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   8082篇
  免费   245篇
  国内免费   7篇
电工技术   77篇
综合类   6篇
化学工业   1526篇
金属工艺   156篇
机械仪表   195篇
建筑科学   455篇
矿业工程   13篇
能源动力   250篇
轻工业   777篇
水利工程   124篇
石油天然气   36篇
无线电   557篇
一般工业技术   1350篇
冶金工业   1604篇
原子能技术   56篇
自动化技术   1152篇
  2023年   41篇
  2022年   89篇
  2021年   115篇
  2020年   106篇
  2019年   110篇
  2018年   128篇
  2017年   147篇
  2016年   130篇
  2015年   160篇
  2014年   212篇
  2013年   485篇
  2012年   383篇
  2011年   472篇
  2010年   334篇
  2009年   366篇
  2008年   483篇
  2007年   420篇
  2006年   346篇
  2005年   346篇
  2004年   280篇
  2003年   257篇
  2002年   243篇
  2001年   144篇
  2000年   119篇
  1999年   148篇
  1998年   218篇
  1997年   154篇
  1996年   173篇
  1995年   117篇
  1994年   124篇
  1993年   115篇
  1992年   82篇
  1991年   53篇
  1990年   79篇
  1989年   95篇
  1988年   62篇
  1987年   66篇
  1986年   63篇
  1985年   89篇
  1984年   77篇
  1983年   82篇
  1982年   63篇
  1981年   66篇
  1980年   39篇
  1979年   56篇
  1978年   57篇
  1977年   45篇
  1976年   58篇
  1975年   44篇
  1973年   38篇
排序方式: 共有8334条查询结果,搜索用时 15 毫秒
1.
Research suggests that schizotypal personality disorder (SPD) is a part of the spectrum of schizophrenia-related illnesses. This article hypothesizes that a deficit in the representation and maintenance of context is a core cognitive disturbance in schizophrenia and that SPD individuals should demonstrate context-processing deficits. To test this hypothesis, the authors administered 3 versions of their AX-CPT task, designed to assess context processing, to 35 healthy controls and 26 individuals with DSM-IV SPD. They also administered working memory and selective attention tasks. SPD individuals displayed context representation deficits similar to those found in schizophrenia but did not show the same additional deficits in context maintenance. Context processing was strongly associated with working memory and selective attention performance in the SPD individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
2.
3.
4.
Area- and time-specific marginal capacity costs of electricity distribution   总被引:2,自引:0,他引:2  
Marginal costs of electricity vary by time and location. In the past, researchers attributed the variations to factors related to electricity generation and transmission. These authors, however, have not analyzed possible variations in marginal distribution capacity costs (MDCC). The objectives of this paper are:
1. (i) to show that large MDCC variations are due to the dispersion in distribution capital expenditures by time and space,
2. (ii) to propose a method for quantifying the area- and time-specific MDCC in the presence of lumpy investments, and
3. (iii) to compare our MDCC estimates to those commonly used in the electric utility industry.
Our proposed method and its results were adopted by the California Public Utilities Commission (CPUC) in 1992 for Pacific Gas and Electric Company (PG&E), the largest privately owned electric utility in the U.S.  相似文献   
5.
6.
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.  相似文献   
7.
Nanostructured polymer blends prepared via anionic ring opening polymerizations of cyclic monomers in the presence of a pre-made polymer melt exhibit a number of special properties over traditional polymer blends and homopolymers. Here, we report on a simple and versatile method of in situ polymerization of macrocyclic carbonates in the presence of a maleic anhydride polypropylene (mPP) matrix and a surface-active compatibilizer (i.e. PC grafted onto a mPP backbone generated in situ) to yield a micro- and nanostructured polymer blends consisting of a polycarbonate (PC) minor phase, and a polypropylene (PP) major phase. By varying the processing conditions and concentration of the macrocyclic carbonate it was possible to reduce the size of the PC dispersions to an average minor diameter of 150 nm. NMR and TEM characterizations indicate that the PC dispersions do not influence crystal content in the PP phase. Overall, the results point to a simple strategy and versatile route to new polymeric materials with enhanced benefits.  相似文献   
8.
9.
Brian Dipert 《电子设计技术》2008,15(6):60-60,62,64,66
认为蜂窝系统是未来收看移动电视的唯一方法很可能是不对的。开路电视广播和卫星电视服务提供商也希望能在移动电视浪潮中成功获利。  相似文献   
10.
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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