全文获取类型
收费全文 | 2346篇 |
免费 | 241篇 |
国内免费 | 246篇 |
专业分类
航空 | 1311篇 |
航天技术 | 792篇 |
综合类 | 269篇 |
航天 | 461篇 |
出版年
2023年 | 13篇 |
2022年 | 36篇 |
2021年 | 54篇 |
2020年 | 45篇 |
2019年 | 39篇 |
2018年 | 59篇 |
2017年 | 45篇 |
2016年 | 32篇 |
2015年 | 41篇 |
2014年 | 85篇 |
2013年 | 83篇 |
2012年 | 106篇 |
2011年 | 123篇 |
2010年 | 121篇 |
2009年 | 146篇 |
2008年 | 176篇 |
2007年 | 93篇 |
2006年 | 88篇 |
2005年 | 88篇 |
2004年 | 66篇 |
2003年 | 69篇 |
2002年 | 58篇 |
2001年 | 87篇 |
2000年 | 69篇 |
1999年 | 99篇 |
1998年 | 98篇 |
1997年 | 61篇 |
1996年 | 88篇 |
1995年 | 61篇 |
1994年 | 84篇 |
1993年 | 61篇 |
1992年 | 61篇 |
1991年 | 35篇 |
1990年 | 42篇 |
1989年 | 59篇 |
1988年 | 37篇 |
1987年 | 19篇 |
1986年 | 25篇 |
1985年 | 23篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 24篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1969年 | 4篇 |
排序方式: 共有2833条查询结果,搜索用时 31 毫秒
11.
Hwu S.U. Loh Y.C. Dobbins J.A. Kroll Q.D. Sham C.C. 《Aerospace and Electronic Systems Magazine, IEEE》2005,20(10):9-14
Computational investigations and experimental measurements were performed to evaluate the Space Shuttle UHF communication system performance for payload bay antenna at the proposed new location. To insure adequate communication coverage at relocated new location, the link margin for the Extravehicular Activity (EVA) astronauts and between Space Shuttle Orbiter and International Space Station (SSO-ISS) during rendezvous were analyzed. The multipath effects from the vehicle structures surrounding the antenna were investigated. The Radio Frequency (RF) electromagnetic radiation to the Orbiter Docking System (ODS) pyrotechnics was also analyzed to ensure the EMC/EMI compliances. 相似文献
12.
A Izumi-Kurotani M Yamashita Y Kawasaki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(1):263-266
Japanese treefrogs (Hyla japonica) are planned to be sent to the space station MIR. Experimental system was developed to observe their behaviors under microgravity. 相似文献
13.
Kuroki F. Wagatsuma Y. Yoneyama T. 《Aerospace and Electronic Systems Magazine, IEEE》2006,21(5):26-29
An FM-CW radar front-end was fabricated in an integrated manner at 60 GHz by using the NRD guide. Main emphasis was placed on compactness in size and high-precise operation in performance. The fabricated radar consists of an FM Gunn oscillator, a balanced mixer, and a planar antenna fed by leaky NRD guide with a mechanically beam-scanning performance. All circuit components and the antenna were contained in a compact housing of 170 /spl times/ 140 mm in area and 25 mm in thickness, and thus, a thin type of millimeter-wave radar front-end was successfully developed. Moreover, an error of distance estimation was measured to be less than a distance of 0.7 m. 相似文献
14.
H. Sakurai Y. Shouji M. Osaki T. Aoki T. Gandou W. Kato Y. Takahashi S. Gunji F. Tokanai 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2492-2496
Daily Be-7 concentrations in air at the height of 15 m are continuously observed at 38°15.2′N, 140°20.9′E, between 2000 and 2001. The average concentration and the relative standard deviation were 4.0 mBq/m3 and 50% in 2000–2001, respectively. The Be-7 concentrations increased 2.5% with the decrease in the sunspot numbers by 6.7% for the term of two years. From the power spectral analysis, the periodicity of 26 days is shown for the daily Be-7 concentrations. The folding analysis indicates that the time variation of the Be-7 concentration is similar to that of the ground-based neutron counting rate, and the phase delay for the minimum portion of Be-7 concentration was roughly 8 days to the maximum sunspot number. These results indicate that the Be-7 concentrations in the air at ground level have 26 day periodicity as a component of time variations and the time variation is caused by the solar modulation of galactic cosmic rays, which corresponds to the variation of the sunspot number due to the rotation of the sun. 相似文献
15.
介绍一种简单有效的纠错编码方法 ,用于资源卫星高密度数字磁记录器 ,使误码率由 10 -6降低到 10 -11,同时介绍它的基本工作原理、实现方案及试验结果。 相似文献
16.
Luh J. Y. S. Shafran Joel S. Harvey C. Arthur 《IEEE transactions on aerospace and electronic systems》1968,(2):218-233
This paper considers the problem arising from the design of an autopilot for a large booster. The motion-controlling actuators of the booster have both position and rate limits. The problem is formulated as a bounded phase-coordinate problem and analyzed by the ``backing out of the target' procedure. A method of constructing the optimal control is presented. An example of an oscillatory system with two control inputs is given, and the optimal control is expressed as an explicit time function. 相似文献
17.
比较两种盲多用户检测算法在动态环境中的收敛性能,并通过计算机进行模拟仿真。其中一种是能随输入信号矢量变化而变化的变步长最小输出能量盲算法;另一种是既保持最小输出能量检测器的全局收敛性,又具有最小均方误差检测器高输出信干比优点的判决反馈变步长盲算法。利用前者在动态强干扰下收敛快及后者在稳态时输出信干比高的优势,将二者结合起来应用到动态环境中,提高系统性能,同时抑制多址干扰和窄带干扰。 相似文献
18.
19.
本文首先从国内外的发展现状,概述了印刷电路板缺陷焊点的几种检测手段。并着重介绍了作者与其同事们正在研制的激光全息印刷电路板焊点缺陷自动检测系统。 相似文献
20.