全文获取类型
收费全文 | 6147篇 |
免费 | 15篇 |
国内免费 | 16篇 |
专业分类
航空 | 2977篇 |
航天技术 | 2148篇 |
综合类 | 18篇 |
航天 | 1035篇 |
出版年
2021年 | 36篇 |
2019年 | 34篇 |
2018年 | 85篇 |
2017年 | 57篇 |
2016年 | 58篇 |
2014年 | 107篇 |
2013年 | 160篇 |
2012年 | 133篇 |
2011年 | 220篇 |
2010年 | 175篇 |
2009年 | 229篇 |
2008年 | 322篇 |
2007年 | 167篇 |
2006年 | 121篇 |
2005年 | 172篇 |
2004年 | 173篇 |
2003年 | 199篇 |
2002年 | 118篇 |
2001年 | 187篇 |
2000年 | 96篇 |
1999年 | 151篇 |
1998年 | 176篇 |
1997年 | 128篇 |
1996年 | 147篇 |
1995年 | 196篇 |
1994年 | 202篇 |
1993年 | 116篇 |
1992年 | 154篇 |
1991年 | 67篇 |
1990年 | 72篇 |
1989年 | 142篇 |
1988年 | 61篇 |
1987年 | 53篇 |
1986年 | 62篇 |
1985年 | 188篇 |
1984年 | 172篇 |
1983年 | 132篇 |
1982年 | 137篇 |
1981年 | 213篇 |
1980年 | 62篇 |
1979年 | 67篇 |
1978年 | 62篇 |
1977年 | 49篇 |
1976年 | 45篇 |
1975年 | 64篇 |
1974年 | 51篇 |
1973年 | 44篇 |
1972年 | 66篇 |
1971年 | 34篇 |
1969年 | 35篇 |
排序方式: 共有6178条查询结果,搜索用时 15 毫秒
121.
F. G. von der Dunk E. Back-Impallomeni S. Hobe R. M. Ramirez de Arellano 《Space Policy》2004,20(3):149-156
At a time when scientific and commercial interest in the Moon is being reinvigorated it is becoming fashionable for ordinary individuals to ‘buy’ plots on the lunar surface, with the ‘vendors’ arguing that an absence of specific prohibition of individual private activity in space makes such action legal. It is therefore time for the legal community to address this situation by investigating just how legal such activity is—and bringing their findings to the attention of governments. This can be done through an examination of the relationship between national law and international space law, of the provisions of international space law—especially Article 2 of the Outer Space Treaty—and by answering any claims to private ownership of immovable property. Aside from the fact that individuals appear to be being duped, the pursuit of property claims on the Moon could impede future activities aimed at benefiting society. 相似文献
122.
G. Brner E. Seiler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
The picture of an exponentially increasing, “inflationary” phase of the early universe (Guth 1981; Linde 1982; Albrecht and Steinhardt 1982) may point the way to an understanding of our present universe without reference to extremely specific initial conditions. The model rests, however, on several assumptions which deserve critical examination. 相似文献
123.
124.
Profiles of the visible Fe X (6374 Å) coronal emission line as a function of height above the limb were obtained out to 1.16 solar radii in a coronal hole using the NSO/Sacramento Peak Observatory Coronagraph, Universal Spectrograph and a CCD camera. These are the first coronal line profiles obtained as a function of height in a coronal hole from the ground. Analysis of the line widths suggests a large component of nonthermal broadening which increases with height ranging from 40 to 60 km/s, depending upon the assumed temperature or thermal component of the profile. 相似文献
125.
126.
A. G. Tuchin 《Cosmic Research》2008,46(6):506-516
The problem of selecting quasi-synchronous orbits of a spacecraft around Phobos is considered. These quasi-synchronous orbits are far (with respect to the Hill’s sphere) quasi-satellite orbits with retrograde rotation in the restricted three body problem. The orbit should pass through a given point at a specified time instant. It should also possess a property of minimum distance from the Phobos surface at every passage above the region of planned landing. The equations of dynamics are represented in the form describing the orbit as a combination of motions in two drifting ellipses, inner and outer ellipses. The center of the outer ellipse is located on the inner ellipse. A formula is derived that relates averaged values of half-axes of the inner and outer ellipses. It is used for construction of the first approximation of numerically designed orbit, which makes it possible to simplify and speed up the computing process. The tables of initial conditions obtained as a result of calculations are presented. 相似文献
127.
Selected new methods and applications of non-linear apodization for irregularly-shaped and parse coherent apertures and arrays are presented. The benefits include unproved impulse response performance, i.e., reduced peak sidelobes and integrated sidelobe power, along with improved mainlobe resolution, compared to classic windowing techniques. Nonlinear apodization (NLA) techniques can also serve as powerful engines for effective superresolution and bandwidth extrapolation of coherent data for filling sparse apertures. The sparse aperture filling property of superresolution algorithms for radar data forms the basis for a new concept which is introduced here: synthetic multiple aperture radar technology (SMART). Increased swath and/or reduced antenna size are some of the benefits postulated for SMART applied to synthetic aperture radar (SAR) systems. The benefits of these new methods and applications for nonlinear apodization are then demonstrated for two specific applications: 1) sidelobe control for Y-type synthetic aperture radiometers, such as the European Soil Moisture and Ocean Salinity (SMOS) system (Kerr et al.) and JPL's proposed GeoSTAR (Lambrigsten) concept; and, 2) filling of sparse synthetic aperture radar data by exploiting the bandwidth extrapolation properties of nonlinear apodization based superresolution techniques. The methods that have been developed and demonstrated herein have potential application to a wide range of passive and active microwave remote sensing and radar systems. 相似文献
128.
The testing and evaluation of sophisticated security systems has remained in the domain of governments in national facilities and the commercial security industry through manufacturers and engineering consultants. As well, the production of testing protocols and industry standards has been developed by national organisations, professional security, and engineering bodies in the appropriate security fields. The Security Systems Research and Testing Laboratory in the School of Engineering and Mathematics at Edith Cowan University (ECU), Perth, Western Australia has commenced operations in research, testing, and evaluation of security systems. This paper wir describe the first year of operation of the Security Systems Research and Testing Laboratory, and will describe the role that testing and evaluation of security systems plays in the education and training of Security Science graduates, as well as the benefits that the Laboratory brings to the security industry through its testing programme. 相似文献
129.
M S Gussenhoven E G Mullen D H Brautigam 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):927-941
The Space Radiation (SPACERAD) experiments on the Combined Release and Radiation Effects Satellite (CRRES) gathered 14 months of radiation particle data in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. When compared to the NASA radiation belt models AP8 and AE8, the data show the proton model (AP8) does not take into account a second belt formed after major solar flare/shock injection events, and the electron model (AE8) is misleading, at best, in calculating dose in near-Earth orbits. The second proton belt, although softer in energy than the main proton belt, can produce upsets in proton sensitive chips and would produce significant dose in satellites orbiting in it. The MeV electrons observed on CRRES show a significant particle population above 5 MeV (not in the AE8 model) which must be included in any meaningful dose predictions for satellites operating between L-shells of 1.7 and 3.0 RE. 相似文献
130.
V Switzer RC rdBogo G A Mickley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):443-451
Application of the degeneration sensitive, cupric-silver staining method to brain sections of male Sprague-Dawley rats irradiated 4 days before sacrifice with 155 Mev protons, 2-8 Gy at 1 Gy/min (N=6) or 22-l0lGy at 20 Gy/min (N=16) or with 18.6 Mev electrons, 32-67 Gy at 20 Gy/min (N=20), doses which elicit behavioral changes (accelerod or conditioned taste aversion), resulted in a display of degeneration of astrocyte-like cell profiles which were not uniformly distributed. Plots of 'degeneration scores' (counts of profiles in 29 areas) vs. dose for the proton and electron irradiations displayed a linear dose response for protons in the range of 2-8 Gy. In the 20-100 Gy range, for both electrons and protons the points were distributed in a broad band suggesting a saturation curve. The dose range in which these astrocyte-like profiles becomes maximal corresponds well with the dose range for the X-ray eradication of a subtype of astrocytes, 'beta astrocytes'. 相似文献