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   18381篇
  免费   33篇
  国内免费   123篇
航空   9933篇
航天技术   5504篇
综合类   241篇
航天   2859篇
  2021年   155篇
  2018年   217篇
  2016年   159篇
  2014年   435篇
  2013年   519篇
  2012年   416篇
  2011年   611篇
  2010年   421篇
  2009年   776篇
  2008年   809篇
  2007年   389篇
  2006年   426篇
  2005年   402篇
  2004年   454篇
  2003年   534篇
  2002年   478篇
  2001年   573篇
  2000年   363篇
  1999年   465篇
  1998年   446篇
  1997年   326篇
  1996年   390篇
  1995年   458篇
  1994年   454篇
  1993年   357篇
  1992年   329篇
  1991年   250篇
  1990年   236篇
  1989年   416篇
  1988年   205篇
  1987年   243篇
  1986年   237篇
  1985年   646篇
  1984年   524篇
  1983年   416篇
  1982年   489篇
  1981年   612篇
  1980年   246篇
  1979年   185篇
  1978年   189篇
  1977年   144篇
  1976年   156篇
  1975年   189篇
  1974年   182篇
  1973年   161篇
  1972年   188篇
  1971年   148篇
  1970年   143篇
  1969年   147篇
  1967年   142篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
381.
382.
A methodology for addressing support equipment obsolescence   总被引:2,自引:0,他引:2  
The rapid growth of technology over the last twenty years is providing vastly improved capabilities for both avionics and avionics test systems. Unfortunately, an environment of rapid technological growth breeds a corresponding environment of rapid technological obsolescence. Test systems developed fifteen years ago are becoming increasingly more difficult to support due to obsolescence issues and, additionally, such a test system does not reflect the current state-of-the-art for automatic test equipment. The ability of a test system to evolve is essential to providing cost-effective support systems for electronic systems. The F-15 Tactical Electronic Warfare System (TEWS) Intermediate Support System (TISS) was developed under the Modular Automatic Test Equipment (MATE) guidelines to support the suite of F-15 electronic warfare LRUs. MATE imposed hardware architecture constraints, which were factors that contributed to its abandonment. However, the modular aspect of MATE has provided a system that can easily evolve with technological advancements. Modularity is the cornerstone of modern software systems and this is the aspect that has been exploited in the evolution of the TISS  相似文献   
383.
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   
384.
A number of previously unclassified multiplets of Fexiv, xiii, xii, and xi produced by transitions of the type 3s 23p n -3s3p n+1 are identified in the XUV spectrum of the Sun. The iron lines account for most of the previously unidentified strong lines between 330 and 370 Å. Solar observations of especial value for the investigation of the 300–400 Å region were the slitless spectroheliograms of September 22, 1968 (Purcell and Tousey, 1969) and November 4, 1969 (Tousey, 1971) — on which the image of a flare was recorded. Other solar identifications in the same spectral region include the resonance lines of Nixvii and Nixviii, and one 3p-3d multiplet of Fexiii. The solar blend at 417 Å involving the Fexv inter-combination line and Sxiv is resolved.  相似文献   
385.
386.
This correspondence describes a novel electronically tracking antenna system for satellite reception in the VHF range. The "hedgehog" antenna consists of several antennas directed in different directions to cover the whole sky. An electronic switch, controlled by the satellite receiver, connects the receiver to the antenna from which the desired satellite signal is obtained. This system is especially suitable for unmanned reliable receiving stations if an antenna gain of the order of 10 dB is enough.  相似文献   
387.
The determination of the range of radar is carried out according to statistical methods which are not always immediate. For this reason, a parametrical method is proposed which condenses the elements necessary for this calculation in the form of three abaci. Furthermore, a general formula condenses this result, and the formula is extended to the other transmission systems.  相似文献   
388.
A position fix in a passive mode using satellites usually necessitates an expensive computer or lengthy hand calculation. This is the largest drawback of passive navigation and it would be more desirable if the user could find his position by a mere glance at a chart and table, as one uses Loran. The first step toward this goal is to use a synchronous satellite because it simplifies the problem. The next step is to find the position of the user by a Loran type of chart, which is universal, and correct this apparent position by looking at a special table which is made according to the amount of perturbation of both the satellite and the user's position. An example of the position fix along the route between Yokohama to Hawaii is shown. The concept can be extended to orbiting satellites due to the rules which govern the motion of satellites, if the fix accuracy is in the order of 2 to 5 miles. This method should be more accurate than the common sextant and more practical due to the fact that the satellite can be used at any time and in any weather. As a total system, it will be better than Omega because it could provide additional navigation information such as communication or traffic control by using satellites.  相似文献   
389.
390.
An expression is derived for the cost resultingfrom the stabilization of a satellite using aspecific optimal control (SOC). An exampleis given in which the optimal and SOC yieldvirtually identical costs.  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