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   5383篇
  免费   7篇
  国内免费   14篇
航空   2296篇
航天技术   1930篇
综合类   15篇
航天   1163篇
  2021年   45篇
  2018年   108篇
  2017年   91篇
  2016年   82篇
  2015年   37篇
  2014年   118篇
  2013年   150篇
  2012年   139篇
  2011年   230篇
  2010年   167篇
  2009年   250篇
  2008年   294篇
  2007年   161篇
  2006年   117篇
  2005年   161篇
  2004年   176篇
  2003年   178篇
  2002年   123篇
  2001年   187篇
  2000年   87篇
  1999年   111篇
  1998年   137篇
  1997年   102篇
  1996年   106篇
  1995年   143篇
  1994年   151篇
  1993年   79篇
  1992年   101篇
  1991年   39篇
  1990年   52篇
  1989年   93篇
  1988年   41篇
  1987年   42篇
  1986年   58篇
  1985年   173篇
  1984年   132篇
  1983年   107篇
  1982年   103篇
  1981年   195篇
  1980年   45篇
  1979年   39篇
  1978年   43篇
  1977年   40篇
  1976年   36篇
  1975年   47篇
  1974年   43篇
  1973年   37篇
  1972年   43篇
  1971年   25篇
  1970年   25篇
排序方式: 共有5404条查询结果,搜索用时 248 毫秒
501.
We present here new XMM-Newton observations of 3 relatively cool clusters at z ≈ 0.4, complemented by archival observations of 3 other clusters at similar redshift. We derived the MT and RT relations from the hydrostatic equation using an isothermal temperature distribution.  相似文献   
502.
The region of South Atlantic Geomagnetic Anomaly (SAGA) was investigated by the Intercosmos-Bulgaria-1300 satellite, launched on August 7, 1981. On the basis of data obtained from 15 orbits during increased geomagnetic activity in August 1981, a map of the Anomaly was elaborated. Two centres of activity were identified. By means of the EMO-5 electrophotometer on board the Intercosmos-Bulgaria-1300 satellite, the atmosphere glow in lines λ 5577 Å, λ 6300 Å and λ 4278 Å was studied.  相似文献   
503.
Thermospheric temperature, composition and wind measurements from the Dynamics Explorer satellite (DE-2) are interpreted using a three dimensional, multiconstituent spectral model. The analysis accounts for tides driven by the absorbed solar radiation as well as energy and momentum coupling involving the magnetosphere and lower atmosphere. We discuss phenomena associated with the annual tide, polar circulation, magnetic storms and substorms.  相似文献   
504.
Monopulse radars have played an important role in air and missile defense systems since the development of the monopulse technique in the late 1940s. This paper outlines the application of monopulse radars in Russian defense systems, starting with the Moscow ABM system and continuing in instrumentation and air defense radars now widely deployed in Russia and elsewhere  相似文献   
505.
The needs of coastal engineering are different from open ocean monitoring or fisheries potential monitoring. A high resolution of 20 meters is essential for identifying several processes that are taking place and influences the coast. A case of application of Landsat MSS to evaluate littoral process highlights the needs for improved spatial resolution. Nevertheless Landsat MSS data for 1981 and 1982 showed that the extent of accretion and erosion that has taken place during this period. Some problems to be addressed for marine remote sensing are mainly regarding the need for insitu data. These aspects are mentioned.  相似文献   
506.
Global Positioning System (GPS) receiver on the CHAllenging Mini-satellite Payload (CHAMP) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, one of four on board the TIMED satellite, provide middle atmosphere temperature profiles by Radio Occultation (RO) and limb viewing infrared emission measurements, respectively. These temperature profiles retrieved by two different techniques in the stratosphere are compared with each other using more than 1300 correlative profiles in March, September and December 2005. The over-all mean differences averaged over 15 and 35 km are approximately −2 K and standard deviation is less than 3 K. Below 20 km of altitude, relatively small mean temperature differences ∼1 K are observed in wide latitudinal range except for June (during the SABER nighttime observation). In the middle to low latitudes, between 30°S and 30°N, the temperature difference increases with height from ∼0–1 K at 15 km, to ∼−4 K at 35 km of altitude. Large temperature differences about −4 to −6 K are observed between 60°S and 30°N and 31–35 km of altitude for all months and between 0° and 30°N below 16 km during June (nighttime).  相似文献   
507.
Complex honeycomb space structures (i.e. antennas, solar panels, etc.) must be inspected and accurately tested before flight.The thermography can be employed with success for the detection of the position of defects (delaminations, noneffective bondings, cracks, etc.) and for the evaluation of their size and geometry in all the cases in which the defect acts as a thermal resistance due to the low conductivity of the air filling the defect volume.The basic idea is to create in the specimen a heat flow distribution that is altered by the presence of the defect.The surface temperature distribution is then measured by means of a thermograph and is correlated with the presence of the defect.A numerical analysis and preliminary experiments have been carried out which show the feasibility of the method as applied to honeycomb structures.  相似文献   
508.
509.
Using full-disk observations obtained with the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) spacecraft, we present variations of the solar acoustic mode frequencies caused by the solar activity cycle. High-degree (100 < ? < 900) solar acoustic modes were analyzed using global helioseismology analysis techniques over most of solar cycle 23. We followed the methodology described in details in [Korzennik, S.G., Rabello-Soares, M.C., Schou, J. On the determination of Michelson Doppler Imager high-degree mode frequencies. ApJ 602, 481–515, 2004] to infer unbiased estimates of high-degree mode parameters ([see also Rabello-Soares, M.C., Korzennik, S.G., Schou, J. High-degree mode frequencies: changes with solar cycle. ESA SP-624, 2006]). We have removed most of the known instrumental and observational effects that affect specifically high-degree modes. We show that the high-degree changes are in good agreement with the medium-degree results, except for years when the instrument was highly defocused. We analyzed and discuss the effect of defocusing on high-degree estimation. Our results for high-degree modes confirm that the frequency shift scaled by the relative mode inertia is a function of frequency and it is independent of degree.  相似文献   
510.
The first application of a magnetic encoder in a space-to-space command link was proven successful in the Gemini rendezvous missions. The functional aspects of the command link and the mechanization of the encoder are described.  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