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   864篇
  免费   26篇
  国内免费   4篇
化学   563篇
晶体学   3篇
力学   13篇
数学   74篇
物理学   241篇
  2023年   5篇
  2022年   4篇
  2021年   6篇
  2020年   19篇
  2019年   10篇
  2018年   11篇
  2017年   13篇
  2016年   22篇
  2015年   10篇
  2014年   19篇
  2013年   44篇
  2012年   38篇
  2011年   35篇
  2010年   31篇
  2009年   25篇
  2008年   51篇
  2007年   55篇
  2006年   46篇
  2005年   35篇
  2004年   55篇
  2003年   22篇
  2002年   27篇
  2001年   35篇
  2000年   30篇
  1999年   22篇
  1998年   13篇
  1997年   13篇
  1996年   17篇
  1995年   8篇
  1994年   8篇
  1993年   12篇
  1992年   6篇
  1991年   6篇
  1990年   7篇
  1989年   7篇
  1988年   5篇
  1987年   11篇
  1986年   9篇
  1985年   14篇
  1984年   13篇
  1983年   7篇
  1982年   10篇
  1981年   6篇
  1980年   6篇
  1979年   8篇
  1978年   5篇
  1977年   8篇
  1976年   5篇
  1975年   4篇
  1974年   4篇
排序方式: 共有894条查询结果,搜索用时 31 毫秒
31.
The one-dimensional intermolecular ferromagnetic interaction of a charge-transfer (CT) complex, (BDTA)[Ni(mnt)2] (BDTA: 1,3,2-benzodithiazolyl, mnt: maleonitriledithiolate), is studied by the Kohn–Sham hybrid density functional method, in order to understand the mechanism of the magnetism. All possible effective exchange integrals, J, between the spin pairs of the system indicate that a ferromagnetic interaction (J = 172 cm−1) exists along the b-axis. Magnetic susceptibility, simulated with the ab initio determined J values by the quantum Monte Carlo (QMC) method, is qualitatively consistent with that measured experimentally.  相似文献   
32.
The methodology for a copper-catalyzed preparation of diaryl chalcogenide compounds from aryl iodides and diphenyl dichalcogenide molecules is reported. Unsymmetrical diaryl sulfide or diaryl selenide can be synthesized from aryl iodide and PhYYPh (Y = S, Se) with a copper catalyst (CuI or Cu(2)O) and magnesium metal in one pot. This reaction can be carried out under neutral conditions according to an addition of magnesium metal as the reductive reagent. Furthermore, it is efficiently available for two monophenylchalcogenide groups generated from diphenyl dichalcogenide.  相似文献   
33.
Chlorination of the N-oxides of furo[2,3-b]- 1a , -[2,3-c]- 1b and -[3,2-c]pyridine 1c with phosphorus oxychloride afforded compounds substituted normally at the α- or λ-position to the ring nitrogen, 2a, 2′a, 2b, 2c, 2′c and 2′c , and in addition, in the case of 1b , compounds substituted on the furan ring, 2′b and 2″b . The structures of these compounds were confirmed from their ir, nmr and mass spectra. The major chlorinated products 2a, 2b and 2c were converted to methoxy- 5a, 5b and 5c , N-pyrrolidyl- 7a, 7b and 7c , and phenylthiofuropyridines 8a, 8b , and 8c .  相似文献   
34.
35.
36.
Spiro[4,5]decanes and polycyclic compounds bearing spiro[4,5]decane systems are important biofunctional molecules. Described are diastereoselective formal (4+1) cycloaddition reactions to afford oxindole-functionalized spiro[4,5]decanes and organocatalytic enantioselective Michael–Henry cascade reactions of the (4+1) cycloaddition products to generate spirooxindole polycyclic derivatives bearing the spiro[4,5]decane system. Spiro[4,5]decanes bearing oxindoles containing three stereogenic centers and spirooxindole polycycles having seven stereogenic centers, including two all-carbon chiral quaternary centers and one tetrasubstituted chiral carbon center, were obtained with high diastereo- and enantioselectivities.  相似文献   
37.
1-Phenylbenzo[b]thiophenium salts are prepared and reacted under thermal and photochemical conditions. The chemical behaviors are discussed.  相似文献   
38.
Formation process of gold nanoparticles was investigated by near-field heterodyne transient grating method. In the absence of the protective agents, although the diffusion of H[AuICl2] could be observed after the photo-reduction of H[AuIIICl4], the diffusion of nanoparticle-seeds was not observed. On the other hand, in the presence of the protective agents, the diffusion of a complex molecule (Au and protective agent) and nanoparticle-seeds could be observed. From these results, it was found that enough amount of the complex is essential for the nanoparticle formation. We also investigated the formation process with four different chemicals as a protective agent. The hydrodynamic radius of nanoparticle-seeds generated in the poly(vinyl pyrrolidone) and TritonX-100 solutions were larger than those generated in the Tween 20 and Brij 58 solutions. The former two have hydrophilic chain in the molecular structure; on the other hand, the latter two have hydrophobic alkyl chain. Based on those facts, we concluded that the interaction between the chains of the complex molecule plays an important role in the nanoparticle formation process.  相似文献   
39.
40.
Various 1,4‐diols are easily accessible from alkenes through iron‐catalyzed aerobic hydration. The reaction system consists of a user‐friendly iron phthalocyanine complex, sodium borohydride, and molecular oxygen. Furthermore, the effect of additional ligands on the iron complex was examined for a model reaction. The second hydroxy group is installed by direct C(sp3) H oxygenation, which is based on a [1,5] hydrogen shift process of a transient alkoxy radical that is formed by formal hydration of the olefin.  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