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   243137篇
  免费   3305篇
  国内免费   1240篇
电工技术   4829篇
综合类   264篇
化学工业   35411篇
金属工艺   10861篇
机械仪表   7068篇
建筑科学   6239篇
矿业工程   481篇
能源动力   6279篇
轻工业   24148篇
水利工程   1836篇
石油天然气   1335篇
武器工业   3篇
无线电   31037篇
一般工业技术   44880篇
冶金工业   50109篇
原子能技术   3860篇
自动化技术   19042篇
  2021年   1563篇
  2019年   1424篇
  2018年   2321篇
  2017年   2224篇
  2016年   2445篇
  2015年   1907篇
  2014年   3161篇
  2013年   10793篇
  2012年   5450篇
  2011年   7788篇
  2010年   6287篇
  2009年   6962篇
  2008年   7561篇
  2007年   7658篇
  2006年   7033篇
  2005年   6520篇
  2004年   6244篇
  2003年   6261篇
  2002年   6240篇
  2001年   6371篇
  2000年   5801篇
  1999年   6417篇
  1998年   16559篇
  1997年   11597篇
  1996年   8948篇
  1995年   6689篇
  1994年   5907篇
  1993年   5727篇
  1992年   4051篇
  1991年   3994篇
  1990年   3582篇
  1989年   3504篇
  1988年   3440篇
  1987年   2907篇
  1986年   2842篇
  1985年   3413篇
  1984年   3050篇
  1983年   2743篇
  1982年   2547篇
  1981年   2568篇
  1980年   2430篇
  1979年   2271篇
  1978年   2235篇
  1977年   2808篇
  1976年   4171篇
  1975年   1899篇
  1974年   1795篇
  1973年   1783篇
  1972年   1460篇
  1971年   1317篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result...  相似文献   
32.
33.
34.
Mitochondrial oxidative damage and dysfunction contribute to a wide range of human diseases. Considering the limitation of conventional antioxidants and that mitochondria are the main source of reactive oxygen species (ROS) which induce oxidative damage, mitochondria-targeted antioxidants which can selectively block mitochondrial oxidative damage and prevent various types of cell death have been widely developed. As a lipophilic cation, triphenylphosphonium (TPP) has been commonly used in designing mitochondria-targeted antioxidants. Conjugated with the TPP moiety, antioxidants can achieve more than 1000-fold higher mitochondrial concentration depending on cell membrane potentials and mitochondrial membrane potentials. Herein we discuss the deficiencies of conventional antioxidants and the advantages of mitochondrial targeting, and review various types of TPP-based mitochondria-targeted antioxidants. These provide theoretical and background support for the design of new anti-oxidant.  相似文献   
35.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity.  相似文献   
36.
37.
ABSTRACT

The concept of digital game-based learning (DGBL) evolves rapidly together with technological enhancements of virtual reality (VR) and smart phones. However, the mental workload (MWL) that VR-training applications demand and motivational qualities originating from user experience (UX) should be identified in order to create effective and enjoyable training/learning challenges that fit with individual users’ capabilities. This study examined the effects of reality-based interaction (RBI) and VR on measures of student motivation and MWL, in a mental arithmetic game for secondary school pupils. In a randomised controlled trial with sixty school children, a mental arithmetic game was tested with three different interaction and two different presentation methods – VR RBI, VR head-mounted-display tapping and tablet flick-gesture. Results found a significant effect of RBI on MWL but no differences in enjoyment of training were found between VR-experience and tablet training-experience. In fact, adding the gaming-context to the mental arithmetic task created an enjoyable, motivating experience regardless of presentation or interaction-style.  相似文献   
38.
39.
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