全文获取类型
收费全文 | 1444篇 |
免费 | 50篇 |
国内免费 | 30篇 |
专业分类
管理学 | 260篇 |
民族学 | 2篇 |
人口学 | 9篇 |
丛书文集 | 27篇 |
理论方法论 | 10篇 |
综合类 | 381篇 |
社会学 | 13篇 |
统计学 | 822篇 |
出版年
2023年 | 8篇 |
2022年 | 11篇 |
2021年 | 17篇 |
2020年 | 31篇 |
2019年 | 30篇 |
2018年 | 33篇 |
2017年 | 50篇 |
2016年 | 42篇 |
2015年 | 59篇 |
2014年 | 50篇 |
2013年 | 329篇 |
2012年 | 96篇 |
2011年 | 61篇 |
2010年 | 62篇 |
2009年 | 52篇 |
2008年 | 64篇 |
2007年 | 61篇 |
2006年 | 51篇 |
2005年 | 57篇 |
2004年 | 42篇 |
2003年 | 43篇 |
2002年 | 27篇 |
2001年 | 27篇 |
2000年 | 21篇 |
1999年 | 24篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 14篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有1524条查询结果,搜索用时 15 毫秒
1.
Proportional hazards are a common assumption when designing confirmatory clinical trials in oncology. This assumption not only affects the analysis part but also the sample size calculation. The presence of delayed effects causes a change in the hazard ratio while the trial is ongoing since at the beginning we do not observe any difference between treatment arms, and after some unknown time point, the differences between treatment arms will start to appear. Hence, the proportional hazards assumption no longer holds, and both sample size calculation and analysis methods to be used should be reconsidered. The weighted log‐rank test allows a weighting for early, middle, and late differences through the Fleming and Harrington class of weights and is proven to be more efficient when the proportional hazards assumption does not hold. The Fleming and Harrington class of weights, along with the estimated delay, can be incorporated into the sample size calculation in order to maintain the desired power once the treatment arm differences start to appear. In this article, we explore the impact of delayed effects in group sequential and adaptive group sequential designs and make an empirical evaluation in terms of power and type‐I error rate of the of the weighted log‐rank test in a simulated scenario with fixed values of the Fleming and Harrington class of weights. We also give some practical recommendations regarding which methodology should be used in the presence of delayed effects depending on certain characteristics of the trial. 相似文献
2.
A. M. Abd El-Raheem 《Journal of Statistical Computation and Simulation》2019,89(16):3075-3104
The generalized half-normal (GHN) distribution and progressive type-II censoring are considered in this article for studying some statistical inferences of constant-stress accelerated life testing. The EM algorithm is considered to calculate the maximum likelihood estimates. Fisher information matrix is formed depending on the missing information law and it is utilized for structuring the asymptomatic confidence intervals. Further, interval estimation is discussed through bootstrap intervals. The Tierney and Kadane method, importance sampling procedure and Metropolis-Hastings algorithm are utilized to compute Bayesian estimates. Furthermore, predictive estimates for censored data and the related prediction intervals are obtained. We consider three optimality criteria to find out the optimal stress level. A real data set is used to illustrate the importance of GHN distribution as an alternative lifetime model for well-known distributions. Finally, a simulation study is provided with discussion. 相似文献
3.
在装备采购中,由于需求单位地域分布和担负的任务各不相同,对装备的品种、数量、时限要求也就不一样,如何使装备采购科学化、合理化,是一个涉及多变量、多目标的复杂系统问题。在综合考虑装备采购各项因素的基础上,构建多约束条件下的多目标模糊指派模型,提出了基于遗传算法的解决方案,最后通过案例进行仿真实验,验证该算法的可行性和有效性,解决了采用传统优化方法难以解决的装备采购优化决策问题。 相似文献
4.
Comparison of Four New General Classes of Search Designs 总被引:1,自引:0,他引:1
A factor screening experiment identifies a few important factors from a large list of factors that potentially influence the response. If a list consists of m factors each at three levels, a design is a subset of all possible 3 m runs. This paper considers the problem of finding designs with small numbers of runs, using the search linear model introduced in Srivastava (1975). The paper presents four new general classes of these 'search designs', each with 2 m −1 runs, which permit, at most, two important factors out of m factors to be searched for and identified. The paper compares the designs for 4 ≤ m ≤ 10, using arithmetic and geometric means of the determinants, traces and maximum characteristic roots of particular matrices. Two of the designs are found to be superior in all six criteria studied. The four designs are identical for m = 3 and this design is an optimal design in the class of all search designs under the six criteria. The four designs are also identical for m = 4 under some row and column permutations. 相似文献
5.
The problem considered is that of finding an optimum measurement schedule to estimate population parameters in a nonlinear model when the patient effects are random. The paper presents examples of the use of sensitivity functions, derived from the General Equivalence Theorem for D-optimality, in the construction of optimum population designs for such schedules. With independent observations, the theorem applies to the potential inclusion of a single observation. However, in population designs the observations are correlated and the theorem applies to the inclusion of an additional measurement schedule. In one example, three groups of patients of differing size are subject to distinct schedules. Numerical, as opposed to analytical, calculation of the sensitivity function is advocated. The required covariances of the observations are found by simulation. 相似文献
6.
For a wide variety of applications, experiments are based on units ordered over time or space. Models for these experiments generally may include one or more of: correlations, systematic trends, carryover effects and interference effects. Since the standard optimal block designs may not be efficient in these situations, orthogonal arrays of type I and type II, which were introduced in 1961 by C.R. Rao [Combinatorial arrangements analogous to orthogonal arrays, Sankhya A 23 (1961) 283–286], have been recently used to construct optimal and efficient designs for many of these experiments. Results in this area are unified and the salient features are outlined. 相似文献
7.
Complete and partial diallel cross designs are examined as to their construction and robustness against the loss of a block of observations. A simple generalized inverse is found for the information matrix of the line effects, which allows evaluation of expressions for the variances of the line-effect differences with and without the missing block. A-efficiencies, based on average variances of the elementary contrasts of the line-effects, suggest that these designs are fairly robust. The loss of efficiency is generally less than 10%, but it is shown that specific comparisons might suffer a loss of efficiency of as much as 40%. 相似文献
8.
9.
对偶线性规划问题性质探析 总被引:1,自引:0,他引:1
探讨对偶线性规划的原始问题与对偶问题的属性,阐述两者的区别和内在联系,用较简便的方法论证其重要性质,揭示可行解与目标函数、可行解与最优解的关系,指出线性规划问题最优解从约束条件较少的对偶问题寻求为另一较简便之方法。 相似文献
10.
组合预测误差信息矩阵研究 总被引:11,自引:0,他引:11
唐小我 《电子科技大学学报(社会科学版)》1992,(4)
研究组合预测误差信息矩阵的结构与组合预测方法性质之间的联系,首次提出冗余信息概念,对最优组合预测方法的组合结构进行了研究。 相似文献