全文获取类型
收费全文 | 99篇 |
免费 | 14篇 |
国内免费 | 10篇 |
专业分类
航空 | 41篇 |
航天技术 | 39篇 |
综合类 | 6篇 |
航天 | 37篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 12篇 |
2012年 | 12篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
排序方式: 共有123条查询结果,搜索用时 15 毫秒
71.
72.
K. Durga Prasad S.V.S. MurtyT. Chandrasekhar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
A novel and versatile wireless light sensing device has been designed and tested for stellar and planetary photometric observations. The device weighing few 10 s of grams finds a number of potential applications in the fields of astronomy and in situ planetary exploration. A Wireless Sensor Network (WSN) using a number of these devices has been deployed to successfully carry out simultaneous photometric observations under different conditions viz. sunlight, twilight, moonlight etc. Observation of a star of known magnitude for flux calibration at low intensity has been carried out by coupling the device to a 1.2 m telescope which demonstrates its sensitivity. A WSN using these devices is further capable of spatio-temporal investigations of sky background intensities. Such a network can also be used to effectively monitor certain astronomical events (lunar eclipse, asteroid occultation etc.) simultaneously from several locations. The capability of the device, level of miniaturization and its versatility makes it a potential tool for many photometric applications. 相似文献
73.
为研究潜艇使用自航式声诱饵对抗条件下直升机空投鱼雷命中概率,基于对舰艇引导直升机空投鱼雷的过程分析,建立了舰艇引导机载鱼雷攻潜的参数解算模型、自航式声诱饵对抗自导鱼雷模型,分析了鱼雷命中条件.以美国MK-46鱼雷为例,运用模拟法仿真研究了在自航式声诱饵对抗条件下机载鱼雷的攻潜效果,结论对自导鱼雷在对抗条件下攻击潜艇的作... 相似文献
74.
75.
N. Prantzos 《Space Science Reviews》2007,130(1-4):27-42
After a short historical (and highly subjective) introduction to the field, I discuss our current understanding of the origin
and evolution of the light nuclides D, 3He, 4He, 6Li, 7Li, 9Be, 10B and 11B. Despite considerable observational and theoretical progress, important uncertainties still persist for each and every one
of those nuclides. The present-day abundance of D in the local interstellar medium is currently uncertain, making it difficult
to infer the recent chemical evolution of the solar neighborhood. To account for the observed quasi-constancy of 3He abundance from the Big Bang to our days, the stellar production of that nuclide must be negligible; however, the scarce observations of its abundance in planetary nebulae seem to contradict this idea. The observed
Be and B evolution as primaries suggests that the source composition of cosmic rays has remained ∼constant since the early
days of the Galaxy, a suggestion with far reaching implications for the origin of cosmic rays; however, the main idea proposed
to account for that constancy, namely that superbubbles are at the source of cosmic rays, encounters some serious difficulties.
The best explanation for the mismatch between primordial Li and the observed “Spite-plateau” in halo stars appears to be depletion
of Li in stellar envelopes, by some yet poorly understood mechanism. But this explanation impacts on the level of the recently
discovered early “6Li plateau”, which (if confirmed), seriously challenges current ideas of cosmic ray nucleosynthesis. 相似文献
76.
77.
78.
提出一种通过对远场散射光分布的统计分析来测量中等以上精度表面粗糙度的新方法。采用半导体激光器作为光源,并使用一维 CCD 器件来探测散射光分布。实验结果表明,在 R_a≤2.2μm 的范围内,远场归一化散射光分布的标准偏差(σ)与标准粗糙度参数 R_a 之间有很好的相关关系。 相似文献
79.
针对双线结构光对缝测量系统中光条中心的提取问题,提出一种基于自适应阈值和傅里叶拟合的光条中心亚像素提取方法。该方法根据双线结构光光带截面灰度呈近似周期性分布的特点,先采用骨架细化法获得条纹中心初始位置,再通过均方灰度梯度求取骨架上每一点的法线方向,然后采用自适应阈值法提取出条纹各列法向宽度值,最后利用条纹法向宽度内的灰度值数据进行傅里叶拟合,求取拟合曲线的峰值,连接峰值点得到光条的中心线。试验结果表明,该方法提取的光条中心点到中心点拟合直线的平均距离为0.1182个像素和0.1428个像素,优于骨架细化法和高斯拟合法,并且该方法能够一次完成两根结构光光条中心的精确提取,对缝的测量精度能够达到0.04mm。 相似文献
80.