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   54485篇
  免费   2209篇
  国内免费   164篇
电工技术   790篇
综合类   271篇
化学工业   10583篇
金属工艺   1183篇
机械仪表   1168篇
建筑科学   2101篇
矿业工程   249篇
能源动力   1132篇
轻工业   5984篇
水利工程   448篇
石油天然气   209篇
武器工业   10篇
无线电   3332篇
一般工业技术   9895篇
冶金工业   12180篇
原子能技术   369篇
自动化技术   6954篇
  2023年   506篇
  2022年   632篇
  2021年   1183篇
  2020年   840篇
  2019年   870篇
  2018年   1420篇
  2017年   1250篇
  2016年   1509篇
  2015年   1328篇
  2014年   1664篇
  2013年   3169篇
  2012年   2448篇
  2011年   2808篇
  2010年   2194篇
  2009年   2101篇
  2008年   2362篇
  2007年   2252篇
  2006年   1768篇
  2005年   1430篇
  2004年   1227篇
  2003年   1124篇
  2002年   986篇
  2001年   792篇
  2000年   701篇
  1999年   871篇
  1998年   3148篇
  1997年   2011篇
  1996年   1463篇
  1995年   1030篇
  1994年   886篇
  1993年   815篇
  1992年   458篇
  1991年   389篇
  1990年   440篇
  1989年   427篇
  1988年   380篇
  1987年   401篇
  1986年   376篇
  1985年   504篇
  1984年   434篇
  1983年   403篇
  1982年   347篇
  1981年   382篇
  1980年   363篇
  1979年   323篇
  1978年   275篇
  1977年   417篇
  1976年   729篇
  1975年   252篇
  1973年   229篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
In this study, the effects of the phosphonic acid based sequestering agent EDTMPA used in the textile dye baths on colour and organic matter removal by ozone oxidation was experimentally investigated. Procion Navy HEXL dyestuff that has been commonly used for the reactive dyeing of cellulose fibers was selected as the model component. The organic matter oxidation by ozone was determined to obey the pseudo-first order kinetics as they are treated singly or in combination. COD removal rates obtained from pseudo-first order reaction kinetics showed that oxidation of Navy HEXL alone (0.0947 L/min) was faster than that of EDTMPA (0.0171 L/min) and EDTMPA with dye (0.0155 L/min) at pH 3.0. It was also found that reaction rates of single EDTMPA removal and EDTMPA and dye mixture removal increased as the reaction pH was increased from 3.0 to 10.5.  相似文献   
33.
It is commonly accepted that hands-on experiences increase both learning and enjoyment during coursework. Mechatronics projects provide both interesting and relevant hands-on experiences for a wide range of topics including design processes, basic mechatronics concepts, technical communication, and working in a group environment. ME2110: Creative Decisions and Design at Georgia Tech integrates mechatronics and technical communication into a sophomore level mechanical design class. This paper describes the course in detail, highlighting the course goals and layout, tools provided to the students, industry involvement, and the main challenges of administering such a course.  相似文献   
34.
35.
This study focuses on the visualization of a series of large earthquake simulations collectively called TeraShake. The simulation series aims to assess the impact of San Andreas Fault earthquake scenarios in Southern California. We discuss the role of visualization in gaining scientific insight and aiding unexpected discoveries.  相似文献   
36.
1前言及历史背景 为避免钢水造成燃烧或破碎引起对人体的可能伤害,必须对连铸平台的平面布置进行分析.  相似文献   
37.
This paper presents the current understanding of the flame retardant mechanism of Casico?. The study includes the flame retardant effect of each individual component: ethylene–acrylate copolymer, chalk and silicone elastomer, as well as the formation of an intumescent structure during heating. The flame retardant properties were investigated by cone calorimetry and oxygen index tests. To obtain insight into the flame retardant mechanism, heat treatment under different conditions has also been performed. The results indicate that the flame retardant mechanism of Casico is complex and is related to a number of reactions, e.g. ester pyrolysis of acrylate groups, formation of carbon dioxide by reaction between carboxylic acid and chalk, ionomer formation and formation of an intumescent structure stabilized by a protecting char. Special emphasis is given to the formation of the intumescent structure and its molecular structure as evaluated from 13C MAS‐NMR and 29Si MAS‐NMR, ESCA and XRD analysis. After treatment at 500°C the intumescent structure consists mainly of silicon oxides and calcium carbonate and after treatment at 1000°C the intumescent structure consists of calcium silicate, calcium oxide and calcium hydroxide. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
38.
Choosing a standard speed for visual inspection is difficult using standard work measurement techniques. This paper uses a different approach, taking a model of human functioning in inspection and deriving an optimum speed of working so as to balance the cost of time against the cost of errors. Random search is used as the model and both self-paced and externally-paced conditions are derived for multiple fault types. Optimization using a Golden Section search is used to provide optimum inspection speed.  相似文献   
39.
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology.  相似文献   
40.
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