全文获取类型
收费全文 | 7268篇 |
免费 | 14篇 |
国内免费 | 18篇 |
专业分类
航空 | 3603篇 |
航天技术 | 2520篇 |
综合类 | 199篇 |
航天 | 978篇 |
出版年
2018年 | 101篇 |
2017年 | 52篇 |
2016年 | 48篇 |
2014年 | 123篇 |
2013年 | 163篇 |
2012年 | 137篇 |
2011年 | 228篇 |
2010年 | 164篇 |
2009年 | 257篇 |
2008年 | 349篇 |
2007年 | 168篇 |
2006年 | 143篇 |
2005年 | 176篇 |
2004年 | 187篇 |
2003年 | 221篇 |
2002年 | 224篇 |
2001年 | 271篇 |
2000年 | 121篇 |
1999年 | 163篇 |
1998年 | 219篇 |
1997年 | 151篇 |
1996年 | 210篇 |
1995年 | 250篇 |
1994年 | 228篇 |
1993年 | 142篇 |
1992年 | 195篇 |
1991年 | 84篇 |
1990年 | 85篇 |
1989年 | 179篇 |
1988年 | 72篇 |
1987年 | 71篇 |
1986年 | 97篇 |
1985年 | 240篇 |
1984年 | 207篇 |
1983年 | 155篇 |
1982年 | 190篇 |
1981年 | 216篇 |
1980年 | 86篇 |
1979年 | 74篇 |
1978年 | 64篇 |
1977年 | 54篇 |
1976年 | 45篇 |
1975年 | 68篇 |
1974年 | 63篇 |
1973年 | 53篇 |
1972年 | 63篇 |
1971年 | 60篇 |
1970年 | 45篇 |
1969年 | 56篇 |
1967年 | 46篇 |
排序方式: 共有7300条查询结果,搜索用时 15 毫秒
91.
92.
This review assumes that many non-US readers may not be well-informed about the steps and work in radar development in the US after WW II to the present. Many know MIT by name and recall the famous Radiation Laboratory Series. But the more recent technical history has been less in the "public domain." In an attempt to correct this, one of the key institutions in the field, the MIT Lincoln Laboratory two years ago produced a special issue of their regular publication. Although the document currently at hand is not a book in the strict sense, the size, shape, and editorial comprehensiveness of the MIT Lincoln Laboratory Journal's Fifty-Year Anniversary Issue (12, 2, 2000) justifies calling this article being treated as a book review. 相似文献
93.
Liu S. Singer C.H. Dougal R.A. 《IEEE transactions on aerospace and electronic systems》2006,42(2):612-624
Electric power anomalies or disturbances can disrupt the normal operation of equipment, accelerate aging, or even cause outright failures thus resulting in increased costs of maintenance and reduced system reliability. Past research on the effects caused by power anomalies has been mostly focused on industrial, commercial, or residential systems, or on power distribution equipment. A literature survey reveals that there is no comprehensive review related to low-voltage (LV) power systems and utilization equipment applicable to military combat vehicles, such as aircraft and ships. This paper summarizes the results of a new literature survey that focused on the causes, effects, and mitigation methods for power anomalies typical of LV mobile power systems. Electric power anomaly cost data collected from the literature are also presented, from which the costs of anomalies to the national defense are estimated using some simple rationales. 相似文献
94.
Holzapfel W. Sofsky M. Neuschaefer-Rube U. 《IEEE transactions on aerospace and electronic systems》2003,39(1):2-12
We discuss autonomous car navigation based on updating dead reckoning (DR) by road profile recognition (RPR). The navigation system requires sensors to detect changes in altitude and driving direction which are installed in modern cars for different purposes (e.g. ABS sensors). The layout of the navigation system is discussed and simulations are carried out over driving distances of approximately 150 km on the basis of realistic road data and ordinary sensor accuracies. Positioning errors of lower than 10 m (standard deviation) are observed. To achieve this accuracy the synchronization error between measured and mapped data must be continually estimated. The introduced navigation method is ideal to complete present commercial car navigation systems using Navstar GPS. 相似文献
95.
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
96.
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
97.
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
98.
99.
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
100.
Michel D. Ingham Robert D. Rasmussen Matthew B. Bennett Alex C. Moncada 《Acta Astronautica》2006,58(12):648-661
It has become clear that spacecraft system complexity is reaching a threshold where customary methods of control are no longer affordable or sufficiently reliable. At the heart of this problem are the conventional approaches to systems and software engineering based on subsystem-level functional decomposition, which fail to scale in the tangled web of interactions typically encountered in complex spacecraft designs. Furthermore, there is a fundamental gap between the requirements on software specified by systems engineers and the implementation of these requirements by software engineers. Software engineers must perform the translation of requirements into software code, hoping to accurately capture the systems engineer's understanding of the system behavior, which is not always explicitly specified. This gap opens up the possibility for misinterpretation of the systems engineer's intent, potentially leading to software errors. This problem is addressed by a systems engineering methodology called State Analysis, which provides a process for capturing system and software requirements in the form of explicit models. This paper describes how requirements for complex aerospace systems can be developed using State Analysis, using representative spacecraft examples. 相似文献