全文获取类型
收费全文 | 1338篇 |
免费 | 297篇 |
国内免费 | 302篇 |
专业分类
航空 | 1041篇 |
航天技术 | 279篇 |
综合类 | 159篇 |
航天 | 458篇 |
出版年
2024年 | 6篇 |
2023年 | 32篇 |
2022年 | 59篇 |
2021年 | 85篇 |
2020年 | 63篇 |
2019年 | 113篇 |
2018年 | 118篇 |
2017年 | 103篇 |
2016年 | 110篇 |
2015年 | 73篇 |
2014年 | 112篇 |
2013年 | 126篇 |
2012年 | 104篇 |
2011年 | 115篇 |
2010年 | 91篇 |
2009年 | 69篇 |
2008年 | 89篇 |
2007年 | 69篇 |
2006年 | 55篇 |
2005年 | 60篇 |
2004年 | 33篇 |
2003年 | 29篇 |
2002年 | 20篇 |
2001年 | 29篇 |
2000年 | 37篇 |
1999年 | 30篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 5篇 |
排序方式: 共有1937条查询结果,搜索用时 390 毫秒
451.
Abstract Recently, psychologists have turned their attention to the study of cast shadows and demonstrated that the human perceptual system values information from shadows very highly in the perception of spatial qualities, sometimes to the detriment of other cues. However with some notable and recent exceptions, computer vision systems treat cast shadows not as signal but as noise. This paper provides a concise yet comprehensive review of the literature on cast shadow perception from across the cognitive sciences, including the theoretical information available, the perception of shadows in human and machine vision, and the ways in which shadows can be used. 相似文献
452.
滚动轴承早期故障信号中的噪声成分会影响到故障特征的提取。为了提高含噪故障信号中滚动轴承早期故障特征提
取的准确性,将基于自适应噪声的完备经验模态分解(CEEMDAN)用于滚动轴承振动信号的降噪中,并对降噪后的轴承故障信号
进行双谱分析。结果表明:CEEMDAN可有效去除轴承振动信号中的低频噪声干扰,经CEEMDAN降噪后的不同轴承故障信号的
双谱全局图存在明显差异,根据这些差异可在宏观上对不同轴承故障加以区分;通过经CEEMDAN降噪后的不同轴承故障信号的
双谱细节图可以正确提取不同轴承故障的特征频率,从而实现对各轴承故障的有效诊断。CEEMDAN降噪结合双谱分析可为滚
动轴承故障诊断提供一种新的有效方法。 相似文献
453.
Abstract Participants (N = 78) studied a visualization of a route through a complex building and walked that route in the real building without further assistance. Erroneous turns on the route as well as indicators of uncertainty such as hesitations were assessed. Three types of route visualizations were compared: (1) an allocentric, map-based visualization with the route indicated in floor maps, (2) an ordered sequence of pictures of decision points shown from the egocentric perspective, and (3) an animation showing a virtual walk of the route from the egocentric perspective. In addition to the experimental variation, gender differences, differences in visual-spatial abilities and differences in self-reported wayfinding strategies were considered as predictor variables. Wayfinding performance did not differ between allocentric (map) and egocentric (decision point pictures and animation) visualizations. However, wayfinding performance was better with animated than with static egocentric visualizations. Individual differences in the ability to encode visual-spatial information from the visualization played a critical role for route learning. Self-reported sense of direction related to egocentric wayfinding strategies also predicted wayfinding performance. Gender differences were attributable to differences in visual-spatial abilities and egocentric wayfinding strategies. Interactions between visualizations and individual differences were not found. It is concluded that animations of virtual walks are suitable to convey route information in complex buildings. Successful acquisition of route knowledge from maps is possible but might depend on the comprehensibility of the structure of the building. 相似文献
454.
Teenie Matlock Spencer C. Castro Morgan Fleming Timothy M. Gann Paul P. Maglio 《Spatial Cognition & Computation》2014,14(4):306-320
When the web became popular, people had to develop ways to talk and think about it. In the mid-1990s, we analyzed spatial language in “web talk.” We found that people described pages as places, and search as motion, both passive and active motion. Here we investigate web talk nearly two decades later. Our analysis reveals that some spatial language has stayed the same, and some has changed. Of special interest is how far fewer motion verbs are used nowadays. We argue that people naturally produce spatial metaphors when talking about new technological domains, and that over time, the most useful elements persist. 相似文献
455.
本文首先阐明对培养学生创新意识培养的认识,然后讲述怎样结合电子技术基础课程的特点建立研究型教学模式,进而介绍丰富的教学实践,以及多层次、系列化和立体化的教材建设,最后说明教学效果。 相似文献
456.
457.
空间前方交会法及其在测试技术中的应用 总被引:2,自引:0,他引:2
分析了空间前方交会法的基本原理,建立了相关的理论模型,并在实验室的条件下严格测试了这种方法的测量精度;探讨了空间前方交会法在位置检测系统的测试过程中应用,详细地给出了测试的步骤以及测试数据的分析处理结果。 相似文献
458.
459.
460.