首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   412760篇
  免费   5819篇
  国内免费   1386篇
电工技术   7704篇
综合类   350篇
化学工业   61998篇
金属工艺   14288篇
机械仪表   11872篇
建筑科学   11637篇
矿业工程   870篇
能源动力   11119篇
轻工业   43798篇
水利工程   3312篇
石油天然气   1835篇
武器工业   13篇
无线电   55390篇
一般工业技术   76619篇
冶金工业   74957篇
原子能技术   5568篇
自动化技术   38635篇
  2021年   2669篇
  2019年   2434篇
  2018年   3840篇
  2017年   3904篇
  2016年   4145篇
  2015年   3427篇
  2014年   5714篇
  2013年   19283篇
  2012年   10205篇
  2011年   14682篇
  2010年   11284篇
  2009年   12885篇
  2008年   13917篇
  2007年   14285篇
  2006年   12778篇
  2005年   11962篇
  2004年   11574篇
  2003年   11280篇
  2002年   10913篇
  2001年   11132篇
  2000年   10271篇
  1999年   10770篇
  1998年   24010篇
  1997年   17588篇
  1996年   13904篇
  1995年   10979篇
  1994年   9771篇
  1993年   9354篇
  1992年   7121篇
  1991年   6790篇
  1990年   6397篇
  1989年   6106篇
  1988年   5860篇
  1987年   4884篇
  1986年   4834篇
  1985年   5978篇
  1984年   5599篇
  1983年   4832篇
  1982年   4496篇
  1981年   4447篇
  1980年   4209篇
  1979年   4080篇
  1978年   3771篇
  1977年   4548篇
  1976年   6100篇
  1975年   3115篇
  1974年   3012篇
  1973年   2890篇
  1972年   2318篇
  1971年   2003篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
We have designed, developed, and tested a very promising thermal image analysis method for polygraph testing. The method achieved a correct classification rate of CCR= 84% on the test population to our avail. This method, once refined, can serve as an additional channel for increasing the reliability and accuracy of traditional polygraph examination. We extract subtle facial temperature fluctuation patterns through nonlinear heat transfer modeling. The modeling transforms raw thermal data to blood flow rate information. Then, we use the slope of the average periorbital blood flow rate as the feature of a binary classification scheme. The results come to support our previous laboratory findings about the importance of periorbital blood flow in anxious states.  相似文献   
182.
In this paper, the space-vector transformation used in machine vector control is applied to power system analysis. The proposed method is used to model electric machines, power electronic converters, transformers, and transmission lines and to analyze power sources and loads with different connections (delta and wye). This method can also be applied to analyze steady-state (or transient phenomena) and unbalanced sources, including harmonics. Models obtained with this method are as simple as those of the per-phase approach. With the space-vector transformation, instantaneous active and reactive power concepts can be generalized, and new power system control strategies can be developed when power electronic converters are used. Steady-state, transient behavior, and harmonic analyses examples and applications are presented to illustrate the performance and advantages of the proposed method. This method can be extended to unbalanced systems (e.g., unsymmetric faults) using instantaneous symmetrical components in polyphase balanced circuits.  相似文献   
183.
This letter further discusses the difference between different definitions of voltage unbalance. Contrary to an earlier letter (see P. Pillay et al., ibid., vol.5, p.50-1, 2001), it is concluded that different definitions may give significantly different results. The two IEEE definitions that were not discussed in the earlier letter give different results and both deviate significantly from the true value (ratio of negative, and positive-sequence voltage) when a zero-sequence component is present.  相似文献   
184.
Summary The equilibrium water contents of linear poly(acrylic acid) sodium salts with different degrees of neutralisation were found to be dependent on temperature and relative humidity. An octahedral model for the primary hydration of poly(acrylic acid) sodium salts (HIRAOKA and YOKOYAMA 1980) was critically evaluated in the light of these findings and an anomaly in the water uptake versus neutralisation curve at approximately 33% neutralisation was explained by the counterion condensation theory. (MANNING 1979).  相似文献   
185.
Fuzzy logic was first suggested as the mechanism by which humans drive cars. This paper addresses the use of fuzzy logic and algorithms towards the intelligent autonomous motion control of land vehicles. To cope with vehicle complexities, internal parametric changes, and with unpredictable environmental effects, the controllers that are presented, whilst heuristic in nature, are self-organizing or self-learning in that they generate automatically by observation an experiential rule base that models the vehicle, and via an appropriate performance index an optimal control rule base that is robust to large parametric changes. The methodology presented is applicable to any complex process which is too difficult to model or control using conventional methods, or which has relied on the experience of a human operator. An overview of fuzzy logic and static fuzzy logic control (akin to expert systems) is provided, together with illustrative examples.  相似文献   
186.
187.
188.
This paper discusses secondary unit substations transformers (USTs) ranging from 300 up through 2500 kVA with 34.5-kV maximum primary voltages and with secondary voltages 600 V and below. Pad-mounted (compartmentalized) transformers are not considered in this paper. The first part of this paper discusses USTs belonging to two general categories, liquid type and dry type (nonliquid type). Liquid types include a discussion of the presently available insulating fluids: mineral oil, high-temperature hydrocarbon fluid, silicone fluids, and the new vegetable-based fluids. Dry types include a discussion of vacuum pressure impregnated polyester, vacuum pressure encapsulated silicone, partial cast, and full cast insulation systems. The National Electric Code (1999) requirements as they affect both liquid- and dry-type USTs for both outdoor and indoor locations are considered. The paper discusses the relative advantages of each UST within each category with respect to the following: (1) first cost; (2) operating costs (losses); (3) overload capability; (4) fan cooling; (5) space factor; (6) environmental factors; (7) sound levels; and (8) maintenance  相似文献   
189.
It is shown that direct compression grade tricalcium phosphate yields linear Heckel plots only if the particle density used is that obtained by liquid pycnometry or mercury porosimetry. If the true density is used (i.e. that obtained by gas displacement), then linearization is not obtained in a pressure range where bonding evidently occurs. It is shown that the pore volume in the range of diameters from 0.5 to 2 μm decreases as tableting pressure increases, and that bonding is associated with the loss of pores of this size.  相似文献   
190.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号