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   36627篇
  免费   1584篇
  国内免费   49篇
电工技术   258篇
综合类   36篇
化学工业   8166篇
金属工艺   690篇
机械仪表   671篇
建筑科学   1113篇
矿业工程   72篇
能源动力   1098篇
轻工业   6518篇
水利工程   347篇
石油天然气   162篇
武器工业   2篇
无线电   1601篇
一般工业技术   5274篇
冶金工业   7090篇
原子能技术   234篇
自动化技术   4928篇
  2024年   68篇
  2023年   269篇
  2022年   737篇
  2021年   1005篇
  2020年   723篇
  2019年   873篇
  2018年   1168篇
  2017年   1136篇
  2016年   1227篇
  2015年   1005篇
  2014年   1324篇
  2013年   2525篇
  2012年   2027篇
  2011年   2265篇
  2010年   1763篇
  2009年   1755篇
  2008年   1600篇
  2007年   1432篇
  2006年   1099篇
  2005年   937篇
  2004年   909篇
  2003年   802篇
  2002年   728篇
  2001年   517篇
  2000年   515篇
  1999年   568篇
  1998年   2401篇
  1997年   1555篇
  1996年   1083篇
  1995年   586篇
  1994年   500篇
  1993年   536篇
  1992年   182篇
  1991年   182篇
  1990年   147篇
  1989年   178篇
  1988年   153篇
  1987年   130篇
  1986年   114篇
  1985年   159篇
  1984年   107篇
  1983年   85篇
  1982年   98篇
  1981年   107篇
  1980年   103篇
  1979年   57篇
  1978年   50篇
  1977年   175篇
  1976年   338篇
  1975年   42篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The aim of our study was to show the results of the Magnetic Resonance Angiography of pelvis and lower extremities. 21 patients with clinical signs of venous thrombosis were examined. The obtained results show the MRA is very useful in evaluation of venous flow.  相似文献   
72.
OBJECTIVE: To assess the effect of long-chain polyunsaturated fatty acids (LCPUFA)- and vitamin E-supplemented formula feeding on erythrocyte and plasma alpha-tocopherol (VE), and plasma retinol (VA) concentrations in neonates and to compare these values with those found in infants feeding on infant formula without LCPUFA or breast milk SETTING: University Hospital of Granada, Spain. SUBJECTS: 49 full-term infants. DESIGN AND INTERVENTION: Subjects who chose not to breast feed were fed either (i) unsupplemented infant formula (F) or (ii) infant formula supplemented with LCPUFA and vitamin E (FL). Alpha-tocopherol and retinol were measured at 7 days, 1 month and 3 months. RESULTS: Plasma and erythrocyte VE concentrations and plasma VE/total lipids ratio increased significantly in all groups at 1 month of life (P < 0.05), but did not change significantly between 1 month and 3 months in any group (P > 0.05). Erythrocyte VE and VA retinol concentrations were higher in infants fed an infant formula than in breast milk-fed infants at 1 month of life (P < 0.05). Finally, there were no significant differences in plasma or erythrocyte VE levels, plasma VA or plasma VE/total lipid ratio between any groups at 3 months of life (P > 0.05). CONCLUSION: Infants fed on LCPUFA- and vitamin E-supplemented infant formula for 3 months have similar vitamin E and A status to infants fed on breast milk or infant formula without LCPUFA supplementation.  相似文献   
73.
74.
75.
76.
77.
78.
79.
Decision making with a fuzzy ontology   总被引:2,自引:2,他引:0  
Knowledge mobilisation is a transition from the prevailing knowledge management technology that has been widely used in industry for the last 20?years to a new methodology and some innovative methods for knowledge representation, formation and development and for knowledge retrieval and distribution. Knowledge mobilisation aims at coming to terms with some of the problems of knowledge management and at the same time to introduce new theory, new methods and new technology. More precisely, this paper presents an outline of a fuzzy ontology as an enhanced version of classical ontology and demonstrates some advantages for practical decision making. We show that a number of soft computing techniques, e.g. aggregation functions and interval valued fuzzy numbers, will support effective and practical decision making on the basis of the fuzzy ontology. We demonstrate the knowledge mobilisation methods with the construction of a support system for finding the best available wine for a number of wine drinking occasions using a fuzzy wine ontology and fuzzy reasoning methods; the support system has been implemented for a Nokia N900 smart phone.  相似文献   
80.
The influence of nonsolvent, crystallinity of the polymer film, and addition of dodecane (a poor solvent for the polymer and for the nonsolvent) on the morphology of polylactides films has been investigated and was related to phase separation behavior. Both amorphous poly‐DL ‐lactide (PDLLA) and crystalline poly‐L ‐lactide (PLLA) were dissolved in dichloromethane, and subsequently films were made by immersion in nonsolvent baths. PDLLA gave dense films without any internal structure, since the structure was not solidified by crystallization or glassification. PLLA films show varying structure depending on the nonsolvent. With methanol, asymmetric morphologies were observed as a result from combined liquid‐liquid demixing and crystallization, while with water symmetric spherulitic structures were formed. As a next step, dodecane was added, which is not miscible with the nonsolvent, and we found it to have a strong influence on the morphology of the films. The PDLLA films with dodecane did not collapse: a closed cell structure was obtained. In PLLA films, dodecane speeds up phase separation and induces faster crystallization in the films, and the porosity, size of the pores, and interconnectivity increased. When the PLLA solutions were subjected to a heat pretreatment, crystallization could be postponed, which yielded a cellular structure around dodecane, which did not contain spherulites anymore. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 959–971, 2007  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