全文获取类型
收费全文 | 820篇 |
免费 | 99篇 |
国内免费 | 187篇 |
专业分类
航空 | 469篇 |
航天技术 | 208篇 |
综合类 | 168篇 |
航天 | 261篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 23篇 |
2014年 | 56篇 |
2013年 | 54篇 |
2012年 | 42篇 |
2011年 | 54篇 |
2010年 | 51篇 |
2009年 | 51篇 |
2008年 | 50篇 |
2007年 | 65篇 |
2006年 | 54篇 |
2005年 | 44篇 |
2004年 | 19篇 |
2003年 | 19篇 |
2002年 | 19篇 |
2001年 | 20篇 |
2000年 | 32篇 |
1999年 | 36篇 |
1998年 | 42篇 |
1997年 | 49篇 |
1996年 | 42篇 |
1995年 | 27篇 |
1994年 | 31篇 |
1993年 | 30篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有1106条查询结果,搜索用时 360 毫秒
141.
142.
143.
144.
Investigations into sensing characteristics of circular thin-plate electrostatic sensors for gas path monitoring 总被引:1,自引:0,他引:1
Circular thin-plate electrostatic sensors are promising in gas path monitoring due to their advantages of non-intrusiveness and easy installation. The spatial sensitivity and filtering effect are two important performance parameters. In this paper, an analytically mathematical model of induced charge on a circular thin-plate electrode is first derived. Then the spatial sensitivity and filtering effect of the circular electrostatic sensor are investigated by numerical calculations. Finally,experimental studies are performed to testify the theoretical results. Both theoretical and experimental results demonstrate that circular thin-plate electrostatic sensors act as a low-pass filter in the spatial frequency domain, and both the spatial filtering effect and the temporal frequency response characteristics depend strongly on the spatial position and velocity of the charged particle. These conclusions can provide guidelines for the optimal design of circular thin-plate electrostatic sensors. 相似文献
145.
论文针对如今招生趋势良好的高校艺术类专业的学生当中存在的一些问题进行了分析和探讨,从树立正确的人生观和价值观、学会感恩以及培养各方面素质全面发展的人才这三个方面入手,建设性地提出了相关的引导学生改进所存在问题的方法和策略. 相似文献
146.
147.
波音系列飞机一定时间后,飞机尾部结构出现疲劳裂纹,需用涡轮检测法进行损伤检查。 相似文献
148.
Since health monitoring of shield tunnels generally employs multiple sensors belonging to different types,a fine analysis on massive monitoring data,as well as further quantitative health grading,is really challenging.An optimized fuzzy clustering analysis method based on the fuzzy equivalence relation is proposed for health monitoring of shield tunnels.Clustering results are auto-generated by using fuzzy similarity-valued map.The results follow the idea of unsupervised classification.Moreover,a convenient new health index HI is proposed for a fast tunnel-health grading.A case study on Nanjing Yangtze River Tunnel is presented to validate this method.Three types of indicators,namely soil pressure,pore water pressure and steel strain,are used to develop the clustering model.The clustering results are verified by analyzing the engineering geological conditions;the validity and the efficacy of the proposed method are also demonstrated.Further,the fuzzy clustering analysis also represents a potential for identifying abnormal monitoring data.This investigation indicates the fuzzy clustering analysis method is capable of characterizing the fuzziness of tunnel health,and beneficial to clarify the tunnel health evaluation uncertainties. 相似文献
149.
根据炮兵作战理论和实际作战流程,建立了用于评定间瞄武器进行火力支援的作战效能模型。该模型不仅可以比较不同火炮系统的作战效能,还可通过修改模型参数使其能反映不同的作战强度,对炮兵的战术决策有一定的参考意义。 相似文献
150.
GuiFeng Wei DanLing Tang Sufen Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(1):12-19
Monitoring of spatial and temporal distribution of chlorophyll (Chl-a) concentrations in the aquatic milieu is always challenging and often interesting. However, the recent advancements in satellite digital data play a significant role in providing outstanding results for the marine environmental investigations. The present paper is aimed to review ‘remote sensing research in Chinese seas’ within the period of 24 years from 1978 to 2002. Owing to generalized distributional pattern, the Chl-a concentrations are recognized high towards northern Chinese seas than the southern. Moreover, the coastal waters, estuaries, and upwelling zones always exhibit relatively high Chl-a concentrations compared with offshore waters. On the basis of marine Chl-a estimates obtained from satellite and other field measured environmental parameters, we have further discussed on the applications of satellite remote sensing in the fields of harmful algal blooms (HABs), primary production and physical oceanographic currents of the regional seas. Concerned with studies of HABs, satellite remote sensing proved more advantageous than any other conventional methods for large-scale applications. Probably, it may be the only source of authentic information responsible for the evaluation of new research methodologies to detect HABs. At present, studies using remote sensing methods are mostly confined to observe algal bloom occurrences, hence, it is essential to coordinate the mechanism of marine ecological and oceanographic dynamic processes of HABs using satellite remote sensing data with in situ measurements of marine environmental parameters. The satellite remote sensing on marine environment and HABs is believed to have a great improvement with popular application of technology. 相似文献