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   1808篇
  免费   219篇
  国内免费   107篇
化学   1488篇
晶体学   3篇
力学   54篇
综合类   14篇
数学   131篇
物理学   444篇
  2024年   8篇
  2023年   33篇
  2022年   106篇
  2021年   131篇
  2020年   107篇
  2019年   89篇
  2018年   53篇
  2017年   84篇
  2016年   100篇
  2015年   94篇
  2014年   99篇
  2013年   131篇
  2012年   87篇
  2011年   94篇
  2010年   87篇
  2009年   115篇
  2008年   93篇
  2007年   82篇
  2006年   103篇
  2005年   80篇
  2004年   81篇
  2003年   53篇
  2002年   37篇
  2001年   25篇
  2000年   22篇
  1999年   27篇
  1998年   22篇
  1997年   15篇
  1996年   15篇
  1995年   6篇
  1994年   7篇
  1993年   6篇
  1992年   4篇
  1991年   4篇
  1990年   3篇
  1989年   4篇
  1988年   2篇
  1987年   5篇
  1986年   7篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   1篇
  1980年   2篇
  1979年   1篇
  1974年   1篇
排序方式: 共有2134条查询结果,搜索用时 31 毫秒
11.
This work presents a formulation based on UPML for truncating conductive media by using a local and non-orthogonal coordinate system to solve Maxwell’s equations by the FDTD method. The detailed procedure for obtaining the UPML equations for this case is shown and the complete equation set is provided.  相似文献   
12.
Hyperbolic virtual polytopes arose originally as polytopal versions of counterexamples to the following A.D.Alexandrov’s uniqueness conjecture: Let K ⊂ ℝ3 be a smooth convex body. If for a constant C, at every point of ∂K, we have R 1CR 2 then K is a ball. (R 1 and R 2 stand for the principal curvature radii of ∂K.) This paper gives a new (in comparison with the previous construction by Y.Martinez-Maure and by G.Panina) series of counterexamples to the conjecture. In particular, a hyperbolic virtual polytope (and therefore, a hyperbolic hérisson) with odd an number of horns is constructed. Moreover, various properties of hyperbolic virtual polytopes and their fans are discussed.  相似文献   
13.
We use a recently published method for the renormalization of the self-energy to calculate the self-energy of 6s and 8d levels to all orders in Zα. We demonstrate the accuracy of the method and its potential for high-n, low-Z applications. We also show that this method is perfectly suited for the evaluation of the two-electron self-energy (self-energy screening). For the first time, evaluation of the screening of the 1s electron by a second one in either the 1s,2s, 2p1/2 or 2p3/2 shells has been performed, for 30 ⩽ Z ⩽92. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
14.
We study the equilibrium statistical mechanics of classical two-dimensional Coulomb systems living on a pseudosphere (an infinite surface of constant negative curvature). The Coulomb potential created by one point charge exists and goes to zero at infinity. The pressure can be expanded as a series in integer powers of the density (the virial expansion). The correlation functions have a thermodynamic limit, and remarkably that limit is the same one for the Coulomb interaction and some other interaction law. However, special care is needed for defining a thermodynamic limit of the free energy density. There are sum rules expressing the property of perfect screening. These generic properties can be checked on the Debye–Hückel approximation, and on two exactly solvable models, the one-component plasma and the two-component plasma, at some special temperature.  相似文献   
15.
The grand canonical ensemble of a two-dimensional Coulomb system with±1 charges is proved to have screening phenomena in its high-temperature region. The Coulomb potential in a finite region is assumed to be (–)–1, where is the Laplacian with zero boundary conditions on. The hard-core condition is not assumed. The model is set up by separating (–)–1 into a shortrange part and a long-range part depending on a parameter. The self-energies are subtracted only for the short-range part and therefore a choice of is a choice of subtraction of self-energies. The method of proof is in general the same as that of Brydges-Federbush Debye screening, except that here a modification for the short-range part of the potentials is needed.  相似文献   
16.
A method for the treatment of long-dimensional chemical data arrays is presented in this work with the aim of maximising classification models. The method is based on the construction of fingerprints and the subsequent generation of a similarity matrix. The similarity calculation has been modified through a scaling process to take into account different significance shown by the variables. The method was applied to spectral measurements of wines and several aspects were studied, namely: threshold considered in the construction of fingerprints and patterns, weighting factor used for scaling, normalisation method, etc. The application of both Principal Components Analysis and Soft-Independent Modelling of Class Analogies to the similarity matrices gave better classifications of the information than those obtained using original data.  相似文献   
17.
Relative protonation energies in the primary, secondary and tertiary aliphatic series of amines are calculated by a semiempirical method employing the virtual charge model. The method accounts quite well for the observed differences between the gas-phase protonation affinities and the protonation enthalpies in solution, but when allowance is made for steric shielding from the bulk solvent for “non-edge” atoms, some anomalies in the uncorrected model are removed. The calculated solute-solvent interactions are related to experimental enthalpies of solution and to trends expected from the Born model.  相似文献   
18.
19.
淫羊藿根与叶活性成分的分析和比较   总被引:8,自引:0,他引:8  
采用细胞膜色谱法(CMC)筛选,并结合离体药理实验确定主要活性成分,利用高效液相色谱法分析比较了淫羊藿根与叶中的活性成分及其差异性.色谱条件为Kromasil ODS 柱(150 mm× 4.6 mm.I.D )流动相甲醇-水(70:30,V:V);检测波长270nm。筛选发现淫羊藿根中的两个有效成分YYH-214和YYH-216对血管有较强的舒张作用,表明活性成分在CMC模型体系中的保留特性与药理作用之间存在良好的相关性。在此色谱条件下淫羊藿叶未检测到这两种活性成分.  相似文献   
20.
A rapid microtiter plate assay for the detection of inhibitors of the Na+, K+-ATPase has been developed. The assay is based on the measurement of inorganic phosphate released from the substrate, ATP, and has been designed to be carried out in the individual wells of a microtiter plate. Since the production of inorganic phosphate is determined colorimetrically, multiple samples can be tested simultaneously using a microtiter plate reader. This microtiter plate assay is particularly useful for screening large numbers of samples, such as microbial culture supernatants.  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