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   51117篇
  免费   2881篇
  国内免费   201篇
电工技术   758篇
综合类   141篇
化学工业   10706篇
金属工艺   2213篇
机械仪表   3326篇
建筑科学   1162篇
矿业工程   33篇
能源动力   2231篇
轻工业   4054篇
水利工程   279篇
石油天然气   132篇
武器工业   4篇
无线电   8051篇
一般工业技术   11016篇
冶金工业   4150篇
原子能技术   668篇
自动化技术   5275篇
  2024年   25篇
  2023年   557篇
  2022年   696篇
  2021年   1530篇
  2020年   1107篇
  2019年   1214篇
  2018年   1479篇
  2017年   1452篇
  2016年   1791篇
  2015年   1337篇
  2014年   2157篇
  2013年   3134篇
  2012年   3351篇
  2011年   3999篇
  2010年   2911篇
  2009年   3020篇
  2008年   2910篇
  2007年   2256篇
  2006年   2126篇
  2005年   1779篇
  2004年   1641篇
  2003年   1602篇
  2002年   1426篇
  2001年   1222篇
  2000年   1055篇
  1999年   972篇
  1998年   1654篇
  1997年   1057篇
  1996年   859篇
  1995年   601篇
  1994年   478篇
  1993年   435篇
  1992年   305篇
  1991年   288篇
  1990年   274篇
  1989年   258篇
  1988年   213篇
  1987年   177篇
  1986年   126篇
  1985年   122篇
  1984年   99篇
  1983年   66篇
  1982年   43篇
  1981年   45篇
  1980年   36篇
  1979年   33篇
  1978年   32篇
  1977年   46篇
  1976年   75篇
  1973年   22篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
33.
34.
Machine Learning - We consider the problem of learning a binary classifier from only positive and unlabeled observations (called PU learning). Recent studies in PU learning have shown superior...  相似文献   
35.
Microsystem Technologies - A color-laser printing system consisting of a tandem laser scanning unit uses four laser diodes and a single polygonal mirror (PM) to expose light onto four...  相似文献   
36.
37.
38.
While exercise training (ET) is an efficient strategy to manage obesity, it is recommended with a dietary plan to maximize the antiobesity functions owing to a compensational increase in energy intake. Capsiate is a notable bioactive compound for managing obesity owing to its capacity to increase energy expenditure. We aimed to examine whether the antiobesity effects of ET can be further enhanced by capsiate intake (CI) and determine its effects on resting energy expenditure and metabolic molecules. Mice were randomly divided into four groups (n = 8 per group) and fed high-fat diet. Mild-intensity treadmill ET was conducted five times/week; capsiate (10 mg/kg) was orally administered daily. After 8 weeks, resting metabolic rate and metabolic molecules were analyzed. ET with CI additively reduced the abdominal fat rate by 18% and solely upregulated beta-3-adrenoceptors in adipose tissue (p = 0.013) but did not affect the metabolic molecules in skeletal muscles. Surprisingly, CI without ET significantly increased the abdominal fat rate (p = 0.001) and reduced energy expenditure by 9%. Therefore, capsiate could be a candidate compound for maximizing the antiobesity effects of ET by upregulating beta-3-adrenoceptors in adipose tissue, but CI without ET may not be beneficial in managing obesity.  相似文献   
39.
With superior properties of Mg such as high hydrogen storage capacity (7.6 wt% H/MgH2), low price, and low density, Mg has been widely studied as a promising candidate for solid-state hydrogen storage systems. However, a harsh activation procedure, slow hydrogenation/dehydrogenation process, and a high temperature for dehydrogenation prevent the use of Mg-based metal hydrides for practical applications. For these reasons, Mg-based alloys for hydrogen storage systems are generally alloyed with other elements to improve hydrogen sorption properties. In this article, we have added Na to cast Mg–La alloys and achieved a significant improvement in hydrogen absorption kinetics during the first activation cycle. The role of Na in Mg–La has been discussed based on the findings from microstructural observations, crystallography, and first principles calculations based on density functional theory. From our results in this study, we have found that the Na doped surface of Mg–La alloy systems have a lower adsorption energy for H2 compared to Na-free surfaces which facilitates adsorption and dissociation of hydrogen molecules leading to improvement of absorption kinetic. The effect of Na on the microstructure of these alloys, such as eutectic refinement and a density of twins is not highly correlated with absorption kinetics.  相似文献   
40.
We demonstrate the structural evolution of polymorphic phases in Al2O3-inserted SrMnO3 ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO3 ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO3 and the secondary hexagonal SrAl2O4 phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO3 phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al2O3-inserted SrMnO3 compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO3.  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