全文获取类型
收费全文 | 6797篇 |
免费 | 39篇 |
国内免费 | 19篇 |
专业分类
航空 | 3305篇 |
航天技术 | 2218篇 |
综合类 | 191篇 |
航天 | 1141篇 |
出版年
2021年 | 59篇 |
2019年 | 48篇 |
2018年 | 132篇 |
2017年 | 88篇 |
2016年 | 82篇 |
2014年 | 141篇 |
2013年 | 182篇 |
2012年 | 166篇 |
2011年 | 270篇 |
2010年 | 187篇 |
2009年 | 301篇 |
2008年 | 294篇 |
2007年 | 182篇 |
2006年 | 147篇 |
2005年 | 155篇 |
2004年 | 172篇 |
2003年 | 208篇 |
2002年 | 223篇 |
2001年 | 257篇 |
2000年 | 123篇 |
1999年 | 153篇 |
1998年 | 187篇 |
1997年 | 134篇 |
1996年 | 165篇 |
1995年 | 210篇 |
1994年 | 170篇 |
1993年 | 116篇 |
1992年 | 156篇 |
1991年 | 69篇 |
1990年 | 77篇 |
1989年 | 152篇 |
1988年 | 71篇 |
1987年 | 73篇 |
1986年 | 64篇 |
1985年 | 193篇 |
1984年 | 159篇 |
1983年 | 137篇 |
1982年 | 148篇 |
1981年 | 200篇 |
1980年 | 87篇 |
1979年 | 57篇 |
1978年 | 68篇 |
1977年 | 45篇 |
1976年 | 52篇 |
1975年 | 59篇 |
1974年 | 50篇 |
1972年 | 54篇 |
1971年 | 53篇 |
1970年 | 36篇 |
1969年 | 38篇 |
排序方式: 共有6855条查询结果,搜索用时 15 毫秒
351.
Bhat A.K.S. Biswas A. Iyengar B.S.R. 《IEEE transactions on aerospace and electronic systems》1995,31(3):1186-1193
A series-parallel resonant converter employing (LC)(LC)-type tank circuit operating in lagging power factor (PF) mode is presented and analyzed using complex ac circuit analysis. Design curves are obtained and the converter is optimized under certain constraints. Detailed Space Integrated Control Experiment (SPICE) simulation results are presented to evaluate the performance of the designed converter under varying load conditions. Results obtained from an experimental converter are also presented. The results obtained from the theory, SPICE simulation, and the experimental converter are compared. The proposed converter has high efficiency from full load to very light load (<10%). Switching frequency variation required for a wide change in the load (near load open circuit to full load) is narrow compared with the series resonant converter (SRC) 相似文献
352.
A survey of current knowledge about Jupiter, Saturn, Uranus, Neptune, Pluto, and their satellites is presented. The best available numerical values are given for physical parameters, including orbital and body properties, atmospheric composition and structure, and photometric parameters. The more acceptable current theories of these bodies are outlined with thorough referencing offering access to the details. The survey attempts to cover the literature through May 1, 1972. Prepared Under Contract No. NAS7-100 National Aeronautics and Space Administration. 相似文献
353.
Belter S.E. Williams C.R. Bass S.C. 《IEEE transactions on aerospace and electronic systems》1976,(6):698-705
The application of 4-bit microprocessors to the communication of the control and status signals found in an advanced aircraft instrument landing system is presented. The advantages as well as some of the peculiarities of such an approach are described. Among the benefits, one must include the possibility of a very convenient and understandable human interface. 相似文献
354.
A. L. Broadfoot B. R. Sandel D. E. Shemansky S. K. Atreya T. M. Donahue H. W. Moos J. L. Bertaux J. E. Blamont J. M. Ajello D. F. Strobel J. C. McConnell A. Dalgarno R. Goody M. B. McElroy Y. L. Yung 《Space Science Reviews》1977,21(2):183-205
The Voyager Ultraviolet Spectrometer (UVS) is an objective grating spectrometer covering the wavelength range of 500–1700 Å with 10 Å resolution. Its primary goal is the determination of the composition and structure of the atmospheres of Jupiter, Saturn, Uranus and several of their satellites. The capability for two very different observational modes have been combined in a single instrument. Observations in the airglow mode measure radiation from the atmosphere due to resonant scattering of the solar flux or energetic particle bombardment, and the occultation mode provides measurements of the atmospheric extinction of solar or stellar radiation as the spacecraft enters the shadow zone behind the target. In addition to the primary goal of the solar system atmospheric measurements, the UVS is expected to make valuable contributions to stellar astronomy at wavelengths below 1000 Å. 相似文献
355.
Coronal holes are the coolest and darkest regions of the upper solar atmosphere, as observed both on the solar disk and above the solar limb. Coronal holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. During the years of the solar minima, coronal holes are generally confined to the Sun??s polar regions, while at solar maxima they can also be found at lower latitudes. Waves, observed via remote sensing and detected in-situ in the wind streams, are most likely responsible for the wind and several theoretical models describe the role of MHD waves in the acceleration of the fast solar wind. This paper reviews the observational evidences of detection of propagating waves in these regions. The characteristics of the waves, like periodicities, amplitude, speed provide input parameters and also act as constraints on theoretical models of coronal heating and solar wind acceleration. 相似文献
356.
The paper presents an improved technique and the results of strength analysis for the aircraft structural elements with a structural defect like an arbitrary shape delamination. 相似文献
357.
The paper presents a technique of calculating the life for gas turbine engine parts in a low cycle area based on the influence coefficients taking into account analytical and operational factors. A statistical method is used to determine the influence coefficients. 相似文献
358.
Kapoor R. Banerjee A. Tsihrintzis G.A. Nandhakumar N. 《IEEE transactions on aerospace and electronic systems》1999,35(3):819-834
We address the problem of detection of targets obscured by a forest canopy using an ultrawideband (UWB) radar. The forest clutter observed in the radar imagery is a highly impulsive random process that is more accurately modeled with the recently proposed class of alpha-stable processes as compared with Gaussian, Weibull, and K-distribution models. With this more accurate model, segmentation is performed on the imagery into forest and clear regions. Further, a region-adaptive symmetric alpha stable (SαS) constant false-alarm rate (CFAR) detector is introduced and its performance is compared with the Weibull and Gaussian CFAR detectors. The results on real data show that the SαS CFAR performs better than the Weibull and Gaussian CFAR detectors in detecting obscured targets 相似文献
359.
D. B. Reisenfeld D. S. Burnett R. H. Becker A. G. Grimberg V. S. Heber C. M. Hohenberg A. J. G. Jurewicz A. Meshik R. O. Pepin J. M. Raines D. J. Schlutter R. Wieler R. C. Wiens T. H. Zurbuchen 《Space Science Reviews》2007,130(1-4):79-86
Analysis of the Genesis samples is underway. Preliminary elemental abundances based on Genesis sample analyses are in good
agreement with in situ-measured elemental abundances made by ACE/SWICS during the Genesis collection period. Comparison of
these abundances with those of earlier solar cycles indicates that the solar wind composition is relatively stable between
cycles for a given type of flow. ACE/SWICS measurements for the Genesis collection period also show a continuum in compositional
variation as a function of velocity for the quasi-stationary flow that defies the simple binning of samples into their sources
of coronal hole (CH) and interstream (IS). 相似文献
360.
Phenneger M. Woodward J. Cox R. Gliniak C. 《Aerospace and Electronic Systems Magazine, IEEE》2008,23(7):4-4
This describes a NOAA-14 spacecraft loss of control event and the lessons learned. The lessons learned are in two categories: contingency recovery operations; and on-orbit propulsion system isolation methods. The work is motivated in recognition of the effort of the NOAA off-line engineering support team and their NOAA civil servant mission leads and operations support staff. 相似文献