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   490篇
  免费   20篇
  国内免费   31篇
化学   108篇
晶体学   1篇
力学   3篇
综合类   2篇
数学   297篇
物理学   130篇
  2024年   3篇
  2023年   4篇
  2022年   8篇
  2021年   10篇
  2020年   11篇
  2019年   10篇
  2018年   11篇
  2017年   3篇
  2016年   8篇
  2015年   10篇
  2014年   5篇
  2013年   32篇
  2012年   11篇
  2011年   25篇
  2010年   16篇
  2009年   25篇
  2008年   39篇
  2007年   23篇
  2006年   35篇
  2005年   25篇
  2004年   26篇
  2003年   20篇
  2002年   23篇
  2001年   18篇
  2000年   18篇
  1999年   19篇
  1998年   10篇
  1997年   18篇
  1996年   5篇
  1995年   4篇
  1994年   6篇
  1993年   1篇
  1992年   3篇
  1991年   7篇
  1990年   10篇
  1989年   4篇
  1988年   5篇
  1987年   5篇
  1986年   5篇
  1985年   4篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   3篇
  1979年   2篇
  1978年   1篇
  1977年   2篇
  1976年   2篇
  1975年   1篇
排序方式: 共有541条查询结果,搜索用时 15 毫秒
1.
We construct a correspondence between the set of partitions of a finite set M and the set of pairs of walks to the same vertex on a graph giving the Bratteli diagram of the partition algebra on M. This is the precise analogue of the correspondence between the set of permutations of a finite set and the set of pairs of Young tableaux of the same shape, called the Robinson–Schensted correspondence.  相似文献   
2.
In the present paper we develop our approach for studying the stability of integer programming problems. We prove that the L-class enumeration method is stable on integer linear programming problems in the case of bounded relaxation sets [9]. The stability of some cutting plane algorithms is discussed.  相似文献   
3.
本文介绍了迈克耳逊干涉仪的彩色光环的产生机理、快速调节与拍摄方法。  相似文献   
4.
Goguadze  D. F. 《Mathematical Notes》2003,74(3-4):346-351
We introduce a generalized notion of semiring and prove that all known properties that semirings have according to the old definition are preserved.  相似文献   
5.
Several sophisticated methods to solution of symmetry specified enumeration problems are available in the modern literature. In this paper we propose a simple technique that allows one to manually compute the exact numbers of fixed-symmetry derivatives for a given structure either with inclusion or ignoring the substitution patterns. The basic idea of the method suggested consists in the derivation of Pólya-like cycle indices for the automorphism groups of specially constructed orbit partition graphs; the expansion of these indices and subsequent simple calculations result in the desired numbers of substituted derivatives with achiral substituents. Limitations of the new technique (and a method suggested earlier) depend on the relevance of the orbit partitions for particular subgroups of the point symmetry group. For illustration purposes, the results obtained for the prismane (D 3h ) and adamantane (T d ) structures are discussed. In the former case the numbers of substituted derivatives can be found for all subgroups of the D 3h group, whereas in the latter case these numbers can be determined for eight out of eleven subgroups of the T d point symmetry group. This work is based on the text of the lecture presented by the authors at the 5th All-Russia Conference on Molecular Modeling (Moscow, April 2007). The paper deals with the methodology and detailed treatment of applied aspects related to solution of enumeration problems for substituted derivatives with prescribed symmetry groups. Unlike the known methods of symmetry specified enumeration, the technique suggested is simple enough and may be regarded as generalization of the Pólya methodology, which is widely used by chemists. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 227–245, February, 2008.  相似文献   
6.
In the set of graphs of order n and chromatic number k the following partial order relation is defined. One says that a graph G is less than a graph H if ci(G) ≤ ci(H) holds for every i, kin and at least one inequality is strict, where ci(G) denotes the number of i‐color partitions of G. In this paper the first ? n/2 ? levels of the diagram of the partially ordered set of connected 3‐chromatic graphs of order n are described. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 210–222, 2003  相似文献   
7.
本文推导了两种非标准色传感器在测色时引入的误差公式,并对其进行分析。最后通过计算8个样品的颜色对分析结果给于验证。  相似文献   
8.
We establish a relation between an exactly solvable boson model and plane partitions, i.e., three-dimensional Young diagrams enclosed in a box of finite size, which allows representing the partition generating functions as correlation functions of an integrable model and deriving the MacMahon formulas for enumerating partitions using the quantum inverse scattering method. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 150, No. 2, pp. 193–203, February, 2007.  相似文献   
9.
The propensity of (natural) polyols dispersed in heavy metal- and zinc-free PVC sheets to improve the initial colour, e.g. the colour during the first minutes of exposure to high processing temperatures (short-term stability), has been investigated. It is shown using W(Lab) values that the initial colour improves upon addition of polyols containing primary hydroxyl groups. The polyols act as HCl scavengers, presumably via an acid-catalysed SN2 substitution of the primary hydroxyl groups by chloride ions. In contrast, polyols with only secondary or tertiary hydroxyl groups accelerate the thermal degradation of PVC. Notwithstanding, the efficacy of the (natural) polyols containing primary hydroxyl groups will be reduced if the polyol is susceptible to competitive acid-catalysed intramolecular cyclodehydration reactions under the processing conditions. This is substantiated by a comparison of the behaviour of mannitol and 3,4-di-O-methyl-d-mannitol. The methylated derivative, which is less prone to undergo intramolecular cyclodehydration, improves the initial colour of heavy metal- and zinc-free PVC sheets more significantly than mannitol itself.  相似文献   
10.
在水溶液中钴(Ⅱ)与亚硝基R盐所形成的配合阴离子可以与有机碱阳离子(结晶紫)缔合形成中性缔合分子。在聚乙烯醇存在下,配合物可稳定存在于水溶液中。钴(Ⅲ)-亚硝基R盐-结晶紫配合物在510nm处有一最大吸收,摩尔吸光系数ε_(510)=1.47×l0~5L·mol~(-1)·cm(-1)。配合物中各组分的摩尔比为:Co:R:CV=1:3:6。反应具有较高的选择性,采用双峰双波长法测定钴可使灵敏度得到进一步提高,相应的摩尔吸光系数ε_(510-640)=4.09×10~5L·mol~(-1)·cm~(-1)。方法用于合成试样中钴的测定,结果满意。  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