全文获取类型
收费全文 | 3850篇 |
免费 | 3篇 |
国内免费 | 9篇 |
专业分类
航空 | 1732篇 |
航天技术 | 1412篇 |
综合类 | 10篇 |
航天 | 708篇 |
出版年
2021年 | 28篇 |
2018年 | 56篇 |
2017年 | 51篇 |
2016年 | 47篇 |
2014年 | 65篇 |
2013年 | 104篇 |
2012年 | 89篇 |
2011年 | 153篇 |
2010年 | 107篇 |
2009年 | 154篇 |
2008年 | 199篇 |
2007年 | 112篇 |
2006年 | 79篇 |
2005年 | 115篇 |
2004年 | 128篇 |
2003年 | 127篇 |
2002年 | 81篇 |
2001年 | 118篇 |
2000年 | 60篇 |
1999年 | 88篇 |
1998年 | 108篇 |
1997年 | 77篇 |
1996年 | 70篇 |
1995年 | 109篇 |
1994年 | 127篇 |
1993年 | 64篇 |
1992年 | 77篇 |
1991年 | 32篇 |
1990年 | 43篇 |
1989年 | 69篇 |
1988年 | 33篇 |
1987年 | 28篇 |
1986年 | 39篇 |
1985年 | 125篇 |
1984年 | 114篇 |
1983年 | 91篇 |
1982年 | 78篇 |
1981年 | 155篇 |
1980年 | 31篇 |
1979年 | 34篇 |
1978年 | 37篇 |
1977年 | 34篇 |
1976年 | 29篇 |
1975年 | 35篇 |
1974年 | 30篇 |
1973年 | 31篇 |
1972年 | 42篇 |
1971年 | 23篇 |
1970年 | 22篇 |
1969年 | 21篇 |
排序方式: 共有3862条查询结果,搜索用时 208 毫秒
641.
This paper is devoted to an experimental study of swept wing leading edge contamination by the turbulence emanating from the wing-wall junction. The main objective is to delay the contamination onset by applying surface suction along the attachment line. Two series of experiments are described; the first one was performed in a small wind tunnel at CERT ONERA, the second one was carried out in the F2 wind tunnel at Le Fauga Mauzac centre. Hot film measurements showed that leading edge contamination could be delayed up to very large Reynolds numbers. We also studied the behaviour of the relaminarized boundary layer downstream of the sucked region, along the span as well as in the chordwise direction. 相似文献
642.
G Horneck H Bucker K Dose K D Martens A Bieger H D Mennigmann G Reitz H Requardt P Weber 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(10):19-27
Bacterial spores are proper test organisms for studying problems of space biology and exobiology. During the Spacelab 1 mission, studies on the limiting factors for survival of Bacillus subtilis spores in free space have been performed. An exposure tray on the pallet of Spacelab 1 accomodated 316 samples of dry spores for treatment with space vacuum and/or the following selected wavelengths of solar UV: > 170 nm, 220 nm, 240nm, 260nm and 280 nm. After recovery, inactivation, mutation induction, reparability, and photochemical damages in DNA and protein have been studied. The results contribute to the understanding of the mechanisms of increased UV sensitivity of bacterial spores in vacuo and to a better assessment of the chance of survival of resistant forms in space and of interplanetary transfer of life. 相似文献
643.
G.S.R. Sarma 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(5):55-58
Asymptotic stability characteristics with respect to the onset of Marangoni convection in a liquid layer under the simultaneous action of a large transverse magnetic field and a large rate of rotation are investigated. In certain parameter ranges there is a decrease in critical Marangoni number for increasing magnetic field and rotation depending on the coupling between interfacial perturbations and rotation. 相似文献
644.
B.V. Dementjev S.G. Kukin M.N. Markov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(10):107-110
The radiation spectra of the ionosphere in the 4–5 μm region have been determined from stratospheric balloons by means of the specially elaborated method of the registration of angular and spectral distribution of the radiation. The radiation bands of 4.4 μm and 4.8 μm which have 0.1–0.2 erg cm?2 sr?1s?1. brightness obtained in two flights, are identified with the vibration-rotation transitions of the ion NO+ (0 - 1) and the molecules N14N15 (0 - 1) and CO (0 - 1) and (3 - 2) from altitudes between 120 and 500 km. 相似文献
645.
G. Erdós J. Kóta 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(3):139-142
We consider regular motion of 50 – 200 GV particles in a large-scale interplanetary magnetic field model which contains a wavy neutral sheet responsible for the sector-structure. Numerical calculations based upon energy losses along various trajectories are carried out to obtain the predicted omni-directional density and anisotropy of cosmic rays at various solar latitudes. A marked difference is found between odd and even solar cycles. The post-1969 field configuration gives small radial and large latitudinal gradient: cosmic ray density increases toward the poles. The latitudinal gradient turns out smaller and of opposite sense for the pre-1969 epoch. Anisotropy changes dramatically as we move off the solar equator: corotation appears to be restricted to low latitudes. 相似文献
646.
647.
P. Fabian R. Borchers D. Gömer S.A. Penkett 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(4):135-138
Stratospheric air samples collected between 10 and 35 km altitude my means of a cryogenic sampler were analyzed by gaschromatography. Thus vertical profiles of source gases for halogen radicals were derived, such as CCl4, CCl3F, CCl2F2, CClF3, CF4, C2F3Cl3, C2F4Cl2, C2F5Cl, C2F6, CH3Cl, CH3CCl3, CHF2Cl, CH3Br, CBrF3, and CBrCl2F. Systematic discrepancies between measured and modelled halocarbon profiles point to deficiencies of present one- and two-dimensional models. Measurements of fully halogenated hydrocarbons provide a tool for systematically studying these deficiencies and thus improving the models. 相似文献
648.
K Baltschukat G Horneck H Bucker R Facius M Schafer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(11):109-115
Using spores of two Bacillus subtilis strains differing in repair capacity, we have studied repair and mutation induction in the spores after irradiation with very heavy ions up to uranium with specific particle energies up to 18.6 MeV/u. The results indicate that repair and mutation induction after heavy ion irradiation are closely related to each other and that both phenomena strongly depend on the atomic number and specific energy of the ions. The effects are discussed in comparison with results obtained after X-irradiation. 相似文献
649.
G. Kremser 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(11):39-47
The measurement of auroral X-rays with balloon-borne instruments is an efficient means to study the behaviour of electrons with energies above about 30 keV in the magnetosphere during disturbed periods. Possibilities will be discussed to continue such measurements in the 1980's. It will be pointed out, what kind of investigations may be performed. Recently developed payloads will be described that can be used as a basis for further technical developments. Satellite projects scheduled for the 1980's will be presented that are suited for coordinated X-ray measurements. 相似文献
650.
G.J. Sofko J.A. Koehler J. Gilmer A.G. McNamara D.R. McDiarmid 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(7):149-152
During August 1981, a 50 MHz c.w. radar system was operated in central Canada to measure auroral scatter amplitudes and Doppler spectra from a scattering region centered near 66° magnetic invariant latitude (L ≈ 6.0). Narrow beams from 3 transmitters, differing in frequency by 1 KHz, were directed to cover a common volume of the ionosphere over a ground location at 56.3°N, 103.5°W. The scattered signals were received on narrow beam antennas at two receiving sites, and recorded in analog form on magnetic tape under the control of an AIM65 microcomputer. The analog tapes were digitized later and FFT-processed to obtain Doppler spectra and amplitudes.The 6 transmission paths were designed to provide several magnetic aspect angles varying by 1.5°-7° from perpendicularity with the earth's field B and two streaming aspect angles differing by ~38°. The objective was to employ controlled geometric factors to study the functional dependency of signal amplitudes and Doppler shifts on magnetic and streaming aspect angles. Several hundred hours of excellent data were obtained in continuous operation during the month of August 1981. Preliminary results will be reported. 相似文献