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   49439篇
  免费   2692篇
  国内免费   155篇
电工技术   708篇
综合类   65篇
化学工业   10593篇
金属工艺   2136篇
机械仪表   3241篇
建筑科学   1099篇
矿业工程   25篇
能源动力   2111篇
轻工业   3887篇
水利工程   271篇
石油天然气   88篇
武器工业   2篇
无线电   7834篇
一般工业技术   10662篇
冶金工业   3881篇
原子能技术   658篇
自动化技术   5025篇
  2024年   50篇
  2023年   570篇
  2022年   870篇
  2021年   1483篇
  2020年   1069篇
  2019年   1176篇
  2018年   1429篇
  2017年   1411篇
  2016年   1750篇
  2015年   1294篇
  2014年   2088篇
  2013年   3006篇
  2012年   3265篇
  2011年   3889篇
  2010年   2814篇
  2009年   2921篇
  2008年   2811篇
  2007年   2185篇
  2006年   2031篇
  2005年   1723篇
  2004年   1571篇
  2003年   1513篇
  2002年   1329篇
  2001年   1134篇
  2000年   996篇
  1999年   928篇
  1998年   1557篇
  1997年   991篇
  1996年   803篇
  1995年   557篇
  1994年   461篇
  1993年   406篇
  1992年   290篇
  1991年   274篇
  1990年   258篇
  1989年   241篇
  1988年   205篇
  1987年   168篇
  1986年   119篇
  1985年   115篇
  1984年   92篇
  1983年   63篇
  1982年   38篇
  1981年   39篇
  1980年   30篇
  1979年   31篇
  1978年   30篇
  1977年   38篇
  1976年   61篇
  1973年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
The electrochemical reduction of carbon dioxide (CO2) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO2 to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO2 to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO2 in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions.  相似文献   
54.
Food Science and Biotechnology - Hardy kiwifruits (Actinidia arguta) contain various bioactive compounds such as vitamin C and phenolics and can withstand cold temperatures. Changes in soluble...  相似文献   
55.
Here, we report a facile approach to electrostatically couple the surface charges of graphite nanoplate (GNP) fillers and poly(methyl methacrylate) (PMMA) polymer particles using ethylene maleic anhydride (EMA) copolymer as an electrostatic coupling agent. Our strategy involved switching the intrinsic repulsive electrostatic interactions between the directly exfoliated GNPs fillers and the PMMA particles to attractive electrostatic surface interactions for preparing core(PMMA)-shell (GNP) precursor in order to optimizing 3-dimensionally dispersed polymer nanocomposite. As a result, the electrical conductivity of the composites dramatically increased by a factor of 16.7 in the EMA-coupled GNP/PMMA composites compared with that of the EMA-free GNP/PMMA composites. In addition, the percolation threshold was also notably reduced from 0.32 to 0.159 vol% after electrostatic coupling of the GNPs fillers and PMMA particles. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48390.  相似文献   
56.
Metals and Materials International - This study investigated the influence of the initial grain size on the plastic deformation and tunnel defects that occurred from friction stir welding of...  相似文献   
57.
We present a distribution‐free tabular cumulative sum chart for monitoring the variability of an autocorrelated process. A quantity known as the asymptotic variance parameter is employed as a measure of the variability, and a distribution‐free tabular cumulative sum chart is applied to variance estimates calculated from batches of nonoverlapping samples. The proposed chart is applicable to a stationary process with a general marginal distribution and a general autocorrelation structure. It also determines control limits analytically without trial‐and‐error simulations. The performance of the proposed chart is tested on stationary processes with both normal and nonnormal marginals with various autocorrelation structures. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
58.
59.
Journal of Mechanical Science and Technology - In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically...  相似文献   
60.
Vegetable soup (VS), a plant-based functional food, has been used as a traditional folk medicine and is attracting attention for its ability to enhance the immune response. β-Glucan, a well-established and effective immunomodulator, has synergistic effects when used in combination with some bioactive compounds. In the present study, we aimed to evaluate the synergistic immunomodulatory effects of the combination of VS and β-glucan on macrophage-mediated immune responses. β-Glucan was demonstrated to synergistically enhance the VS-stimulated immune response, including the production of interleukin-6, tumor necrosis factor-α, and nitric oxide, mainly through the mitogen-activated protein kinase pathway in macrophages. In addition, this combination has the potential for further development in functional foods with immune-enhancing activity.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10068-021-00888-x.  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