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   3680篇
  免费   48篇
  国内免费   6篇
电工技术   49篇
综合类   16篇
化学工业   530篇
金属工艺   41篇
机械仪表   61篇
建筑科学   149篇
矿业工程   4篇
能源动力   58篇
轻工业   232篇
水利工程   34篇
石油天然气   2篇
武器工业   1篇
无线电   363篇
一般工业技术   477篇
冶金工业   1311篇
原子能技术   35篇
自动化技术   371篇
  2021年   31篇
  2019年   20篇
  2018年   41篇
  2017年   34篇
  2016年   31篇
  2015年   20篇
  2014年   50篇
  2013年   181篇
  2012年   75篇
  2011年   103篇
  2010年   85篇
  2009年   92篇
  2008年   104篇
  2007年   96篇
  2006年   84篇
  2005年   90篇
  2004年   83篇
  2003年   77篇
  2002年   73篇
  2001年   73篇
  2000年   68篇
  1999年   86篇
  1998年   359篇
  1997年   207篇
  1996年   171篇
  1995年   142篇
  1994年   113篇
  1993年   104篇
  1992年   61篇
  1991年   45篇
  1990年   65篇
  1989年   58篇
  1988年   53篇
  1987年   54篇
  1986年   56篇
  1985年   53篇
  1984年   43篇
  1983年   38篇
  1982年   32篇
  1981年   41篇
  1980年   41篇
  1979年   35篇
  1978年   26篇
  1977年   54篇
  1976年   69篇
  1975年   24篇
  1974年   24篇
  1973年   18篇
  1972年   19篇
  1971年   18篇
排序方式: 共有3734条查询结果,搜索用时 15 毫秒
21.
Visual and auditory stimulus discrimination tasks, analogous to those used in the Reitan-Klove Sensory Perceptual Examination, were performed by 12 cocaine-dependent and 5 alcohol-dependent patients after 1 week, 3 weeks, and 3 months of verified abstinence. Sixteen control subjects, who were not substance-dependent, performed the same tasks after comparable intervals. During each task, either visual or auditory stimuli were presented in the left, in the right, or in both sensory fields. A simple key press was made to discriminate these conditions. Cocaine-dependent patients responded more slowly than control subjects during both tasks. The reaction-time slowing persisted across all three sessions, spanning a 3-month period of abstinence. There were no significant differences between the cocaine-dependent and control groups in response accuracy. In the context of other findings, these findings are interpreted as reflecting an enduring effect of prior cocaine dependence on motor as opposed to sensory functioning.  相似文献   
22.
23.
  相似文献   
24.
Melvin Webber's seminal papers of 1963/64, which posited the arrival of a Nonplace Urban Realm and called upon planners to abandon their obsession with space, have proved highly prescient: metropolitan areas have deconcentrated and spread as he suggested, and the arrival of the informational age further reinforces these trends by creating a spaceless economy. But urban agglomeration economies do continue to operate, and traditional urban nodes will remain important in the new space‐economy.  相似文献   
25.
The 5 Kd (MW), retinoic acid responsive thymosin beta-10 protein is expressed at relatively high levels in embryonic tissues, and its mRNA is abundant in a variety of tumors and tumor cell lines. Recently this protein (together with other members of the same protein family) was found to be a major intracellular G-actin binding protein. In the present study, plasmid-driven overexpression of thymosin beta-10 gene results in increased susceptibility of permanently transfected fibroblasts to undergo apoptosis. Conversely, knockout of the endogenous gene via overexpression of the antisense mRNA inhibited cell death induced by TNF-alpha and calcium ionophore A23187. Differential expression of thymosin beta-10 influenced cell proliferation, cell morphology, and expression/distribution of the antiapoptotic protein bcl-2. The presence of increased cytoplasmic thymosin beta-10 precipitated significant disruption of phalloidin-stained actin stress fibers while knockout of thymosin expression promoted F-actin assembly. These and other observations suggest that thymosin beta-10 (a) plays a significant and possibly obligatory role in cellular processes controlling apoptosis possibly by acting as an actin-mediated tumor suppressor, (b) perhaps functions as a neoapoptotic influence during embryogenesis, and (c) may mediate some of the pro-apoptotic anticancer actions of retinoids.  相似文献   
26.
27.
A simple measurement system is described for evaluating damage to graphite-epoxy panels, such as those used in high-performance aircraft. The system uses a heating laser and infrared imaging system to measure thermal performance. Thermal conductivity or diffusivity is a sensitive indicator of damage in materials, allowing this thermal measurement to show various degrees of damage in graphite-epoxy composites. Our measurements track well with heat-flux damage to graphite epoxy panels. This measurement system, including analysis software, could easily be used in the field, such as on the deck of an aircraft carrier or at remote air strips.  相似文献   
28.
Structural equation modeling was used to test theoretically based models in which psychological separation and attachment security variables were related to career indecision and those relations were mediated through vocational self-concept crystallization. In contrast to previous studies, which have found either weak or no support for a relation between separation or attachment security variables and career indecision, results based on a sample of 350 college students indicated that some components of separation and attachment security did relate to career indecision in a theoretically supportable direction. Results also revealed that regardless of whether global or component career indecision measures were used, separation and attachment security effects on indecision were at least partially mediated through vocational self-concept crystallization. The strongest mediated relations were observed for the effects of attachment anxiety and maternal separation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
29.
Understanding how aging influences cognition across different cultures has been hindered by a lack of standardized, cross-referenced verbal stimuli. This study introduces a database of such item-level stimuli for both younger and older adults, in China and the United States, and makes 3 distinct contributions. First, the authors specify which item categories generalize across age and/or cultural groups, rigorously quantifying differences among them. Second, they introduce novel, powerful methods to measure between-group differences in freely generated ranked data, the rank-ordered logit model and Hellinger Affinity. Finally, a broad archive of tested, cross-linguistic stimuli is now freely available to researchers: data, similarity measures, and all stimulus materials for 105 categories and 4 culture-by-age groups, comprising over 10,000 fully translated unique item responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
30.
Gamebirds provide a considerable incentive to plant and manage new woodlands. The supplementary income thus generated can improve their overall value. Other studies suggest that Short Rotation Coppice (SRC) crops may provide an attractive habitat for some gamebird species and could increase the value of the crop. To investigate this, the use by pheasants and partridge of different types of SRC at one site was assessed.

A method using sand quadrats to record gamebird footprints and hence relative use was developed. Pheasant footprints were recorded more frequently in the quadrats alongside the willow coppice, whereas partridge footprints occurred more frequently alongside the poplar coppice. Footprint analysis offers a reliable method of investigating how gamebirds use different types of SRC within small areas. The results are considered in terms of the placement of short rotation coppice plantations in the landscape to improve their ecological design.  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