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   3394篇
  免费   93篇
  国内免费   4篇
电工技术   41篇
综合类   6篇
化学工业   612篇
金属工艺   118篇
机械仪表   78篇
建筑科学   120篇
矿业工程   14篇
能源动力   105篇
轻工业   219篇
水利工程   20篇
石油天然气   20篇
无线电   398篇
一般工业技术   582篇
冶金工业   747篇
原子能技术   18篇
自动化技术   393篇
  2022年   45篇
  2021年   36篇
  2020年   33篇
  2019年   42篇
  2018年   34篇
  2017年   47篇
  2016年   49篇
  2015年   35篇
  2014年   75篇
  2013年   206篇
  2012年   102篇
  2011年   148篇
  2010年   93篇
  2009年   85篇
  2008年   128篇
  2007年   116篇
  2006年   114篇
  2005年   117篇
  2004年   86篇
  2003年   89篇
  2002年   74篇
  2001年   68篇
  2000年   71篇
  1999年   60篇
  1998年   192篇
  1997年   127篇
  1996年   101篇
  1995年   69篇
  1994年   80篇
  1993年   87篇
  1992年   41篇
  1991年   43篇
  1990年   50篇
  1989年   55篇
  1988年   36篇
  1987年   42篇
  1986年   36篇
  1985年   39篇
  1984年   25篇
  1983年   40篇
  1982年   42篇
  1981年   27篇
  1980年   32篇
  1979年   24篇
  1978年   20篇
  1977年   32篇
  1976年   37篇
  1975年   21篇
  1973年   33篇
  1972年   29篇
排序方式: 共有3491条查询结果,搜索用时 31 毫秒
1.
We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations.  相似文献   
2.
A hybrid power compensator (HPC) consisting of a static VAr compensator and a dynamic compensator needs to be optimally controlled during the compensation of nonlinear loads. The HPC must be controlled to meet minimum requirements in terms of power factor and harmonic distortion, while at the same time minimizing its total cost. An artificial neural network (ANN) is used to control the HPC amidst a very dynamic power system environment. The performance of a reference ANN is evaluated while controlling an HPC connected to a typical nonlinear industrial load. The training and performance of the ANN is then optimized in terms of training set size, training set packing and ANN topology and the performance compared to the reference ANN. This paper highlights the importance of optimising the mentioned ANN parameters to achieve optimum ANN training and modeling accuracy. The results obtained reveals that the application of an ANN in controlling an HPC is feasible given that the ANN parameters are chosen appropriately.  相似文献   
3.
ABSTRACT: Shellac and wax-based citrus coatings were applied to Fallglo, Robinson, Sunburst, Dancy and Murcott tangerines, Nova and Orlando tangelos, and Temple oranges. Flavor volatiles were measured before and after storage. Concentrations of ethyl acetate, ethyl butyrate, isopentanol and 2-methyl-3-buten-2-ol increased markedly for fruit with shellac-based coatings, and were highly correlated with ethanol content, but at different ratios for the different varieties. The concentration increases were relatively less for fruit coated with the wax-based coatings, and suggest that high-gloss shellac and resin-based coatings are not appropriate for tangerines.  相似文献   
4.
5.
台北101层国际金融中心之结构施工技术与其设计考量概述   总被引:1,自引:0,他引:1  
本文旨在简要说明目前正在施工中之超高层大楼—台北国际金融中心之结构系统、钢结构工程、钢筋混凝土工程基础与深开挖工程等特殊施工技术,并佐以相关之设计考量与施工规划概要,以供工程界做参考。  相似文献   
6.
The results presented in the literature, which attempt to elucidate the mechanisms by which triglyceride oils are bleached by earths, are reviewed. The impact of this work and how the mechanistic proposals affect changes in oil properties are considered, with particular emphasis on the needs of the palm oil processor. Important properties include color, metals and phosphorus content and oxidative stability of the oil. Investigations made in our own laboratories have been aimed at elucidating the effect of varying physical and chemical properties of the bleaching earth on the quality of bleached and deodorized oils. Techniques used in this work are pore-size distribution, surface area, scanning and transmission electron microscopy and a variety of chemical and X-ray analysis methods. The ability to vary such parameters in montmorillonite clays by alteration of process conditions to give materials with specific performance characteristics is demonstrated. Comparisons are made between acid-activated montmorillonites and other clay types.  相似文献   
7.
8.
Defect equilibria for binary semiconducting compound phases which exhibit ionized native donor and acceptor defects were considered, and equations describing the pressure-temperature-composition relationships for these compound phases were derived. These equations were used to analyze experimental data from the literature for tin telluride. Excellent agreement was obtained between calculated thermodynamic and phase boundary values and experimental data. The approach presented is readily extended to obtain equations for the thermodynamic properties of ternary and higher order semiconducting compound phases.  相似文献   
9.
Egghe  Leo 《Scientometrics》2004,60(3):497-509
We show that the composition of two information production processes (IPPs), where the items of the first IPP are the sources of the second, and where the ranks of the sources in the first IPP agree with the ranks of the sources in the second IPP, yields an IPP which is positively reinforced with respect to the first IPP. This means that the rank-frequency distribution of the composition is the composition of the rank-frequency distribution of the first IPP and an increasing function φ, which is explicitly calculable from the two IPPs' distributions. From the rank-frequency distribution of the composition, we derive its size-frequency distribution in terms of the size-frequency distribution of the first IPP and of the function φ. The paper also relates the concentration of the reinforced IPP to that of the original one. This theory solves part of the problem of the determination of a third IPP from two given ones (so-called three-dimensional informetrics). In this paper we solved the “linear” case, i.e., where the third IPP is the composition of the other two IPPs. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
10.
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