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351.
若图G=(V,E),给定方向为D,A表示一个非平凡的阿贝尔群,F(G,A)表示映射f:E(G)→A的集合。若对任意f∈F(G,A)存在映射c:V(G)→A,使得G中的每一条有向边e=uυ∈E(G)(方向是u→υ)满足c(u)-c(v)≠f(e),这时说图G是A-可染的。使得图G在方向D下是A-可染的,A的最小阶数为图G的群色数,记为χg(G)。在分析单圈图和双圈图特性的基础上,讨论了它们的群色数。对于单圈图、双圈图可得出其群色数都是3。 相似文献
352.
李早 《合肥工业大学学报(社会科学版)》2004,18(3):92-96
圆形是最基本的几何图形之一 ,在各种艺术形式中都占据着特殊的地位。文章从形态构成角度出发 ,结合建筑形态的实例对以圆为母题的建筑造型与空间进行了分类研究 ,力图使建筑创作领域的研究更加多元化。 相似文献
353.
This article provides an introductory summary to the formulation and application of exponential random graph models for social networks. The possible ties among nodes of a network are regarded as random variables, and assumptions about dependencies among these random tie variables determine the general form of the exponential random graph model for the network. Examples of different dependence assumptions and their associated models are given, including Bernoulli, dyad-independent and Markov random graph models. The incorporation of actor attributes in social selection models is also reviewed. Newer, more complex dependence assumptions are briefly outlined. Estimation procedures are discussed, including new methods for Monte Carlo maximum likelihood estimation. We foreshadow the discussion taken up in other papers in this special edition: that the homogeneous Markov random graph models of Frank and Strauss [Frank, O., Strauss, D., 1986. Markov graphs. Journal of the American Statistical Association 81, 832–842] are not appropriate for many observed networks, whereas the new model specifications of Snijders et al. [Snijders, T.A.B., Pattison, P., Robins, G.L., Handock, M. New specifications for exponential random graph models. Sociological Methodology, in press] offer substantial improvement. 相似文献
354.
This article reviews new specifications for exponential random graph models proposed by Snijders et al. [Snijders, T.A.B., Pattison, P., Robins, G.L., Handcock, M., 2006. New specifications for exponential random graph models. Sociological Methodology] and demonstrates their improvement over homogeneous Markov random graph models in fitting empirical network data. Not only do the new specifications show improvements in goodness of fit for various data sets, but they also help to avoid the problem of near-degeneracy that often afflicts the fitting of Markov random graph models in practice, particularly to network data exhibiting high levels of transitivity. The inclusion of a new higher order transitivity statistic allows estimation of parameters of exponential graph models for many (but not all) cases where it is impossible to estimate parameters of homogeneous Markov graph models. The new specifications were used to model a large number of classical small-scale network data sets and showed a dramatically better performance than Markov graph models. We also review three current programs for obtaining maximum likelihood estimates of model parameters and we compare these Monte Carlo maximum likelihood estimates with less accurate pseudo-likelihood estimates. Finally, we discuss whether homogeneous Markov random graph models may be superseded by the new specifications, and how additional elaborations may further improve model performance. 相似文献
355.
本文介绍了几种应用在化学上的重要的拓扑指数,讨论了它们的定义及求算,指出了它们在有机化合物结构与性能关系研究中的应用. 相似文献
356.
伍启期 《佛山科学技术学院学报(社会科学版)》1995,(4)
用母函数、事件、乘法原理研究了一类一圈图的计数,给出了这类图的个数的母函数及其显式,对个数的显式进行了构图验证,指出了这些有圈图所对应的分子结构式。 相似文献
357.
Nam-Ky Nguyen 《统计学通讯:模拟与计算》2013,42(3):911-923
This paper describes an efficient algorithm for the construction of optimal or near-optimal resolvable incomplete block designs (IBDs) for any number of treatments v < 100. The performance of this algorithm is evaluated against known lattice designs and the 414 or-designs of Patterson & Williams [36]. For the designs under study, it appears that our algorithm is about equally effective as the simulated annealing algorithm of Venables & Eccleston [42]. An example of the use of our algorithm to construct the row (or column) components of resolvable row-column designs is given. 相似文献
358.
359.
Virginie Gabrel 《Journal of Combinatorial Optimization》2006,11(3):341-346
In this paper, we compare several 0-1 linear programs for solving the satellite mission planning problem. We prove that one
of them presents a smaller integrality gap. Our explanation is based on stable set polytope formulations for perfect graphs. 相似文献
360.
Chiuyuan Chen 《Journal of Combinatorial Optimization》2003,7(1):79-86
A graph is hamiltonian if it has a hamiltonian cycle. It is well-known that Tutte proved that any 4-connected planar graph is hamiltonian. It is also well-known that the problem of determining whether a 3-connected planar graph is hamiltonian is NP-complete. In particular, Chvátal and Wigderson had independently shown that the problem of determining whether a maximal planar graph is hamiltonian is NP-complete. A classical theorem of Whitney says that any maximal planar graph with no separating triangles is hamiltonian, where a separating triangle is a triangle whose removal separates the graph. Note that if a planar graph has separating triangles, then it can not be 4-connected and therefore Tutte's result can not be applied. In this paper, we shall prove that any maximal planar graph with only one separating triangle is still hamiltonian. 相似文献