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   28359篇
  免费   4775篇
  国内免费   4253篇
化学   21134篇
晶体学   523篇
力学   1711篇
综合类   344篇
数学   3248篇
物理学   10427篇
  2024年   60篇
  2023年   472篇
  2022年   695篇
  2021年   898篇
  2020年   994篇
  2019年   1126篇
  2018年   945篇
  2017年   981篇
  2016年   1320篇
  2015年   1369篇
  2014年   1654篇
  2013年   2215篇
  2012年   2584篇
  2011年   2763篇
  2010年   1934篇
  2009年   1968篇
  2008年   2071篇
  2007年   1946篇
  2006年   1741篇
  2005年   1419篇
  2004年   1259篇
  2003年   1007篇
  2002年   1085篇
  2001年   935篇
  2000年   725篇
  1999年   565篇
  1998年   420篇
  1997年   297篇
  1996年   304篇
  1995年   248篇
  1994年   239篇
  1993年   203篇
  1992年   163篇
  1991年   136篇
  1990年   128篇
  1989年   116篇
  1988年   67篇
  1987年   63篇
  1986年   61篇
  1985年   57篇
  1984年   35篇
  1983年   20篇
  1982年   8篇
  1981年   13篇
  1980年   7篇
  1979年   14篇
  1976年   8篇
  1975年   7篇
  1957年   6篇
  1936年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Yang  Yu  Guangrong  Zhao  Xiaojing  Wang  Wu  Liang 《Structural chemistry》2021,32(6):2099-2106
Structural Chemistry - Density functional theory (DFT) calculations were employed to study the 5-fluorouracil (5FU) drug interaction strength with perfect and defective forms of boron carbide...  相似文献   
952.
The convenient cross-coupling of sp2 or sp3 carbons with a specific boron vertex on carborane cage represents significant synthetic values and insurmountable challenges. In this work, we report an Rh-catalyzed reaction between o-carborane and N-acyl-glutarimides to construct various Bcage−C bonds. Under the optimized condition, the removable imine directing group (DG) leads to B(3)− or B(3,6)−C couplings, while the pyridyl DG leads to B(3,5)−Ar coupling. In particular, an unexpected rearrangement of amide reagent is observed in pyridyl directed B(4)−C(sp3) formation. This scalable protocol has many advantages, including easy access, the use of cheap and widely available coupling agents, no requirement of an external ligand, base or oxidant, high efficiency, and a broad substrate scope. Leveraging the RhI dimer and twisted amides, this method enables straightforward access to diversely substituted and therapeutically important carborane derivatives at boron site, and provides a highly valuable vista for carborane-based drug screening.  相似文献   
953.
Danshen (DS) is a widely used traditional Chinese medicine for treating cardiovascular and cerebrovascular diseases. A simple, rapid and sensitive method was developed for identification of the in vivo metabolites in urine of WZS‐miniature pigs after oral administration of DS decoction by HPLC coupled with diode array detection with electrospray ionization tandem ion trap and time‐of‐flight mass spectrometry. This method has been successfully applied to simultaneous identification of 50 compounds (including 11 new ones) in pig urine. In addition, one new compound, (3‐hydroxyphenyl) crylic acid glycine methyl ester (C1), along with eight known ones were first isolated by column chromatography and identified by spectroscopic means, including 1D/2DNMR and mass spectrometry, as reference substances. Ten phenolic compounds (protocatechuic aldehyde, protocatechuic acid, caffeic acid, danshensu, ferulic acid, isoferulic acid, rosmarinic acid and salvianolic acid A/B/D) were found to be the main absorbed original constituents of DS decoction, which underwent the metabolic reactions of glucuronidation, sulfation, methylation, hydrogenation and glycine conjugation in vivo. In conclusion, the developed method is applicable to the analysis and identification of constituents in biological matrices after administration of DS decoction. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
954.
5-(7-Hydroxyheptyl)-1,2-dithiolan-3-one 1-oxide was designed and synthesized in our laboratories that contain the heterocycle of 1,2-dithiolan-3-one 1-oxide, a reactive core of antibiotic leinamycin. In addition, the activated ester of 5-(7-hydroxyheptyl)-1,2-dithiolan-3-one 1-oxide was prepared, which presumably is useful for coupling this DNA-cleaving functionality to certain DNA-binding agents.  相似文献   
955.
956.
957.
958.
959.
960.
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