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   4927篇
  免费   43篇
  国内免费   14篇
航空   2209篇
航天技术   1843篇
综合类   27篇
航天   905篇
  2021年   50篇
  2019年   48篇
  2018年   173篇
  2017年   102篇
  2016年   75篇
  2015年   32篇
  2014年   126篇
  2013年   147篇
  2012年   121篇
  2011年   213篇
  2010年   158篇
  2009年   229篇
  2008年   294篇
  2007年   148篇
  2006年   117篇
  2005年   129篇
  2004年   138篇
  2003年   166篇
  2002年   114篇
  2001年   159篇
  2000年   84篇
  1999年   102篇
  1998年   123篇
  1997年   88篇
  1996年   96篇
  1995年   125篇
  1994年   113篇
  1993年   85篇
  1992年   114篇
  1991年   45篇
  1990年   44篇
  1989年   97篇
  1988年   41篇
  1987年   46篇
  1986年   38篇
  1985年   142篇
  1984年   117篇
  1983年   104篇
  1982年   105篇
  1981年   127篇
  1980年   60篇
  1979年   51篇
  1978年   39篇
  1977年   25篇
  1976年   26篇
  1975年   23篇
  1974年   25篇
  1973年   21篇
  1972年   20篇
  1970年   18篇
排序方式: 共有4984条查询结果,搜索用时 15 毫秒
991.
Methods were suggested in /1,2,3/ to find the maximum electron density NmF (or NmF2) and the) corresponding height hmF (hmF2) in the ionosphere through a combination of measurements on two airglow lines: the UV oxygen line at λ135.6 nm and the red oxygen line near λ630 nm.  相似文献   
992.
In the present analysis, the mass spectrometer data from the ISS-b satellite, available in the form of contour plots at an average height of 1100 km for every alternate hour, is used. This analysis showed some interesting results in terms of the diurnal variation of the transition heights; at times dominance of He+ over the other ions, and the seasonal variations of different constituents. In the development of ion composition models, it is suggested that this type of result should be taken into consideration.  相似文献   
993.
994.
To test whether gravity is required for normal amphibian development, Xenopus laevis females were induced to ovulate aboard the orbiting Space Shuttle. Eggs were fertilized in vitro, and although early embryonic stages showed some abnormalities, the embryos were able to regulate and produce nearly normal larvae. These results demonstrate for the first time that a vertebrate can ovulate in the virtual absence of gravity, and that the eggs can develop to a free-living stage.  相似文献   
995.
For the Closed Ecological Life Support System (CELSS) of a manned lunar base which is planned to be built on the moon early in the 21st century, several proposed programs exist to grow vegetables inside a farming module. At the 40th IAF (Malaga, 1989) the author et al presented a proposal for supplying food and nutrients to a crew of eight members, a basic concept which is based on growing four kinds of vegetables. This paper describes measures for biohazard protection in farming modules. In this study, biohazard protection means prevention of the dispersion of plant diseases to other plant species or other portions of farming beds.  相似文献   
996.
997.
The filtrate of non-catalytical wet-oxidation sewage sludge was wet-oxidized again at 290 degrees C and 300 degrees C with a Ru-Rh catalyst. At each temperature, repeated batch tests were carried out. Both oxidation and denitrification efficiency of organic matter in the raw material were studied. In the 16 times batch tests at 300 degrees C, high and stable oxidation occurred. 98.0% of organic carbon in the raw material was oxidized and 98.3% of organic nitrogen was denitrified. At 290 degrees C, though high and stable denitrification occurred, oxidation did not occur highly and stably. A catalytic wet-oxidation system studied at 300 degrees C will be useful as a waste management system for a human life support system, where almost all food is resupplied from the earth. This system can prevent organic waste accumulation in the life support system.  相似文献   
998.
Protective effects of indomethacin, a prototype prostaglandin-inhibiting agent, against early and late sequelae of radiation injury (after X-rays or gamma rays) in mice were investigated. The following tissues or organs were examined: hematopoietic tissue, esophagus, jejunum, colon, lung, hair follicles, and tissues involved in the development of radiation-induced leg contractures. In addition, the effect of indomethacin was tested against radiation-induced carcinogenesis. In all experiments, the radiation was delivered as a single dose. Indomethacin led to significant protection of hematopoietic tissue, by a factor of 1.3. There was also some protection against radiation-induced pneumonitis and against radiation-induced carcinogenesis (protection factor of 1.2). The other tissues tested showed no change in their radioresponse after being treated with indomethacin. Thus, indomethacin can act as a radioprotective agent against both early and late sequelae of radiation, but its effect is dependent on the tissue tested. This protection is smaller than that observed with WR-2721. However, indomethacin combined with WR-2721 produced a radioprotective effect greater than the radioprotection achieved by individual treatments.  相似文献   
999.
Based on the 1974–78 NOAA data, characteristic features of the variability of the Earth's radiation budget and its components over the area of the Northern Atlantic have been analyzed. Calculations of the mean square deviation for the ERB and its components have let to the conclusions that anomalous regions of maximum variability may be considered as energy-active zones.  相似文献   
1000.
The gas exchange portion of a phase-separated loop bioreactor was tested with respect to oxygen mass transfer and micromixing in accelerations of 0.01g, 1g, and 2g. A plot of the overall mass transfer coefficient versus gravity indicates the rate of oxygen transfer does not change as a function of acceleration. Also, it was determined that the micromixing did not exhibit significant changes in the various gravitational fields. These observations indicate the loop bioreactor should function independent of acceleration.  相似文献   
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