全文获取类型
收费全文 | 5632篇 |
免费 | 5篇 |
国内免费 | 15篇 |
专业分类
航空 | 2608篇 |
航天技术 | 2131篇 |
综合类 | 15篇 |
航天 | 898篇 |
出版年
2021年 | 39篇 |
2018年 | 85篇 |
2017年 | 70篇 |
2016年 | 58篇 |
2015年 | 29篇 |
2014年 | 100篇 |
2013年 | 144篇 |
2012年 | 125篇 |
2011年 | 213篇 |
2010年 | 148篇 |
2009年 | 230篇 |
2008年 | 291篇 |
2007年 | 146篇 |
2006年 | 107篇 |
2005年 | 160篇 |
2004年 | 165篇 |
2003年 | 199篇 |
2002年 | 111篇 |
2001年 | 197篇 |
2000年 | 99篇 |
1999年 | 158篇 |
1998年 | 165篇 |
1997年 | 126篇 |
1996年 | 120篇 |
1995年 | 176篇 |
1994年 | 198篇 |
1993年 | 90篇 |
1992年 | 119篇 |
1991年 | 51篇 |
1990年 | 65篇 |
1989年 | 118篇 |
1988年 | 46篇 |
1987年 | 57篇 |
1986年 | 54篇 |
1985年 | 173篇 |
1984年 | 141篇 |
1983年 | 126篇 |
1982年 | 125篇 |
1981年 | 206篇 |
1980年 | 55篇 |
1979年 | 56篇 |
1978年 | 52篇 |
1977年 | 46篇 |
1976年 | 41篇 |
1975年 | 49篇 |
1974年 | 39篇 |
1973年 | 36篇 |
1972年 | 58篇 |
1970年 | 29篇 |
1969年 | 31篇 |
排序方式: 共有5652条查询结果,搜索用时 93 毫秒
951.
K.-P. Wenzel R. Reinhard T.R. Sanderson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(3):105-108
ISEE-3 observations of a long-lasting low-energy proton intensity increase during the 25 September 1978 shock event are presented as an example for interplanetary particle acceleration in association with shock waves. The observations are discussed in the light of current models for particle acceleration. The particular shape of the time intensity behaviour of the particle intensity increase, the existence of a shock spike and the observed particle distributions indicate that the particles are accelerated at the shock by the induced electric field . 相似文献
952.
Brewster L.T. Stigall P.D. 《IEEE transactions on aerospace and electronic systems》1988,24(6):682-692
Aircraft vertical profile simulation is realized using a demand-driven minimal-calculation directed graph structure to reduce calculation time and to force synchronization of the performance measurement functions with the system state variables. Performance-directed model adaptation makes dynamic vertical profile path corrections, in the presence of fixed drag variations, possible. Drag variations ranging from +10% to -10% yielded fuel consumption improvements of less than 1% in the majority of the cases. Calculation time improvement for path simulation ranges from a factor of 1.19 in the worst case to 1.5 in the best case 相似文献
953.
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
954.
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
955.
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
956.
957.
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
958.
M.J. Rycroft P.S. Cannon T. Turunen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):449-454
ELF and VLF radio signals were recorded in the afternoon to early morning (local time) between 24 March and 4 April 1979, in Northern Scandinavia. Apart from signals of natural origin, timing signals, i.e. six pips of equal duration of 105 ± 8 ms, at 1 kHz ± 0.5 Hz, were observed on the hour UT. Such signals only occur on days of relatively high geomagnetic activity during enhanced auroral electrojet activity. They are believed to be generated by non-linear demodulation (self-detection) of signals from two or more amplitude modulated transmitters in the USSR, operating at 173, 200, 236, 263 and 657 kHz. The simplest explanation for the observations is provided by the three transmitters operating at 173 kHz. 相似文献
959.
H. Oya T. Ono 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):217-220
The stimulated plasma wave experiment (SPW) has been successfully carried out in the plasmasphere and the magnetosphere along the JIKIKEN (EXOS-B) satellite orbit where the plasma parameters indicate wide variety of the combination of the electron number density, ranging from 1/cc to 104/cc, and the electron cyclotron frequency, ranging from 6 kHz to 200 kHz.The upper hybrid resonances FUHR usually persists for long periods up to 125 msec and the electron cyclotron resonances nFH are stimulated at frequencies with the very high harmonic number n; sometimes, the nFH resonance takes place for n=47.All the features of the resonances including FOn reflect the characteristics of the magnetospheric plasma that contains the energetic and non-Maxwellian components of the particles. The measurement of the plasma resonance contributes to the detection of the local electron density and the magnetic field intensity. The mode of the propagating radio waves is also determined being compared with the observed local plasma resonance frequency Fp. 相似文献
960.
V.L. Swaminathan D.S. Kamat A.M. Rakshit D.K. Chakraborty T.K. Kurien 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(2):55-58
Geological analysis and evaluation of digitally processed and enhanced LANDSAT MSS data products for three test areas of Singhbhum Shear Zone, India has led to certain significant results regarding optimisation and utility of such techniques for geological studies and obtaining additional/new information regarding lithology and structure. Three band-to-band ratio images are found to give best results. Lithologic formations could be subdivided into a number of units. The Westward and southeastward extension of the shear zone could be delineated thereby indicating scope of mineralisation in these parts. 相似文献