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   32453篇
  免费   1224篇
  国内免费   1649篇
化学   11180篇
晶体学   229篇
力学   452篇
综合类   70篇
数学   18718篇
物理学   4677篇
  2023年   381篇
  2022年   239篇
  2021年   338篇
  2020年   505篇
  2019年   770篇
  2018年   712篇
  2017年   526篇
  2016年   544篇
  2015年   677篇
  2014年   1014篇
  2013年   2411篇
  2012年   1195篇
  2011年   2307篇
  2010年   1814篇
  2009年   2203篇
  2008年   2528篇
  2007年   2326篇
  2006年   1789篇
  2005年   1302篇
  2004年   1165篇
  2003年   1020篇
  2002年   1272篇
  2001年   724篇
  2000年   678篇
  1999年   741篇
  1998年   583篇
  1997年   500篇
  1996年   557篇
  1995年   595篇
  1994年   535篇
  1993年   403篇
  1992年   374篇
  1991年   284篇
  1990年   246篇
  1989年   243篇
  1988年   167篇
  1987年   171篇
  1986年   160篇
  1985年   216篇
  1984年   173篇
  1983年   90篇
  1982年   156篇
  1981年   148篇
  1980年   108篇
  1979年   88篇
  1978年   92篇
  1977年   75篇
  1976年   66篇
  1975年   26篇
  1974年   30篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
《Mendeleev Communications》2022,32(1):126-128
3-Aryl-5-methylidene-2-thiohydantoins were constructed in one-pot reaction of aryl isothiocyanates and 3-morpholino- alanine in alkaline medium with the subsequent treatment with boiling hydrochloric acid.  相似文献   
2.
Reactivity studies of the GeII→B complex L(Cl)Ge⋅BH3 ( 1 ; L=2-Et2NCH2-4,6-tBu2-C6H2) were performed to determine the effect on the GeII→B donation. N-coordinated compounds L(OtBu)Ge⋅BH3 ( 2 ) and [LGe⋅BH3]2 ( 3 ) were prepared. The possible tuning of the GeII→B interaction was proved experimentally, yielding compounds 1-PPh2-8-(LGe)-C10H6 ( 4 ) and L(Cl)Ge⋅GaCl3 ( 5 ) without a GeII→B interaction. In 5 , an unprecedented GeII→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the GeII→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed.  相似文献   
3.
《Mendeleev Communications》2022,32(5):629-631
The Michael–Mannich cascade cyclization of cyano olefins, ethyl 4,4,4-trifluoro-3-oxobutanoate, aromatic aldehydes and ammonium acetate provides convenient stereoselective formation of ethyl 5,5-dicyano-4,6-diaryl-2-hydroxy-2-(trifluoromethyl)piperidine-3-carboxylates with fourstereogenic centers and dialkyl 4,6-diaryl-5-cyano-2-hydroxy-2-(trifluoromethyl)piperidine-3,5-dicarboxylates with five stereogenic centers. Ammonium acetate plays dual role, acting as a base and as a nitrogen source.  相似文献   
4.
Like the lower central series of a nilpotent group, filters generalize the connection between nilpotent groups and graded Lie rings. However, unlike the case with the lower central series, the associated graded Lie ring may share few features with the original group: e.g. the associated Lie ring can be trivial or arbitrarily large. We determine properties of filters such that every isomorphism between groups is induced by an isomorphism between graded Lie rings.  相似文献   
5.
6.
7.
8.
In this study, the functional interaction of HPLW peptide with VEGFR2 (Vascular Endothelial Growth Factor Receptor 2) was determined by using fast 15N‐edited NMR spectroscopic experiments. To this aim, 15N uniformly labelled HPLW has been added to Porcine Aortic Endothelial Cells. The acquisition of isotope‐edited NMR spectroscopic experiments, including 15N relaxation measurements, allowed a precise characterization of the in‐cell HPLW epitope recognized by VEGFR2.  相似文献   
9.
In the view of substrate availability, atomic efficiency and cost, directly using arenols as coupling partners in cross‐coupling, would be one of the most attractive goals. Up to date, many efforts have been made to activate the C—O bond of phenols with different strategies, for example, through in‐situ formed intermediates, through a catalytic reductive dearomatization‐condensation‐rearomatization sequence or catalytic deoxygenation. In this review, we summarized recent advances in cross‐couplings of arenols as the electrophiles via C—O activation.  相似文献   
10.
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