全文获取类型
收费全文 | 5868篇 |
免费 | 2篇 |
国内免费 | 11篇 |
专业分类
航空 | 3119篇 |
航天技术 | 1561篇 |
综合类 | 181篇 |
航天 | 1020篇 |
出版年
2021年 | 29篇 |
2018年 | 208篇 |
2017年 | 156篇 |
2016年 | 71篇 |
2015年 | 35篇 |
2014年 | 74篇 |
2013年 | 105篇 |
2012年 | 147篇 |
2011年 | 284篇 |
2010年 | 220篇 |
2009年 | 301篇 |
2008年 | 277篇 |
2007年 | 245篇 |
2006年 | 90篇 |
2005年 | 135篇 |
2004年 | 129篇 |
2003年 | 143篇 |
2002年 | 181篇 |
2001年 | 206篇 |
2000年 | 94篇 |
1999年 | 125篇 |
1998年 | 156篇 |
1997年 | 99篇 |
1996年 | 140篇 |
1995年 | 168篇 |
1994年 | 146篇 |
1993年 | 99篇 |
1992年 | 125篇 |
1991年 | 57篇 |
1990年 | 64篇 |
1989年 | 126篇 |
1988年 | 59篇 |
1987年 | 64篇 |
1986年 | 52篇 |
1985年 | 154篇 |
1984年 | 120篇 |
1983年 | 108篇 |
1982年 | 118篇 |
1981年 | 154篇 |
1980年 | 56篇 |
1979年 | 46篇 |
1978年 | 57篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 48篇 |
1974年 | 39篇 |
1972年 | 49篇 |
1971年 | 47篇 |
1970年 | 30篇 |
1969年 | 33篇 |
排序方式: 共有5881条查询结果,搜索用时 248 毫秒
641.
642.
Lehman D. Clark K. Cook B. Gavit S. Kayali S. McKinney J. Milkovich D. Reh K. Taylor R. Casani J. Griebel T. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(3):12-21
Congress authorized NASA's Prometheus Project in February 2003, with the first Prometheus mission slated to explore the icy moons of Jupiter. The project had two major objectives: 1) to develop a nuclear reactor that would provide unprecedented levels of power and show that it could be processed safely and operated reliably in space for long-duration, deep-space exploration; and 2) to explore the three icy moons of Jupiter - Callisto, Ganymede, and Europa - and return science data that would meet the scientific goals as set forth in the Decadal Survey Report of the National Academy of Sciences. Early in project planning, it was determined that the development of the Prometheus nuclear-powered spaceship would be complex and require the intellectual knowledge residing at numerous organizations across the country. In addition, because of the complex nature of the project and the multiple partners, approaches beyond those successfully used to manage a typical JPL project would be needed. This describes the key experiences in managing Prometheus, which should prove useful for future projects of similar scope and magnitude. 相似文献
643.
Network management is one of the key technologies needed to fulfill the requirements. In other words, a new paradigm for network management is also needed, in order to address the requirements arising both from the ATN side and the telecommunication side of the new telecommunication infrastructure. In particular, the new network management paradigm will incorporate the ATN management framework consisting of related standards, along with the telecommunication management framework, notably Telecommunication Management Network (TMN) standards from ITU-T. 相似文献
644.
Rowbotham John R. Sanneman Richard W. 《IEEE transactions on aerospace and electronic systems》1967,(4):604-612
The results of a study of the characteristics of the second-order Type II phase-locked loop with a Gaussian noise input, and obtained by digital computer simulation, are presented. The digital simulation is described and the random state variables are defined such that their characteristics can be interpreted in terms of existing phase portraits of autonomous phase-locked loops. The statistics associated with the state variables, which are phase error and a measure of frequency error, and those associated with the number of cycles skipped and the mean time to unlock, are given. 相似文献
645.
646.
647.
R. Von Steiger 《Space Science Reviews》1998,85(1-2):407-418
This rapporteur paper discusses the solar corona and the solar wind in the context of their chemical composition. The abundances
of elements, both obtained by optical and by in situ observations, are used to infer the sources of the slow solar wind and
of the fast streams. The first ionisation potential (FIP) fractionation effect is also discussed, in particular the agreed
basics and the open questions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
648.
D. A. Gurnett R. R. Anderson F. L. Scarf R. W. Fredricks E. J. Smith 《Space Science Reviews》1979,23(1):103-122
In this paper we present an initial survey of results from the plasma wave experiments on the ISEE-1 and -2 spacecraft which are in nearly identical orbits passing through the Earth's magnetosphere at radial distances out to about 22.5R
e
. Essentially every crossing of the Earth's bow shock can be associated with an intense burst of electrostatic and whistler-mode turbulence at the shock, with substantial wave intensities in both the upstream and downstream regions. Usually the electric and magnetic field spectrum at the shock are quite similar for both spacecraft, although small differences in the detailed structure are sometimes apparent upstream and downstream of the shock, probably due to changes in the motion of the shock or propagation effects. Upstream of the shock emissions are often observed at both the fundamental, f
-
p
, and second harmonic, 2f
p
-
, of the electron plasma frequency. In the magnetosphere high resolution spectrograms of the electric field show an extremely complex distribution of plasma and radio emissions, with numerous resonance and cutoff effects. Electron density profiles can be obtained from emissions near the local electron plasma frequency. Comparisons of high resolution spectrograms of whistler-mode emissions such as chorus detected by the two spacecraft usually show a good overall similarity but marked differences in detailed structure on time scales less than one minute. Other types of locally generated waves, such as the (n+1/2)f
-
g
electron cyclotron waves, show a better correspondence between the two spacecraft. High resolution spectrograms of kilometric radio emissions are also presented which show an extremely complex frequency-time structure with many closely spaced narrow-band emissions. 相似文献
649.
R. N. DeWitt 《Space Science Reviews》1967,7(2-3):211-227
650.
L.M. Mukhin D.F. Nenarokov N.V. Porschnev V.B. Bondarev B.G. Gelman G. Israel F. Raulin J. Runavot R. Thomas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1987,7(12):329-335
SIGMA - 3 gas chromatograph on board VEGA 1 and 2 landing probes has been operated successfully in the 60 - 50 km altitude range, providing several in - situ chemical analysis of the gas and the aerosols of Venus cloud layers. Post flight calibration required to derive atmospheric abundancies from gas chromatograms were carried out using the SIGMA - 3 spare model. A Venus atmospheric aerosol simulation chamber was used in which sulfuric acid droplets were generated. Preliminary results of these calibration experiments indicate that the concentration of sulfuric acid in the upper part of the clouds ( 60 to 55 km) is about 1 mg/m3 and suggest that an additional constituant must be present in noticeable amount in the aerosols. From these experiments the mixing ratio upper limits of SO2 is 100 ppmV and of H2S and COS is few 10 ppmV. 相似文献