全文获取类型
收费全文 | 4407篇 |
免费 | 11篇 |
国内免费 | 11篇 |
专业分类
航空 | 1688篇 |
航天技术 | 1498篇 |
综合类 | 20篇 |
航天 | 1223篇 |
出版年
2022年 | 16篇 |
2021年 | 49篇 |
2019年 | 21篇 |
2018年 | 151篇 |
2017年 | 118篇 |
2016年 | 128篇 |
2015年 | 47篇 |
2014年 | 144篇 |
2013年 | 165篇 |
2012年 | 145篇 |
2011年 | 220篇 |
2010年 | 172篇 |
2009年 | 265篇 |
2008年 | 276篇 |
2007年 | 168篇 |
2006年 | 100篇 |
2005年 | 127篇 |
2004年 | 133篇 |
2003年 | 148篇 |
2002年 | 109篇 |
2001年 | 163篇 |
2000年 | 62篇 |
1999年 | 79篇 |
1998年 | 84篇 |
1997年 | 63篇 |
1996年 | 77篇 |
1995年 | 104篇 |
1994年 | 85篇 |
1993年 | 48篇 |
1992年 | 68篇 |
1991年 | 18篇 |
1990年 | 30篇 |
1989年 | 66篇 |
1988年 | 21篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 118篇 |
1984年 | 78篇 |
1983年 | 66篇 |
1982年 | 64篇 |
1981年 | 119篇 |
1980年 | 33篇 |
1979年 | 21篇 |
1978年 | 19篇 |
1977年 | 25篇 |
1976年 | 20篇 |
1975年 | 24篇 |
1974年 | 23篇 |
1972年 | 15篇 |
1971年 | 14篇 |
排序方式: 共有4429条查询结果,搜索用时 15 毫秒
921.
B.E. Woodgate M.-J. Martres J.B. Smith K.T. Strong M.K. McCabe M.E. Machado V. Gaisauskas R.T. Stewart P.A. Sturrock 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):11-17
Studies of groups of homologous flares in active regions in 1980 have been made using a variety of space and ground based instruments. Detailed properties of three of these groups have been studied, and are combined to form a possible sequence of events. 相似文献
922.
W Heinrich E V Benton B Wiegel G Rusch E Becker 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):969-977
Radiation effects of cosmic ray nuclei are generally described as a function of the particle LET. For a large number of space missions LET spectra have been measured and models have been developed to calculate these spectra that include the effects of geomagnetic shielding and shielding provided by material. In this paper we compare measured and calculated LET spectra. For low earth orbits events with high local energy deposition, i.e., short range secondaries, contribute significantly to the measured spectra. These events are produced by nuclear interactions, mainly induced by protons from the south atlantic anomaly. The technique to include these contributions in the models depends on the size of radiation sensitive volumes. For sizes comparable to or larger than the range of target secondaries it is essential to separate contributions by target interactions from those of cosmic rays. This separation is possible in experiments which use stacks of plastic nuclear track detectors. The yield of short range events generated by protons and measured in the detector can be calibrated from accelerator experimental data. We present first results for CR-39 detectors. 相似文献
923.
A chirp scaling approach for processing squint mode SAR data 总被引:5,自引:0,他引:5
Davidson G.W. Cumming I.G. Ito M.R. 《IEEE transactions on aerospace and electronic systems》1996,32(1):121-133
Image formation from squint mode synthetic aperture radar (SAR) is limited by image degradations caused by neglecting the range-variant filtering required by secondary range compression (SRC). Introduced here is a nonlinear FM chirp scaling, an extension of the chirp scaling algorithm, as an efficient and accurate approach to range variant SRC. Two methods of implementing the approach are described. The nonlinear FM filtering method is more accurate but adds a filtering step to the chirp scaling algorithm, although the extra computation is less than that of a time domain residual compression filter. The nonlinear FM pulse method consists of changing the phase modulation of the transmitted pulse, thus avoiding an increase in computation. Simulations show both methods significantly improve resolution width and sidelobe level, compared with existing SAR processors for squint angles above 10 deg for L-band and 20 deg for C-band 相似文献
924.
Corsini G. Gini F. Greco M.V. Verrazzani L. 《IEEE transactions on aerospace and electronic systems》1995,31(3):1202-1204
Maximum Likelihood (ML) algorithms and Cramer-Rao (CR) bounds for the location and scale parameters of the Gumbel distribution are discussed. First we consider the case in which the scale parameter is known, obtaining the estimator of the location parameter by solving the likelihood equation and then evaluating its performance. We next consider the case where both the location parameter and the scale parameter are unknown and need to be estimated simultaneously from the reference samples. For this case, performance is analyzed by means of Monte Carlo simulation and compared with the asymptotic CR bound 相似文献
925.
A technique is presented for predicting the bistatic radar cross section (RCS) of an opaque, arbitrarily shaped object at angles near forward scatter. Babinet's principle is employed to approximate the object's scattering pattern as the two-dimensional Fourier transform of its silhouette. Calculations for spheres and right-circular cylinders are shown to agree with predictions based on exact Mie theory, method of moments, and physical optics. Restrictions on the applicability of the method are presented. 相似文献
926.
R. Z. Sagdeev G. A. Avanesov I. V. Barinov A. I. Debabov V. A. Kvasikov V. I. Moroz V. A. Shamis V. I. Tarnapolski D. A. Usikov Ya. L. Ziman B. S. Zhukov B. A. Smith S. Larson F. Szabo K. Szeg A. Kondor L. Vrhalmi E. Mernyi L. Szabo I. Toth P. Cruvellier A. Abergel J. -L. Bertaux J. E. Blamont M. Danz D. Mhlmann H. Stiller H. P. Zapfe 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(12):95-104
The VEGA-1 and VEGA-2 spacecraft made their closest approach to Comet Halley on 6 and 9 March, respectively. In this paper those results of the onboard imaging experiment which were obtained around closest approach are discussed. The nucleus of the comet was clearly identifiable as an irregularly shaped object, with overall dimensions of (16±1)×(8±1)×(8±1) km. The nucleus rotates in the prograde sense about an axis nearly perpendicular to the orbital plane with a period of 53±2 hours. Its albedo is only Many of the jet features observed during the second fly-by have been spatially reconstructed. Their sources form a quasi-linear structure on the surface. The dust above the surface is shown to be generally optically thin with the exception of certain specific dust jets. Brightness features on the surface are clearly seen. Correlating our data with other measurements, we conclude that the dirty snow-ball model will probably need to be revised. 相似文献
927.
A basic class of three-phase inverters with nonpulsating terminal currents, namely, the four-topology four-inductor four-capacitor class is derived and studied. The expressions of duty-ratios required for low-harmonic dc-to-three-phase-ac conversion, ranges of output voltage variation, and component stresses for given specifications of inverters are derived. The characteristics of inverters include low-harmonic power conversion, low component stresses, variable-frequency variable-amplitude output voltages of values both below and above the dc input value, and the use of minimum number of inductors to achieve nonpulsating terminal currents 相似文献
928.
L.A. Sromovsky H.E. Revercomb V.E. Suomi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(9):37-40
New Venus temperature profiles, derived from engineering measurements of the Small Probe Net Flux Radiometer (SNFR) instruments generally confirm to high accuracy the vertical structure and horizontal temperature contrast results of Seiff et al. /1/. 相似文献
929.
M. O. Riazantseva O. V. Khabarova G. N. Zastenker J. D. Richardson 《Cosmic Research》2005,43(3):157-164
This work is devoted to studying the sharp boundaries of small-scale structures of the solar wind according to the data of measurements with high time resolution onboard the INTERBALL-1 satellite and simultaneous measurements of the WIND spacecraft. Such issues as the character of change of various plasma and magnetic field parameters on these boundaries, the duration of boundary passage and the balance of the total (thermal plus magnetic) pressure on the boundaries of the structures are considered. On the basis of the vast statistical material available, the typical conditions in the solar wind are investigated, in which such sharp boundaries are observed.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 3, 2005, pp. 163–170.Original Russian Text Copyright © 2005 by Riazantseva, Khabarova, Zastenker, Richardson. 相似文献
930.
J. M. Cassanto H. I. Ziserman D. K. Chapman Z. R. Korszun P. Todd 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1988,8(12):141-146
Microgravity experiments designed for execution in Get-Away Special canisters, Hitchhiker modules, and Reusable Re-entry Satellites will be subjected to launch and re-entry accelerations. Crew-dependent provisions for preventing acceleration damage to equipment or products will not be available for these payloads during flight; therefore, the effects of launch and re-entry accelerations on all aspects of such payloads must be evaluated prior to flight. A procedure was developed for conveniently simulating the launch and re-entry acceleration profiles of the Space Shuttle (3.3 and 1.7 × g maximum, respectively) and of two versions of NASA's proposed materials research Re-usable Re-entry Satellite (8 × g maximum in one case and 4 × g in the other). By using the 7 m centrifuge of the Gravitational Plant Physiology Laboratory in Philadelphia it was found possible to simulate the time dependence of these 5 different acceleration episodes for payload masses up to 59 kg. A commercial low-cost payload device, the “Materials Dispersion Apparatus” of Instrumentation Technology Associates was tested for (1) integrity of mechanical function, (2) retention of fluid in its compartments, and (3) integrity of products under simulated re-entry g-loads. In particular, the sharp rise from 1 g to maximum g-loading that occurs during re-entry in various unmanned vehicles was successfully simulated, conditions were established for reliable functioning of the MDA, and crystals of 5 proteins suspended in compartments filled with mother liquor were subjected to this acceleration load. 相似文献