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   264篇
  免费   41篇
  国内免费   31篇
航空   147篇
航天技术   97篇
综合类   39篇
航天   53篇
  2024年   3篇
  2023年   6篇
  2022年   10篇
  2021年   15篇
  2020年   11篇
  2019年   5篇
  2018年   13篇
  2017年   8篇
  2016年   19篇
  2015年   16篇
  2014年   19篇
  2013年   6篇
  2012年   9篇
  2011年   8篇
  2010年   13篇
  2009年   9篇
  2008年   17篇
  2007年   6篇
  2006年   14篇
  2005年   8篇
  2004年   13篇
  2003年   21篇
  2002年   12篇
  2001年   14篇
  2000年   13篇
  1999年   5篇
  1998年   14篇
  1997年   11篇
  1996年   5篇
  1995年   2篇
  1994年   1篇
  1993年   4篇
  1992年   2篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
排序方式: 共有336条查询结果,搜索用时 62 毫秒
151.
基于COM的可互换虚拟仪器驱动技术研究   总被引:2,自引:0,他引:2  
提出了基于COM(Component Object Model)的可互换虚拟仪器驱动器的模型,分析了其实现互换的方法,并提出了在该模型下的仪器仿真驱动方案,最后将该模型的驱动器和现有VPP(VXI Plug&Play)、IVI(Interchangeable Virtual Instrument)驱动器进行了对比分析,其结果表明,基于COM的可互换虚拟仪器驱动器在互换性、平台适应能力、远程访问能力以及仿真能力等方面具有更加优良的综合性能.    相似文献   
152.
目标与背景的对比度分析及其应用   总被引:5,自引:0,他引:5  
较深入地分析了目标与背景的对比度及其时间、空间和光谱特性,介绍了基于目标与背景的对比度的红外对抗和反对抗措施,如变频技术、变向技术、假目标等红外对抗措施以及太赫兹波探测、时间鉴别法和光谱鉴别法等红外反对抗措施.  相似文献   
153.
Abstract

Events, like objects, can be decomposed into parts. Path, the spatiotemporal trajectory of an object during an event, is the most commonly labeled event feature across the world's languages, provides important social information, and is increasingly central to theories of general event segmentation. However, little is understood about how adults visually segment paths. We apply theories developed for object segmentation to help understand path segmentation. Overall subjects segmented equivalent object shapes and event paths in similar ways following patterns predicted by Singh and Hoffman's (2001) Singh, M. and Hoffman, D. D. 2001. “Parts-based representations of visual shape and implications for visual cognition.”. In From fragments to objects—Segmentation and grouping in vision Edited by: Shipley, T. F. and Kellman, P. J. 401459. New York, NY: Elsevier Science..  [Google Scholar] geometric analysis of object parts. There were two notable differences between object and event segmentation: (1) event parsing occurred at points of negative curvature minima and positive curvature maxima as opposed to simply negative curvature minima; and (2) event parsing was more frequent and variable than object parsing. Implications of these results for event perception and categorization are discussed.  相似文献   
154.
In the framework of the study of supernova remnants and their complex interaction with the interstellar medium and the circumstellar material, we focus on the galactic supernova remnant W49B. Its morphology exhibits an X-ray bright elongated nebula, terminated on its eastern end by a sharp perpendicular structure aligned with the radio shell. The X-ray spectrum of W49B is characterized by strong K emission lines from Si, S, Ar, Ca, and Fe. There is a variation of the temperature in the remnant with the highest temperature found in the eastern side and the lowest one in the western side. The analysis of the recent observations of W49B indicates that the remnant may be the result of an asymmetric bipolar explosion where the ejecta are collimated along a jet-like structure and the eastern jet is hotter and more Fe-rich than the western one. Another possible scenario associates the X-ray emission with a spherical explosion where parts of the ejecta are interacting with a dense belt of ambient material. To overcome this ambiguity we present new results of the analysis of an XMM-Newton observation and we perform estimates of the mass and energy of the remnant. We conclude that the scenario of an anisotropic jet-like explosion explains quite naturally our observation results, but the association of W49B with a hypernova and a γ-ray burst, although still possible, is not directly supported by any evidence.  相似文献   
155.
研究了SNMP及其相关协议,讨论了协议实现的方案,并以以太网相连的工作站为开发平台,实现了网络管理软件,完成了SNMP规定的基本功能。  相似文献   
156.
Although considerations of discourse coherence and cognitive processing suggest that communicators should adopt consistent perspectives when describing spatial scenes, in many cases they switch perspectives. Ongoing research examining cognitive costs indicates that these are small and exacted in establishing a mental model of a scene but not in retrieving information from a well-known scene. A perspective entails a point of view, a referent object, and terms of reference. These may change within a perspective, exacting cognitive costs, so that the costs of switching perspective may not be greater than the costs of maintaining the same perspective. Another project investigating perspective choice for self and other demonstrates effects of salience of referent object and ease of terms of reference. Perspective is mixed not just in verbal communications but also in pictorial ones, suggesting that at times, switching perspective is more effective than maintaining a consistent one.  相似文献   
157.
线画图是人们之间以及人与计算机之间交换三维物体信息的主要来源之一。在计算机视觉研究领域中,线画图标记是对物体进行定性分析的一种有效方法,通过线画图的一致性标记,可排除许多不可能的物体结构,为线画图的定量分析减少工作量。曲面立休的线画图标记是一项非常困难的多作。回转体是一类特残的曲面立体,本文在前人线画图标记的研究成果基础上研究了回转体立体线画图的标记形式,得出了回转体线画图标记的新的节点型式。新的标记方法适用于由平面立体和回转体组合而成的复杂立体的线画图。  相似文献   
158.
针对如何部署光学探测设备才能更好实现对空间目标的高精度高频度监视问题,考虑光照条件、相对关系及探测性能,构建了天/地基空间目标探测与成像仿真模型;按照轨道特征选取了94颗LEO(Low Earth Orbit,低地球轨道)卫星、63颗GEO(Geosynchronous Earth Orbit,地球同步轨道)卫星和18颗大椭圆轨道卫星,选用春夏秋冬典型季节的特定时间长度,仿真分析了国内地基、南北极科考站、LEO卫星、准GEO卫星等多平台光电手段的位置探测和成像观测能力;比对分析地基平台纬度和季节、天基平台轨道高度和倾角对探测能力的影响得出:南北极科考站相比于国内站点可提高重点季节的探测时效性,98°倾角LEO平台对低轨目标成像时效性方面更具优势,等.在此基础上,提出了我国空间目标光电观测设备天地一体的布局构想.  相似文献   
159.
卢万杰  徐青  蓝朝桢  吕亮 《宇航学报》2020,41(8):1105-1114
针对空间目标态势威胁响应和预警研究不完善的问题,为实现空间目标行为和事件的智能推理、实时响应和主动预警,保障航天活动和空间利益,提出面向行为与事件的空间目标态势本体模型(BEO-SO2)。基于基本形式本体(BFO),构建空间目标态势行为与事件本体模型。在统一时空框架下建立空间目标关系模型,实现空间目标行为执行和事件发生过程的动态推演。以空间目标碰撞威胁为背景,设计对象实体等级体系和碰撞威胁行为与事件要素,建立碰撞威胁推理规则,基于空间目标态势行为与事件本体进行实现、验证与展示。结果表明,空间目标态势行为与事件本体能够实现空间目标碰撞威胁的等级推理与预警,并指导进一步的空间活动,为航天任务与空间活动提供有效保障。  相似文献   
160.
Space object material identification method based on Tucker decomposition is proposed and demonstrated experimentally. Space target generally has a low spatial resolution because of the limitation in detection distance. Hyperspectral imaging (HSI) technology can capture the image from visible light to shortwave infrared continuously while providing the spatial and spectral information of the target, thereby introducing a new space target detection and identification approach. However, the data obtained by the HSI system often contain mixed pixels, thereby causing difficulties in target material identification. In this work, a material identification method of hyperspectral data based on Tucker decomposition is proposed by combining mixed spectral theory with tensor decomposition. The feasibility of the method is verified by using satellite model hyperspectral data with different spatial resolutions compared with the endmember obtained from the non-negative matrix decomposition (NMF), independent component analysis (ICA), tensor singular value decomposition (t-SVD). The average CORR of NMF, ICA, t-SVD and the proposed method is 0.2694, 0.5818, 0.6397 and 0.937, correspondingly. Therefore, the proposed method has demonstrated a more remarkable performance in terms of material identification, the analysis results of the material abundance distribution that used the proposed method.  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