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21.
Ahmed N. Albatineh Hafiz M. R. Khan Bashar Zogheib Golam B. M. Kibria 《统计学通讯:模拟与计算》2017,46(5):4018-4034
This article investigates the effects of number of clusters, cluster size, and correction for chance agreement on the distribution of two similarity indices, namely, Jaccard and Rand indices. Skewness and kurtosis are calculated for the two indices and their corrected forms then compared with those of the normal distribution. Three clustering algorithms are implemented: complete linkage, Ward, and K-means. Data were randomly generated from bivariate normal distributions with specified means and variance covariance matrices. Three-way ANOVA is performed to assess the significance of the design factors using skewness and kurtosis of the indices as responses. Test statistics for testing skewness and kurtosis and observed power are calculated. Simulation results showed that independent of the clustering algorithms or the similarity indices used, the interaction effect cluster size x number of clusters and the main effects of cluster size and number of clusters were found always significant for skewness and kurtosis. The three way interaction of cluster size x correction x number of clusters was significant for skewness of Rand and Jaccard indices using all clustering algorithms, but was not significant using Ward's method for both Rand and Jaccard indices, while significant for Jaccard only using complete linkage and K-means algorithms. The correction for chance agreement was significant for skewness and kurtosis using Rand and Jaccard indices when complete linkage method is used. Hence, such design factors must be taken into consideration when studying distribution of such indices. 相似文献
22.
The hypothesis of structural stability that the regression coefficients do not change over time is central to all applications of linear regression models. It is rather surprising that existing theory as well as practice focus on testing for structural change under homoskedasticity – that is, regression coefficients may change, but the variances remain the same. Since structural change can, and often does, involve changes in variances, this is a puzzling gap in the literature. Our main focus in this paper is to utilize a newly developed test (MZ) by Maasoumi et al. (2010) that tests simultaneously for break in regression coefficients as well as in variance. Currently, the sup F test is most widely used for structural change. This has certain optimality properties shown by Andrews (1993). However, this test assumes homoskedasticity across the structural change. We introduce the sup MZ test which caters to unknown breakpoints, and also compare it to the sup F. Our Monte Carlo results show that sup MZ test incurs only a low cost in case of homoskedasticity while having hugely better performance in case of heteroskedasticity. The simulation results are further supported by providing a real-world application. In real-world datasets, we find that structural change often involves heteroskedasticity. In such cases, the sup F test can fail to detect structural breaks and give misleading results, while the sup MZ test works well. We conclude that the sup MZ test is superior to current methodology for detecting structural change. 相似文献
23.
The statistical inference problem on effect size indices is addressed using a series of independent two-armed experiments
from k arbitrary populations. The effect size parameter simply quantifies the difference between two groups. It is a meaningful
index to be used when data are measured on different scales. In the context of bivariate statistical models, we define estimators
of the effect size indices and propose large sample testing procedures to test the homogeneity of these indices. The null
and non-null distributions of the proposed testing procedures are derived and their performance is evaluated via Monte Carlo
simulation. Further, three types of interval estimation of the proposed indices are considered for both combined and uncombined
data. Lower and upper confidence limits for the actual effect size indices are obtained and compared via bootstrapping. It
is found that the length of the intervals based on the combined effect size estimator are almost half the length of the intervals
based on the uncombined effect size estimators. Finally, we illustrate the proposed procedures for hypothesis testing and
interval estimation using a real data set. 相似文献
24.
Nazir Ahmed Chaudhry 《统计学通讯:理论与方法》2013,42(9):3283-3313
Using the idea of impirical influence function, Hinkley (1977), the weighted jackknife technique is extended to ratio estimation. A weighted jackknife variance estimator for the ratio estimator is developed. Using the prediction theory approach, the properties of the weighted jackknifed variance estimator are examined. The implications of the failures of regression model on the behaviour of the weighted jackknifed variance estimator, for ratio estimation, are also studied. 相似文献
25.
In a federal system of government, powers are shared by the national and sub-national units in accordance with the provisions
of the Constitution. However, the process of policy implementation may differ on the basis of allocation of power and the
nature of the system. Canada and the United States of America adopted federal systems of government, and faced similar pressures
for implementing policies on environmental issues. Yet, the degree of success and outcome appear to be different due to variations
in the strength of the respective federalist systems. An analysis of the various aspects of the federal system in the two
countries reveals noticeable differences in institutional configurations, relationship between national and sub-national units,
and variances in intra-institutional relations. All these have contributed to a divergence in the past, but there is an emerging
trend of convergence as both the Canadian and American governments are gradually moving away from their existing patterns
of policy implementation toward a new approach involving private-sector initiatives and self-enforcement with strong inclinations
toward voluntarization, corporatization and marketization. 相似文献
26.
In this paper we explore annual earnings as well as full-time monthly earnings differentials resulting from sexual orientation. We observe that gay males are at an earnings disadvantage compared to male heterosexuals regardless of which earnings measure we use. This earnings disadvantage is found to be larger when we compare gay and heterosexual males who are working full-time. In addition, the disadvantage is larger in the private than in the public sector. Lesbians, however, earn more than heterosexual females. This earnings advantage is considerably smaller when we study full-time monthly rather than annual earnings but an earnings advantage for lesbians at the top of the earnings distribution is documented regardless of which earnings measure we use. In addition, lesbians are doing better than female heterosexuals in the public sector. To sum up, the results indicate that gay males face obstacles on the labor market that hinder them from reaching top-level positions and high earnings. The earnings advantage observed for lesbians is likely to stem from the fact that lesbians devote more time to market work than heterosexual females do. 相似文献
27.
In this article, we present a broad-based view of psychology in the Arab countries. We begin by casting light on the relevant contributions by ancient Arab scholars in the Middle Ages. Given that systematic scientific investigation of this legacy has been minuscule, we argue that in the future, scholars seeking to provide a more balanced and comprehensive history of Arab psychology should reanalyze these works. We point out that in the early decades of the modern twentieth century, Western psychology was introduced in the Arab countries, especially in Egypt—the gateway through which such psychology was introduced and practiced. By the early 1960s, a number of universities had been established in some Arab countries, and Egyptian academicians, including psychologists, were invited to perform teaching, research, and administration tasks. Their legacy was a discipline bearing most of the strengths and weaknesses of Egyptian psychology, although in spite of such commonalties, there exist also some interesting differences characterizing psychology in the various Arab countries. The final section of the article summarizes some key aspects endemic to psychology in the Arab countries. 相似文献
28.
M.S. Ahmed 《Australian & New Zealand Journal of Statistics》1998,40(3):373-376
Kiregyera (1984), Mukerjee, Rao & Vijayan (1987), and Tripathi & Ahmed (1995) considered a number of regression-type estimators where information on two auxiliary variables related to study variable is available at different levels. Mukerjee et al . (1987) suggested three estimators and computed their mean square errors, but the computations seem to be incorrect. This note corrects them, and finds their estimators are no better than that of Kiregyera (1984). The estimator suggested by Tripathi & Ahmed (1995) is the best in the sense of having the smallest mean square error. 相似文献
29.
Fran Crawford Savana Sabine Agustine Leah Earle Ahmed Bawa Kuyini-Abubakar Yoni Luxford Hurriyet Babacan 《Social Work Education》2015,34(5):586-599
Climate change poses significant threat to the wellbeing of global society. Addressing this change has as yet generated no fixed blueprint for social work practice and education. This paper reports on a formative evaluation of one Australian initiative to address this transformative opening in social work field education. Prompted by service users' and workers' experience of the impact of drought, a rurally located social work course team amended the field education curriculum to include a focus on Environment and Sustainability. This learning goal was added to the existing learning goals derived from the Australian Association of Social Workers (AASW) Practice Standards. Students and field supervisors were surveyed on their experience of meeting this new learning goal. While most expressed confidence in understanding the concepts involved, they clearly lacked assurance in interpreting these in practice encounters. Considering their qualitative input suggests that this topic is making a transition from being on the margins of social work to becoming mainstream. Their open-ended responses indicate that the incorporation of environmental sustainability into practice is at a threshold stage of development. Further enactment of eco-social work at the local level is concluded to be supported by using a transformative learning framework in facilitating critical reflection and collaborative dialogue for effective change. 相似文献