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   117678篇
  免费   10965篇
  国内免费   6208篇
电工技术   7119篇
技术理论   5篇
综合类   8213篇
化学工业   19457篇
金属工艺   6484篇
机械仪表   7509篇
建筑科学   8220篇
矿业工程   2627篇
能源动力   3127篇
轻工业   10616篇
水利工程   2347篇
石油天然气   4637篇
武器工业   948篇
无线电   14478篇
一般工业技术   14872篇
冶金工业   5767篇
原子能技术   1444篇
自动化技术   16981篇
  2024年   523篇
  2023年   1719篇
  2022年   3362篇
  2021年   4552篇
  2020年   3355篇
  2019年   3009篇
  2018年   3304篇
  2017年   3655篇
  2016年   3658篇
  2015年   4824篇
  2014年   5984篇
  2013年   7459篇
  2012年   8059篇
  2011年   9026篇
  2010年   8074篇
  2009年   7650篇
  2008年   7557篇
  2007年   6977篇
  2006年   6602篇
  2005年   5591篇
  2004年   4167篇
  2003年   3617篇
  2002年   3775篇
  2001年   3145篇
  2000年   2530篇
  1999年   2128篇
  1998年   1898篇
  1997年   1522篇
  1996年   1265篇
  1995年   1054篇
  1994年   925篇
  1993年   755篇
  1992年   543篇
  1991年   441篇
  1990年   338篇
  1989年   290篇
  1988年   228篇
  1987年   160篇
  1986年   138篇
  1985年   124篇
  1984年   108篇
  1983年   71篇
  1982年   81篇
  1981年   65篇
  1980年   64篇
  1979年   57篇
  1978年   42篇
  1977年   61篇
  1976年   99篇
  1975年   56篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The fabric and faces of threat, and the expediency and efficiency in the communication of threat, are examined with a threat appraisal model. This model is empirically tested on an ongoing communication challenge, the issuance of terror alerts by the United States' Department of Homeland Security (DHS), focusing on how threat is appraised by both the conservative and liberal audiences. Findings showed a shared view by the DHS and conservative audiences on the levels and nature of threats; liberal audiences thought otherwise. Though there appeared to be a consensus between the conservative and liberal audiences on the efficacy of threat communication, more internal consistency within DHS is needed to optimise its effectiveness.  相似文献   
32.
Choung  Jae-Yong  Min  Hong-Ghi  Park  Myeong-Cheol 《Scientometrics》2003,58(1):115-128
In recent years, the topic of knowledge production has been widely investigated in the advanced countries. However, the process by which knowledge is produced in the developing countries has not been fully explored or characterized. In Korea, the science and engineering fields strongly reflect systems of knowledge production in the universities and demonstrate the dynamics of systems of innovation for knowledge production. Through using a case study including data for knowledge production, in the field of information and telecommunication, the following general trends were observed. Firstly, there has been a trend towards increasing the capabilities for knowledge production, via domestic and foreign collaboration. Secondly, there has been an increasing trend towards the diversification of knowledge sources such as university-industry, and university-public research institutes. Finally, the establishment of a nation's knowledge base is influenced by governmental research and development policies. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
33.
Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for NO reduction by NH3 was examined in a fixed-bed flow reactor. The deactivation of the catalyst was strongly dependent on reaction temperature. At high reaction temperatures over 300°C, the catalyst did not lose its initial activity up to 50 h of operation, regardless of SO2 feed concentration from 500 to 20,000 ppm. However, at low reaction temperatures near 250°C, apparent deactivation did occur. Changes in the physicochemical properties such as surface area and sulfur content of deactivated catalyst well correlated with catalyst activity, depending upon reaction temperatures. The deactivation was due to pore blocking and/or filling by deactivating agents, which plugged and/or filled the pores of catalyst. The deactivating agents deposited on the catalyst surface were presumed to be (NH4)2SO4 and/or (NH4)HSO4 from the results of TGA and ion-chromatography measurement.  相似文献   
34.
High level expression of recombinant human tumour necrosis factor β (rh TNF-β) in Escherichia coli results in the formation of two portions of protein, namely soluble active protein and insoluble protein which is inactive and aggregates in the form of inclusion bodies (IBs). In this study, a procedure for purification and renaturation of rh TNF-β from inclusion bodies has been designed and verified experimentally with a product purity of more than 90% and a recovery of about 30%. The procedure includes washing of IBs with specific wash buffer (Triton X-100/EDTA/lysozyme/PMSF), their solubilization with 8 mol dm?3 alkaline urea, purification with ion-exchange columns, refolding with renaturation buffer and finally concentration and desalination with an ultrafiltration membrane. The characteristics of the renatured protein were identical with those of purified protein from the soluble fraction as demonstrated by (1) SDS-PAGE, (2) cytotoxic activity on mouse L929 cells, (3) N-terminal amino acid sequence, and (4) gel filtration chromatography.  相似文献   
35.
36.
Four-channel receiver arrays have been fabricated by monolithically integrating diffused InGaAs JFET-based electronics with InGaAs pin photodiodes. Cascode and simple inverter transimpedance amplifier circuits have been produced, both of which use a micro-FET as a tunable feedback element to vary bandwidth between 20 and 800 MHz. A sensitivity of -28.2 dBm was achieved at 1.25 Gbit/s with crosstalk between adjacent channels of -50 dB (electrical).<>  相似文献   
37.
38.
Piezoelectric Nanogenerators for Self-Powered Nanodevices   总被引:1,自引:0,他引:1  
A novel approach converts nanoscale mechanical energy into electric energy for self-powering nanodevices.In our own work, we've used piezoelectric zinc-oxide nanowire (ZnO NW) arrays to demonstrate a novel approach for converting nanoscale mechanical energy into electric energy. Here, we review the fundamental principle behind the nanogenerator, present an approach for improving its performance, and discuss some of the challenges we face in pushing this technology to reach its potential.  相似文献   
39.
文中解决了2-重自补图的计数问题,获得了具有p个顶点的2-重自补图的数目是其中Z(A)表示置换群A的圈指标,S ̄(2)_p表示p次对称群的对群.  相似文献   
40.
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   
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