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   4916篇
  免费   45篇
  国内免费   4篇
电工技术   35篇
综合类   4篇
化学工业   471篇
金属工艺   36篇
机械仪表   58篇
建筑科学   175篇
矿业工程   15篇
能源动力   68篇
轻工业   237篇
水利工程   12篇
石油天然气   18篇
无线电   231篇
一般工业技术   395篇
冶金工业   2798篇
原子能技术   28篇
自动化技术   384篇
  2021年   18篇
  2019年   22篇
  2017年   21篇
  2016年   28篇
  2015年   24篇
  2014年   39篇
  2013年   145篇
  2012年   72篇
  2011年   116篇
  2010年   95篇
  2009年   84篇
  2008年   117篇
  2007年   104篇
  2006年   118篇
  2005年   78篇
  2004年   79篇
  2003年   87篇
  2002年   82篇
  2001年   60篇
  2000年   60篇
  1999年   119篇
  1998年   649篇
  1997年   405篇
  1996年   292篇
  1995年   198篇
  1994年   152篇
  1993年   169篇
  1992年   73篇
  1991年   59篇
  1990年   70篇
  1989年   67篇
  1988年   81篇
  1987年   74篇
  1986年   69篇
  1985年   69篇
  1984年   49篇
  1983年   60篇
  1982年   58篇
  1981年   52篇
  1980年   69篇
  1979年   46篇
  1978年   37篇
  1977年   93篇
  1976年   130篇
  1975年   44篇
  1974年   44篇
  1973年   34篇
  1972年   26篇
  1971年   17篇
  1970年   17篇
排序方式: 共有4965条查询结果,搜索用时 140 毫秒
91.
The detection and measurement of somatic cell mutation in vivo is an important subject of research for the assessment of human cancer risk induced by various environmental genotoxic factors. The possible mechanisms which influence the persistence of mutant cells of the hematoimmune system in the peripheral blood are presented. The erythroid system is a system which accumulates mutational lesions and so stably generates red blood cells with various phenotypic changes.  相似文献   
92.
In 3 experiments, the authors assessed whether attitude strength moderates the susceptibility of attitudes to item context effects in surveys. In Experiment 1, respondents completed multiple measures of attitude strength. Three weeks later, respondents participated in a context experiment. Results revealed that respondents with weak attitudes exhibited significantly larger context effect for 1 of 2 issues. In Experiment 2, the results of Experiment 1 were conceptually replicated by use of measures of interattitudinal embeddedness to assess attitude strength. In Experiment 3, significant strength-moderated context effects were found when attitude strength was assessed in a multi-item, multidimensional manner but not when it was assessed with a single item. Discussion focuses on measurement and theoretical issues related to the moderation and mediation of context effects in attitude surveys. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
93.
94.
95.
In the budding yeast, Saccharomyces cerevisiae, four separate but structurally related mitogen-activated protein kinase (MAPK) activation pathways are known. The best understood of these regulates mating. Pheromone binding to receptor informs cells of the proximity of a mating partner and induces differentiation to a mating competent state. The MAPK activation cascade mediating this signal is made up of Ste11 (a MEK kinase [MEKK]), Ste7 (a MAPK/ERK kinase [MEK]), and the redundant MAPK-related Fus3 and Kss1 enzymes. Another MAPK activation pathway is important for cell integrity and regulates cell wall construction. This cascade consists of Bck1 (a MEKK), the redundant Mkk1 and Mkk2 enzymes (MEKs), and Mpk1 (a MAPK). We exploited these two pathways to learn about the coordination and signal transmission fidelity of MAPK activation cascades. Two lines of evidence suggest that the activities of the mating and cell integrity pathways are coordinated during mating differentiation. First, cells deficient in Mpk1 are susceptible to lysis when they make a mating projection in response to pheromone. Second, Mpk1 activation during pheromone induction coincides with projection formation. The mechanism underlying this coordination is still unknown to us. Our working model is that projection formation generates a mobile second messenger for activation of the cell integrity pathway. Analysis of a STE7 mutation gave us some unanticipated but important insights into parameters important for fidelity of signal transmission. The Ste7 variant has a serine to proline substitution at position 368. Ste7-P368 has higher basal activity than the wild-type enzyme but still requires Ste11 for its function. Additionally, the proline substitution enables the variant to transmit the signal from mammalian Raf expressed in yeast. This novel activity suggests that Ste7-P368 is inherently more permissive than Ste7 in its interactions with MEKKs. Yet, Ste7-P368 cross function in the cell integrity pathway occurs only when it is highly overproduced or when Ste5 is missing. This behavior suggests that Ste5, which has been proposed to be a tether for the kinases in the mating pathway, contributes to Ste7 specificity and fidelity of signal transmission.  相似文献   
96.
The primary objective of this investigation was to demonstrate a new method of measuring activities. The mass spectrometric analysis of effusates from a unique valved Knudsen cell was used to determine the activity of Ag in the liquid Ag−Cu system at 1400 K. The alloy compositions were varied from one composition extreme to the otherin situ. The system exhibits positive deviation from ideal behavior, and the results are in agreement with previous investigations and are summarized by the equation
  相似文献   
97.
98.
99.
Consumer confidence is at its lowest ebb since 1980. Economic growth is at a standstill & unemployment & inflation are both rising. Here's a front-line report from more than three dozen operators who are fending off the recession's dual pressures of slow sales & rising costs. They are using discount pricing, partnering with vendors, setting pay for performance standards & a variety of other recession-beating practices.  相似文献   
100.
The yield stress is a simple function of the deformation ratio in the direction of testing for specimens oriented by uniaxial or biaxial stretching or rolling. Unless the yield stress increases more rapidly than in proportion to the deformation ratio, there will be instability during tensile creep under high loads. The relative merit of various polymers differs for creep and stress relaxation. Fatigue and bend recovery are also related to the molecular structure.  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