全文获取类型
收费全文 | 7715篇 |
免费 | 39篇 |
国内免费 | 32篇 |
专业分类
航空 | 3568篇 |
航天技术 | 2851篇 |
综合类 | 23篇 |
航天 | 1344篇 |
出版年
2021年 | 68篇 |
2019年 | 51篇 |
2018年 | 147篇 |
2017年 | 108篇 |
2016年 | 94篇 |
2015年 | 43篇 |
2014年 | 173篇 |
2013年 | 207篇 |
2012年 | 205篇 |
2011年 | 285篇 |
2010年 | 188篇 |
2009年 | 340篇 |
2008年 | 385篇 |
2007年 | 230篇 |
2006年 | 182篇 |
2005年 | 229篇 |
2004年 | 220篇 |
2003年 | 254篇 |
2002年 | 170篇 |
2001年 | 250篇 |
2000年 | 163篇 |
1999年 | 181篇 |
1998年 | 212篇 |
1997年 | 156篇 |
1996年 | 206篇 |
1995年 | 256篇 |
1994年 | 255篇 |
1993年 | 124篇 |
1992年 | 190篇 |
1991年 | 77篇 |
1990年 | 75篇 |
1989年 | 178篇 |
1988年 | 64篇 |
1987年 | 63篇 |
1986年 | 86篇 |
1985年 | 230篇 |
1984年 | 200篇 |
1983年 | 147篇 |
1982年 | 177篇 |
1981年 | 218篇 |
1980年 | 60篇 |
1979年 | 50篇 |
1978年 | 57篇 |
1977年 | 53篇 |
1976年 | 41篇 |
1975年 | 52篇 |
1974年 | 53篇 |
1973年 | 41篇 |
1970年 | 41篇 |
1969年 | 41篇 |
排序方式: 共有7786条查询结果,搜索用时 0 毫秒
611.
Energetic solar proton events within the energy interval 1–48 MeV at the stage of their decay are considered over the period of 1974–2001. The dependence of the characteristic decay time on the proton energy in the assumed power-law representation τ(E) =E ?n is analyzed for the events with an exponential decay form. The dependence of n on the heliolongitude of the flare (the particles source on the Sun) is studied. 相似文献
612.
Abraham D. Krikorian F.Ronald Dutcher Carol E. Quinn F.C. Steward 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(14):117-127
Morphogenetically competent proembryonic cells and well-developed somatic embryos of carrot at two levels of organization were exposed for 18.5 days to a hypogravity environment aboard the Soviet Biosatellite Cosmos 1129. It was confirmed that cultured totipotent cells of carrot can give rise to embryos with well-developed roots and minimally developed shoots. It was also shown that the space hypogravity environment could support the further growth of already-organized, later somatic embryonic stages and give rise to fully developed embryo-plantlets with roots and shoots. 相似文献
613.
The results of a preliminary analysis of microperturbations on the International Space Station during physical exercises of the crew are presented. The goal of this paper is to identify the parameters of perturbations when physical exercises are performed. The results of measurements by sensors of microaccelerations of both Russian and American segments during physical exercises in the service module of the Russian segment are analyzed. 相似文献
614.
On the basis of generalization of the results of extensive trajectory calculations for trial charged particles moving in the geomagnetic field the method of calculation of effective vertical cutoff rigidity, taking into account the values of K p -index and local time, is developed. The IGRF and Tsyganenko-89 models are used for the geomagnetic field. A comparison of the results of model simulations with the experimental data on penetration of charged particles into near-Earth space is made, and penetration functions for typical spacecraft orbits are calculated. 相似文献
615.
Performance analysis of echolocation systems requires knowledge of the probability density function (pdf) or cumulative distribution function (cdf) of a matched filter output. A method is presented to estimate these and other probability functions from data by estimating the failure rate function, a function employed in reliability theory. The method can also be used to derive approximations to closed-form probability functions. The method is demonstrated using experimental sonar and radar clutter data and a closed-form radar clutter model 相似文献
616.
The commenters point out that the idea using a two-dimensional digital correlation technique to perform synthetic-aperture-radar (SAR) processing, presented as new in the above-titled paper (see ibid., vol.24, p.218-23, May 1988), was described by them as early as 1978 and has since been described by other authors. They discuss some of these earlier studies. The author replies that he was unaware of the earlier work, and that he did not intend to convey the impression that the nonseparable transform domain processor that he presented was the first 相似文献
617.
This remote assistance trial, performed within the framework of the manned space flight Altaïr, was carried out by CADMOS (CNES), with the cooperation of the Sub-directorate of CNES Operational Systems, Medes, LBM of Tours and Christol Consultants. It consisted of supplying the cosmonaut performing the Orthostatism experiment (echograph acquisition) on board the Mir station with realtime assistance by an expert (LBM of Tours) working from the ground on the CADMOS premises. The various steps of the approach followed during the preparation phase are described, as well as the technical means of communication used between the Mir station and CADMOS. 相似文献
618.
V. M. Soldatkin A. A. Arkhipov V. A. Olaev A. A. Uglov 《Russian Aeronautics (Iz VUZ)》2012,55(2):184-191
We consider the function, the problems being solved and the construction principles for a starting system of warning the critical regimes for a single-rotor helicopter at parking, taxiing and maneuvering on the ground, takeoff and landing as well as at descending and hovering regimes. The structural-functional scheme and the algorithms of system channel warning are presented. 相似文献
619.
The matched filter ambiguity function is presented for a burst waveform composed of repeated subbursts, each one of which consists of N pulses in which the phase is varied quadratically from pulse to pulse. The resulting ambiguity function exhibits small residual ambiguities along the delay axis separated by the reciprocal of the pulse repetition frequency (PRF). A cross-ambiguity function is derived which reduces these ambiguities to zero amplitude. A third cross-ambiguity function is presented for a receiver matched to a generalized Hamming weighted repeated quadratic burst. The location in the delay/Doppler plane of the waveform ambiguities for these waveforms is compared with that of an uncoded pulse burst. 相似文献
620.
The need to acquire a better knowledge of the main biological problems induced by microgravity implies--in addition to human experimentation--the use of animal models, and primates seem to be particularly well adapted to this type of research. The major areas of investigation to be considered are the phospho-calcium metabolism and the metabolism of supporting tissues, the hydroelectrolytic metabolism, the cardiovascular function, awakeness, sleep-awakeness cycles, the physiology of equilibrium and the pathophysiology of space sickness. Considering this program, the Centre d'Etudes et de Recherches de Medecine Aerospatiale, under the sponsorship of the Centre National d'Etudes Spatiales, developed both a program of research on restrained primates for the French-U.S. space cooperation (Spacelab program) and for the French-Soviet space cooperation (Bio-cosmos program), and simulation of the effects of microgravity by head-down bedrest. Its major characteristics are discussed in the study. 相似文献