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   17909篇
  免费   2588篇
  国内免费   2180篇
化学   13534篇
晶体学   277篇
力学   982篇
综合类   189篇
数学   1738篇
物理学   5957篇
  2024年   36篇
  2023年   270篇
  2022年   530篇
  2021年   581篇
  2020年   622篇
  2019年   630篇
  2018年   501篇
  2017年   506篇
  2016年   812篇
  2015年   797篇
  2014年   947篇
  2013年   1300篇
  2012年   1572篇
  2011年   1614篇
  2010年   1155篇
  2009年   1002篇
  2008年   1150篇
  2007年   978篇
  2006年   975篇
  2005年   929篇
  2004年   738篇
  2003年   650篇
  2002年   720篇
  2001年   483篇
  2000年   435篇
  1999年   392篇
  1998年   289篇
  1997年   270篇
  1996年   257篇
  1995年   241篇
  1994年   190篇
  1993年   176篇
  1992年   164篇
  1991年   138篇
  1990年   125篇
  1989年   100篇
  1988年   86篇
  1987年   57篇
  1986年   61篇
  1985年   63篇
  1984年   33篇
  1983年   29篇
  1982年   21篇
  1981年   20篇
  1980年   9篇
  1979年   7篇
  1974年   2篇
  1971年   2篇
  1957年   6篇
  1936年   1篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
82.
83.
84.
85.
86.
Ming-Qian  Sun  Jian-Xun  Liu  Lan  Miao  Jin  Cao  Cheng-Ren  Lin  Lei  Li  Jianxun  Ren 《Chromatographia》2012,75(9-10):491-497

In this study, serum metabolic profiles of mini-pigs with atherosclerosis (AS) were analyzed by LC–TOFMS. Partial least-squares to latent structure-discriminant analysis and orthogonal projection to latent structure-discriminant analysis were used for group differentiation and selection of potential biomarkers. The mini-pig disease models were constructed by feeding a high-fat diet and inducing coronary injury, in accordance with the mechanism of AS pathogenesis. To characterize the development of AS, serum samples were collected and analyzed at two time points (two and ten weeks). Separate distinct clustering of results from normal and model mini-pigs could be observed for both the two and ten-week samples. With the development of AS, the metabolism of the model mini-pigs was more substantially disturbed. Major metabolites contributing to the discrimination were fatty acids, lysophosphatidylcholines, and bile acids. These potential biomarkers are related with inflammation, oxidative stress, and abnormal lipid and energy metabolism.

  相似文献   
87.
The corrosion inhibition of ammonium heltamolybdate (AH) and calcium gluconate (CG) for AA6061 alloy in 3% NaCl solution was investigated by the electrochemical measurements. It indicates that AH inhibits the corrosion of AA6061 alloy and acts as an anodic inhibitor. Maximum inhibition efficiency reaches 74.3% at the concentration of 1 × 10?4 mol.l?1 AH. The results of the electrochemical studies reveal AH is physically adsorbed on the AA6061 alloy surface and the adsorption follows Langmuir isotherm. The combination of AH and CG enhances the inhibition efficiency to 95.9%. The enhanced inhibition is attributed to the promotion of AH adsorption by CG. The mixture of AH and CG is a mixed‐type inhibitor and renders the corrosion potential to more positive values. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
88.
89.
Abstract

Sixteen novel 3-methylthio-5-substituted benzamido-6-arylamino-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4 (5H)-one derivatives (4a–p) were successfully synthesized from iminophosphoranes, aryl isocyanate, and substituted benzoylhydrazine. The structures of the title compounds were elucidated by FT-IR, 1H NMR, 13C NMR, and HRMS. Herbicidal activity of the compounds 4a–p against Brassica napus (rape), Echinochloa crusgalli (barnyard grass), Cucumis sativus (cucumber), and Triticum aestivum (wheat) were determined. The results showed that 5-(2-chlorobenzamido)-6-phenylamino-3-methylthio-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4 (5H)-one (4c) displayed remarkable inhibition activity against the stalk and root of rape with 100% inhibition rate at the dosages of 10?mg/L and 100?mg/L, and 5-(4-nitrobenzamido)-6-phenylamino-3-methylthio-1-phenyl-1H-pyrazolo[3,4-d]pyrimidin-4 (5H) -one (4d) exhibited excellent activity against the stalk and root of barnyard grass with 100% inhibition rate at the same dosages.  相似文献   
90.
Abstract

A new (E)-pyrene-1-carbaldehyde O-tert-butyldimethylsilyl oxime 3 was synthesized for the detection of chemical warfare nerve agents, O-isopropyl methylphosphonofluoridate (GB) and O-pinacolyl methylphosphonofluoridate (GD). 1H NMR spectrum showed that the tert-butyldimethylsilyl (TBDMS) group was deprotected using TBAF and the oximate supernucleophile was made. Upon addition of chemical warfare agents (GB and GD) (50 mol%), the reaction was completely finished within 5 min and also the color change of reaction mixture was observed under a hand-held UV lamp with the naked eye.  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