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   270834篇
  免费   18363篇
  国内免费   9294篇
电工技术   12968篇
技术理论   24篇
综合类   14700篇
化学工业   43181篇
金属工艺   13703篇
机械仪表   15360篇
建筑科学   18367篇
矿业工程   7887篇
能源动力   6815篇
轻工业   15452篇
水利工程   4193篇
石油天然气   16664篇
武器工业   1651篇
无线电   26898篇
一般工业技术   30573篇
冶金工业   34129篇
原子能技术   2428篇
自动化技术   33498篇
  2024年   1048篇
  2023年   3988篇
  2022年   6584篇
  2021年   9180篇
  2020年   7086篇
  2019年   6048篇
  2018年   7158篇
  2017年   8158篇
  2016年   7727篇
  2015年   9611篇
  2014年   11650篇
  2013年   13658篇
  2012年   16303篇
  2011年   17816篇
  2010年   14059篇
  2009年   13418篇
  2008年   12927篇
  2007年   12455篇
  2006年   12886篇
  2005年   13995篇
  2004年   9761篇
  2003年   8220篇
  2002年   6280篇
  2001年   5611篇
  2000年   5701篇
  1999年   7043篇
  1998年   11556篇
  1997年   8237篇
  1996年   6680篇
  1995年   4938篇
  1994年   3873篇
  1993年   3056篇
  1992年   1775篇
  1991年   1524篇
  1990年   1232篇
  1989年   1012篇
  1988年   824篇
  1987年   555篇
  1986年   475篇
  1985年   362篇
  1984年   207篇
  1983年   194篇
  1982年   251篇
  1981年   273篇
  1980年   260篇
  1979年   95篇
  1978年   123篇
  1977年   628篇
  1976年   1354篇
  1975年   107篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
134.
135.
Programs for rule based electromyography (EMG) interpretation and reporting are described. A number of parameters are obtained during an EMG investigation. The combination of these data leads to a neurophysiological conclusion. Knowledge from the literature, research and experience is the basis for rule development. Rules have been developed for 14 of the most commonly used classifications of an EMG. The syntax is relatively easy and the user may change the rules, add rules or apply the system for other types of data. The results are displayed in a new graphical way. The system presented here is part of an integrated EMG laboratory with administrative routines, distributed databases for storage of results and routines for automatic report generation.  相似文献   
136.
Mutual information-based analysis of JPEG2000 contexts.   总被引:4,自引:0,他引:4  
Context-based arithmetic coding has been widely adopted in image and video compression and is a key component of the new JPEG2000 image compression standard. In this paper, the contexts used in JPEG2000 are analyzed using the mutual information, which is closely related to the compression performance. We first show that, when combining the contexts, the mutual information between the contexts and the encoded data will decrease unless the conditional probability distributions of the combined contexts are the same. Given I, the initial number of contexts, and F, the final desired number of contexts, there are S(I, F) possible context classification schemes where S(I, F) is called the Stirling number of the second kind. The optimal classification scheme is the one that gives the maximum mutual information. Instead of using an exhaustive search, the optimal classification scheme can be obtained through a modified generalized Lloyd algorithm with the relative entropy as the distortion metric. For binary arithmetic coding, the search complexity can be reduced by using dynamic programming. Our experimental results show that the JPEG2000 contexts capture the correlations among the wavelet coefficients very well. At the same time, the number of contexts used as part of the standard can be reduced without loss in the coding performance.  相似文献   
137.
介绍了子午轮胎硫化的各种介质性能要求及介质供应工艺流程,分析了各种介质的质量要求.介绍了系统各参数的控制调节项目及运行技术管理的一些措施.  相似文献   
138.
介绍并分析了春光油田现代油藏经营管理模式的构建与运作及实施效果.  相似文献   
139.
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry  相似文献   
140.
Oxide films were deposited on different substrates by laser molecular beam epitaxy. Reflection high-energy electron diffraction was performed to in situ investigate the change of growth mode and the lattice relaxation during the growth. An asymmetrical phenomenon was found in the two kinds of strain states, compressive stress and tensile stress of heterostructures with different lattice mismatch. In the case of BaTiO3/SrTiO3 (2.2%), 2D layer-by-layer growth mode without lattice relaxation can be maintained for a longer period for BTO films on STO with compressive stress, comparing to STO films on BTO with tensile stress. When MgO films were deposited on SrTiO3 with a large mismatch of 7.8%, compressive stress leads to rapid lattice relaxation with a very thin wet layer, and 3D strained island were observed. As a comparison, SrTiO3 films on MgO with tensile stress were configured. No RHEED patterns can be observed duo to a large tensile stress.  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