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   18969篇
  免费   39篇
  国内免费   128篇
航空   10211篇
航天技术   5561篇
综合类   243篇
航天   3121篇
  2021年   158篇
  2018年   263篇
  2016年   175篇
  2014年   437篇
  2013年   521篇
  2012年   437篇
  2011年   661篇
  2010年   480篇
  2009年   833篇
  2008年   856篇
  2007年   439篇
  2006年   439篇
  2005年   420篇
  2004年   463篇
  2003年   548篇
  2002年   492篇
  2001年   600篇
  2000年   368篇
  1999年   462篇
  1998年   457篇
  1997年   332篇
  1996年   405篇
  1995年   472篇
  1994年   456篇
  1993年   365篇
  1992年   336篇
  1991年   249篇
  1990年   243篇
  1989年   413篇
  1988年   211篇
  1987年   240篇
  1986年   243篇
  1985年   650篇
  1984年   524篇
  1983年   411篇
  1982年   492篇
  1981年   622篇
  1980年   246篇
  1979年   189篇
  1978年   189篇
  1977年   146篇
  1976年   156篇
  1975年   190篇
  1974年   181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 15 毫秒
71.
This paper discusses the advantages of incorporating active sidesticks into a modern aircraft cockpit. Active sidestick controllers for manual pilot inputs in pitch and roll are examined for commercial transport aircraft. Options and requirements for sidesticks are reviewed. The recommendation of an active sidestick controller is developed providing both cross-cockpit coupling and autopilot backdrive capability. These characteristics provide pilot cues identical to traditional cable-linked column/yoke configurations  相似文献   
72.
Software applications that require a high learning curve, a mountain of documentation, and weeks of training should be things of the past. Today's applications need to be simple to learn and to use. The human/computer interface should be intuitive and consistent. Context sensitive help should be available to keep the user on track. This paper provides some guidelines for taking commercial world concepts and applying them to the Automatic Test Equipment world. Examples included are from the Integrated Maintenance Information System (IMIS)  相似文献   
73.
This article is a synthesis of interviews with women working and writing in the areas of space law and policy. One initial focus of the interviews was to explore whether, as a result of the growing numbers of women working in aerospace-related fields, there might be certain women's agendas developing as well. Taken together, the responses of the 10 women interviewed clearly acknowledge the importance of the feminine perspective, while rejecting the appropriateness or necessity of concentration on specific ‘women's issues’ and favouring cooperative efforts to address problems of global concern.  相似文献   
74.
Recent multiwavelength monitoring of active galactic nuclei (AGN), particularly with the IUE satellite, has produced extraordinary advances in our understanding of the energy-generation mechanism(s) in the central engine and of the structure of the surrounding material. Examples discussed here include both ordinary AGN and blazars (the collective name for highly variable, radio-loud AGN like BL Lac objects and Optically Violently Variable quasars). In the last decade, efforts to obtain single-epoch multiwavelength spectra led to fundamentally new models for the structure of AGN, involving accretion disks for AGN and relativistic jets for blazars. Recent extensions of multiwavelength spectroscopy into the temporal domain have shown that while these general pictures may be correct, the details were probably wrong. Campaigns to monitor Seyfert 1 galaxies like NGC 4151, NGC 5548 and Fairall 9 at infrared, optical, ultraviolet and X-ray wavelengths indicate that broad-emission line regions are stratified by ionization, density, and velocity; argue against a standard thin accretion disk model; and suggest that X-rays represent primary rather than reprocessed radiation. For blazars, years of radio monitoring indicated emission from an inhomogeneous synchrotron-emitting plasma, which could also produce at least some of the shorter-wavelength emission. The recent month-long campaign to observe the BL Lac object PKS 2155-304 has revealed remarkably rapid variability that extends from the infrared through the X-ray with similar amplitude and little or no discernible lag. This lends strong support to relativistic jet models and rules out the proposed accretion disk model for the ultraviolet-X-ray continuum.  相似文献   
75.
Computational investigations and experimental measurements were performed to evaluate the Space Shuttle UHF communication system performance for payload bay antenna at the proposed new location. To insure adequate communication coverage at relocated new location, the link margin for the Extravehicular Activity (EVA) astronauts and between Space Shuttle Orbiter and International Space Station (SSO-ISS) during rendezvous were analyzed. The multipath effects from the vehicle structures surrounding the antenna were investigated. The Radio Frequency (RF) electromagnetic radiation to the Orbiter Docking System (ODS) pyrotechnics was also analyzed to ensure the EMC/EMI compliances.  相似文献   
76.
77.
A portable millimeter wave test radar system, also suitable for battery operation, gives interesting possibilities for clutter recordings at hard-to-reach sites. The designed system covers all common radar frequencies from the Ka- to V-bands and enables spatial detection of targets or clutter elements within an adjustable time gate, whereby spatial clutter profiles of rain can be analyzed. The construction allows full operation with non-scanning antennas as well. This is advantageous when measuring temporal RCS variations of selected targets or surface clutter from snow dunes.  相似文献   
78.
This review assumes that many non-US readers may not be well-informed about the steps and work in radar development in the US after WW II to the present. Many know MIT by name and recall the famous Radiation Laboratory Series. But the more recent technical history has been less in the "public domain." In an attempt to correct this, one of the key institutions in the field, the MIT Lincoln Laboratory two years ago produced a special issue of their regular publication. Although the document currently at hand is not a book in the strict sense, the size, shape, and editorial comprehensiveness of the MIT Lincoln Laboratory Journal's Fifty-Year Anniversary Issue (12, 2, 2000) justifies calling this article being treated as a book review.  相似文献   
79.
Japanese treefrogs (Hyla japonica) are planned to be sent to the space station MIR. Experimental system was developed to observe their behaviors under microgravity.  相似文献   
80.
An FM-CW radar front-end was fabricated in an integrated manner at 60 GHz by using the NRD guide. Main emphasis was placed on compactness in size and high-precise operation in performance. The fabricated radar consists of an FM Gunn oscillator, a balanced mixer, and a planar antenna fed by leaky NRD guide with a mechanically beam-scanning performance. All circuit components and the antenna were contained in a compact housing of 170 /spl times/ 140 mm in area and 25 mm in thickness, and thus, a thin type of millimeter-wave radar front-end was successfully developed. Moreover, an error of distance estimation was measured to be less than a distance of 0.7 m.  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