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   15276篇
  免费   1510篇
  国内免费   857篇
电工技术   592篇
技术理论   2篇
综合类   1728篇
化学工业   1585篇
金属工艺   449篇
机械仪表   803篇
建筑科学   1893篇
矿业工程   841篇
能源动力   393篇
轻工业   1352篇
水利工程   543篇
石油天然气   1003篇
武器工业   86篇
无线电   670篇
一般工业技术   1738篇
冶金工业   1421篇
原子能技术   131篇
自动化技术   2413篇
  2024年   55篇
  2023年   180篇
  2022年   523篇
  2021年   564篇
  2020年   516篇
  2019年   475篇
  2018年   424篇
  2017年   412篇
  2016年   543篇
  2015年   645篇
  2014年   1051篇
  2013年   978篇
  2012年   1127篇
  2011年   1238篇
  2010年   978篇
  2009年   964篇
  2008年   785篇
  2007年   950篇
  2006年   827篇
  2005年   746篇
  2004年   624篇
  2003年   527篇
  2002年   475篇
  2001年   357篇
  2000年   255篇
  1999年   224篇
  1998年   204篇
  1997年   166篇
  1996年   119篇
  1995年   108篇
  1994年   79篇
  1993年   59篇
  1992年   67篇
  1991年   52篇
  1990年   39篇
  1989年   36篇
  1988年   26篇
  1987年   17篇
  1986年   27篇
  1985年   20篇
  1984年   20篇
  1983年   19篇
  1982年   16篇
  1980年   8篇
  1966年   10篇
  1964年   13篇
  1960年   7篇
  1957年   10篇
  1956年   7篇
  1955年   8篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
51.
The paper examines the problem of a penny-shaped crack which is formed by the development of a crack in both the fibre and the matrix of a composite consisting of an isolated elastic fibre located in an elastic matrix of infinite extent. The composite region is subjected to a uniform strain field in the direction of the fibre. The paper presents two integral-equation based approaches for the analysis of the problem. The first approach considers the formulation of the complete integral equations governing the associated elasticity problem for a two material region. The second approach considers the boundary integral equation formulation of the problem. Both methods entail the numerical solution of the governing integral equations. The solutions to these integral equations are used to evaluate the stress intensity factor at the boundary of the penny-shaped crack.  相似文献   
52.
Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark‐ignition engine, having cylindrical disc‐shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark‐ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
53.
本文对代数曲面的几何连续拼接作了研究,给出了多个代数曲面的几何连续过渡方法,同时给出了一种基于分片的曲面过渡方法。  相似文献   
54.
In 1993, the American Society for Testing and Materials carried out a field test of newly calculated tristimulus weighting factors. These weighting factors had been calculated by a method proposed by Venable. the test also included a method of correction for bandpass dependence put forth by Stearns. the purpose of the trial was to assess the possible reduction in bandpass dependence introduced by each of these sets of weights. A large number of sets of spectral data were gathered from the cooperators in the field test. Results of integration by the various sets of tristimulus weighting factors were calculated. A total of 15 120 color differences were calculated and statistics were derived to test the probable error resulting from each method of correction. Errors attributable to bandpass dependence were on the order of a few tenths to as much as one CIELAB unit when uncorrected weight sets were used. These errors could be reduced to a few hundreths of a CIELAB unit, and in some cases to a few thousandths of a unit, by employing one correcting strategy or the other. an overall mix of strategies was ultimately chosen to minimize the bandpass dependence over the entire range of weight sets. Utilizing this mixed strategy, the median error introduced into 10-nm integration by bandpass dependence was only 0.004 CIELAB units. © 1995 John Wiley & Sons, Inc.  相似文献   
55.
化学镀SiCp/Ni-P复合镀层与基体结合强度及其影响因素   总被引:1,自引:0,他引:1  
论述了SiCp/Ni-P复合镀层与钢基体的结合强度及其影响因素。复合镀层中离界面5μm厚度以内区域的组成及应力状态对镀层/基体的界面结合有决定性作用,在该区域以外SiC粒径变化不影响镀层的结合强度。适当的热处理可提高界面结合力。  相似文献   
56.
本文重点探讨了如何将矢量图形进行参数化重建,即从只具备纯几何信息的矢量图中抽取元素间的拓扑信息,从而保证尺寸变动时保持拓扑关系不变,并能对多视图进行同步处理。这一方法的最大优点是用户作图时不受约束,因为系统只处理最终图形。另外,该思想并不局限于Auto CAD环境上,可方便地推广到其它二维绘图系统中。  相似文献   
57.
实证分析:上市公司资本结构的影响因素   总被引:13,自引:0,他引:13  
在国内外相关研究的基础上,利用我国资本市场的公开数据,对上市公司资本结构的影响因素进行实证研究,得出了若干重要结论。  相似文献   
58.
Drug users are particularly at risk for contracting the human immunodeficiency virus and serve as a major mechanism for spreading the virus to other sectors of the population. As a result drug abuse treatment and potential behavioral change strategies are primary public health issues. The purpose of this article is to review the contributions included in this special edition, which represent an effort to describe the most current thinking in the field with a blend of theoretical, review, and empirical articles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
59.
在对影响体育教学质量的几种环境因素分析的基础上,提出了克服体育实践教学环境 因素的消极影响的主要措施以及正确利用这些物理因素的积极作用。  相似文献   
60.
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