首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   8580篇
  免费   17篇
  国内免费   35篇
航空   3933篇
航天技术   3053篇
综合类   29篇
航天   1617篇
  2021年   81篇
  2019年   56篇
  2018年   172篇
  2017年   115篇
  2016年   116篇
  2015年   53篇
  2014年   205篇
  2013年   256篇
  2012年   239篇
  2011年   366篇
  2010年   263篇
  2009年   392篇
  2008年   451篇
  2007年   247篇
  2006年   190篇
  2005年   219篇
  2004年   222篇
  2003年   262篇
  2002年   182篇
  2001年   265篇
  2000年   161篇
  1999年   208篇
  1998年   240篇
  1997年   138篇
  1996年   214篇
  1995年   246篇
  1994年   247篇
  1993年   152篇
  1992年   187篇
  1991年   70篇
  1990年   72篇
  1989年   195篇
  1988年   83篇
  1987年   81篇
  1986年   85篇
  1985年   254篇
  1984年   188篇
  1983年   154篇
  1982年   159篇
  1981年   289篇
  1980年   79篇
  1979年   67篇
  1978年   66篇
  1977年   58篇
  1975年   76篇
  1974年   53篇
  1973年   49篇
  1972年   49篇
  1970年   55篇
  1969年   48篇
排序方式: 共有8632条查询结果,搜索用时 15 毫秒
901.
The finite-difference method acceptable for on-board computers is applied to analyze the thermo-stressed state for the thermal-barrier coating of a perforated turbine blade and its wall at transient and stationary conditions of air-breathing jet engine operation during a flight.  相似文献   
902.
The paper presents the results of calculating nonstatitionary heat exchange between a heattransfer agent (water) and a gadolinium working element of the thermomagnetic engine with the use of ANSYS 13.0 certified software. Recommendations for designing the thermomagnetic engine working elements are given based on the analysis of calculation results.  相似文献   
903.
Effect of the size of rhizospheric bacterial populations on germination of seeds and development of simple terrestrial "wheat plants--rhizospheric microorganisms--artificial soil" and "wheat plants-artificial soil" systems has been studied. Experiments demonstrated that within specify ranges in the inoculate, the rhizospheric bacteria are capable of increasing the yield of germinated seeds and stimulate the growth of plantlets. Germination of seeds inoculated with bacteria was either stimulated, or inhibited or remained at control levels depending on the amount of bacteria. Plant biomass growth and total photoassimilation has been found to depend on the amount of bacteria on the plant roots: the higher the amount of bacteria on plant roots, the smaller is the biomass of plants but the total photoassimilation is, higher. Thus, depending on the amount of bacteria on the roots of plants the system either increases the biomass of plants or increases the total photoassimilation, i.e. "pumps" carbon through itself involving bacteria. Grant numbers: N99-04-96017, N15.  相似文献   
904.
EUVITA is a set of 8 extreme UV normal incidence imaging telescopes, each of them sensitive in a narrow band (λ/Δλ = 15 to 80), centered at wavelengths between 50 and 175 Å. Each telescope has an effective area of a few cm2; a field of view of 1.2° and a spatial resolution of 10 arcsec.

EUVITA will be flown on the Russian mission SPECTRUM X-G. This satellite will be launched in a highly eccentric orbit with a period of 4 days, allowing long, uninterrupted observations (e.g. 105 seconds). EUVITA's narrow spectral bands allow the measurement of source parameters such as temperature or power law index as well as interstellar absorption, and will resolve groups of strong lines emitted by optically thin hot plasmas.  相似文献   

905.
The Hopkins Ultraviolet Telescope (HUT) was flown aboard the space shuttle Columbia as part of the Astro-1 mission during December 1990. During the nine-day flight, HUT carried out 3 Å resolution spectrophotometry of a wide variety of astronomical objects, including a number of stellar targets, in the 912–1860 Å range of the far ultraviolet. A few nearby stars were observed in the 415–912 Å range of the extreme ultraviolet as well. For nearly all of these targets, the spectra obtained by HUT are the first ever obtained in the spectroscopically rich region between Lyman (1216 Å) and the Lyman limit (912 Å). Here, we present highlights of the results obtained by HUT in a variety of areas of stellar astronomy.  相似文献   
906.
Hard X-ray observations of Cyg X-3 in the energy range 20–100 keV were made with a Balloon-borne telescope using two large area proportional counters. The source was seen with a total significance of 20.

A 121 s periodicity was seen during Fourier analysis of the data. The phenomenon can be interpreted as due to transient pulsation since no other peak was seen in our data. Quasi-periodic oscillation in the range 0.06–20 mHz have been observed from Cyg X-3 at lower energies. Interestingly, most of the reported periods are multiple of the present measurements. The observed pulsation at high energies indicate the occasional unstable behaviour of the inner parts of the accretion disk connected with the basic rotation period of the compact object.

The 4.8h modulation, characteristic of the orbital period of the binary system was seen in the data, with a broad maximum between the phase 0.3 to 0.7.  相似文献   

907.
In evaluating the prospects for the development of a commercially viable RLV, it may be useful to examine ’lessons learned‘ from previous space commercialization efforts– both those that succeeded and those that did not. It can be argued that several distinct streams of market and technological development may have to converge for successful commercialization of space systems to occur. Factors influencing the prospects for commercialization include the size and growth rate of the potential customer base, the extent to which a governmental customer exists to underpin the market, the development of associated ’value-added‘ markets, the stability of governmental policies, the availability of enabling or enhancing infrastructure, the levels of technological and business risk, and the degree to which competitive markets exist. This paper examines two previous space commercialization experiences, evaluates the relative importance of the various factors that influence the prospects for success of commercialization efforts, and assesses the implications of those factors for the commercial viability of the proposed RLV.  相似文献   
908.
909.
910.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号