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   487461篇
  免费   5668篇
  国内免费   1773篇
电工技术   9249篇
综合类   464篇
化学工业   72121篇
金属工艺   25460篇
机械仪表   17799篇
建筑科学   10932篇
矿业工程   3192篇
能源动力   10896篇
轻工业   36368篇
水利工程   5454篇
石油天然气   9870篇
武器工业   25篇
无线电   54984篇
一般工业技术   101158篇
冶金工业   83895篇
原子能技术   10844篇
自动化技术   42191篇
  2021年   3486篇
  2019年   3322篇
  2018年   12485篇
  2017年   12881篇
  2016年   10095篇
  2015年   4399篇
  2014年   6739篇
  2013年   18775篇
  2012年   12668篇
  2011年   21025篇
  2010年   18027篇
  2009年   18279篇
  2008年   18785篇
  2007年   20338篇
  2006年   12038篇
  2005年   13767篇
  2004年   11886篇
  2003年   11619篇
  2002年   10632篇
  2001年   10362篇
  2000年   9597篇
  1999年   10020篇
  1998年   24672篇
  1997年   17446篇
  1996年   13598篇
  1995年   10226篇
  1994年   8974篇
  1993年   9072篇
  1992年   6732篇
  1991年   6690篇
  1990年   6211篇
  1989年   6079篇
  1988年   6085篇
  1987年   5229篇
  1986年   5236篇
  1985年   6038篇
  1984年   5550篇
  1983年   5137篇
  1982年   4696篇
  1981年   4691篇
  1980年   4599篇
  1979年   4501篇
  1978年   4500篇
  1977年   5162篇
  1976年   6868篇
  1975年   4000篇
  1974年   3776篇
  1973年   3859篇
  1972年   3335篇
  1971年   3013篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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   
92.
93.
94.
95.
96.
97.
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   
98.
99.
An automated system for integrated electrophysical and optical studies of semiconductor nanoheterostructures, which operates in a wide temperature range from 15 to 475 K, is designed. The setup is intended to measure the temperature and frequency admittance and electroluminescence spectra of light-emitting diode and laser chips formed on substrates of diameter up to 50.2 mm, and the distribution of parameters over the wafer. The setup includes the closed-cycle helium cryogenic station, LCR meter, and temperature controller. The characterization results of nanoheterostructures with InGaN/GaN multiple quantum wells, which are used for creating highly efficient white and blue light-emitting diodes, are presented.  相似文献   
100.
The influence of the thermal cycling conditions on the thermal-cycling creep of a TN-1 alloy and the related irreversible deformations is studied. The conditions under which an anomalous increase in the irreversible deformations begins are determined. The structural mechanism of the irreversible deformations of an equiatomic alloy is shown to be analogous to the structural mechanism of metal creep at high temperatures: it predominantly has a dislocation character. It is proposed to use the effect of anomalous increase in the deformation of materials with reversible martensitic transformations for forming parts made of these materials at low temperatures.  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