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   412755篇
  免费   39645篇
  国内免费   27530篇
电工技术   29759篇
技术理论   58篇
综合类   55336篇
化学工业   40384篇
金属工艺   14263篇
机械仪表   24383篇
建筑科学   52446篇
矿业工程   20243篇
能源动力   14319篇
轻工业   22184篇
水利工程   22550篇
石油天然气   21292篇
武器工业   5013篇
无线电   28877篇
一般工业技术   31087篇
冶金工业   20419篇
原子能技术   4018篇
自动化技术   73299篇
  2024年   1670篇
  2023年   4835篇
  2022年   9368篇
  2021年   11001篇
  2020年   11865篇
  2019年   10020篇
  2018年   9529篇
  2017年   11547篇
  2016年   13592篇
  2015年   14679篇
  2014年   24031篇
  2013年   22938篇
  2012年   28455篇
  2011年   30396篇
  2010年   23948篇
  2009年   24892篇
  2008年   23794篇
  2007年   29585篇
  2006年   27165篇
  2005年   23749篇
  2004年   19870篇
  2003年   17708篇
  2002年   14291篇
  2001年   12121篇
  2000年   10241篇
  1999年   8258篇
  1998年   6434篇
  1997年   5561篇
  1996年   5123篇
  1995年   4379篇
  1994年   3771篇
  1993年   2786篇
  1992年   2389篇
  1991年   1832篇
  1990年   1545篇
  1989年   1354篇
  1988年   1009篇
  1987年   698篇
  1986年   542篇
  1985年   458篇
  1984年   449篇
  1983年   308篇
  1982年   289篇
  1981年   206篇
  1980年   173篇
  1979年   164篇
  1978年   83篇
  1977年   84篇
  1975年   63篇
  1959年   62篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
The adoption of unified fracture mechanics terminology (UFMT) will promote efficient communication between specialists in different fields of fracture research, harmonization of national and international standards relating to fracture mechanics, and last but not least improvement of the existing methodology for teaching and education in fatigue and fracture. In this paper the definitions of some basic and related terms included in different standards on fracture mechanics terminology are confronted with one another. Alternative definitions of the same terms are offered. By this strategy the author tries to show that the definitions of basic and related terms appropriate for the UFMT should emerge as a consequence of harmonizing a crack model with an actual crack and then both taken together with a fracture model, laboratory test methods, and failure assessment codes.Published in Problemy Prochonsti, No. 1, pp. 17–29, January, 1996.This paper is published as a matter of discussion.  相似文献   
23.
24.
本文介绍了一种实用的数据库设计方法,它以实体分析法为理论基础,通过对我们日常使用的表进行聚集和归类,完成数据库的逻辑设计,所设计的数据库满足BNOF范式。同时该方法可操作性较强,本文还介绍了自行设计的ERCM数据库辅助设计工具。  相似文献   
25.
26.
Buffalo milk Cheddar cheese samples of different ages were analysed for compositional attributes (CA), ripening indices (RI) and Instron Textural Profile (ITP). All samples were compositionally alike, except for pH and salt-in-moisture (SM) contents. RI showed significant variations. CA and RI showed highly significant correlations within themselves and with each other, except for moisture with pH, SM with moisture, MNFS, Fat and FDM and Fat with MNFS. The ITPs of cheeses showed significant variations and had highly significant intercorrelations indicating their interdependence. CA (except moisture and MNFS) and RI showed a highly significant correlationship with ITPs. Moisture content showed a highly significant correlationship with all ITPs, except cohesiveness and springiness, where it was significant. MNFS content showed significant correlations only with hardness and brittleness. Stepwise regression analysis revealed that MI was the most predominant factor influencing cheese texture, followed by pH, SM, FDM and TVFA. Knowing Ca and RI, the textural properties of cheeses can be forecast through mathematical equations. Similarly the age of cheese can also be predicted if RI and/or textural properties are known.  相似文献   
27.
What has become known as Community Operational Research has been around in the UK for many years. The election of Jonathan Rosenhead as President of the UK OR Society in 1986–87 was the catalyst for bringing together and expanding activities which had been carried out largely by individuals working in isolation on a voluntary basis. The following five years have seen the establishment of the Community OR Unit at Northern College, the Centre for Community OR at Hull University and the Community OR Network, which supports the activities of volunteer OR workers across the UK. This paper reviews the range and types of work which have been undertaken by various practitioners. An assessment of the success of community OR is made and a number of issues which have arisen are discussed. Finally, given the diverse nature of community OR, its practice and practitioners, there is some discussion about the future of the area.  相似文献   
28.
The hydrolysis of isocyanic acid in the gaseous phase has been investigated at temperatures between 553 and 613 K by mass spectrometry and evaluated to obtain the corresponding kinetic data. The reaction order and reaction constant have been determined. Finally, the influence of water on the catalysed formation of melamine from isocyanic acid under the operating conditions employed has been investigated in order to determine whether there is a need to try the process gas.  相似文献   
29.
A general numerical model is described for the dissolution kinetics of spherical particles in binary systems for any combination of first order reactions at the particle-matrix interface and long distance diffusion within the matrix. The model is applicable to both finite and infinite media and handles both complete and partial particle dissolution. It is shown that interfacial reactions can have a strong effect on the dissolution kinetics, the solute concentration at the particle-matrix interface and the solute concentration profile in the matrix.  相似文献   
30.
Results from applying the model on a sample of contractors, the majority of whom were international and operating in Egypt, reinforces the credibility of the developed methodology, claim the authors.  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