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   92716篇
  免费   14008篇
  国内免费   212篇
电工技术   1562篇
综合类   101篇
化学工业   26876篇
金属工艺   2401篇
机械仪表   3753篇
建筑科学   2885篇
矿业工程   59篇
能源动力   2966篇
轻工业   10601篇
水利工程   532篇
石油天然气   256篇
武器工业   2篇
无线电   15680篇
一般工业技术   21148篇
冶金工业   6508篇
原子能技术   640篇
自动化技术   10966篇
  2023年   546篇
  2022年   862篇
  2021年   1617篇
  2020年   2279篇
  2019年   3859篇
  2018年   4163篇
  2017年   4405篇
  2016年   5107篇
  2015年   4804篇
  2014年   5502篇
  2013年   7999篇
  2012年   5631篇
  2011年   6067篇
  2010年   5356篇
  2009年   5453篇
  2008年   4795篇
  2007年   4215篇
  2006年   3761篇
  2005年   3185篇
  2004年   3082篇
  2003年   2889篇
  2002年   2804篇
  2001年   2296篇
  2000年   2201篇
  1999年   1603篇
  1998年   2252篇
  1997年   1493篇
  1996年   1230篇
  1995年   984篇
  1994年   762篇
  1993年   714篇
  1992年   516篇
  1991年   529篇
  1990年   448篇
  1989年   420篇
  1988年   334篇
  1987年   291篇
  1986年   281篇
  1985年   255篇
  1984年   220篇
  1983年   164篇
  1982年   166篇
  1981年   141篇
  1980年   143篇
  1979年   107篇
  1978年   102篇
  1977年   134篇
  1976年   169篇
  1975年   85篇
  1974年   80篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
In order to extend the expressive power of deductive databases, a formula that can have existential quantifiers in prenex normal form in a restricted way is defined as an extended rule. With the extended rule, we can easily define a virtual view that requires a division operation of relational algebra to evaluate. The paper addresses a recursive query evaluation where at least one formula in a recursive rule set is of an extended rule. We investigate transformable recursions as well as four cases of non-transformable recursions of transitive-closure-like and linear type. The work reveals that occurrence of an existentially quantified variable in the extended recursive body predicate might dramatically limit the level of recursive search. In particular, the number of iterations to answer extended queries can be determined, independently of database contents  相似文献   
162.
163.
164.
A method for modeling the learning of belief combination in evidential reasoning using a neural network is presented. A centralized network composed of multiple exponential bidirectional associative memories (eBAM's) sharing a single output array of neurons is proposed to process the uncertainty management of many pieces of evidence simultaneously. The stability of the proposed multiple eBAM network is proved. The sufficient condition to recall a stored pattern pair is discussed. Most important of all, a majority rule of decision making in presentation of multiple evidence is also found by the study of signal-noise-ratio of multiple eBAM network. A guaranteed stable state condition, i.e., the condition for the fastest recall of a pattern pair, is also studied. The result is coherent with the intuition of reasoning.  相似文献   
165.
A wide variety of speech recognition distortion measures have been proposed and tested, including some especially effective ones. It is shown that there is a general framework, based on the concepts of information theory, linking most of these measures. The distortion measure between any two speech spectra can be defined in terms of the distortions between the associated probability distributions. This general framework defines three broad families of distortion measures for speech recognition and provides a consistent way of combining the energy and the spectral information of a phonetic event. In addition, the cepstral-domain representation for several distortion measures is derived, allowing comparison of these measures in a domain that also yields convenient equations for their practical implementation  相似文献   
166.
167.
To ensure the core status can meet the requirements of thermal limits, stability and other constraints during the power ascension process of a nuclear power plant, operators usually gradually increase power based on onsite measurements and experience. To reduce the operator’s burden, this research develops a method to find an optimal power ascension path that can be followed by operators. The power ascension path is formulated as a multiobjective optimization problem with the following constraints: power ascension time, thermal limits, core stability and maximum rod line. A genetic algorithm is adopted to obtain the optimal power ascension path. The results show that using our approach full power can be achieved quickly, while maintaining reasonable margins of thermal limit and stability, in addition to satisfying maximum rod line criteria.  相似文献   
168.
The purpose of this study was to analyze the symbolization of colors as cultural codes, based on costume colors. In order to study the significance of colors in cultural changes, we carried out a quantitative analysis and interpreted it from the perspective of cultural semiotics. The range of this study was focused on Korean costume colors, over diverse diachronic stages of Korean culture. For this study 1535 color samples were collected, measured with a spectrophotometer, and analyzed quantitatively according their diachronic stages of origin. As a result, red, blue, and yellow were found to be the most frequently used colors during the Chosun Dynasty, a period based on Confucianism. These colors acted as cultural codes with cultural significance. During the Modern times pink, light blue, and black increased in frequency and represented the reception of western culture, the changing sex role of women in society, and utilitarianism. In these days, neutral colors and grayish tones of all colors are the most significant colors of high frequency. The use of such colors is closely related to industrialization, mechanization, functionalism, and the changes of women's sex roles in the societies. They are used as cultural codes, especially to emphasize a rational and masculine image rather than a feminine image. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 71–79, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20290  相似文献   
169.
The final closed-form expression for bit error probability (BEP) is presented for a DS-CDMA system using a maximal ratio combining (MRC) diversity over a Rician fading channel. The accuracy of the BEP estimate evaluated by this expression is verified by comparison with a semi-analytic simulation result. The effect that diversity order has on the BEP is also considered for typical multipath delay profiles with different Rician ratios  相似文献   
170.
The electrical properties of thin-film ferroelectric capacitors are known to degrade severely when exposed to hydrogen. In this study, we directly measured the effects of the grain boundary on the hydrogen-induced degradation in ferroelectric Pb(Zr, Ti)O3 (PZT) thin films by the location of the top Pt electrode either inside the grains or at the grain boundary. A strong relationship between the grain boundary and the electrical properties of ferroelectric capacitors as a result of hydrogen annealing was found. The degradation of the electrical properties in thin-film ferroelectric capacitors after hydrogen annealing is mainly due to the presence of the grain boundary in the ferroelectric thin film  相似文献   
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