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   4146篇
  免费   242篇
  国内免费   4篇
电工技术   61篇
综合类   1篇
化学工业   985篇
金属工艺   141篇
机械仪表   82篇
建筑科学   90篇
矿业工程   14篇
能源动力   150篇
轻工业   504篇
水利工程   13篇
石油天然气   11篇
无线电   107篇
一般工业技术   691篇
冶金工业   1066篇
原子能技术   26篇
自动化技术   450篇
  2023年   29篇
  2022年   79篇
  2021年   126篇
  2020年   98篇
  2019年   85篇
  2018年   168篇
  2017年   160篇
  2016年   176篇
  2015年   137篇
  2014年   168篇
  2013年   281篇
  2012年   199篇
  2011年   243篇
  2010年   168篇
  2009年   142篇
  2008年   128篇
  2007年   134篇
  2006年   87篇
  2005年   63篇
  2004年   61篇
  2003年   53篇
  2002年   53篇
  2001年   28篇
  2000年   19篇
  1999年   21篇
  1998年   176篇
  1997年   198篇
  1996年   137篇
  1995年   90篇
  1994年   47篇
  1993年   64篇
  1992年   18篇
  1991年   9篇
  1990年   19篇
  1989年   14篇
  1988年   14篇
  1987年   11篇
  1986年   10篇
  1985年   15篇
  1984年   32篇
  1983年   19篇
  1982年   39篇
  1981年   45篇
  1980年   55篇
  1979年   27篇
  1978年   37篇
  1977年   110篇
  1976年   234篇
  1975年   13篇
  1973年   12篇
排序方式: 共有4392条查询结果,搜索用时 15 毫秒
101.
102.
The precipitation process in alloys containing 4% Ti and 5 to 16% Ni was investigated using transmission electron microscopy, hardness and electrical conductivity measurements. After ageing, spherical -Ni3Ti precipitates with ordered DO22 superlattice were observed in alloys CuTiNi5 to 10 and the L12 superlattice in the CuTi4Ni16 alloy. With increasing nickel content the size of precipitates decreases; this has only a minor influence on the age hardening. The CuTiNi10 alloy has the best electrical conductivity approaching 18m–1mm–2.  相似文献   
103.
104.
The Parity Path problem is to decide if a given graph contains both an induced path of odd length and an induced path of even length between two specified vertices. In the related problems Odd Induced Path and Even Induced Path, the goal is to determine whether an induced path of odd, respectively even, length between two specified vertices exists. Although all three problems are NP-complete in general, we show that they can be solved in $\mathcal{O}(n^{5})$ time for the class of claw-free graphs. Two vertices s and t form an even pair in G if every induced path from s to t in G has even length. Our results imply that the problem of deciding if two specified vertices of a claw-free graph form an even pair, as well as the problem of deciding if a given claw-free graph has an even pair, can be solved in $\mathcal{O}(n^{5})$ time and $\mathcal{O}(n^{7})$ time, respectively. We also show that we can decide in $\mathcal{O}(n^{7})$ time whether a claw-free graph has an induced cycle of given parity through a specified vertex. Finally, we show that a shortest induced path of given parity between two specified vertices of a claw-free perfect graph can be found in $\mathcal {O}(n^{7})$ time.  相似文献   
105.
106.
Iron-ruthenium catalysts prepared by impregnation of calcination products of -, , -and -iron oxide-hydroxides with either ruthenium chloride or ruthenium red were tested for the activity for the water-gas shift reaction. The effect of support, ruthenium containing impregnation agent and thermal treatment on catalyst performance was discussed.  相似文献   
107.
This paper describes the quattor tool suite, a new system for the installation, configuration, and management of operating systems and application software for computing fabrics. At present Unix derivatives such as Linux and Solaris are supported. Quattor is a powerful, portable and modular open source solution that has been shown to scale to thousands of computing nodes and offers a significant reduction in management costs for large computing fabrics. The quattor tool suite includes innovations compared to existing solutions which make it very useful for computing fabrics integrated into grid environments. Evaluations of the tool suite in current large scale computing environments are presented.  相似文献   
108.
The performance of older adults and depressed people on linear order reasoning is hypothesized to be best explained by different theoretical models. Whereas depressed younger adults are found to be impaired in generative inference making, older adults are well capable of making such inferences but exhibit problems with working memory (Experiments 1 and 2). Restriction of the available study time impairs reasoning by nondepressed control participants and. as such, proves to be a good model of older adults' but not depressed participants' limitations (Experiment 3). These results are replicated comparing depressed and older participants with a control group in the same study, providing increased power and linking the results to additional control measures of processing speed and working memory (Experiment 4). (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
109.
In this paper, we investigate formulation of non-local memory effect hysteretic loops in presliding domain of friction by examining the dynamic responses of a single-degree-of-freedom friction oscillator. We modify the Maxwell slip model introducing characteristic features of asperities and perform detailed examination of the system from two perspectives. The first one, termed by us as microscale, presents contribution of each individual asperity to the total friction force, whereas the second one, termed by us as macroscale, concerns friction force behaviour of the whole model treated as the unity, with a special emphasis on non-local memory effect hysteretic loops formulation, complemented by time responses.  相似文献   
110.
Five groups of winter-housed cows (n = 10 per group) that calved in the winter were used to assess the effect of beta-carotene supplementation on postpartum reproductive performance. Near parturition and immediately after calving the beta-carotene concentrations of the blood plasma were decreased and no differences could be found between the control and the supplemented groups. The results obtained at postpartum day 60 suggest that supplementation of the daily winter ration with 300 mg of synthetic beta-carotene with or without vitamins A, D3 and E exerts the most favourable effect on reproduction, as judged not only from B-carotene and vitamin A contents of the blood plasma, colostrum and milk but also from the improved fertility indices. The number of inseminations per cow was reduced and the conception rate was significantly higher in cows supplied additionally with 300 mg of synthetic beta-carotene with or without vitamins A, D3 and E. It can be concluded that beta-carotene is an important factor in bovine reproduction and that its specific role cannot be taken over by vitamin A.  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