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   8020篇
  免费   13篇
  国内免费   17篇
航空   3942篇
航天技术   2670篇
综合类   194篇
航天   1244篇
  2021年   66篇
  2018年   146篇
  2017年   90篇
  2016年   97篇
  2014年   169篇
  2013年   191篇
  2012年   212篇
  2011年   299篇
  2010年   194篇
  2009年   338篇
  2008年   392篇
  2007年   201篇
  2006年   167篇
  2005年   196篇
  2004年   195篇
  2003年   248篇
  2002年   243篇
  2001年   314篇
  2000年   142篇
  1999年   189篇
  1998年   233篇
  1997年   165篇
  1996年   188篇
  1995年   248篇
  1994年   236篇
  1993年   140篇
  1992年   183篇
  1991年   91篇
  1990年   84篇
  1989年   191篇
  1988年   82篇
  1987年   93篇
  1986年   80篇
  1985年   218篇
  1984年   184篇
  1983年   159篇
  1982年   180篇
  1981年   239篇
  1980年   89篇
  1979年   72篇
  1978年   79篇
  1977年   52篇
  1976年   60篇
  1975年   65篇
  1974年   61篇
  1973年   46篇
  1972年   66篇
  1971年   62篇
  1970年   44篇
  1969年   47篇
排序方式: 共有8050条查询结果,搜索用时 421 毫秒
731.
It is important to use models developed specifically for the equatorial ionospheric estimation for real-time applications, particularly in Satellite Navigation. This work demonstrates a methodology for improved predictions of VTEC in real time using the model developed for the equatorial ionosphere by the authors. This work has been done using TEC data of the low solar activity period of 2005 obtained using dual frequency GPS receivers installed under the GAGAN project of ISRO. For the purpose, the model is first used in conjunction with Kriging technique. Improvement in accuracy is observed when compared with the estimations from the model alone using the measurements as true reference. Further improvement is obtained by Bayesian combination of these estimates with independent Neural Network based predictions. Statistical performance of improvement is provided. An improvement of ∼1 m in confidence level of estimation of VTEC is obtained.  相似文献   
732.
Security applications of computer vision   总被引:1,自引:0,他引:1  
In an age which bears witness to a proliferation of Closed Circuit Television (CCTV) cameras for security and surveillance monitoring, the use of image processing and computer vision techniques which were provided as top end bespoke solutions can now be realised using desktop PC processing. Commercial Video Motion Detection (VMD) and Intelligent Scene Monitoring (ISM) systems are becoming increasingly sophisticated, aided, in no small way, by a technology transfer from previously exclusively military research sectors. Image processing is traditionally concerned with pre-processing operations such as Fourier filtering, edge detection and morphological operations. Computer vision extends the image processing paradigm to include understanding of scene content, tracking and object classification. Examples of computer vision applications include Automatic Number Plate Recognition (ANPR), people and vehicle tracking, crowd analysis and model based vision. Often image processing and computer vision techniques are developed with highly specific applications in mind and the goal of a more global understanding computer vision system remains, at least for now, outside the bounds of present technology. This paper will review some of the most recent developments in computer vision and image processing for challenging outdoor perimeter security applications. It also describes the efforts of development teams to integrate some of these advanced ideas into coherent prototype development systems  相似文献   
733.
734.
The basic principles of selecting some design parameters of a lightweight airplane for the contemporary Russian market are presented. Recommendations for selecting these parameters with the service requirements specified are given based on the study performed.  相似文献   
735.
The present experimental knowledge of electron precipitation in the auroral zone is summarized, using observations primarily from riometer, balloon, rocket and satellite studies. This includes the association of electron precipitation events with aurora, magnetic disturbances as well as temporal and spatial aspects of the particle bombardment.  相似文献   
736.
737.
Flutter and time errors are critical factors in all instrumentation recording. This paper presents analytically the relationship between flutter, time base error, and time base error difference (sometimes called jitter), and the effects of these factors on direct and FM recording. Methods of measuring these quantities are discussed and experimental examples are given. Finally, a measurement method for the interchannel time error is presented, and some trends of correlation among all channels are discussed.  相似文献   
738.
The possibility of using solar sails in Earth orbit is investigated. The characteristic parameters of a solar sail consisting of six spheres attached by mutually orthogonal long rods are estimated.  相似文献   
739.
S 《航空港》2012,(5):60-65
到过法国的旅游者,一般都知道巴黎有两个著名的歌舞表演厅,—个是位于市中心香榭丽舍大道的丽都,一个是位于城北蒙马特高地脚下白色广场附近的红磨坊。屋顶上装着长长的、闪烁着红光的大叶轮的红磨坊则是较为地道的法国式歌舞厅。MCG公司以法国红磨坊红磨坊为设计理念,把次情景带进了香港兰桂坊酒店Bisous酒吧。然而Bisous的设计并非照搬红色的浪漫风情,而是将未来趋势的一种极简概念设计结合了新的元素,将红磨坊的主题得以抽象化和现代化。以现今最时新的手法,完整地呈现了"红磨坊"的内心世界,概念可能不算创新,但精彩程度符合了当下时尚的思想!  相似文献   
740.
Amphibians possess the ability to vomit in response to a variety of stimuli that provoke emesis in mammals. Pharmacological studies have establish that the ejection of gastric contents and the basic mechanism for vomiting have been phylogenetically conserved among these tetrapods. As part of on-going comparative studies on emesis in vertebrates, we previously documented that some postmetamorphic anurans and salamander larvae experience motion-induced emesis when exposed to the provocative stimulus of parabolic aircraft flight. However, more recent experiments suggest that there are strict conditions for inducing emesis in amphibians exposed to parabolic flight and that amphibians are not as sensitive to this stimulus as mammals. Further studies on emesis in lower vertebrates may help us understand the processes that cause emesis in abnormal gravitational regimes.  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