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   138065篇
  免费   22306篇
  国内免费   6790篇
电工技术   8551篇
技术理论   3篇
综合类   8287篇
化学工业   30527篇
金属工艺   6837篇
机械仪表   7727篇
建筑科学   9874篇
矿业工程   3277篇
能源动力   3905篇
轻工业   14025篇
水利工程   2853篇
石油天然气   4785篇
武器工业   1284篇
无线电   18656篇
一般工业技术   21216篇
冶金工业   4568篇
原子能技术   1543篇
自动化技术   19243篇
  2024年   438篇
  2023年   1324篇
  2022年   2718篇
  2021年   4141篇
  2020年   4261篇
  2019年   5417篇
  2018年   5544篇
  2017年   6344篇
  2016年   6582篇
  2015年   8024篇
  2014年   9126篇
  2013年   11103篇
  2012年   10035篇
  2011年   10493篇
  2010年   10281篇
  2009年   9852篇
  2008年   9464篇
  2007年   9069篇
  2006年   8353篇
  2005年   6710篇
  2004年   5278篇
  2003年   4512篇
  2002年   4378篇
  2001年   3748篇
  2000年   3143篇
  1999年   1940篇
  1998年   966篇
  1997年   808篇
  1996年   646篇
  1995年   532篇
  1994年   421篇
  1993年   323篇
  1992年   220篇
  1991年   184篇
  1990年   137篇
  1989年   130篇
  1988年   79篇
  1987年   70篇
  1986年   65篇
  1985年   27篇
  1984年   29篇
  1983年   33篇
  1982年   29篇
  1981年   29篇
  1980年   20篇
  1979年   19篇
  1978年   12篇
  1977年   15篇
  1976年   16篇
  1959年   17篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
85.
Imperfection in information can be considered a crosscutting concern that manifests itself in diverse kinds of imprecision, uncertainty, or inconsistency in the data models of a software system. The extension of existing programming and querying interfaces for the different aspects of information imperfection requires a proper modularization of the different concerns of numerical imprecision handling, so that the extensions do not interfere with existing programming practices and do not obscure the original design. Aspect‐oriented design (AOD) enables such a form of nonintrusive extensions to be added to existing software libraries, clearly separating fuzziness or other imperfections in data as a differentiated concern that can be considered from the early phases of development. In this article, a general framework for aspect‐based extension of data models and fuzzy databases is described, and some design and implementation issues of such AOD‐based extensions on OJB database libraries are described as a case study. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 1199–1216, 2006.  相似文献   
86.
The objective of this study is to determine the chemical kinetics of desulphurization of Thai limestone in an atmospheric fluidized bed combustor (AFBC). The experiments, which employed the batch technique using the limestone samples from six major sources in Thailand, were performed in a laboratory‐scale AFBC. The results obtained were analysed and correlated in the form of apparent reaction rate and deactivation rate constants as a function of operating conditions of the furnace and their properties, respectively. The formulae derived from these correlations were kept as general as possible in order that they could be used as input parameters for the selected mathematical model of desulphurization in an AFBC that is suitable for practical use. The predicted results were in good agreement with the experimental data reported in the literature. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
87.
Failure analysis of hollow glasses The failure analysis is very important to clarify damages of hollow glasses. Damages of glass bottle through over pressure are very often linked with damages to persons. This is the reason why the causal research is from particular importance. Different surface characteristics of glass fragments as well as the fracture pattern give hints to the direction of the crack, the stress just before breakage and the reason of stress. A reconstruction of the bottle is a further helpful instrument for cause studies. The difference of the various characteristics of the surface will be explained. Further on there will be discussed different reasons and mechanism of fracture.  相似文献   
88.
89.
化学镀Ni—P镀层的X射线衍射研究   总被引:2,自引:0,他引:2  
根据X射线衍射分析结果,对化学镀高P(含P>11wt%或19at%)Ni-P镀层加热时效时,镀层成分和加热温度对结构转变的影响作了研究,结果表明,高P共晶、过共晶(含P>11wt%或19at%)合金的结构转变有如下特征:(1)相同加热时效条件下,Ni-P合金的结构转变与成分有密切关系:(2)对同一成分的过共晶合金,Ni-P合金的结构转变与时效温度密切相关;(3)过共晶合金在290~360℃温度范围内时效处理,出现Ni_xP_y介稳相,X射线衍射分析认为Ni_xP_y为Ni_(12)P_5。  相似文献   
90.
In order to investigate the formation of organic salts of drugs, two salts of pindolol were prepared using salt-forming agents which were crystalline and suitable for physical studies in the solid state. The stoichiometry of the products, pindolol benzoate and pindolol 2-methoxyphenylacetate, was established by elemental analysis. The precipitates formed were assessed by differential scanning calorimetry (DSC), thermogravimetry (TG), x-ray powder diffractometry (XRPD) and Fourier transform-infrared spectrometry (FT-IR). According to the TG and DSC curves, there was no water of crystallization in the precipitates, and the products were thermally stable. Both precipitates gave one sharp melting endotherm which differed from the endotherms of the starting compounds. The x-ray dipaction pattern of the precipitates direred clearly from those of the starting materials, acid and base. The products showed absorption by FT-IR typical of carboxylic acid salts at about 1640-1540 cm-1. The carbonyl absorption indicative of the carboxylic acid group of benzoic acid or 2-methonyphenylacetic acid was not detectable in the spectra of the precipitates. All this indicates that two new crystalline organic salts (1:1) were formed during the syntheses.  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