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261.
This paper investigates two problems related to the determination of critical edges for the minimum cost assignment problem. Given a complete bipartite balanced graph with n vertices on each part and with costs on its edges, kMost Vital Edges Assignment consists of determining a set of k edges whose removal results in the largest increase in the cost of a minimum cost assignment. A dual problem, Min Edge Blocker Assignment, consists of removing a subset of edges of minimum cardinality such that the cost of a minimum cost assignment in the remaining graph is larger than or equal to a specified threshold. We show that kMost Vital Edges Assignment is NP-hard to approximate within a factor c<2 and Min Edge Blocker Assignment is NP-hard to approximate within a factor 1.36. We also provide an exact algorithm for kMost Vital Edges Assignment that runs in O(nk+2). This algorithm can also be used to solve exactly Min Edge Blocker Assignment. 相似文献
262.
263.
The problem we consider in this article is motivated by data placement, in particular data replication in distributed storage and retrieval systems. We are given a set V of v servers along with b files (data, documents). Each file is replicated on exactly k servers. A placement consists in finding a family of b subsets of V (representing the files) called blocks, each of size k. Each server has some probability to fail and we want to find a placement that minimizes the variance of the number of available files. It was conjectured that there always exists an optimal placement (with variance better than any other placement for any value of the probability of failure). We show that the conjecture is true, if there exists a well‐balanced design—that is, a family of blocks—each of size k, such that each j‐element subset of V, , belongs to the same or almost the same number of blocks (difference at most one). The existence of well‐balanced designs is a difficult problem as it contains, as a subproblem, the existence of Steiner systems. We completely solve the case and give bounds and constructions for and some values of v and b. 相似文献
264.
《Optimization》2012,61(8):1039-1073
This article deals with multicriteria optimization models and algorithms of movement scheduling for many objects to synchronize their movement (2CMSS problem). The model consists of two parts: (1) node–disjoint path planning visiting specified nodes for K objects with a given vector of intermediate nodes for each one (NDSP problem); (2) movement synchronization in some intermediate nodes (MS problem). For synchronous movement, two categories of criteria are defined: time of movement and ‘distance’ of K-moved objects from the movement pattern. We defined the problem as a discrete-continuous, non-linear, two-criteria mathematical programming problem. We proposed to use a two-stage algorithm to solve the 2CMSS problem (as lexicographic solution): At first we have to find the vector of node–disjoint shortest paths for K objects visiting intermediate nodes to set optimal paths under the assumption that we use maximal possible velocities on each arc belonging to a path for each object (solution of the NDSP problem), and next we try to decrease the values of velocities to optimize the second criterion (synchronization, solution of the MS problem). Experimental analyses of effectiveness and complexity of the algorithms are presented. 相似文献
265.
Shuji Yamamoto Atsushi Yamashita 《Proceedings of the American Mathematical Society》2006,134(12):3715-3719
In this paper we construct compact metric spaces , which are topologically distinct but whose topological sums and are homeomorphic.
266.
By Petersen's theorem, a bridgeless cubic graph has a 2‐factor. H. Fleischner extended this result to bridgeless graphs of minimum degree at least three by showing that every such graph has a spanning even subgraph. Our main result is that, under the stronger hypothesis of 3‐edge‐connectivity, we can find a spanning even subgraph in which every component has at least five vertices. We show that this is in some sense best possible by constructing an infinite family of 3‐edge‐connected graphs in which every spanning even subgraph has a 5‐cycle as a component. © 2009 Wiley Periodicals, Inc. J Graph Theory 62: 37–47, 2009 相似文献
267.
Analytical mathematics and digital simulation are used to predict the response, to a potential jump, of the junction between
insulating and conducting regions of an electrode. The simulation is carried out differentially and employs other novel features.
Concentrations in the vicinity of edges of positive and negative curvatures, as well as straight edges, are analyzed by the
model and thereby the faradaic current densities and currents are predicted. It is shown that, in addition to the well-understood
cottrellian current arising from the surface of the conducting electrode, currents are generated that are proportional to
the length of the edge and to its curvature. These results are then applied to inlaid disks and to partially blocked electrodes.
The possibility is explored of using the response to a potential step to gain information on the geometry of a partially blocked
electrode. 相似文献
268.
Bofeng Huo Qingsong Du Ping Li Yang Wu Jun Yin Hong-Jian Lai 《Journal of Graph Theory》2023,102(1):107-127
A cycle of a matroid is a disjoint union of circuits. A matroid is supereulerian if it contains a spanning cycle. To answer an open problem of Bauer in 1985, Catlin proved in [J. Graph Theory 12 (1988) 29–44] that for sufficiently large , every 2-edge-connected simple graph with and minimum degree is supereulerian. In [Eur. J. Combinatorics, 33 (2012), 1765–1776], it is shown that for any connected simple regular matroid , if every cocircuit of satisfies , then is supereulerian. We prove the following. (i) Let be a connected simple regular matroid. If every cocircuit of satisfies , then is supereulerian. (ii) For any real number with , there exists an integer such that if every cocircuit of a connected simple cographic matroid satisfies , then is supereulerian. 相似文献
269.
A new route to obtain a large figure of merit (>1) is reported, for the first time, by considering a one-dimensional quasiperiodic lattice where an electron can hop beyond usual nearest-neighbor sites. A finite positional correlation is imposed among the constituent lattice sites, following the well-known Aubry-André-Harper (AAH) form. In the presence of second-neighbor hopping, the AAH lattice exhibits energy dependent mobility edge which plays the central role for efficient energy conversion. Employing a tight-binding framework, all the thermoelectric quantities are computed based on the standard nonequilibrium Green's function formalism. The analysis can be utilized to investigate thermoelectric phenomena in similar kinds of other aperiodic systems possessing higher order electron hopping. 相似文献