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   62894篇
  免费   6032篇
  国内免费   3166篇
电工技术   4377篇
技术理论   3篇
综合类   4347篇
化学工业   9721篇
金属工艺   3729篇
机械仪表   4454篇
建筑科学   4985篇
矿业工程   2229篇
能源动力   1680篇
轻工业   4574篇
水利工程   1313篇
石油天然气   3342篇
武器工业   609篇
无线电   7334篇
一般工业技术   6943篇
冶金工业   2809篇
原子能技术   751篇
自动化技术   8892篇
  2024年   315篇
  2023年   1159篇
  2022年   2226篇
  2021年   2903篇
  2020年   2368篇
  2019年   1757篇
  2018年   2113篇
  2017年   2282篇
  2016年   2128篇
  2015年   3087篇
  2014年   3698篇
  2013年   4218篇
  2012年   4644篇
  2011年   4794篇
  2010年   4244篇
  2009年   3913篇
  2008年   3708篇
  2007年   3499篇
  2006年   3429篇
  2005年   2790篇
  2004年   1905篇
  2003年   1498篇
  2002年   1325篇
  2001年   1094篇
  2000年   1069篇
  1999年   1104篇
  1998年   894篇
  1997年   779篇
  1996年   709篇
  1995年   575篇
  1994年   434篇
  1993年   331篇
  1992年   262篇
  1991年   198篇
  1990年   147篇
  1989年   140篇
  1988年   97篇
  1987年   61篇
  1986年   53篇
  1985年   28篇
  1984年   25篇
  1983年   17篇
  1982年   22篇
  1981年   17篇
  1980年   19篇
  1979年   4篇
  1977年   1篇
  1966年   2篇
  1959年   4篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
A new efficient method for synthesising nitriles, important organic reagents, is reported in this paper. In an environmentally benign solvent‐free system, aryl carboxylic acids were converted into the corresponding nitriles via one‐pot reactions, by amidation with ethyl carbamate followed by dehydration with thionyl chloride, in excellent yields. The results showed that the method has the advantages of lower cost, higher yield, less pollution and greater ease of work‐up. Copyright © 2008 Society of Chemical Industry  相似文献   
82.
83.
84.
This paper presents the rapid, low-temperature bonding between silicon and steel using the rapid thermal annealing process. Three different thin-film adhesion layer systems including silver, gold, and nickel were utilized as the intermediate bonding material to assist the eutectic Pb/Sn bonding between silicon and steel. The bonding temperature was set at 220/spl deg/C for 20 s, with a 20-s ramp-up time. Five experiments were conducted to determine the strength of the bond, including static tensile and compressive four-point bend tests, axial extension tests, tensile bending fatigue tests, and corrosion resistance tests. The test results have shown that the gold adhesion layer is the most robust, demonstrating minimal creep during fatigue tests, no delamination during the tensile or compressive four-point bend tests, and acceptable strength during the axial extension tests. Additionally, all adhesion layers have withstood four months of submersion in various high-temperature solutions and lubricants without failure. Simulations of the axial stresses and strains that developed during the four-point bend and axial extension tests were performed and showed that the presence of the silicon die provides a local reinforcement of the bond as observed in the experimental tests.  相似文献   
85.
棉织物手感值的模糊综合评判研究   总被引:4,自引:0,他引:4  
利用模糊综合评判数学模型对棉织物的手感值进行了计算与分析,这种方法简单、可靠,与主观评估结果有很好的一致性,为纺织生产的质量判断提供了便利。  相似文献   
86.
3-D MCM封装技术及其应用   总被引:1,自引:0,他引:1  
介绍了超大规模集成电路(VLSI)用的3-D MCM封装技术的最新发展,重点介绍了3-D MCM封装垂直互连工艺,分析了3-D MCM封装技术的硅效率、复杂程度、热处理、互连密度、系统功率与速度等问题,并对3-D MCM封装的应用作了简要说明。  相似文献   
87.
This paper investigates three kinds of permanent-magnet arrays used in planar motors with polarity centers distributed in the lattices of a matrix. The magnetic field of every kind of magnet array is analyzed by analytical methods. First, we give a Laplace equation of magnetic scalar potential and a series of boundary conditions. Then, we derive the analytical expressions of magnet field strength and magnet flux density in the air gap of each kind of magnet array by the method of separation of variables. Finally, we compare the three types of magnet arrays on the basis of the analytical solutions.  相似文献   
88.
Today, there's an urgent need for well-trained pervasive computing engineers and scientists. Pervasive computing has evolved into a critical field, influencing a broad range of industries from healthcare to manufacturing to defense. However, most computer engineering and computer science programs pay marginal attention, at best, to the field. In this issue, the authors of the Rochester Institute of Technology describes a set of courses on pervasive computing topics and a supporting laboratory designed for both computer engineering and computer science students  相似文献   
89.
Domain-Driven, Actionable Knowledge Discovery   总被引:1,自引:0,他引:1  
Data mining increasingly faces complex challenges in the real-life world of business problems and needs. The gap between business expectations and R&D results in this area involves key aspects of the field, such as methodologies, targeted problems, pattern interestingness, and infrastructure support. Both researchers and practitioners are realizing the importance of domain knowledge to close this gap and develop actionable knowledge for real user needs.  相似文献   
90.
Two fundamental concepts and quantities, realization factors and performance potentials, are introduced for Markov processes. The relations among these two quantities and the group inverse of the infinitesimal generator are studied. It is shown that the sensitivity of the steady-state performance with respect to the change of the infinitesimal generator can be easily calculated by using either of these three quantities and that these quantities can be estimated by analyzing a single sample path of a Markov process. Based on these results, algorithms for estimating performance sensitivities on a single sample path of a Markov process can be proposed. The potentials in this paper are defined through realization factors and are shown to be the same as those defined by Poisson equations. The results provide a uniform framework of perturbation realization for infinitesimal perturbation analysis (IPA) and non-IPA approaches to the sensitivity analysis of steady-state performance; they also provide a theoretical background for the PA algorithms developed in recent years  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