全文获取类型
收费全文 | 62篇 |
免费 | 11篇 |
国内免费 | 10篇 |
专业分类
航空 | 36篇 |
航天技术 | 23篇 |
综合类 | 1篇 |
航天 | 23篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 2篇 |
2014年 | 1篇 |
2013年 | 5篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2010年 | 5篇 |
2009年 | 1篇 |
2008年 | 3篇 |
2007年 | 4篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2004年 | 9篇 |
2003年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有83条查询结果,搜索用时 343 毫秒
21.
Jia Luo Han Wang Xiaohua Xu Fangfang Sun 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(10):3088-3101
GPS radio occultation (RO) ionospheric products obtained by Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission during the year of 2014 and the observations from 3 digisonde stations which are located at different latitudes are used to study the influence of different time and space collocation windows on the comparisons of the ionospheric characteristic parameters (ICPs), including the peak density and peak height, derived from the two techniques. The results show that the correlation coefficients (CC) and the standard deviation of the absolute biases (SDAB) between the ICPs derived from the two techniques vary distinctly under different spatial and time collocation windows. Generally, the CC (SDAB) of the ICPs decrease (increase) as the size of the collocation window increases in time dimension or in space dimension. The rate of change of the statistic parameters with the increase in the size of the collocation window in time dimension and space dimension is analyzed for each digisonde station. It is found that within the collocation window of , the influence of the increase of in the space window on the statistical comparison is much more significant than that of the increase of 1?min in the time window, and it is suggested that there can be appropriate relaxation on the time window within the threshold of 60?min to get a balance between the quality of the comparison results and the number of the matched pairs. In addition, it is found that the same variations in the longitude window and in the latitude window may have different influences on the comparison results when the horizontal gradients in electron density are distinctly different along different directions at the digisonde station, and strict space collocation window is preferred when comparing the observations from COSMIC RO with those from the digisonde station in such cases. 相似文献
22.
Jianguo Yan Zhen Zhong Fei Li James M. Dohm Jinsong Ping Jianfeng Cao Xie Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
We analyzed the 150 × 150 lunar gravity field models, LP150Q, GLGM-3 and SGM150, using the power spectrum on the lunar nearside and farside, the lunar global and localized gravity/topography admittance and correlation, and Chang’E-2 precision orbit determination to investigate which model is a more effective tool to estimate geophysical parameters and determine the lunar satellite precision orbit. Results indicate that all gravity field models can be used to estimate the lunar geophysical parameters of the nearside of the Moon. However, SGM150 is better in such computation of the farside. Additionally, SGM150 is shown to be the most useful model for determining the lunar satellite orbit. 相似文献
23.
测定飞行推力和极曲线新方法 总被引:2,自引:0,他引:2
根据飞机在纵向运动时沿风轴方向的运动方程,重新定义飞机的推力和阻力,提出了一种新的测定飞行推力和阻力的方法,并将此法用于某型飞机的风洞与飞行试验极曲线相关性研究,取得了好的结果. 相似文献
24.
25.
26.
唐盛元 《中国空间科学技术》1988,(4)
本相关装置和浮动门限判决法是在“阿波罗”系统的基础上改制而成的。比较适用于音—码混合测距系统。与“阿波罗”系统比,相关损耗降低6dB。浮动门限判决法与“阿波罗”系统的最大似然法比较,结构极其简单,使用效果很好。 相似文献
27.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2622-2635
Land cover classification in mixed land cover scenarios is challenging with PolSAR data. Polarimetric decomposition techniques are most popular methods for PolSAR data classification in recent times. These techniques focus on identification of dominant scattering phenomena and hence result in sub-optimal classification in mixed land cover scenarios. Alternatively, polarization signatures (PSs) are good illustrations of SAR target responses as they depict a detailed physical information from target backscatter. Researchers have successfully utilized SAR PSs for land cover (LC) classification. Some reports suggested utilizing correlation between observed PSs and standard target PSs as features for LC classification. This paper presents a study on improved utilization of PSs for optimal LC classification in mixed class scenarios. First, PS based SAR features are derived using fully polarimetric SAR data. The features represent a degree of similarity between observed and standard PSs. The derived features are termed as polarization signatures correlation features or PSCFs. The novel PSCFs are analyzed, evaluated and compared with decomposition based features for the purpose of LC classification. Classification performance indicators highlight potential of PSCFs for mixed LC classification problems. Therefore, further an adaptive and optimal LC class boundary estimation approach for LC classification is proposed and developed. Observed PSs and reference LC class PS statistics are used to build empirical models between classification performance indicators and LC class boundaries. The empirical models are optimized using the evolutionary genetic algorithm to maximize classification performance. A decision tree is constructed based on the optimal class boundaries to prepare LC classification. The proposed classification approach is compared with some recent popular classifiers and comparison suggests that the proposed approach provides satisfactory results for mixed LC classification scenarios. 相似文献
28.
分析了宽带信号角跟踪的特殊问题及其实现方案。基于互相关函数的角误差检测方法,推导出了在非相关噪声及相关噪声背景下差路信号的输出信噪比及其角度随机误差的数学表达式,进而给出了带宽增益和最佳带宽的概念,以及提高输出信噪比的方法。为了在低载噪比(C/N)时获得角捕获所需要的和路信号以及差路的归一化信号,提出了四通道单脉冲方案。最后归纳出了低C/N时宽带信号角捕获和角跟踪的几种方法并提出了建议。 相似文献
29.
30.
Jiwon Seo Todd WalterPer Enge 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Deep and frequent Global Positioning System (GPS) signal fading due to strong ionospheric scintillation is a major concern for GPS-guided aviation in equatorial areas during high solar activity. A GPS aviation receiver may lose carrier tracking lock under deep fading, and a lost channel cannot be used for position calculation until lock is reestablished. Hence, frequent loss of lock due to frequent fading can significantly reduce the availability of GPS aviation. However, the geometric diversity of the satellites can mitigate scintillation impact on GPS aviation depending on the correlation level of deep fades between satellites. This paper proposes a metric to measure the correlation level of two fading channels from the perspective of GPS aviation. Using this metric, the satellite-to-satellite correlation is studied based on real scintillation data. The low satellite-to-satellite correlation shown in this paper envisions notable availability benefit from the geometric diversity of satellites under strong scintillation. In addition, this paper proposes a way to generate correlated fading processes with arbitrary correlation coefficients. Using this correlated fading process model, the availability of Localizer Performance with Vertical guidance (LPV)-200 under severe scintillation scenarios is analyzed. The result emphasizes the importance of a fast reacquisition capability of an aviation receiver after a brief outage, which is not currently mandated by the aviation receiver performance standards. 相似文献