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   5095篇
  免费   224篇
  国内免费   36篇
化学   3269篇
晶体学   26篇
力学   111篇
数学   843篇
物理学   1106篇
  2023年   35篇
  2021年   67篇
  2020年   90篇
  2019年   104篇
  2018年   50篇
  2017年   53篇
  2016年   155篇
  2015年   146篇
  2014年   159篇
  2013年   224篇
  2012年   306篇
  2011年   328篇
  2010年   172篇
  2009年   151篇
  2008年   267篇
  2007年   209篇
  2006年   211篇
  2005年   187篇
  2004年   183篇
  2003年   134篇
  2002年   127篇
  2001年   102篇
  2000年   94篇
  1999年   67篇
  1998年   51篇
  1997年   63篇
  1996年   81篇
  1995年   74篇
  1994年   73篇
  1993年   75篇
  1992年   73篇
  1991年   58篇
  1990年   61篇
  1989年   61篇
  1988年   50篇
  1987年   46篇
  1986年   60篇
  1985年   68篇
  1984年   47篇
  1983年   43篇
  1982年   48篇
  1981年   37篇
  1980年   35篇
  1979年   39篇
  1978年   48篇
  1977年   46篇
  1976年   39篇
  1975年   38篇
  1974年   39篇
  1973年   47篇
排序方式: 共有5355条查询结果,搜索用时 15 毫秒
101.
We discuss and analyze a family of trees grown on a Cayley tree, that allows for a variable exponent in the expression for the mass as a function of chemical distance, M(l)l dl . For the suggested model, the corresponding exponent for the mass of the skeleton,d l s , can be expressed in terms ofd l asd l s = 1,d l d l c = 2;d l s = d l –1,d 1 d l c = 2, which implies that the tree is finitely ramified ford l 2 and infinitely ramified whend l 2. Our results are derived using a recursion relation that takes advantage of the one-dimensional nature of the problem. We also present results for the diffusion exponents and probability of return to the origin of a random walk on these trees.  相似文献   
102.
103.
104.
In this paper procedures for the characterization of individual aerosol particles by element mapping in the electron microprobe are presented. The number, size and qualitative chemical composition of particles is derived from a combination of secondary or backscattered electron images and element distribution maps. Accuracy of the size distribution and reliability of the qualitative analysis procedure were checked with silicate samples. In order to obtain a semi-quantitative estimate of the chemical composition of individual particles the count rates taken from element distribution maps are corrected for matrix and geometric effects using particle ZAF procedures.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday  相似文献   
105.
From 17 transitions in the singly ionized Sb II spectrum the hyperfine structure (A andB splitting constants) of the complete excited configurations 5p6s and 5p6p were determined by means of optical interference spectroscopy. In addition, a theoretical analysis both of the fine structure and also of the hyperfine structure was carried out (in the case of 5p6p of the general typenpn′p for the first time in literature). For the 3 levels 5p6p 3 P 1, 5p7p 3 D 2 and 5p6p 1 P 1 a different classification was found and consistent values for the fine structure parameters, mixing coefficients and single electron hyperfine structure splitting parametersa nl ik andb nl ik were obtained. The three new determinations in Sb II of the quadrupole moment (in barn) of121Sb (Q(5p6s)=?0.55(5);Q(5p6p)=?0.57(5) from the 5p-electron andQ(5p6p)=?0.7(2) from the 6p-electron) are well agreeing with each other but differ to former values from SbI. The core polarization and isotope shift of the lines, however, are compatible with our former results in SbI.  相似文献   
106.
Starting from earlier work by Baudler we introduce a chemical heuristic for the systematic deduction and classification of covalent partial structures of phosphorus in polycyclic phosphanes, phosphorus-rich polycyclic phosphides, and allotropes of phosphorus except the black forms. This approach is used to direct ab initio techniques (which also confirm the rules) in the quest for as yet unknown forms of molecular or macromolecular phosphorus. Based on calculated stabilities of systematically generated structural alternatives we rationalize the stabilities of Hittorf's phosphorus and of molecular P4, confirm the possible existence of at least one other crystalline allotropic form of phosphorus, and provide insight into the probable structure of amorphous red phosphorus. In total, the combined approach of chemical heuristics and large scale ab initio calculations presented in this work supplies a coherent chemical understanding of covalent polyphosphorus structures.  相似文献   
107.
108.
109.
A high-performance liquid chromatography-mass spectrometry method has been developed for the simultaneous determination of native carnitine and eight acylcarnitines in urine. The procedure uses a solid-phase extraction on a cation-exchange column and the separation is performed without derivatization within 17 min on a reversed-phase C8 column in the presence of a volatile ion-pairing reagent. The detector was an ion trap mass spectrometer and quantification was carried out in the MS-MS mode. Validation was done for aqueous standards at ranges between 0.75 and 200 micromol/l, depending on the compound. Carnitine was quantified in urine and comparison with a radioenzymatic assay gave a satisfactory correlation (R2 = 0.981). The assay could be successfully applied to the diagnostic of pathological acylcarnitines profile of metabolic disorders in urines of patients suffering from different organic acidurias.  相似文献   
110.
The development of theoretical tools for the study of dynamical phenomena of many-particle systems on the quantum level is a fundamental challenge since many decades. A lot of efforts have been invested on Feynman's path integral approach, however, no computationally tractable method for investigating realistic systems could be developed up to now. In this paper we propose an alternative representation of the real-time many-body evolution operator formulated within the framework of the auxiliary field formalism. Our goal is to derive a new auxiliary field functional integral representation, in which the large oscillations of the functional integrand are reduced, in order to render the auxiliary field approach more attractive for real-time computation. This objective is attained using a generalized version of the method of Gaussian equivalent representation of Efimov and Ganbold [Phys. Stat. Sol. 168 (1991) 165], which eliminates the low-order fluctuations of the auxiliary field from the interaction functional.  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