全文获取类型
收费全文 | 2775篇 |
免费 | 693篇 |
国内免费 | 424篇 |
专业分类
航空 | 2025篇 |
航天技术 | 565篇 |
综合类 | 374篇 |
航天 | 928篇 |
出版年
2024年 | 4篇 |
2023年 | 40篇 |
2022年 | 115篇 |
2021年 | 125篇 |
2020年 | 149篇 |
2019年 | 105篇 |
2018年 | 128篇 |
2017年 | 135篇 |
2016年 | 122篇 |
2015年 | 152篇 |
2014年 | 163篇 |
2013年 | 183篇 |
2012年 | 191篇 |
2011年 | 197篇 |
2010年 | 163篇 |
2009年 | 204篇 |
2008年 | 192篇 |
2007年 | 164篇 |
2006年 | 133篇 |
2005年 | 141篇 |
2004年 | 102篇 |
2003年 | 105篇 |
2002年 | 140篇 |
2001年 | 113篇 |
2000年 | 71篇 |
1999年 | 95篇 |
1998年 | 69篇 |
1997年 | 58篇 |
1996年 | 51篇 |
1995年 | 32篇 |
1994年 | 41篇 |
1993年 | 43篇 |
1992年 | 37篇 |
1991年 | 43篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1977年 | 1篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有3892条查询结果,搜索用时 203 毫秒
1.
2.
电子信息设备工作时无意发射的电磁波中包含有用信息,会导致电磁信息泄漏,从而威胁设备的信息安全。现有的电磁信息泄漏检测方法,在复杂现场环境下,难以从具有不确定性的电磁泄漏信号中提取有用信息。面向电磁信息安全问题,开展了电磁信息泄漏检测研究,提出了一种基于深度学习的检测方法。设计了一个适用于电磁泄漏信号的一维卷积神经网络,并结合改进的梯度加权类激活映射方法,在未知电磁信息泄漏特征的前提下,通过深度学习实现电磁信息泄漏特征的智能标定和自动提取,从而解决了现场环境下电磁信息泄漏检测难以提取有用信息的问题。分别通过实测和仿真对比实验,验证了所提方法的有效性。 相似文献
3.
An active design method of tooth profiles for cycloid gears based on their meshing efficiency is proposed.This method takes the meshing efficiency as one of the design variables to determine the tooth profiles. The calculation method for the meshing efficiency of planetary transmission is analyzed and the equation of the meshing efficiency is deduced. Relationships between the meshing efficiency,the radius of the pin wheel and the eccentric distance are revealed. The design constraint quations and the strength constraint quations are deduced. On the basis of this,a design procedure is laid out. Some examples using different input parameters are conducted to demonstrate the feasibility of the approach. A dynamic simulation of the rigid-flexible coupling of cycloid gears is also presented. The results show that the proposed design method is more flexible to control the tooth profiles by changing the input values of the transmission efficiency. 相似文献
4.
Pengbin Guo Jian Sun Shuling Hu Ju Xue 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(3):787-798
Pulsar navigation is a promising navigation method for high-altitude orbit space tasks or deep space exploration. At present, an important reason for restricting the development of pulsar navigation is that navigation accuracy is not high due to the slow update of the measurements. In order to improve the accuracy of pulsar navigation, an asynchronous observation model which can improve the update rate of the measurements is proposed on the basis of satellite constellation which has a broad space for development because of its visibility and reliability. The simulation results show that the asynchronous observation model improves the positioning accuracy by 31.48% and velocity accuracy by 24.75% than that of the synchronous observation model. With the new Doppler effects compensation method in the asynchronous observation model proposed in this paper, the positioning accuracy is improved by 32.27%, and the velocity accuracy is improved by 34.07% than that of the traditional method. The simulation results show that without considering the clock error will result in a filtering divergence. 相似文献
5.
7.
8.
9.
本文通过引入工程设计中的优化方法,分别对室内空气环境下铝合金(LY12-CZ)材料疲劳裂纹扩展的数学模型,以及环境条件下(3.5%NaCl水溶液浸泡)该材料腐蚀疲劳裂纹扩展的数学模型进行了探讨。在已知标准试样在不同的环境下疲劳裂纹扩展实验dadNi,ΔKi的条件下,采用优化方法进行参数寻优,可方便地得到与其对应的疲劳裂纹扩展的dadN~ΔK最优数学模型 相似文献
10.
Further study of the Pencil-MUSIC algorithm 总被引:1,自引:0,他引:1
Qi Cheng Yingbo Hua 《IEEE transactions on aerospace and electronic systems》1996,32(1):284-299
For finding 2-D angles and polarizations of waves arriving at a rectangular array of crossed dipoles, the Pencil-MUSIC method can achieve the near optimum performance with much less computational burden than the MUSIC (multiple signal classification). Following an angle-only ESPRIT (estimation of signal parameters via rotational invariance techniques) method, an angle-only Pencil-MUSIC can be easily formulated which is far more accurate than the former especially in the coherent case. The angle-only Pencil-MUSIC is analyzed and compared with the original Pencil-MUSIC. The new version sacrifices the polarization estimation to achieve about 8 times more efficient computation The accuracy of the new version seems no more than 4 times worse in terms of estimation deviation 相似文献