全文获取类型
收费全文 | 1540篇 |
免费 | 228篇 |
国内免费 | 268篇 |
专业分类
航空 | 1280篇 |
航天技术 | 298篇 |
综合类 | 210篇 |
航天 | 248篇 |
出版年
2024年 | 11篇 |
2023年 | 26篇 |
2022年 | 23篇 |
2021年 | 64篇 |
2020年 | 57篇 |
2019年 | 62篇 |
2018年 | 69篇 |
2017年 | 79篇 |
2016年 | 120篇 |
2015年 | 66篇 |
2014年 | 113篇 |
2013年 | 90篇 |
2012年 | 101篇 |
2011年 | 155篇 |
2010年 | 70篇 |
2009年 | 102篇 |
2008年 | 112篇 |
2007年 | 84篇 |
2006年 | 84篇 |
2005年 | 78篇 |
2004年 | 68篇 |
2003年 | 50篇 |
2002年 | 77篇 |
2001年 | 44篇 |
2000年 | 31篇 |
1999年 | 35篇 |
1998年 | 37篇 |
1997年 | 21篇 |
1996年 | 14篇 |
1995年 | 24篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 14篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 2篇 |
1987年 | 1篇 |
排序方式: 共有2036条查询结果,搜索用时 265 毫秒
851.
介绍了波音737飞机舱门排故的一般性原则,针对常见故障,分析了故障原因和故障隔离方法,对排故人员有一定的参考作用. 相似文献
852.
为解决采用静态框架描述故障案例存在的问题,提出一种基于知网的软件故障案例语义表示方法.通过分析案例的语义匹配准则,给出表示方法的具体语法描述规范.在此基础上,结合实际案例,分析软件故障领域中实体、事件、属性和属性值4类义原及其相互关系,并用KDML语言进行统一描述.实验表明,与传统基于关键字的模糊匹配方法相比,采用基于... 相似文献
853.
854.
855.
针对近距航天器测距的需要,将CCSDS(空间数据系统咨询委员会)近距-1协议的定时业务与微波双向单程测距法相结合进行测距。该法以直序扩频技术来获得高精度传输帧ASM(附属同步标识)最后1位下降沿的时刻,并以时间码形式,通过帧数据域在测距星之间相互对传,综合考虑协议给出的信号物理特性,对所给出的方法进行了误差分析。分析表明,航天器之间距离不远,相对速度不大时,该法具有较高精度,且与数据通信共用1套设备,降低了成本。 相似文献
856.
Daniele Bortoluzzi Pierre A. Mäusli Riccardo Antonello Philipp M. Nellen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In the frame of space missions, mechanisms often constitute critical systems whose functionality and performance need to be tested on ground before the mission launch. The LISA scientific space mission will detect gravitational waves by measuring the relative displacement of pairs of free-floating test masses set into geodesic motion onboard of three spacecrafts. Inside each satellite, the injection of the test masses from the caged configuration into the geodesic trajectory will be performed by the grabbing positioning and release mechanism. To provide a successful injection, the test masses must be dynamically released with a minimal residual velocity against adhesion with the holding device. A parameter that determines the test mass residual velocity is the quickness of the retraction of the holding device. The need arises then to characterize the dynamic response of the release mechanism in order to predict its behaviour in the in-flight conditions. Once a validated model of the mechanism is available, the compliance of the system to the tight requirement on the maximum allowed residual velocity of the test mass may be verified. Starting from an electro-mechanical model of the mechanism dynamics, this paper presents the results of the experimental identification of its relevant parameters. 相似文献
857.
858.
John Bateman 《Spatial Cognition & Computation》2013,13(4):295-314
Abstract Ernest Davis' article “Qualititative Spatial Reasoning in Interpreting Text and Narrative” discusses challenges that the interpretation of natural language appears to raise for the formalization of commonsense spatial reasoning. Davis finds these to be of “surprising logical complexity,” but also “erratic” in that they do not show a logical structuring of the problem space that could guide productive research. In this response I argue that much of the apparent lack of structure Davis laments is due to the very style of formal modeling he pursues. By augmenting logical considerations with substantial input from other disciplines and by adopting a heterogeneous and modular approach to formalization, I suggest that the problem space is by no means as ill-structured as Davis presents it. 相似文献
859.
We examined the use of hand gestures while people solved spatial reasoning problem in which they had to infer motion from static diagrams (mental animation problems). In Experiment 1, participants were asked to think aloud while solving mental animation problems. They gestured on more than 90% of problems, and most gestures expressed information about the component motions that was not stated in words. Two further experiments examined whether the gestures functioned in the mechanical inference process, or whether they merely served functions of expressing or communicating the results of this process. In these experiments, we examined the effects of instructions to think aloud, restricting participants' hand motions, and secondary tasks on mental animation performance. Although participants who were instructed to think aloud gestured more than control groups, some gestures occurred even in control conditions. A concurrent spatial tapping task impaired performance on mechanical reasoning, whereas a simple tapping task and restricting hand motions did not. These results indicate that gestures are a natural way of expressing the results of mental animation processes and suggest that spatial working memory and premotor representations are involved in mental animation. They provide no direct evidence that gestures are functional in the thought process itself, but do not rule out a role for overt gestures in this type of spatial thinking. 相似文献
860.