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121.
Vojtech Blint 《Journal of Discrete Algorithms》2003,1(3-4):339-355
Let G be an undirected graph with two edge costs (c-cost and d-cost). We want to minimize the diameter of a spanning subgraph S (under d-cost) subject to the constraint that the total cost of the edges in S (with respect to c) does not exceed a given budget. We prove that this problem is non-approximable, even in some special cases. Similar results are proved if the stretch factor or the root stretch factor is considered instead of the diameter. 相似文献
122.
陈协彬 《数学物理学报(A辑)》2003,23(1):65-76
设G是路或圈的笛卡尔乘积图,t(G)表示G的支撑树数.该文借助于第二类Chebyshev多项式给出t(G)的公式,并考虑了t(G)的线性递归关系及渐近性态. 相似文献
123.
Gido Scharfenberger‐Fabian 《Mathematical Logic Quarterly》2011,57(6):591-610
Assuming Jensen's principle ?+ we construct Souslin algebras all of whose maximal chains are pairwise isomorphic as total orders, thereby answering questions of Koppelberg and Todor?evi?. 相似文献
124.
Chip-Firing and the Critical Group of a Graph 总被引:12,自引:0,他引:12
N.L. Biggs 《Journal of Algebraic Combinatorics》1999,9(1):25-45
A variant of the chip-firing game on a graph is defined. It is shown that the set of configurations that are stable and recurrent for this game can be given the structure of an abelian group, and that the order of the group is equal to the tree number of the graph. In certain cases the game can be used to illuminate the structure of the group. 相似文献
125.
Three-dimensional cellular automaton simulation of tumour growth in inhomogeneous oxygen environment
H. Hötzendorfer W. Estelberger F. Breitenecker 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(2):177-189
Cellular automaton theory has previously been used to study cell growth. In this study, we present a three-dimensional cellular automaton model performing the growth simulation of normal and cancerous cells. The necessary nutrient supply is provided by an artificial arterial tree which is generated by constrained constructive optimization. Spatial oxygen diffusion is approximated again by a cellular automaton model. All results could be illustrated dynamically by three-dimensional volume visualization. Because of the chosen modelling approach, an extension of the model to simulate angiogenic processes is possible. 相似文献
126.
A Heuristic for Moment-Matching Scenario Generation 总被引:1,自引:0,他引:1
Kjetil Høyland Michal Kaut Stein W. Wallace 《Computational Optimization and Applications》2003,24(2-3):169-185
In stochastic programming models we always face the problem of how to represent the random variables. This is particularly difficult with multidimensional distributions. We present an algorithm that produces a discrete joint distribution consistent with specified values of the first four marginal moments and correlations. The joint distribution is constructed by decomposing the multivariate problem into univariate ones, and using an iterative procedure that combines simulation, Cholesky decomposition and various transformations to achieve the correct correlations without changing the marginal moments.With the algorithm, we can generate 1000 one-period scenarios for 12 random variables in 16 seconds, and for 20 random variables in 48 seconds, on a Pentium III machine. 相似文献
127.
If the dimension of a linear space is not greater than 3, then the characteristic polynomial of the Coxeter transformation associated with any symmetric matrix is invariant under the natural action of the symmetric group. If the dimensionality is greater than 3, then this statement does not hold. The set of all trees such that the spectrum of their associated Coxeter transformation contains negative one is three-dimensional. 相似文献
128.
Eric S. Egge 《Discrete Mathematics》2006,306(6):552-563
Gire, West, and Kremer have found ten classes of restricted permutations counted by the large Schröder numbers, no two of which are trivially Wilf-equivalent. In this paper we enumerate eleven classes of restricted signed permutations counted by the large Schröder numbers, no two of which are trivially Wilf-equivalent. We obtain five of these enumerations by elementary methods, five by displaying isomorphisms with the classical Schröder generating tree, and one by giving an isomorphism with a new Schröder generating tree. When combined with a result of Egge and a computer search, this completes the classification of restricted signed permutations counted by the large Schröder numbers in which the set of restrictions consists of two patterns of length 2 and two of length 3. 相似文献
129.
Yury Nikulin 《Journal of Heuristics》2008,14(4):391-402
This paper addresses the robust spanning tree problem with interval data, i.e. the case of classical minimum spanning tree
problem when edge weights are not fixed but take their values from some intervals associated with edges. The problem consists
of finding a spanning tree that minimizes so-called robust deviation, i.e. deviation from an optimal solution under the worst
case realization of interval weights. As it was proven in Kouvelis and Yu (Robust Discrete Optimization and Its Applications,
Kluwer Academic, Norwell, 1997), the problem is NP-hard, therefore it is of great interest to tackle it with some metaheuristic approach, namely simulated
annealing, in order to calculate an approximate solution for large scale instances efficiently. We describe theoretical aspects
and present the results of computational experiments. To the best of our knowledge, this is the first attempt to develop a
metaheuristic approach for solving the robust spanning tree problem. 相似文献
130.
This paper provides a method of finding the optimal expansion process and discusses the marginal analysis for expansion of the competence set when the cost functions are asymmetric. The concept of tree expansion process is introduced, and a method of finding the optimal tree expansion process is given. The paper also shows a way to identify the optimal competence set when both the expected return and cost are considered. 相似文献