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   196篇
  免费   13篇
  国内免费   2篇
化学   142篇
晶体学   2篇
力学   4篇
数学   22篇
物理学   41篇
  2023年   3篇
  2021年   4篇
  2020年   6篇
  2019年   3篇
  2018年   1篇
  2017年   1篇
  2016年   9篇
  2015年   10篇
  2014年   5篇
  2013年   15篇
  2012年   18篇
  2011年   13篇
  2010年   5篇
  2009年   7篇
  2008年   18篇
  2007年   9篇
  2006年   11篇
  2005年   12篇
  2004年   8篇
  2003年   6篇
  2002年   11篇
  2001年   2篇
  2000年   2篇
  1999年   4篇
  1998年   2篇
  1997年   5篇
  1996年   3篇
  1995年   3篇
  1994年   1篇
  1993年   3篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1982年   4篇
  1973年   1篇
  1968年   1篇
排序方式: 共有211条查询结果,搜索用时 31 毫秒
41.
We present an ab initio study of the structural and electronic properties of the halogen-bridged MMX single polymer [Pt2(CH3CS2)4I]n and of various possible modifications of its sequence, in the framework of density functional theory. The computed band structure of the infinite regular polymer reveals a net metallic character; this evidence is compatible with the outcome of recent measurements done in the solid phase at room temperature. By taking the regular [Pt2(CH3CS2)4I]n polymer as our reference system, we analyzed the origin and the robustness of the metallic state along the chain with respect to a large set of geometrical and chemical perturbations of the subunits. In particular, we considered partial substitutions of the metal, halide, and dithiocarboxylate ligand subunits, as well as structural strain, defects, and magnetic effects. Our results demonstrate that the metallic character of single MMX chains is very resistant to a wide range of possible distortions that can occur in reality.  相似文献   
42.
We report on a novel highly semiconducting 1D coordination polymer architecture obtained by the reaction of a Cu(II) salt with 2,2'-dipyridyldisulfide under microwave solvothermal conditions. This reaction proceeds with an unusual C-S and S-S bond cleavage of the 2,2'-dipyridyldisulfide ligand. The unprecedented architecture of this coordination polymer consists of a 1D chain formed by the assembling of Cu9 cluster cages. The electrical conductivity behavior of this novel material suggests new perspectives for the use of coordination polymers as electrical conducting materials.  相似文献   
43.
Three new compounds of formula [Pt2(SSCR)4] (R = CH3, (CH2)4CH3, cyclohexyl) have been prepared and characterized by X-ray diffraction. Their crystal structures consist of one-dimensional linear chains formed by stacking of the dimetallic complexes in which the alkyl group on the dithioacetate modulates the intermetallic distances between dimetallic entities. Direct current electrical conductivity studies show that crystals of the three compounds behave as semiconductors and their conductivity values are directly connected to the intermolecular metal-to-metal distances. These experimental results are supported by density functional theory calculations.  相似文献   
44.
A new deterministic branch and bound algorithm is presented in this paper for the global optimization of continuous problems that involve concave univariate, bilinear and linear fractional terms. The proposed algorithm, the branch and contract algorithm, relies on the use of a bounds-contraction subproblem that aims at reducing the size of the search region by eliminating portions of the domain in which the objective function takes only values above a known upper bound. The solution of contraction subproblems at selected branch and bound nodes is performed within a finite contraction operation that helps reducing the total number of nodes in the branch and bound solution tree. The use of the proposed algorithm is illustrated with several numerical examples.  相似文献   
45.
46.
47.
Not only UV radiation can bring about the dimerization of the pyrimidine nucleobase uracil, a metal ion can as well! The reaction proceeds by a reductive elimination process of two cis-oriented uracil entities, each bonded to AuIII through C5 [Eq. (a)]. R/R′=H/CH3, CH3/CH3, H,C5H9O4  相似文献   
48.
49.
50.
The multidimensional Conformational Potential Energy Hypersurface (PEHS) of cyclotrisarcosyl was comprehensively investigated at the DFT (B3LYP/6-31G(d), B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p)), levels of theory. The equilibrium structures, their relative stability, and the Transition State (TS) structures involved in the conformational interconversion pathways were analyzed. Aug-cc-pVTZ//B3LYP/6-311++G(d,p) and MP2/6-31G(d)//B3LYP/6-311++G(d,p) single point calculations predict a symmetric cis-cis-cis crown conformation as the energetically preferred form for this compound, which is in agreement with the experimental data. The conformational interconversion between the global minimum and the twist form requires 20.88 kcal mol-1 at the MP2/6-31G(d)//B3LYP/6-311++G(d,p) level of theory. Our results allow us to form a concise idea about the internal intricacies of the PEHSs of this cyclic tripeptide, describing the conformations as well as the conformational interconversion processes in this hypersurface. In addition, a comparative analysis between the conformational behaviors of cyclotrisarcosyl with that previously reported for cyclotriglycine was carried out  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