全文获取类型
收费全文 | 2927篇 |
免费 | 4篇 |
国内免费 | 6篇 |
专业分类
航空 | 1240篇 |
航天技术 | 762篇 |
综合类 | 8篇 |
航天 | 927篇 |
出版年
2022年 | 6篇 |
2021年 | 22篇 |
2019年 | 7篇 |
2018年 | 181篇 |
2017年 | 156篇 |
2016年 | 83篇 |
2015年 | 37篇 |
2014年 | 70篇 |
2013年 | 68篇 |
2012年 | 89篇 |
2011年 | 198篇 |
2010年 | 164篇 |
2009年 | 212篇 |
2008年 | 210篇 |
2007年 | 185篇 |
2006年 | 52篇 |
2005年 | 100篇 |
2004年 | 80篇 |
2003年 | 83篇 |
2002年 | 53篇 |
2001年 | 92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 | 25篇 |
1992年 | 37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2937条查询结果,搜索用时 500 毫秒
931.
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
932.
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
933.
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
934.
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
935.
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
936.
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
937.
L A Somova N S Pechurkin V I Polonsky T I Pisman A B Sarangova M Andre G M Sadovskaya 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(10):1939-1943
The effect has been studied of inoculation of seeds of wheat with two species of rhizospheric microorganisms--Pseudomonas fluorescens and Pseudomonas putida--on young plant growth with complete and with nitrogen deficit mineral nutrition. With complete mineral medium, plants grown from seeds inoculated with bacteria of Pseudomonas genus (experiment plants) have been found to have better growth over plants not inoculated with these bacteria (control plants). The experiment plants had increased transpiration and their biomass had higher organic nitrogen content. With nitrogen deficit medium, the plants inoculated with bacteria and those without them, have not revealed changes in growth. Neither case demonstrated competition of microorganisms with plants for nitrogen sources. 相似文献
938.
I. Apáthy I. Szemerey P. Bencze K. Kovács V. Afonin V. Bezrukih K. Gringauz N. Shutte 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(12):101-105
Ion temperature and total ion concentration measured on 25th October 1977 during the flight of the geophysical rocket “Vertical-6” are analyzed. The solar EUV fluxes determined in five wave-length bands with a photoelectron analyzer are also given. The observed anomalous variation of ion temperature between 700 and 900 km and the measured ion concentration can be explained, if the charge exchange reactions H+ ? O+ and diffusion are taken into account. 相似文献
939.
The effect of I F filter bandwidth to I F frequency ratio on the probability of error in a binary bandpass communication system with nonreturn-to-zero (NRZ) and split-phase (SP) signals is investigated. ed. Explicit results are given for the case when the bandpas I F filter is transformed from a single-pole low-pass filter. 相似文献
940.
I. Kimura H. Matsumoto K. Hashimoto T. Mukai R.A. Helliwell T.F. Bell U.S. Inan J.P. Katsufrakis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):197-202
A Japanese magnetospheric satellite Jikiken (EXOS-B) was used to observe Siple transmissions and VLF emissions triggered by the Siple signals. Energetic particle fluxes were also observed at the same time. The first experiments were made during July, August and September in 1979 and the second experiments were made during December in 1979 and January in 1980. The Siple triggered emissions were observed in August. This report reviews the preliminary results. 相似文献