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131.
Robert V. Breunig 《Econometric Reviews》2001,20(3):353-367
The commonly used survey technique of clustering introduces dependence into sample data. Such data is frequently used in economic analysis, though the dependence induced by the sample structure of the data is often ignored. In this paper, the effect of clustering on the non-parametric, kernel estimate of the density, f(x), is examined. The window width commonly used for density estimation for the case of i.i.d. data is shown to no longer be optimal. A new optimal bandwidth using a higher-order kernel is proposed and is shown to give a smaller integrated mean squared error than two window widths which are widely used for the case of i.i.d. data. Several illustrations from simulation are provided. 相似文献
132.
C. E. Stein S. Bennett S. Crook & F. Maddison 《Journal of the Royal Statistical Society. Series A, (Statistics in Society)》2001,164(1):23-27
In 1997 intense media coverage raised public concerns about germ warfare simulation experiments conducted by the Ministry of Defence during the 1960s, which included the release of bacteria over Dorset. Families in East Lulworth, Dorset, have linked this with allegedly high rates of miscarriages, still-births, congenital malformations, learning and other neurodevelopmental disabilities in their village. The response of the Dorset Health Authority (DHA) included the examination of background information from the Ministry of Defence, national data on congenital malformations in Dorset, health information collected by campaigners and a systematic health survey conducted by the DHA among former and current residents of East Lulworth. The investigation did not confirm the presence of a cluster. It is debatable whether the DHA should have proceeded with their survey when none of the other more immediately available results indicated the presence of a cluster. 相似文献
133.
Marschner IC 《Pharmaceutical statistics》2007,6(1):23-33
Clinical trials are often designed to compare several treatments with a common control arm in pairwise fashion. In this paper we study optimal designs for such studies, based on minimizing the total number of patients required to achieve a given level of power. A common approach when designing studies to compare several treatments with a control is to achieve the desired power for each individual pairwise treatment comparison. However, it is often more appropriate to characterize power in terms of the family of null hypotheses being tested, and to control the probability of rejecting all, or alternatively any, of these individual hypotheses. While all approaches lead to unbalanced designs with more patients allocated to the control arm, it is found that the optimal design and required number of patients can vary substantially depending on the chosen characterization of power. The methods make allowance for both continuous and binary outcomes and are illustrated with reference to two clinical trials, one involving multiple doses compared to placebo and the other involving combination therapy compared to mono-therapies. In one example a 55% reduction in sample size is achieved through an optimal design combined with the appropriate characterization of power. 相似文献
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Motivated by recent failures of polling to estimate populist party support, we propose and analyze two methods for asking sensitive multiple-choice questions where the respondent retains some privacy and therefore might answer more truthfully. The first method consists of asking for the true choice along with a choice picked at random. The other method presents a list of choices and asks whether the preferred one is on the list or not. Different respondents are shown different lists. The methods are easy to explain, which makes it likely that the respondent understands how her privacy is protected and may thus entice her to participate in the survey and answer truthfully. The methods are also easy to implement and scale up. 相似文献
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For a trial with primary endpoint overall survival for a molecule with curative potential, statistical methods that rely on the proportional hazards assumption may underestimate the power and the time to final analysis. We show how a cure proportion model can be used to get the necessary number of events and appropriate timing via simulation. If phase 1 results for the new drug are exceptional and/or the medical need in the target population is high, a phase 3 trial might be initiated after phase 1. Building in a futility interim analysis into such a pivotal trial may mitigate the uncertainty of moving directly to phase 3. However, if cure is possible, overall survival might not be mature enough at the interim to support a futility decision. We propose to base this decision on an intermediate endpoint that is sufficiently associated with survival. Planning for such an interim can be interpreted as making a randomized phase 2 trial a part of the pivotal trial: If stopped at the interim, the trial data would be analyzed, and a decision on a subsequent phase 3 trial would be made. If the trial continues at the interim, then the phase 3 trial is already underway. To select a futility boundary, a mechanistic simulation model that connects the intermediate endpoint and survival is proposed. We illustrate how this approach was used to design a pivotal randomized trial in acute myeloid leukemia and discuss historical data that informed the simulation model and operational challenges when implementing it. 相似文献
140.
本文利用空间杜宾模型实证研究了生产性服务业集聚对长三角城市群经济增长效率的影响及空间溢出效应。结果表明,生产性服务业集聚不仅能够显著提升本地区的经济增长效率,还对邻近城市具有正向的空间溢出效应,但这种影响在生产性服务业的细分行业之间存在一定异质性。进一步分析发现,生产性服务业集聚的MAR外部性和Jacobs外部性都有利于长三角城市群经济增长效率的提升,而Porter 外部性对经济增长效率具有负面影响。在空间溢出效应方面,Jacobs外部性对经济发展水平相近的城市具有负向溢出效应,Porter外部性对人力资本水平相近的城市具有正向溢出效应。此外,生产性服务业与制造业协同集聚对本地区和人力资本水平相近城市的经济增长效率具有显著促进作用,但对邻近城市和经济发展水平相近城市的经济增长效率因“虹吸效应”而产生一定的抑制作用。这些研究,对如何更有针对性地加快提升长三角城市群经济增长效率,提供了有价值的理论依据。 相似文献