全文获取类型
收费全文 | 5312篇 |
免费 | 26篇 |
国内免费 | 14篇 |
专业分类
航空 | 2399篇 |
航天技术 | 1833篇 |
综合类 | 19篇 |
航天 | 1101篇 |
出版年
2021年 | 49篇 |
2019年 | 33篇 |
2018年 | 117篇 |
2017年 | 92篇 |
2016年 | 86篇 |
2015年 | 39篇 |
2014年 | 125篇 |
2013年 | 148篇 |
2012年 | 141篇 |
2011年 | 204篇 |
2010年 | 159篇 |
2009年 | 237篇 |
2008年 | 299篇 |
2007年 | 148篇 |
2006年 | 117篇 |
2005年 | 149篇 |
2004年 | 146篇 |
2003年 | 182篇 |
2002年 | 117篇 |
2001年 | 202篇 |
2000年 | 107篇 |
1999年 | 120篇 |
1998年 | 141篇 |
1997年 | 100篇 |
1996年 | 134篇 |
1995年 | 164篇 |
1994年 | 132篇 |
1993年 | 78篇 |
1992年 | 115篇 |
1991年 | 43篇 |
1990年 | 49篇 |
1989年 | 114篇 |
1988年 | 53篇 |
1987年 | 53篇 |
1986年 | 55篇 |
1985年 | 154篇 |
1984年 | 126篇 |
1983年 | 102篇 |
1982年 | 113篇 |
1981年 | 147篇 |
1980年 | 41篇 |
1979年 | 33篇 |
1978年 | 36篇 |
1977年 | 39篇 |
1976年 | 29篇 |
1975年 | 48篇 |
1974年 | 39篇 |
1973年 | 26篇 |
1972年 | 36篇 |
1971年 | 21篇 |
排序方式: 共有5352条查询结果,搜索用时 15 毫秒
601.
S.J. Wang D. Maia M. Pick G. Aulanier J.-M. Malherbe J.-P. Delaboudinire 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2273
We present our research on a fast and decelerating partial halo coronal mass ejection (CME) event detected in multi-wavelengths in the chromosphere and the corona on 14 October, 1999. The event involved a whole complex active area which spanned more than 40° of heliolongitude. It included a strong solar flare (XI/1N) and a complex eruptive filament within an active region of the entire complex. Especially, several radio sources were detected in the decimetric range prior to the CME by the Nançay Radioheliograph (NRH). A linear force-free field extrapolation of the Michelson Doppler Imager (MDI) magnetogram was performed to calculate the magnetic topology of the complex prior to the triggering of the event. The presence of a coronal null point combined with the occurrence of two distant and nearly simultaneous radio sources put strong arguments in favor of the generalized breakout model for the triggering of the eruption. The analysis of the subsequent development of the event suggests that large interconnecting loops were ejected together with the CME. 相似文献
602.
Purpose of the work is to analyze and to summarize the data of investigations into human hemodynamics performed over 20 years aboard orbital stations Salyut-7 and Mir with participation of 26 cosmonauts on space flights (SF) from 8 to 438 days in duration. The ultrasonic techniques and occlusive plethysmography demonstrated dynamics of changes in the cardiovascular system during SF of various durations. The parameters of general hemodynamics, the pumping function of the heart and arterial circulation in the brain remained stable in all the space flights; however, there were alterations in peripheral circulation associated with blood redistribution and hypovolemie in microgravity. The anti-gravity distribution of the vascular tone decayed gradually as unneeded. The most considerable changes were observed in leg vessels, equally in arteries (decrease in resistance) and veins (increase in maximum capacity). The lower body negative pressure test (LBNP) revealed deterioration of the gravity-dependent reactions that changed for the worse as SF duration extended. The cardiovascular deconditioning showed itself as loss of descent acceleration tolerance and orthostatic instability in the postflight period. 相似文献
603.
We consider the stability of stationary motions of a model of a spacecraft as a system of coaxial bodies with small asymmetry caused by the shift of the axes of dynamic symmetry of bodies relative to the axis of rotation. We determine the stationary motions of the system; their stability is studied with respect to both the projections of angular velocity and the position of the axis of rotation. The sufficient conditions for the stability of these stationary motions are obtained by constructing a Lyapunov function, and the necessary conditions are obtained by analyzing the corresponding linearized equations of perturbed motion. 相似文献
604.
The possibility of using the mode of single-axis solar orientation is considered for a satellite placed into a nearly circular orbit with an altitude of 900 km and bearing a solar sail. The satellite (together with the sail) has an axisymmetric structure, its symmetry axis being the principal central axis of the maximum moment of inertia. The center of the sail pressure lies on this axis and is displaced with respect to the satellite's center of mass. The symmetry axis of the satellite is set to the Sun so that its center of mass would be located between the Sun and the pressure center and would rotate around this axis with an angular velocity of a few degrees per second. The satellite's axis of symmetry makes a slow precession under the action of the gravitational moment and the moment of light pressure forces. Though the maximum magnitudes of these moments are comparable, the moment of the light pressure forces dominates and controls the precession in such a way that the symmetry axis orientation to the Sun remains unchanged. 相似文献
605.
In developing radio-electronic devices (RED) of spacecraft operating in the fields of ionizing radiation in space, one of the most important problems is the correct estimation of their radiation tolerance. The “weakest link” in the element base of onboard microelectronic devices under radiation effect is the integrated microcircuits (IMC), especially of large scale (LSI) and very large scale (VLSI) degree of integration. The main characteristic of IMC, which is taken into account when making decisions on using some particular type of IMC in the onboard RED, is the probability of non-failure operation (NFO) at the end of the spacecraft’s lifetime. It should be noted that, until now, the NFO has been calculated only from the reliability characteristics, disregarding the radiation effect. This paper presents the so-called “reliability” approach to determination of radiation tolerance of IMC, which allows one to estimate the probability of non-failure operation of various types of IMC with due account of radiation-stimulated dose failures. The described technique is applied to RED onboard the Spektr-R spacecraft to be launched in 2007. 相似文献
606.
K. S. Kuz’mina I. K. Marchevskii V. S. Moreva E. P. Ryatina 《Russian Aeronautics (Iz VUZ)》2017,60(3):398-405
A high-accuracy numerical scheme is proposed for vortex methods of flow simulation around airfoils of arbitrary shape including airfoils with sharp edges, because it does not require the solution continuity on the airfoil. 相似文献
607.
J D Fernstrom 《Acta Astronautica》1981,8(9-10):1035-1042
The rates of synthesis by brain neurons of the neurotransmitters serotonin, acetylcholine, and the catecholamines depend on the brain levels of the respective precursor molecules. Brain levels of each precursor are influenced by their blood concentration, and for the amino acid precursors, by the blood levels of other amino acids as well. Since diet readily alters blood concentrations of each of these precursors, it thereby also influences the brain formation of their neurotransmitter products. 相似文献
608.
Samaan M.A. Mortari D. Junkins J.L. 《IEEE transactions on aerospace and electronic systems》2005,41(4):1246-1254
Star identification can be accomplished by several different available algorithms that identify the stars observed by a star tracker. However, efficiency and reliability remain key issues and the availability of new active pixel cameras requires new approaches. Two novel algorithms for recursive mode star identification are presented here. The first approach is derived by the spherical polygon search (SP-search) algorithm, it was used to access all the cataloged stars observed by the sensor field-of-view (FOV) and recursively add/remove candidate cataloged stars according to the predicted image motion induced by camera attitude dynamics. Star identification is then accomplished by a star pattern matching technique which identifies the observed stars in the reference catalog. The second method uses star neighborhood information and a catalog neighborhood pointer matrix to access the star catalog. In the recursive star identification process, and under the assumption of "slow" attitude dynamics, only the stars in the neighborhood of previously identified stars are considered for star identification in the succeeding frames. Numerical tests are performed to validate the absolute and relative efficiency of the proposed methods. 相似文献
609.
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
610.
E. H. B. M. Gronenschild R. Mewe N. J. Westergaard J. Heise F. D. Seward T. Chlebowski N. P. M. Kuin A. C. Brinkman J. H. Dijkstra H. W. Schnopper 《Space Science Reviews》1981,30(1-4):185-189
The binary system Capella (G6 III + F9 III) has been observed on 1979 March 15 and on 1980 March 15–17 with the Objective Grating Spectrometer (OGS) onboard theEinstein Observatory. The spectrum measured with the 1000 l/mm grating covers the range 5–30 Å with a resolution < 1 Å. The spectra show evidence for a bimodal temperature distribution of emission measure in an optically thin plasma with one component 5 million degrees and the other one 10 million degrees. Spectral features can be identified with line emissions from O VIII, Fe XVII, Fe XVIII, Fe XXIV, and Ne X ions. Good spectral fits have been obtained assuming standard cosmic abundances. The data are interpreted in terms of emission from hot static coronal loops rather similar to the magnetic arch structures found on the Sun. It is shown that the conditions required by this model exist on Capella. Mean values of loop parameters are derived for both temperature components. 相似文献