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   2260篇
  免费   73篇
  国内免费   15篇
化学   1830篇
晶体学   10篇
力学   30篇
数学   234篇
物理学   244篇
  2023年   9篇
  2022年   15篇
  2021年   24篇
  2020年   39篇
  2019年   35篇
  2018年   27篇
  2017年   26篇
  2016年   55篇
  2015年   41篇
  2014年   53篇
  2013年   124篇
  2012年   149篇
  2011年   173篇
  2010年   110篇
  2009年   101篇
  2008年   174篇
  2007年   161篇
  2006年   130篇
  2005年   159篇
  2004年   152篇
  2003年   110篇
  2002年   109篇
  2001年   17篇
  2000年   20篇
  1999年   11篇
  1998年   13篇
  1997年   19篇
  1996年   24篇
  1995年   11篇
  1994年   15篇
  1993年   14篇
  1992年   19篇
  1991年   15篇
  1990年   11篇
  1989年   15篇
  1988年   7篇
  1986年   8篇
  1985年   11篇
  1984年   10篇
  1983年   9篇
  1982年   17篇
  1981年   8篇
  1980年   11篇
  1979年   11篇
  1978年   9篇
  1977年   10篇
  1976年   16篇
  1975年   10篇
  1973年   6篇
  1970年   4篇
排序方式: 共有2348条查询结果,搜索用时 0 毫秒
1.
2.
BIT Numerical Mathematics - In uncertainty quantification, it is commonly required to solve a forward model consisting of a partial differential equation (PDE) with a spatially varying uncertain...  相似文献   
3.
Dipetalolactone and 4‐methyldipetalolactone are prepared in excellent yield by a one‐pot tandem propargylation/Claisen rearrangement/cyclization reaction of the corresponding 5,7‐dihydroxycoumarins with 3‐chloro‐3‐methylbut‐1‐yne in the presence of Cs2CO3 under microwave irradiation. The analogous reactions of propargyl chloride with esculetins or 5,7‐dihydroxycoumarins led to dipropargyloxy derivatives. The later by treatment with gold nanoparticles supported on TiO2 or BF3.Et2O in N,N‐dimethylformamide (DMF) under microwave irradiation resulted in very good to excellent yield to the corresponding fused dipyranocoumarins. The reactions of esculetins with 3‐chloro‐3‐methylbut‐1‐yne gave mainly exomethylene fused dioxino[g]coumarins.  相似文献   
4.
5.
6.
7.
Adsorption and coadsorption studies on free silver clusters show that nitrogen physisorbs like rare gases, whereas oxygen chemisorbs with similarities and differences to bulk silver surfaces. Silver nanoparticles activate, or even dissociate adsorbed oxygen molecules. The global electron configurations of the adsorbent and adsorbate dominate the stability at small clusters. This is more important than geometry and site effects. Due to electronic shell effects and electron pairing, the activation of oxygen strongly varies with size. At more than 40 free electrons in the complex, such quantum effects start to blur. The size dependence becomes smoother and general trends govern the reactivity, which is driven by the interaction between the charge state of the nanoparticle and the charge transfer of the reaction.  相似文献   
8.
In our article, we reported the observation of monoclinic M2 to M1 structural phase transition in VO2 single crystal near the temperature of ~49 °C. However, the re‐examination of Laue patterns reveals that previously defined monoclinic M1 and M2 phases can be interpreted as monoclinic M2 and triclinic T phases instead. Careful experimental geometry calibration and further refinement of the lattice parameter ratios and angles show that monoclinic M2 and triclinic T phases fit better with the experimental data. On the other hand, our previous misidentification of the insulating phases does NOT affect the conclusions of our article. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)  相似文献   
9.
Fluorocarbons often have distinct miscibility properties compared to their nonfluorinated analogues. These differences may be attributed to van der Waals dispersion forces or solvophobic effects, but their contributions are notoriously difficult to separate in molecular recognition processes. Here, molecular torsion balances were used to compare cohesive alkyl and perfluoroalkyl interactions in a range of solvents. A simple linear regression enabled the energetic partitioning of solvophobic and van der Waals forces in the self‐association of apolar chains. The contributions of dispersion interactions in apolar cohesion were found to be strongly attenuated in solution compared to the gas phase, but still play a major role in fluorous and organic solvents. In contrast, solvophobic effects were found to be dominant in driving the association of apolar chains in aqueous solution. The results are expected to assist the computational modelling of van der Waals forces in solution.  相似文献   
10.
Trianguleniums are fascinating conjugated hexacyclic cations that exhibit interesting electronic and optical properties. Herein, the electrogenerated chemiluminescence (ECL) emission of this family of fluorescent dyes is reported for the first time. Redox behavior and fluorescence properties of eight cationic triangulene luminophores with different heteroatom patterns in the core structure and various pending substituents were examined to rationalize the ECL. Clearly, the more electron‐rich the carbocation, the more efficient the corresponding ECL; two very distinct classes of triangulenes can be drawn from these studies by using an ECL wall sufficiency formalism.  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