全文获取类型
收费全文 | 58篇 |
免费 | 25篇 |
国内免费 | 24篇 |
专业分类
航空 | 70篇 |
航天技术 | 13篇 |
综合类 | 1篇 |
航天 | 23篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 5篇 |
2013年 | 3篇 |
2012年 | 4篇 |
2011年 | 3篇 |
2010年 | 5篇 |
2009年 | 8篇 |
2008年 | 1篇 |
2007年 | 1篇 |
2006年 | 4篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有107条查询结果,搜索用时 31 毫秒
51.
52.
《中国航空学报》2021,34(10):220-236
Research on the transition phase of tail-sitter Unmanned Aerial Vehicles (UAVs) is crucial for trajectory planning and performance analysis. This study focuses on the analysis of the transition characteristics and path of a small dual-rotor tail-sitter UAV, including static and dynamic computations. The system input time delay and actuator dynamics are specifically considered during the dynamic analysis, and these actual physical properties ensure that the computation results are reliable and reasonable. The UAV steady-state limit is obtained through static analysis, which is also adopted to verify the correctness of the dynamic results. In regard to the dynamic analysis, several typical transition approaches are computed based on different initial states and optimization objective functions, and the different computations are applicable under specific task conditions. The off-line dynamic results of the transition path and actuator output sequence could also be adopted as reference values for the transition process during real flight. A comparison of the static and dynamic results illustrates the necessity of combining these two methods for UAV transition characteristic analysis. Furthermore, the UAV conceptual parameters related to the transition path are also studied, and the obtained quantitative characteristics provide feedback for the UAV conceptual design. 相似文献
53.
探索涡扇发动机加力过程中喷管喉部面积与加力供油量的匹配机理,寻找改善发动机加力特性的技术途径对发动机加力系统设计工作具有重要的意义。结合某型涡扇发动机加力供油时序、燃油填充时序和尾喷管面积调节规律,建立考虑加力燃烧室和外涵道动态容积效应的发动机加力接通与切断过程数学模型,进行涡扇发动机加力过程的特性计算,研究喷管喉部面积调节延迟对加力过渡过程的影响。结果表明:在加力接通过程中,喷管延迟调节对风扇稳定裕度和转速的影响不大于 4%,对主机稳定裕度和转速的影响不大于 1%;当喷管面积调节延迟或出现卡滞故障时,为了保证主机稳定工作,可适当减少加力供油量以改善喷管流通能力,提高安全稳定裕度;特殊情况下,则应继续增加主燃烧室供油量,以保证加力推力。 相似文献
54.
55.
SiⅡ辐射线源区的高度表征了太阳大气过渡区的底层高度.通过对超紫外线的辐射强度结构和无力场外推所得的三维磁场结构作相关分析来求相关高度是一种研究超紫外辐射线源区高度的新方法.有研究发现,该方法得到的冕洞区SiⅡ辐射线源区的高度比传统观点所认为的高.由于目前运用该方法的数据分析有限,需要用更多的数据进一步验证这一结果.运用该方法分析了SOHO/SUMER观测到的位于太阳南极冕洞之下的日面区域SiⅡ辐射线数据和美国National Solar Observatory/Kitt Peak(NSO/KP)测量的磁场数据,得到冕洞区SiⅡ辐射线源区的相关高度约为5.0Mm.该结果支持了冕洞区的过渡区底层高度比宁静区的要高的结论.同时发现了新的现象,并对其原因进行推测. 相似文献
56.
57.
The acquisition of survey knowledge for local and global landmark configurations under time pressure
Sascha Credé Tyler Thrash Christoph Hölscher Sara Irina Fabrikant 《Spatial Cognition & Computation》2019,19(3):190-219
The influence of stress states on cognition is widely recognized. However, the manner in which stress affects survey knowledge acquisition is still unresolved. For the present study, we investigated whether survey knowledge acquisition during a stressful task (i.e., under time pressure) is more accurate for the mental representation of global or local landmarks. Participants navigated through virtual cities with a navigation aid and explicit learning instructions for different landmark configurations. Participants’ judgments of relative direction (JRDs) suggest that global landmark configurations were not represented more accurately than local landmark configurations and that survey knowledge acquisition was not impaired under time pressure. In contrast to prior findings, our results indicate the limitations of the utility of global landmarks for spatial knowledge acquisition. 相似文献
58.
59.
There is a general agreement that landmarks in route directions should be perceptually salient and stable objects. Yet, other attributes, such as (animated) motion, can also attract visual attention and make entities salient. In the present study, we investigate if and when speakers refer to moving entities in route directions and how listeners evaluate such instructions. We asked speakers to watch short videos of different crossroads with and without moving landmarks and give directions to listeners, who in turn had to choose a street on which to continue (Experiment 1) or choose the instruction they most preferred among three route directions (Experiment 2). Results reveal that speakers mentioned moving entities, especially when the trajectory was informative for the place where a turn should be taken (Experiment 1). Listeners had no problem understanding instructions with moving landmarks (Experiment 1). Yet, participants chose instructions with stable landmarks more often (Experiment 2). These results are discussed in relation to automatic route directions generation. 相似文献
60.