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   260968篇
  免费   4287篇
  国内免费   1820篇
电工技术   5415篇
技术理论   5篇
综合类   1164篇
化学工业   42087篇
金属工艺   11022篇
机械仪表   7745篇
建筑科学   6595篇
矿业工程   1660篇
能源动力   5594篇
轻工业   25823篇
水利工程   2891篇
石油天然气   5998篇
武器工业   243篇
无线电   27798篇
一般工业技术   49233篇
冶金工业   47253篇
原子能技术   5616篇
自动化技术   20933篇
  2021年   2489篇
  2019年   2124篇
  2018年   3393篇
  2017年   3364篇
  2016年   3687篇
  2015年   2802篇
  2014年   4588篇
  2013年   11367篇
  2012年   7699篇
  2011年   10201篇
  2010年   8132篇
  2009年   8677篇
  2008年   9481篇
  2007年   9597篇
  2006年   8441篇
  2005年   7389篇
  2004年   6658篇
  2003年   6204篇
  2002年   6208篇
  2001年   6319篇
  2000年   5909篇
  1999年   5877篇
  1998年   12872篇
  1997年   9538篇
  1996年   7277篇
  1995年   5528篇
  1994年   5082篇
  1993年   4952篇
  1992年   3943篇
  1991年   3752篇
  1990年   3827篇
  1989年   3772篇
  1988年   3531篇
  1987年   3019篇
  1986年   3051篇
  1985年   3410篇
  1984年   3321篇
  1983年   3075篇
  1982年   2698篇
  1981年   2902篇
  1980年   2643篇
  1979年   2839篇
  1978年   2736篇
  1977年   2842篇
  1976年   3696篇
  1975年   2457篇
  1974年   2290篇
  1973年   2320篇
  1972年   1981篇
  1971年   1785篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
901.
A clinical study on functions of the cerebral cortex is reported. In this regard, 107 patients with a supratentorial expanding mass have been investigated before and after surgical removal of the lesion. The results obtained are discussed in the light of what is available in the literature.  相似文献   
902.
Jankovic  G. Black  L. 《Spectrum, IEEE》1996,33(11):62-69
The World Wide Web (WWW) is famous for weaving far-flung fans with like interests into true communities. It also puts a spin all its own on product and information delivery. Nowhere is this more apparent than in a global industry such as electrical and electronic engineering. The Web is still unmatched in its ability to receive and distribute information and software, and to encourage interaction and collaboration. These strengths stem from the Web's combination of many of the best features of existing media-audio, video, text, and graphics-to which it adds some unique new talents, such as the ability to manipulate information through software. Most corporations acknowledge the opportunities the Web presents. The paper presents some guidelines on how best to start turning them to advantage  相似文献   
903.
904.
All fields of engineering, whether chemical, civil, electrical, materials, mechanical, etc., encompass a common body of essential mathematics and science. In the freshman year of Drexels E4 program, this common mathematical and scientific foundation is cultivated in the Mathematical and Scientific Foundations of Engineering I, II and III (MSFE I, MSFE II, MSFE III). In an integrated fashion, MSFE I presents the essential calculus, physics and engineering mechanics vital to the freshman engineering student. In the first two quarters, MSFE II presents chemistry with clearly defined engineering applications and significance: in the third quarter, MSFE II presents living systems with the same thrust. Also in the third quarter, MSFE III presents basic circuits and circuit elements, and a brief introduction to electromagnetic theory.  相似文献   
905.
The influence of extra-cellular polymeric substances in microbiologically influenced corrosion Unexpected pitting failures in copper potable water installations have occurred in some countries (Germany, Sweden, Scotland, South-West England, Saudi-Arabia) in the mid-eighties. These failures could not be expected in a single case based on the chemical composition of the potable water. Further typical manifestation characteristics of this microbiologically influenced corrosion have been i.) an uptake of dissolved and undissolved copper species in an obsolete, non regular fashion, ii.) black layers of copper(II)-oxide on the inner tube surface, accompanied by posniakite and malachite in the pitting areas, and, iii.) the detection of extracellular polymeric substances (EPS). These EPS consist partly of polysaccharides. They could either be produced by microorganisms within the potable water installation or be transported in a dissolved or undissolved state into the installation. Consequently, they sediment on the inner surfaces of the copper tubes. The physico-chemical properties of some kinds of EPS, especially their membrane properties and their cation selectivity, play a key role in this corrosion process. This is shown exemplarily performing diffusion potential measurements and contact corrosion experiments.  相似文献   
906.
907.
908.
909.
Intercellular communication is needed for both the generation of the mesodermal germ layer and its division into distinct subpopulations. To dissect the functions of fibroblast growth factor receptor-1 (FGFR1) during mouse gastrulation as well as to gain insights into its possible roles during later embryonic development, we have introduced specific mutations into the Fgfr1 locus by gene targeting. Our results show functional dominance of one of the receptor isoforms and suggest a function for the autophosphorylation of site Y766 in the negative regulation of FGFR1 activity. Y766F and hypomorphic mutations in Fgfr1 generate opposite phenotypes in terms of homeotic vertebral transformations, suggesting a role for FGFR1 in patterning the embryonic anteriorposterior axis by way of regulation of Hox gene activity.  相似文献   
910.
This study focuses on improving microcalcification classification by establishing an efficient computer-aided diagnosis system that extracts Daubechies-4 and biorthogonal wavelet features. These wavelets were chosen because they have been used in military target recognition and fingerprint recognition research with images characterized by low contrast, similar to mammography. Feature selection techniques are employed to further increase classification performance. The artificial neural network feature selection techniques are complemented by a conventional decision boundary-based feature selection method. The results using the wavelet features are compared to more conventional measures of image texture, angular second moment, and Karhunen Loeve coefficients. The use of alternative signal processing to compare wavelet and neural techniques allows for a measure of the problem difficulty. It is concluded that advances and contributions have been made with the introduction of two novel feature extraction methods for breast cancer diagnosis, wavelets and eigenmasses. Additionally, feature selection techniques are demonstrated, compared, and validated, transforming adequate discrimination power into promising classification results  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