全文获取类型
收费全文 | 6455篇 |
免费 | 315篇 |
国内免费 | 383篇 |
专业分类
航空 | 3170篇 |
航天技术 | 2209篇 |
综合类 | 612篇 |
航天 | 1162篇 |
出版年
2022年 | 32篇 |
2021年 | 63篇 |
2020年 | 37篇 |
2019年 | 50篇 |
2018年 | 89篇 |
2017年 | 54篇 |
2016年 | 85篇 |
2015年 | 72篇 |
2014年 | 182篇 |
2013年 | 210篇 |
2012年 | 202篇 |
2011年 | 292篇 |
2010年 | 242篇 |
2009年 | 289篇 |
2008年 | 383篇 |
2007年 | 260篇 |
2006年 | 207篇 |
2005年 | 231篇 |
2004年 | 196篇 |
2003年 | 211篇 |
2002年 | 251篇 |
2001年 | 297篇 |
2000年 | 160篇 |
1999年 | 238篇 |
1998年 | 268篇 |
1997年 | 194篇 |
1996年 | 218篇 |
1995年 | 210篇 |
1994年 | 193篇 |
1993年 | 149篇 |
1992年 | 168篇 |
1991年 | 100篇 |
1990年 | 84篇 |
1989年 | 122篇 |
1988年 | 56篇 |
1987年 | 63篇 |
1986年 | 47篇 |
1985年 | 139篇 |
1984年 | 128篇 |
1983年 | 84篇 |
1982年 | 114篇 |
1981年 | 130篇 |
1980年 | 34篇 |
1979年 | 24篇 |
1978年 | 29篇 |
1977年 | 29篇 |
1975年 | 25篇 |
1974年 | 28篇 |
1970年 | 23篇 |
1969年 | 28篇 |
排序方式: 共有7153条查询结果,搜索用时 15 毫秒
61.
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
62.
Teofilo V.L. Merritt L.V. Hollandsworth R.P. 《Aerospace and Electronic Systems Magazine, IEEE》1997,12(11):30-36
A lithium ion battery charger has been developed for four and eight cell batteries or multiples thereof. This charger has the advantage over those using commercial lithium ion charging chips in that the individual cells are allowed to be taper charged at their upper charging voltage rather than be cutoff when all cells of the string have reached the upper charging voltage limit. Since 30-60% of the capacity of lithium ion cells may be restored during the taper charge, this charger has a distinct benefit of fully charging lithium ion batteries by restoring all of the available capacity to all of its cells 相似文献
63.
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
64.
Space technology revolutionizes navigation. It will become the method for any task of position, velocity, range determination and time distribution. The existing navigation satellite systems of the USA (GPS) and of Russia (GLONASS) are military systems. They only partly meet the requirements of civil safety critical applications. A global civil navigation satellite system (GNSS) is required. The European Union (EU) has recognized the importance of satellite based navigation and its role for transportation in general and for the development of the Trans-European Network (TEN) in particular. It has therefore decided to become a major partner in the development of the GNSS. In this article a concept is proposed which starts with a European regional segment (ENSS) as an element for the integrated global system. This concept requires the establishment of international standards to enable seamless global service. It has the advantage of meeting both the particular demands of regions and civil user groups. 相似文献
66.
67.
A multiple model adaptive estimator (MMAE) has been formulated to estimate the state of a dynamic system modeled by a linear stochastic differential equation, from which measurements, described as a noise-corrupted space-time point process functionally related to that state, are extracted. Assumed certainty equivalence is used to combine such an estimator with the LQ full-state feedback controller to synthesize a practical, implementable controller. Performance of the estimator and resultant controller characteristics are investigated via simulation as a function of approximation method used to limit the full-scale estimator to finite dimensionality and also as a function of important parameters defining the dynamics and observation processes. 相似文献
68.
69.
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
70.