全文获取类型
收费全文 | 1911篇 |
免费 | 293篇 |
国内免费 | 284篇 |
专业分类
航空 | 1182篇 |
航天技术 | 506篇 |
综合类 | 368篇 |
航天 | 432篇 |
出版年
2024年 | 12篇 |
2023年 | 42篇 |
2022年 | 35篇 |
2021年 | 66篇 |
2020年 | 62篇 |
2019年 | 53篇 |
2018年 | 81篇 |
2017年 | 77篇 |
2016年 | 91篇 |
2015年 | 75篇 |
2014年 | 94篇 |
2013年 | 92篇 |
2012年 | 146篇 |
2011年 | 157篇 |
2010年 | 144篇 |
2009年 | 132篇 |
2008年 | 118篇 |
2007年 | 127篇 |
2006年 | 134篇 |
2005年 | 122篇 |
2004年 | 91篇 |
2003年 | 80篇 |
2002年 | 55篇 |
2001年 | 61篇 |
2000年 | 55篇 |
1999年 | 35篇 |
1998年 | 38篇 |
1997年 | 28篇 |
1996年 | 21篇 |
1995年 | 30篇 |
1994年 | 23篇 |
1993年 | 28篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 2篇 |
1986年 | 3篇 |
排序方式: 共有2488条查询结果,搜索用时 24 毫秒
531.
王昌金 《北京航空航天大学学报》1998,(3):391
采用等高线地图作为分布交互仿真环境中计算机生成兵力的地域表示.介绍等高线电子地图下计算机生成兵力系统地域表示和推理的一种方法.通过对地域显示、通视性检测和地形检测等几个基本问题的分析,表明采用该方法是可行的.具有地域表示范围大、地域推理简单明了的特点,并且地域数据真实、修改方便.这种方法比多边形地域表示法更适用于海上和空中大范围训练作战环境的仿真. 相似文献
532.
533.
534.
Yi He Youdong Chen Wenhui Wang Haowen Yan Lifeng Zhang Tao Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(4):1267-1283
Large-scale land creation projects involving the cutting of mountains to infill gullies for construction have been carried out in Lanzhou New District (LZND). However, there is an urgent need for comprehensive and detailed research on the spatiotemporal evolution of ground deformation in LZND. Based on Sentinel-1A SAR data, combined with the urban geological background, the ground deformation in LZND from 2017 to 2019 was analysed. Two independent, multi-temporal techniques, persistent scatterers interferometry (PS-InSAR) and the small baseline subset (SBAS-InSAR), were used to calculate the deformation time series, and the results were cross-verified. The time series-monitoring results of the SBAS and PS calculations exhibited strong consistency in LZND and verified the high reliability of the experimental results. The results showed the whole surface of the LZND from March 2017 to October 2019 maintained stability, and the deformation rate was primarily in the range of ?10 to 10 mm/year. However, ground deformation in the Xicha area was evident. The maximum annual deformation rates monitored by SBAS-InSAR and PS-InSAR were ?52.48 mm/year and ?56.35 mm/year, respectively. The most typical deformation areas include the built-up area and the land creation area. The surface subsidence area was concentrated in the filling area. The ground deformation range of LZND kept expanding and accelerating from 2017 to 2019. Land creation, urban construction, geology and precipitation were the primary factors contributing to local severe ground deformation. The results of this study provide reference for the regional urban planning in LZND. 相似文献
535.
从工程应用角度基于IPT工作模式,建立详细初步设计阶段以电子样机、虚拟仿真技术等为手段,同步开展使用与维修保障设计分析的流程和方法。以某型飞机舵机A为实例,对建立的方法进行应用,实践表明,建立的方法适用、有效、符合工程实际。该方法的建立,将对详细初步设计阶段一级IPT成员同步开展使用与维修保障设计、分析工作提供有力的技术支撑,对提高军用飞机使用与维修保障设计水平具有重要意义。 相似文献
536.
Kangkang Liu Guozhu Li Baiqi Ning 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(11):3612-3620
The small-scale wave-like structure (SSWS) of F region bottomside plasma density was proposed to be an important seeding for equatorial plasma bubble (EPB) generation, and employed in theoretical simulations of EPBs in recent years. The seeding role of SSWS, however, is waiting to be demonstrated by observation. Here we present two cases of SSWS and EPB observed by the Fuke all-sky airglow imager (19.3°N, 109.1°E; dip latitude 14.3°N). For each case, the results show that two large-scale wave-like structures (LSWSs) initially appeared around sunset in the longitude regions separated by 3–4°, but EPB irregularities were only generated in one of the LSWSs where SSWSs were seen riding on LSWS. For the other LSWS, no SSWS and EPB irregularities were seen. Considering that the two LSWSs were situated closely in longitude where the amplitude of pre-reversal enhancement of background eastward electric field should be similar, the observation that EPB was only generated in the longitude with simultaneous LSWS and SSWS could provide supporting evidence for SSWS seeding of EPB. 相似文献
537.
538.
通过研究某型干扰机对多普勒雷达速度跟踪系统的干扰方式,分析假多普勒频率产生的干扰工作机理,研究对抗科目训练中该模式干扰效果不佳的具体原因,提出了采用数字移向技术替代行波管移相,增大对雷达回波原载频的抑制度,增强干扰效果。通过对样机的测试验证,给出了两种移相电路的假多普勒干扰比较。 相似文献
539.
通过对国内外飞机管路系统设计技术以及传统管路设计制造方法的分析表明,管路数字化设计技术不仅是飞机协同设计的重要环节,也是实现模拟星向数字量转换的有效途径。本文针对管路系统设计技术应川现状,提出了飞机管路系统数字化设计技术应用方案,阐述了实现飞机管路系统数字化设计的技术方法 相似文献
540.
Abstract Existing methods for land surface form characterisation often focus on relatively simple landform element classifications and do not evaluate results with large scale participant experiments. This piece of research takes a semantics-grounded approach to characterising the landform valley. Based on definitions three algorithms to characterise valleys in a fuzzy way are introduced. Comparison of the results to assessments regarding the degree of being in a valley gained from over 800 participants in a questionnaire survey yields significant amounts of explained variance (R 2 = 0.35–0.37). Furthermore, accounting for very ambiguously perceived stimuli showing vast low places leads to markedly improved regressions (R 2 = 0.45–0.49), weighting of the data with a measure of uncertainty in judgment even more so (R 2 = 0.50–0.55). 相似文献