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   851篇
  免费   8篇
  国内免费   65篇
化学   399篇
晶体学   9篇
力学   28篇
综合类   1篇
数学   273篇
物理学   214篇
  2023年   11篇
  2022年   18篇
  2021年   13篇
  2020年   11篇
  2019年   18篇
  2018年   12篇
  2017年   24篇
  2016年   16篇
  2015年   18篇
  2014年   40篇
  2013年   58篇
  2012年   54篇
  2011年   57篇
  2010年   38篇
  2009年   73篇
  2008年   84篇
  2007年   69篇
  2006年   51篇
  2005年   32篇
  2004年   25篇
  2003年   19篇
  2002年   18篇
  2001年   16篇
  2000年   11篇
  1999年   10篇
  1998年   13篇
  1997年   8篇
  1996年   9篇
  1995年   19篇
  1994年   9篇
  1993年   8篇
  1992年   10篇
  1991年   4篇
  1990年   5篇
  1989年   4篇
  1988年   4篇
  1987年   3篇
  1986年   4篇
  1985年   6篇
  1984年   4篇
  1983年   1篇
  1982年   3篇
  1981年   6篇
  1980年   2篇
  1978年   1篇
  1977年   1篇
  1974年   1篇
  1973年   2篇
  1971年   1篇
排序方式: 共有924条查询结果,搜索用时 15 毫秒
91.
一种故障树分析的新算法   总被引:13,自引:0,他引:13  
本论文中,首先引入了BDD(BrinaryDecisionDiagrams-BDD)的概念,介绍由故障树到BDD转化算法一递归法,及BDD进行故障树分析的方法。  相似文献   
92.
合成了掺杂Y^3 和Gd^3 的Phen-Eu(Ⅲ)二元固体配合物,确定了它们的组成,测定了固体配合物的红外光谱和荧光光谱,并首次探讨了掺杂Y^3 和Gd^3 的Phen-Eu(Ⅲ)二元固体配合物荧光强度的影响。  相似文献   
93.
In this note some new characterization results for multistate systems are obtained. In particular, a new characterization of the Natvig class of multistate systems is presented, which provides us an easy-to-use method of classifying multistate systems. Examples are given to illustrate our results.  相似文献   
94.
The simple Flory-Huggins model can be combined with the lattice gas as was done by Tompa and others. Here the same method is used to obtain the van der Waals equation of state for a binary gas-liquid system containing a solute consisting of segmented molecules. The simplified equation of state developed here is useful for the study of the critical properties of such systems, in particular, the dependence of the various parameters on the chain length of the molecules.  相似文献   
95.
An original method to detect images in defocused scenes by means of a binary joint transform correlation is presented. Defocused images are described in frequency domain as the product between the Fourier transform of the in-focus scene by the optical transfer function of the imaging lens. This function, which presents positive and negative values, introduces sign errors in the joint power spectrum. The goal of this study is to detect the sign of the optical transfer function starting from the defocused image by means of a digital algorithm. Information provided by the algorithm allows to compensate the sign errors in the binary joint power spectrum and to obtain invariant correlations with respect to defocusing. Theoretical analysis and digital experiments to test the procedure are provided.  相似文献   
96.
The properties of binary operations in a real interval are considered and used in the discussion of generalized operations on fuzzy sets, on fuzzy numbers and on fuzzy probabilistic sets.  相似文献   
97.
Given the integer polyhedronP t := conv{x ∈ℤ n :Axb}, whereA ∈ℤ m × n andb ∈ℤ m , aChvátal-Gomory (CG)cut is a valid inequality forP 1 of the type λτAx⩽⌊λτb⌋ for some λ∈ℝ + m such that λτA∈ℤ n . In this paper we study {0, 1/2}-CG cuts, arising for λ∈{0, 1/2} m . We show that the associated separation problem, {0, 1/2}-SEP, is equivalent to finding a minimum-weight member of a binary clutter. This implies that {0, 1/2}-SEP is NP-complete in the general case, but polynomially solvable whenA is related to the edge-path incidence matrix of a tree. We show that {0, 1/2}-SEP can be solved in polynomial time for a convenient relaxation of the systemAx<-b. This leads to an efficient separation algorithm for a subclass of {0, 1/2}-CG cuts, which often contains wide families of strong inequalities forP 1. Applications to the clique partitioning, asymmetric traveling salesman, plant location, acyclic subgraph and linear ordering polytopes are briefly discussed.  相似文献   
98.
Given the values of a 3-dimensional function at unevenly spaced grid points on the grid structure of a channel, we describe a new analytical algorithm to determine the function value at an arbitrary point inside the channel. This algorithm has been implemented on a Univac 1100/81 computer in PL/I.  相似文献   
99.
Let s=(s1,…,sm) and t=(t1,…,tn) be vectors of non-negative integer-valued functions with equal sum . Let N(s,t) be the number of m×n matrices with entries from {0,1} such that the ith row has row sum si and the jth column has column sum tj. Equivalently, N(s,t) is the number of labelled bipartite graphs with degrees of the vertices in one side of the bipartition given by s and the degrees of the vertices in the other side given by t. We give an asymptotic formula for N(s,t) which holds when S→∞ with 1?st=o(S2/3), where and . This extends a result of McKay and Wang [Linear Algebra Appl. 373 (2003) 273-288] for the semiregular case (when si=s for 1?i?m and tj=t for 1?j?n). The previously strongest result for the non-semiregular case required 1?max{s,t}=o(S1/4), due to McKay [Enumeration and Design, Academic Press, Canada, 1984, pp. 225-238].  相似文献   
100.
We study the following problem: an instance is a word with every letter occurring twice. A solution is a 2-coloring of its letters such that the two occurrences of every letter are colored with different colors. The goal is to minimize the number of color changes between adjacent letters.This is a special case of the paint shop problem for words, which was previously shown to be NP-complete. We show that this special case is also NP-complete and even APX-hard. Furthermore, derive lower bounds for this problem and discuss a transformation into matroid theory enabling us to solve some specific instances within polynomial time.  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