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61.
本文研究了带有不连续项的 Volterra积分方程的最小和最大解 ,并证明了参考文献 [1]中的主要结果的条件可被较弱条件代替 相似文献
62.
Jing Qin 《Scandinavian Journal of Statistics》1998,25(4):681-691
We use Owen's (1988, 1990) empirical likelihood method in upgraded mixture models. Two groups of independent observations are available. One is z 1 , ..., z n which is observed directly from a distribution F ( z ). The other one is x 1 , ..., x m which is observed indirectly from F ( z ), where the x i s have density ∫ p ( x | z ) dF ( z ) and p ( x | z ) is a conditional density function. We are interested in testing H 0 : p ( x | z ) = p ( x | z ; θ ), for some specified smooth density function. A semiparametric likelihood ratio based statistic is proposed and it is shown that it converges to a chi-squared distribution. This is a simple method for doing goodness of fit tests, especially when x is a discrete variable with finitely many values. In addition, we discuss estimation of θ and F ( z ) when H 0 is true. The connection between upgraded mixture models and general estimating equations is pointed out. 相似文献
63.
从Navier-Stokes方程出发,采用层流模型描述水流动状态,并在欧拉坐标系中用速度-压力修正法对模型进行求解,考虑到转轮内流道几何形状比较复杂,故采用有限元法进行数值离散,并将该解法用FORTRAN语言编制计算程序,对三峡工程混 式水轮机转轮内部的流场进行数值计算,分析了转轮内的速度和压力分布。 相似文献
64.
Stuart R. Lipsitz Garrett M. Fitzmaurice Geert Molenberghs & Lue Ping Zhao 《Journal of the Royal Statistical Society. Series C, Applied statistics》1997,46(4):463-476
Patients infected with the human immunodeficiency virus (HIV) generally experience a decline in their CD4 cell count (a count of certain white blood cells). We describe the use of quantile regression methods to analyse longitudinal data on CD4 cell counts from 1300 patients who participated in clinical trials that compared two therapeutic treatments: zidovudine and didanosine. It is of scientific interest to determine any treatment differences in the CD4 cell counts over a short treatment period. However, the analysis of the CD4 data is complicated by drop-outs: patients with lower CD4 cell counts at the base-line appear more likely to drop out at later measurement occasions. Motivated by this example, we describe the use of `weighted' estimating equations in quantile regression models for longitudinal data with drop-outs. In particular, the conventional estimating equations for the quantile regression parameters are weighted inversely proportionally to the probability of drop-out. This approach requires the process generating the missing data to be estimable but makes no assumptions about the distribution of the responses other than those imposed by the quantile regression model. This method yields consistent estimates of the quantile regression parameters provided that the model for drop-out has been correctly specified. The methodology proposed is applied to the CD4 cell count data and the results are compared with those obtained from an `unweighted' analysis. These results demonstrate how an analysis that fails to account for drop-outs can mislead. 相似文献
65.
赵时仁 《湛江师范学院学报》2001,22(6):25-28
从基础热力学函数的相互关系出发,结合偏微商运算基本原理,归纳热力学函数偏微商变换的常用途径,并对化学热力学函数偏微商式的证明方法及技巧进行一些具体研讨。 相似文献
66.
Ordinal regression is used for modelling an ordinal response variable as a function of some explanatory variables. The classical technique for estimating the unknown parameters of this model is Maximum Likelihood (ML). The lack of robustness of this estimator is formally shown by deriving its breakdown point and its influence function. To robustify the procedure, a weighting step is added to the Maximum Likelihood estimator, yielding an estimator with bounded influence function. We also show that the loss in efficiency due to the weighting step remains limited. A diagnostic plot based on the Weighted Maximum Likelihood estimator allows to detect outliers of different types in a single plot. 相似文献
67.
Peter Hall & Brett Presnell 《Journal of the Royal Statistical Society. Series B, Statistical methodology》1999,61(3):661-680
Contamination of a sampled distribution, for example by a heavy-tailed distribution, can degrade the performance of a statistical estimator. We suggest a general approach to alleviating this problem, using a version of the weighted bootstrap. The idea is to 'tilt' away from the contaminated distribution by a given (but arbitrary) amount, in a direction that minimizes a measure of the new distribution's dispersion. This theoretical proposal has a simple empirical version, which results in each data value being assigned a weight according to an assessment of its influence on dispersion. Importantly, distance can be measured directly in terms of the likely level of contamination, without reference to an empirical measure of scale. This makes the procedure particularly attractive for use in multivariate problems. It has several forms, depending on the definitions taken for dispersion and for distance between distributions. Examples of dispersion measures include variance and generalizations based on high order moments. Practicable measures of the distance between distributions may be based on power divergence, which includes Hellinger and Kullback–Leibler distances. The resulting location estimator has a smooth, redescending influence curve and appears to avoid computational difficulties that are typically associated with redescending estimators. Its breakdown point can be located at any desired value ε∈ (0, ½) simply by 'trimming' to a known distance (depending only on ε and the choice of distance measure) from the empirical distribution. The estimator has an affine equivariant multivariate form. Further, the general method is applicable to a range of statistical problems, including regression. 相似文献
68.
Serge B. Provost 《统计学通讯:理论与方法》2013,42(6):2247-2259
Some test statistics for the structural coefficients of simultaneous equations model often referred to as the multivariate linear functional relationship model are proposed in this article. The following cases are considered: the covariance matrix of errors is either unknown, known up to a proportionality factor, or completely known. The exact and approximate distributions of the proposed test statistics, as well as those of some that are known, are also given. 相似文献
69.
Bovas Abraham 《商业与经济统计学杂志》2013,31(4):356-361
A simple modification is suggested for the construction of transfer function models relating an output variable Yt to an input variable Xt when the model for Xt contains operators that cancel out. In addition, the evaluation of transfer function models is discussed by comparing the forecasts with the actual observations. 相似文献
70.