全文获取类型
收费全文 | 5105篇 |
免费 | 6篇 |
国内免费 | 16篇 |
专业分类
航空 | 2530篇 |
航天技术 | 1798篇 |
综合类 | 18篇 |
航天 | 781篇 |
出版年
2021年 | 28篇 |
2019年 | 28篇 |
2018年 | 77篇 |
2017年 | 44篇 |
2016年 | 45篇 |
2014年 | 100篇 |
2013年 | 140篇 |
2012年 | 106篇 |
2011年 | 176篇 |
2010年 | 137篇 |
2009年 | 207篇 |
2008年 | 269篇 |
2007年 | 126篇 |
2006年 | 110篇 |
2005年 | 131篇 |
2004年 | 129篇 |
2003年 | 168篇 |
2002年 | 86篇 |
2001年 | 170篇 |
2000年 | 84篇 |
1999年 | 132篇 |
1998年 | 149篇 |
1997年 | 122篇 |
1996年 | 138篇 |
1995年 | 184篇 |
1994年 | 164篇 |
1993年 | 100篇 |
1992年 | 135篇 |
1991年 | 52篇 |
1990年 | 57篇 |
1989年 | 129篇 |
1988年 | 58篇 |
1987年 | 46篇 |
1986年 | 57篇 |
1985年 | 145篇 |
1984年 | 148篇 |
1983年 | 91篇 |
1982年 | 138篇 |
1981年 | 145篇 |
1980年 | 48篇 |
1979年 | 48篇 |
1978年 | 56篇 |
1977年 | 28篇 |
1976年 | 27篇 |
1975年 | 58篇 |
1974年 | 39篇 |
1973年 | 32篇 |
1972年 | 39篇 |
1969年 | 27篇 |
1967年 | 25篇 |
排序方式: 共有5127条查询结果,搜索用时 31 毫秒
901.
The Goddard Experiment Package will measure the ultraviolet spectral emittance of stars and nebulae. It has a spectral resolution of 2 ? in the 1050-? to 4000-? band. The telescope has a 38-inch clear aperture and automatically reduces the spectral data to digital form. Guidance accuracy is 1 of second arc. 相似文献
902.
A direct iterative method of solving for Tandem equilibria by moving magnetic field lines in a manner to satisfy the linearized equilibrium equations converges much more rapidly than standard relaxation techniques, typically in under a fifty iterations. At the highest 's the number of iterations increase, but is still far less than other methods. In quadrupole tandem mirror equilibrium, octupole and higher distortions of the flux surfaces are important which forces us to abandon finite differences in the angle-like flux variable and resort to a spectral decomposition to solve the equilibrium equations. We display equilibria at the high expected for MFTF-B and show how Finite Larmor Radius (FLR) effects strongly suppress these azimuthal distortions. 相似文献
903.
The effects of prolonged bedrest in antiorthostatic position (-4 degrees head down) on electrolyte balance were studied in 4 young volunteers. An increase was noted in sodium excretion during the first 4 days. Plasma renin activity and plasma aldosterone varied in parallel manner during the same period. Potassium balance and creatinine clearance were not significantly modified. In light of these data we feel that prolonged bedrest in antiorthostatic position constitutes an effective way to simulate on earth metabolic and hormonal modifications occurring in man under weightlessness conditions. 相似文献
904.
V. C. Liu 《Space Science Reviews》1969,9(4):423-490
The gas dynamics of interactions of a tenuous ionosphere with moving satellites and probes that have bearings on the diagnostics of the ionosphere are discussed. Emphasis is on the cases where the body is moving at mesothermal speeds, namely intermediate between the thermal speeds of ions and electrons of the ambient ionosphere. Methods of collision-free plasma kinetics with self-consistent field are used. The development of the topics for discussion starts with stationary Langmuir probe which entails the basic mechanism of body-plasma interaction that becomes further intricated as the body moves at a higher and higher speed. Applications of the theory of plasma interaction to meteors which move in the ionosphere are also presented. 相似文献
905.
Scott WB 《Aviation week & space technology》2005,162(17):62-64
NASA's Artificial Gravity program consists of a team of researchers from Wyle Laboratories, NASA Johnson Space Center, and the University of Texas Medical Branch (UTMB). The short-radius centrifuge (SRC), built by Wyle Laboratories, will be integrated with UTMB's conducted bedrest studies, which mimic the detrimental effects of weightlessness (or microgravity). Bedrest subjects will be spun on the SRC at various accelerations and for various time periods, while being monitored medically. Parameters such as bone loss, muscle atrophy, balance control, and oxygen consumption will then be compared in order to research ways of mitigating the impact on astronauts' physiology. Other potential benefits from these studies extend to population groups on Earth, such as bedridden patients. 相似文献
906.
B. B. Kreisman 《Cosmic Research》2005,43(2):84-106
A monodromy matrix calculated at a single arbitrary point of the periodic solution to a Hamiltonian system allows one to obtain both the direction of continuation for the family of solutions of the first (in Poincarés sense) kind and the multiplicity and direction of branching for periodic solutions of the second kind. In case of resonances 1 : 1 and 1 : 2 one needs to take into account the structure of elementary divisors of the monodromy matrix. Using the planar circular restricted three-body problem as an example, the infiniteness of the process of branching for a nonintegrable system and its finiteness for an integrable system are demonstrated. It is proved that periodic solutions of both first and second kinds which are obtained by continuation of symmetric periodic solutions of a restricted problem are also symmetric. The only exception is the case of resonance 1 : 1 and two second-order cells of the monodromy matrix in the Jordanian form. In this case, all periodic solutions of the second kind turned out to be nonsymmetrical. Examples of the families of nonsymmetrical periodic solutions are given.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 2, 2005, pp. 88–110.Original Russian Text Copyright © 2005 by Kreisman. 相似文献
907.
Jaekl P Zikovitz DC Jenkin MR Jenkin HL Zacher JE Harris LR 《Acta Astronautica》2005,56(9-12):1033-1040
We measured the amount of visual movement judged consistent with translational head movement under normal and microgravity conditions. Subjects wore a virtual reality helmet in which the ratio of the movement of the world to the movement of the head (visual gain) was variable. Using the method of adjustment under normal gravity 10 subjects adjusted the visual gain until the visual world appeared stable during head movements that were either parallel or orthogonal to gravity. Using the method of constant stimuli under normal gravity, seven subjects moved their heads and judged whether the virtual world appeared to move “with” or “against” their movement for several visual gains. One subject repeated the constant stimuli judgements in microgravity during parabolic flight. The accuracy of judgements appeared unaffected by the direction or absence of gravity. Only the variability appeared affected by the absence of gravity. These results are discussed in relation to discomfort during head movements in microgravity. 相似文献
908.
The COSAC (Cometary Sampling and Composition Experiment) onboard the Rosetta mission is a combined gas chromatograph (GC)-mass spectrometer (MS). It is situated on Philae, the lander of the mission, which is intended to land on the nucleus of comet 67P/Churyumov- Gerasimenko. The purpose of the experiment is to analyze the volatile fraction of soil samples retrieved by a drill. For investigation, the samples will be pyrolysed, and the emanating gases fed into a GC, into an MS, or the combination of both. In the first part of this paper, the bioastronomical relevance of such measurements is outlined. In the second part the details of the hardware and its performance are described. 相似文献
909.
It is thought that the chiral molecules of living material can induce circular polarization in light at levels much higher than expected from abiotic processes. We therefore obtained high quality imaging circular polarimetry of the martian surface during the favorable opposition of 2003 to seek evidence of anomalous optical activity. We used two narrow-band filters covering 43% of the martian surface, 15% of it in-depth. With polarization noise levels <0.1% (4.3 upper limits 0.2-0.3%) and spatial resolution 210 km, we did not find any regions of circular polarization. When data were averaged over the observed face of the planet, we did see a small non-zero circular polarization 0.02%, which may be due to effects associated with the opposition configuration though it is at the limit of the instrumental capability. Our observations covered only a small fraction of parameter space, so although we obtained a null result, we cannot exclude the presence of optical activity at other wavelengths, in other locations, or at higher spatial resolution. 相似文献
910.
Singh S.N. Bhattacharya K.C. Ramaswamy S. Rao C.S. 《IEEE transactions on aerospace and electronic systems》1975,(5):905-907
It is shown that when the gyro spin vector is in opposition to the spin vector of the vehicle, the output differential equation of the gyro becomes unstable for large vehicle spin values. When the gyro is used with its spin vector along the spin vector of the vehicle, the steady-state response of the gyro is a nonlinear function of the roll rate of the vehicle. 相似文献