首页 | 官方网站   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   58316篇
  免费   2794篇
  国内免费   195篇
工业技术   61305篇
  2023年   514篇
  2022年   316篇
  2021年   1424篇
  2020年   1013篇
  2019年   1039篇
  2018年   1348篇
  2017年   1360篇
  2016年   1698篇
  2015年   1342篇
  2014年   2084篇
  2013年   3549篇
  2012年   3248篇
  2011年   3995篇
  2010年   3053篇
  2009年   3235篇
  2008年   3009篇
  2007年   2548篇
  2006年   2297篇
  2005年   2004篇
  2004年   1901篇
  2003年   1759篇
  2002年   1707篇
  2001年   1337篇
  2000年   1254篇
  1999年   1251篇
  1998年   2387篇
  1997年   1553篇
  1996年   1233篇
  1995年   1026篇
  1994年   779篇
  1993年   742篇
  1992年   518篇
  1991年   514篇
  1990年   444篇
  1989年   420篇
  1988年   336篇
  1987年   294篇
  1986年   282篇
  1985年   265篇
  1984年   225篇
  1983年   168篇
  1982年   164篇
  1981年   146篇
  1980年   145篇
  1979年   115篇
  1978年   115篇
  1977年   159篇
  1976年   201篇
  1975年   99篇
  1974年   88篇
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
51.
52.
53.
Recent studies have shown that lotus (Nelumbo nucifera) leaf has various pharmacological effects. However, there have been no scientific investigations into these leaves as a fermented crude liquid. This study compared the in vitro antioxidant capacity of lotus leaf‐fermented broth (LLFB) with that of 57° Brix sugar broth (SB) as a control over a period of 6 months based on 1,1‐diphenyl‐2‐picrylhydrazyl radical scavenging activity, ferric ion reducing power, superoxide dismutase‐like activity, tyrosinase inhibition and nitrite scavenging activity. The dominant species during fermentation process were Leuconostoc lactis and Saccharomyces cerevisiae for LLFB. A total of thirty‐six metabolites such as alkaloids, fatty acids, organic acids, phenolics, sugar and sugar derivatives, ethyl esters and monoterpenoids differed between SB and LLFB using gas chromatography–mass spectrometry. Meanwhile, nine volatile compounds in LLFB contributed pleasant, slightly sweetish and fruity odour of condiment and sensory evaluation score of 4.06 ± 1.52 in the proportion of 1:9 LLFB/water.  相似文献   
54.
Many e-commerce companies collect users’ personal data for marketing purposes despite privacy concerns. Information-collecting companies often offer a monetary reward to users to alleviate privacy concerns and ease the collection of personal information. This study focused on the negative effects of monetary rewards on both information privacy concerns (IPC) and information disclosure. A survey approach was used to collect data and 370 final responses were analysed using a two-way analysis of variance and a binomial logistic regression model. The results show that monetary rewards increase IPC when an information-collecting company requires sensitive information. Additional results indicate that building trust is a more effective way of collecting personal data. This study identifies how organisations can best execute information-collection activities and contributes additional insights for academia and practitioners.  相似文献   
55.
56.
57.
A device able to electrokinetically concentrate cationic samples has many potential medical and industrial applications, but until now has remained undeveloped due to the lack of a commercial anion-permselective material leading to a prohibitively complex fabrication procedure. Herein, a novel multiscale-porous anion exchange membrane (MP-AEM) that enables the convenient and scalable electrokinetic concentration of cationic species is proposed. A mechanically enhanced multiscale-porous structure with a solid framework is realized by adopting polyester resin as an additive to overcome the intrinsic limitations of the AEM material. The scalable MP-AEM-embedded electrokinetic concentrator is devised based on the peculiar properties of the MP-AEM that for allow both ion and fluid transport. With the MP-AEM, the concentrator is fabricated in a highly streamlined manner consisting only of a simple insertion and assembly. The concentration performance of the MP-AEM-embedded electrokinetic concentrator is demonstrated with a positively charged fluorescent dye and a fluorescein-labeled protein, and the results show enrichment factors of 250 and 500, respectively. The MP-AEM makes cationic electrokinetic concentration more accessible and scalable, thereby enabling further progress in a wide range of fields.  相似文献   
58.
This paper examines what influences trust in mobile social commerce environment. Drawing on trust-based acceptance model (i.e. cognitive and emotional trust) and online review features (i.e. profile photo, linguistic style, and reported experience), we examine how these factors affect trust in mobile social commerce. Hypotheses were tested using survey data. The results of our model showed that there are significant influences of profile photo, reported experience, cognitive, and emotional trust towards trust in ms-commerce. This work contributes to existing literature by examining the roles of previous trust in mobile payments and online reviews on trust in mobile social commerce.  相似文献   
59.
Chun  Dong Hyun  Rhim  Geun Bae  Youn  Min Hye  Deviana  Deviana  Lee  Ji Eun  Park  Ji Chan  Jeong  Heondo 《Topics in Catalysis》2020,63(9-10):793-809
Topics in Catalysis - Fischer–Tropsch synthesis (FTS) is a promising way to produce clean liquid fuels and high value-added chemicals from low-value carbon-containing resources such as coal,...  相似文献   
60.
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   
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-23

京公网安备 11010802026262号