when failure occurrences were uniquely associated with the operating environment, situations which can result in no-fault found, or could-not duplicate (CND) failures upon test. We also observed cases where the BIT failed to observe failures, and in some cases pointed to the wrong cause of failure. These and other advantages and disadvantages of BIT implementation are discussed 相似文献
672.
For systems of autonomous satellite navigation, it is proposed to use television signals of stationary television centers positioned along the flight path in the band of satellite radio coverage as sources of primary navigation information. Television signal processing allows one to determine the time instants of transit through traverses of the television centers. An algorithm of calculating the parameters of satellite motion by times of transit through traverses is developed. 相似文献
673.
674.
I. M. Sidorov 《Cosmic Research》2004,42(1):60-72
We propose to develop a scheme for a group of space objects which includes a set of orbital tethers and exchange masses. These objects are injected into circumterrestrial orbits. A variety of problems can be solved with the help of this space system, namely, transport problems and problems of converting the electric power generated onboard spacecraft into mechanical energy of motion of the space objects. In the future, natural celestial bodies (in particular, the Moon) can be considered as elements of the system. This opens up the possibility of using the energy of motion of the Moon both for solving transport problems and for generating electric power onboard spacecraft. 相似文献
675.
A.A. Imshenetsky L.A. Kuzyurina V.M. Jakshina I.K. Dorofeyeva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(14):173-177
The influence of lowered gravitation on biomass and CO2 production in , a xerophyte, and , an aqueous spirillum, in liquid nutrient medium on a horizontal clinostat at 0.1 has been studied. As controls we considered: 1) growth under stationary conditions of cultivation with test tubes oriented horizontally; 2) growth on a synchronously revolving centrifuge; and 3) growth on a swing with stirring. A horizontal clinostat at 0.1 g stimulates biomass production and CO2 release in as compared with the controls. growth is reduced as a result of clinostating. The best development and CO2 production are observed under stationary conditions. The results do not support the assumption that microorganisms living in water are more resistant to lowered gravitation than those living in soil. 相似文献
676.
The fundamentals of fractal geometry are reviewed, and its application to the millimeter-wave radar detection of stationary targets in a clutter background is described. First, high-range-resolution (HRR) profiles are used to determine the fractal interpolation functions needed to create fractal signatures. The fractal dimension is then determined for these signatures. On the basis of the value of the fractal dimension, the signature is declared to represent either a target of interest or clutter. The results of a CFAR (constant false alarm rate) simulation are presented to illustrate the performance of the method. They indicate that the fractal dimension feature used seems to be independent of amplitude. Thus, the fractal dimension information combined with traditional amplitude processing techniques will improve probabilities of detection 相似文献
677.
I.A. Zhulin V.M. Kostin I.A. Pimenov Ju.Ja. Ruzhin V.S. Skomarovsky Ju.M. Zhuchenko Ju.A. Romanovsky 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):319-323
Evidence for an enhancement of the electron flux associated with a barium chaped charge release from “SPOLOKH-2” rocket payload, launched from Volgograd (L = 2.2) on June 29, 1978, will be presented. There is also evidence for a periodic train of particle bursts occurring with about 11 second period during more than 100 seconds after the release. The observed phenomena is interpreted as a “trigger-effect”. 相似文献
678.
The detection performance of a single-channel MTI receiver with post-detection integration, for a Swerling I target, has been evaluated by a Monte Carlo simulation. It is shown that a fairly good approximation is obtained by applying the ?effective number of independent integrated samples? to the standard detection curves. The ?I-only? loss is about 2 dB for integration of more than 20 pulses; thus this receiver is acceptable if implementation constraints dictate it. 相似文献
679.
The mutual potential of 2 solid bodies is a function of the six parameters defining the relative position of these two bodies, it is not a function of only either 3 or 5 parameters as it is implicitly assumed in most studies.The sixth parameter, “the potential torsion” is related to the orientation of the two bodies around the axis of the two centers, its influence is small. An upper limit is given. 相似文献
680.
I. N. Toptyghin 《Space Science Reviews》1980,26(2):157-213
The theory and observational evidence pertaining to particle acceleration by shock waves in astrophysical objects and in space are systematized. Recent works showing observational and theoretical aspects of the problem dealing with shocks in turbulent media are emphasized. The acceleration of particles by shocks in turbulent media is observed in interplanetary space. This acceleration mechanism is of particular interest from the point of view of the origin of cosmic rays, providing the degree form of the spectrum. The index of the spectrum is close to the observable one for galactic cosmic rays. It depends slightly on specific conditions in the acceleration region. Electron and nucleus acceleration in supernova remnants and in radiogalaxies is discussed, and theory and observational data are compared. The theory of particle acceleration by supersonic turbulence is outlined. 相似文献