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41.
Nesrin Alkan 《统计学通讯:模拟与计算》2017,46(4):3201-3212
The Markov chain Monte Carlo (MCMC) method generates samples from the posterior distribution and uses these samples to approximate expectations of quantities of interest. For the process, researchers have to decide whether the Markov chain has reached the desired posterior distribution. Using convergence diagnostic tests are very important to decide whether the Markov chain has reached the target distribution. Our interest in this study was to compare the performances of convergence diagnostic tests for all parameters of Bayesian Cox regression model with different number of iterations by using a simulation and a real lung cancer dataset. 相似文献
42.
This paper reviews global and multiple tests for the combination ofn hypotheses using the orderedp-values of then individual tests. In 1987, Röhmel and Streitberg presented a general method to construct global level α tests based on orderedp-values when there exists no prior knowledge regarding the joint distribution of the corresponding test statistics. In the case of independent test statistics, construction of global tests is available by means of recursive formulae presented by Bicher (1989), Kornatz (1994) and Finner and Roters (1994). Multiple test procedures can be developed by applying the closed test principle using these global tests as building blocks. Liu (1996) proposed representing closed tests by means of “critical matrices” which contain the critical values of the global tests. Within the framework of these theoretical concepts, well-known global tests and multiple test procedures are classified and the relationships between the different tests are characterised. 相似文献
43.
44.
殷昭芹 《宁夏大学学报(人文社会科学版)》2004,26(6):101-103
以测试理论和《大学英语教学大纲》为依据,以教学主体和教材为研究对象,分析宁夏大学《大学英语》三级成就测试作文题库,指出其在内容效度方面存在的三方面问题:(1)考试目的不明确;(2)命题不规范;(3)写作内容与形式不具代表性。提出提高考试命题人员的测试理论知识水平、制订考试规范和组建测试小组等改进建议,进一步建立科学、合理和规范的大学英语测试体系。 相似文献
45.
Clinical trials and other types of studies often examine the effects of a particular treatment or experimental condition on a number of different response variables. Although the usual approach for analysing such data is to examine each variable separately, this can increase the chance of false positive findings. Bonferroni's inequality or Hotelling's T2 statistic can be employed to control the overall type I error rate, but these tests generally lack power for alternatives in which the treatment improves the outcome on most or all of the endpoints. For the comparison of independent groups, O'Brien (1984) developed a rank-sum type test that has greater power than the Bonferroni and T2 procedures when one treatment is uniformly better (i.e. for all endpoints) than the other treatment(s). In this paper we adapt the rank-sum test to studies involving paired data and demonstrate that it, too, has power advantages for such alternatives. Simulation results are described, and an example from a study measuring the effects of sleep loss on glucose metabolism is presented to illustrate the methodology. 相似文献
46.
The main problem in applying the mean-variance portfolio selection consists of the fact that the first
two moments of the asset returns are unknown. In practice the optimal portfolio weights have to be estimated.
This is usually done by replacing the moments by the classical unbiased sample estimators. We provide a comparison
of the exact and the asymptotic distributions of the estimated portfolio weights as well as a sensitivity
analysis to shifts in the moments of the asset returns. Furthermore we consider several types of shrinkage
estimators for the moments. The corresponding estimators of the portfolio weights are compared with each
other and with the portfolio weights based on the sample estimators of the moments. We show how the uncertainty
about the portfolio weights can be introduced into the performance measurement of trading strategies. The
methodology explains the bad out-of-sample performance of the classical Markowitz procedures. 相似文献
47.
We establish consistency of posterior distribution when a Gaussian process prior is used as a prior distribution for the unknown binary regression function. Specifically, we take the work of Ghosal and Roy [2006. Posterior consistency of Gaussian process prior for nonparametric binary regression. Ann. Statist. 34, 2413–2429] as our starting point, and then weaken their assumptions on the smoothness of the Gaussian process kernel while retaining a stronger yet applicable condition about design points. Furthermore, we extend their results to multi-dimensional covariates under a weaker smoothness condition on the Gaussian process. Finally, we study the extent to which posterior consistency can be achieved under a general model where, when additional hyperparameters in the covariance function of a Gaussian process are involved. 相似文献
48.
Gianluca Cubadda 《Statistical Methods and Applications》1994,3(1):37-50
Summary In this paper a new simple test for cointegration at any frequency is presented. This method can thus be applied to test for
cointegration both at the zero and at the seasonal frequencies. It requires the estimation of the coherency spectrum of weakly
stationary processes, therefore only standard spectral theory is involved. The testing procedure is similar to the one suggested
by Phillips and Ouliaris (1988) and recently generalized by Joyeux (1992) to frequencies different from zero, but it does
not suffer of some problems connected with the use of principal components methods in the frequency domain.
Invited paper at the Conference held in Bologna, Italy, 27–28 May 1993, on ?Statistical Tests: Methodology and Econometric
Applications?. 相似文献
49.
The likelihood-ratio test statistic for testing homogeneity of exponential means with an ordered alternative has a rather complex null distribution. Expressions for the mean and variance of its null distribution are derived, and the accuracy of a two-moment chi-squared approximation is studied. The coefficients needed to implement the approximation are tabled. The application of these results in testing for a constant versus a nondecreasing intensity in a nonhomogeneous Poisson process is also discussed. 相似文献
50.
刘士淦 《内蒙古工业大学学报》1989,8(1):107-114
本文主要通过异步电动机电压矩阵方程[1],推导出异步电动机的动态结构图,然后推导出交—直—交电流型变频调速双闭环系统的动态结构图。利用该结构图,在模拟机 DMJ—313上对负载扰动进行了仿真研究。试验表明,调整调节器参数,可使负载扰动指标达到满意的要求,为在设计中选择调节器参数提供了依据。 相似文献