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   56862篇
  免费   2483篇
  国内免费   204篇
电工技术   872篇
综合类   101篇
化学工业   10851篇
金属工艺   2071篇
机械仪表   3074篇
建筑科学   1239篇
矿业工程   53篇
能源动力   2158篇
轻工业   4067篇
水利工程   253篇
石油天然气   211篇
武器工业   2篇
无线电   10029篇
一般工业技术   11244篇
冶金工业   5824篇
原子能技术   632篇
自动化技术   6868篇
  2023年   536篇
  2022年   836篇
  2021年   1412篇
  2020年   997篇
  2019年   1009篇
  2018年   1332篇
  2017年   1327篇
  2016年   1652篇
  2015年   1305篇
  2014年   2036篇
  2013年   3485篇
  2012年   3203篇
  2011年   3911篇
  2010年   2983篇
  2009年   3168篇
  2008年   2922篇
  2007年   2465篇
  2006年   2245篇
  2005年   1940篇
  2004年   1851篇
  2003年   1700篇
  2002年   1653篇
  2001年   1292篇
  2000年   1209篇
  1999年   1183篇
  1998年   2199篇
  1997年   1438篇
  1996年   1208篇
  1995年   963篇
  1994年   724篇
  1993年   683篇
  1992年   491篇
  1991年   494篇
  1990年   417篇
  1989年   404篇
  1988年   323篇
  1987年   276篇
  1986年   254篇
  1985年   231篇
  1984年   199篇
  1983年   151篇
  1982年   152篇
  1981年   131篇
  1980年   129篇
  1979年   102篇
  1978年   94篇
  1977年   123篇
  1976年   158篇
  1975年   80篇
  1974年   74篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
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   
132.
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   
133.
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   
134.
Language-level support for object persistence frees programmers from having to confront a broad class of database issues from within their applications. By virtue of its metaobject protocol, CLOS is a language whose semantics can be tailored by individual programmers. We used the metaobject protocol to extend CLOS with support for object persistence. Our goal was to obtain a version of CLOS with persistence to which we could easily port a commercial geometric CAD modeling system. We describe the design and implementation of our persistence extension and highlight the strengths and weaknesses exhibited by the CLOS metaobject protocol during our experiment. For many aspects of the implementation we found that the metaobject protocol was ideal. In other cases we had to choose among paying a large performance penalty, extending the protocol, and bypassing the protocol by modifying the language implementation directly.  相似文献   
135.
136.
137.
Density-Induced Support Vector Data Description   总被引:6,自引:0,他引:6  
  相似文献   
138.
A novel circuit for realising negative immittance using a single plus-type second-generation current conveyor is proposed. The immittance values of the the circuit, which only use four passive elements, can be orthogonally adjusted. The circuit does not require component matching  相似文献   
139.
Computational simulations of superplastic forming by 2-D plane strain including simple analytical and finite element and 3-D finite element modeling were compared with each other. The piece being formed was a rectangular pan with a female die. The effect of die entrance radii upon pressurization rate and thickness distribution was examined. Experimental work was conducted on superplastic aluminum-lithium 8090 material for comparison with predictions from simulations.  相似文献   
140.
Abstract The key research question for this study was to ask whether or not innovative teaching practices would lead to the development of learning outcomes essential for preparing the younger generation for the challenges of life in the knowledge society of the 21st century, and if so, how are the pedagogical features related to the different learning outcomes. Preliminary analyses of the case study data collected from the SITES M2 Study in Hong Kong reveal that where the development of more significant learning gains were observed, the cases possess characteristics additional to the criteria defined in the Study for selection of innovation. More importantly, it was found that the impact of the pedagogical practices was not determined simply by the aggregation of characteristics of the practices per se , nor on the technologies used, but on whether 'empowerment' permeates the curriculum goal and process. Further, this paper claims that these affective and socio-cognitive learning outcomes are more important as preparation for lifelong learning in the 21st century than 'knowledge management competencies'.  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