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   1781篇
  免费   248篇
  国内免费   90篇
航空   407篇
航天技术   877篇
综合类   25篇
航天   810篇
  2024年   2篇
  2023年   33篇
  2022年   33篇
  2021年   71篇
  2020年   63篇
  2019年   46篇
  2018年   60篇
  2017年   16篇
  2016年   29篇
  2015年   50篇
  2014年   179篇
  2013年   116篇
  2012年   74篇
  2011年   173篇
  2010年   118篇
  2009年   110篇
  2008年   106篇
  2007年   88篇
  2006年   82篇
  2005年   105篇
  2004年   65篇
  2003年   46篇
  2002年   59篇
  2001年   43篇
  2000年   50篇
  1999年   64篇
  1998年   38篇
  1997年   28篇
  1996年   29篇
  1995年   25篇
  1994年   10篇
  1993年   17篇
  1992年   10篇
  1991年   19篇
  1990年   14篇
  1989年   12篇
  1988年   22篇
  1987年   8篇
  1986年   4篇
  1984年   2篇
排序方式: 共有2119条查询结果,搜索用时 31 毫秒
81.
Spacecraft that are launched to operate in Earth orbit are susceptible to impacts by meteoroids and pieces of orbital debris (MMOD). The effect of a MMOD particle impact on a spacecraft depends on where the impact occurs, the size, composition, and speed of the impacting object, the function of the impacted system. In order to perform a risk analysis for a particular spacecraft under a specific mission profile, it is important to know whether or not the impacting particle (or its remnants) will exit the rear of an impacted spacecraft wall. A variety of different ballistic limit equations (BLEs) have been developed for many different types of structural wall configurations. BLEs can be used to optimize the design of spacecraft wall parameters so that the resulting configuration is able to withstand the anticipated variety of on-orbit high-speed impact scenarios. While the level of effort exerted in studying the response of metallic multi-wall systems to high speed particle impact is quite substantial, the extent of the effort to study composite material and composite structural systems under similar impact conditions has been much more limited. This paper presents an overview of the activities performed to assess the resiliency of composite structures and materials under high speed projectile impact. The activities reviewed will be those that have been aimed at increasing the level of protection afforded to spacecraft operating in the MMOD environment, and more specifically, on those activities performed to mitigate the mechanical and structural effects of an MMOD impact.  相似文献   
82.
CCSDS(空间数据系统咨询委员会)建议有利于增强测控系统互联互通互支持能力,满足未来航天任务对空间信息高速传输及灵活高效信息调度机制的要求,应当作为我国构建天地一体化信息网络的首选标准。提出了加强顶层设计、循序渐进地推进CCSDS建议在我国实现工程化应用的总体思路,并提出在应用过程中应当注重创新任务操作模式、关注信息安全、深化关键技术研究与验证。  相似文献   
83.
舱内航天服散热途径分析   总被引:1,自引:0,他引:1  
为分析常压下航天员穿着舱内航天服时的散热性能,6名健康男性青年按二次复合设计分组共进行24人次试验,经分析计算了获得了服装各散热途径的散热率随通风气源参数及人体活动水平变化的数学模型。对影响服装散热性能的因素及服装散热特性进行了分析讨论。  相似文献   
84.
AMDA (Automated Multi-Dataset Analysis), a new data analysis service, recently opened at the French Plasma Physics Data Center (CDPP). AMDA is developed according to the Virtual Observatory paradigm: it is a web-based facility for on-line analyses of space physics. Data may come from its own local database as well as remote ones. This tool allows the user to perform classical manipulations such as data visualization, parameter computation and data extraction. AMDA also offers innovative functionalities such as event searches on the content of the data in either visual or automated ways, generation, use and management of time tables (event lists). The general functionalities of AMDA are presented in the context of Space Weather with example scientific use cases.  相似文献   
85.
The main point of the paper is to use the simultaneous measurements of the energetic particle flux by TriTel and those of electron density by a Langmuir probe to study the question of to what extent solar electromagnetic and corpuscular radiation (galactic cosmic rays, particle precipitation from the radiation belts) are responsible for the ionization of the atmosphere. The electron density measured by the Langmuir probe is the sum of the ionization produced by the solar electromagnetic radiation and that due to the corpuscular radiation. The ionization produced by the solar electromagnetic radiation may be computed. The flux of energetic particles in an energy range may be determined by taking the difference between the threshold energy of the TriTel telescopes and the energy corresponding to the local cut-off rigidity. As the ESEO satellite will have a quasi-polar and circular orbit, the cut-off rigidity will change from low to high latitudes, thus enabling the assignment of different energy bands for the telescopes. Thus, it will be possible to determine which energy bands of particle produce ionization at different latitudes.  相似文献   
86.
Using data from the General Social Survey, this research identifies the issue public of US space policy. Highlighting the need to understand and identify the portion of the public that supports space activities, this study underscores the limited appeal of space for the public as a whole. We find that those who support space activities tend to be younger, male, Republican, and have a higher level of education and socioeconomic status. Because these characteristics make up a relatively small proportion of the American population, those supporting space activities must broaden the appeal of space, making it more accessible and understandable for those with whom the issue does not have much saliency.  相似文献   
87.
88.
现代小卫星与大众化空间时代   总被引:1,自引:1,他引:0  
通过论述现代小卫星技术30年的发展历程,总结其技术发展水平并举出现阶段的典型应用实例,讨论小卫星未来的发展方向,论述大众化空间与现代小卫星的关系,总结现代小卫星技术服务于大众化空间的各项特征。  相似文献   
89.
Progress in information technology has enabled to collecting data in near real-time. This significantly improves our ability to monitor space weather conditions. We deliver information on near real-time space weather conditions via the internet. We have started two collaborations with space weather users. One is a measurement of geomagnetically induced current (GIC) of power grids in collaboration with a Japanese power company. The other concerns radiation hazards for aircrews. The radiation exposure level for aircrews was been determined by the Japanese government by the end of 2005. The proposed upper limit is 5 mSV a year. We are actively seeking ways to contribute to this subject. Our activities at the Japanese space weather center are reported in this paper.  相似文献   
90.
Control Moment Gyroscope (CMG) is an effective candidate for agile satellites and large spacecraft attitude control because of its powerful torque amplification capability. The most serious situation, however, in using CMG is the inherent geometric singularity problem, where there’s no torque output along a particular direction. Space expansion method has been proposed in this work for the singularity analysis. Based on inverse mapping transformation, an expanded Jacobian matrix which is a full rank square matrix is obtained. The singular angle sets of the 3-parallel cluster and pyramid cluster are distinguished using space expansion method. An effective hybrid steering strategy, able to deal with the elliptic singularity, is further proposed. Simulation results demonstrate the excellent performance of the proposed steering logic compared to the generalized singular robust logic and pseudo inverse logic in terms of energy consumption and torque error.  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