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61.
Heejeong K. Latimer Lee-Ann Jaykus Roberta A. Morales Peter Cowen & Douglas Crawford-Brown 《Risk analysis》2001,21(2):295-306
This article describes the development of a weighted composite dose – response model for human salmonellosis. Data from previously reported human challenge studies were categorized into two different groups representing low and moderately virulent/pathogenic Salmonella strains based on a disease end point. Because epidemiological data indicate that some Salmonella strains are particularly pathogenic, and in the absence of human feeding study data for such strains, Shigella dysenteriae was used as a proxy for highly virulent strains. Three single-hit dose – response models were applied to the human feeding study data and evaluated for best fit using maximum likelihood estimation: (1) the exponential (E-1pop), (2) the two-subpopulation exponential (E-2pop), and (3) the Beta-Poisson (BP). Based on the goodness-of-fit test, the E-1pop and BP were the best-fit models for low and moderately virulent/pathogenic Salmonella strains, and the E-2pop and BP models were better for highly virulent/pathogenic strains. Epistemic analysis was conducted by determining the degree of confidence associated with the selected models, which was found to be 50%/50% (E-1pop/BP) for low and moderately pathogenic Salmonella strains, and 9.8%/90.2% (E-2pop/BP) for highly virulent strains. The degree of confidence for each component model and variations in the proportion of strains within each virulence/pathogenicity category were incorporated into the overall composite model. This study describes the influence of variation in strain virulence and host susceptibility on the shape of the population dose – response relationship. 相似文献
62.
63.
Shang Zhao Douglas A. Wolfe Tsai-Shang Huang Gerald S. Frankel 《Journal of statistical planning and inference》2007
A generalized brick wall model is developed to describe intergranular corrosion in Equi-axed AA7178-T6 and Wingskin AA7178-T6 aluminum alloys. The intergranular corrosion rate is highly related to grain size and shape. High strength aluminum alloys are often elongated and anisotropic, with the fastest nominal IGC growth rate in the longitudinal direction (L) or long transverse direction (T) and the slowest in the short transverse direction (S). We propose a three-way intersection model and use it to simulate the corrosion kinetics for each direction. With a proper combination of model parameters, the generalized IGC model provides a good fit to experimental data developed by the foil penetration technique. 相似文献
64.
This study examined top management team departures in U.S. manufacturing firms acquired by a foreign multinational during the six-year period following acquisition. Results indicated that greater cultural distance between the United States and the home country of the foreign multinational, higher levels of international integration in the target industry, and poor preacquisition performance in the U.S. target company were related to greater postacquisition top management departures. These effects were moderated significantly by the foreign acquirer’s international business and U.S. acquisition experience and showed different patterns over the short-term, intermediate-term, and long-term. Implications for future research on top management teams involved in cross-border acquisitions are discussed. 相似文献
65.
We consider the properties of the trimmed mean, as regards minimax-variance L-estimation of a location parameter in a Kolmogorov neighbourhood K() of the normal distribution: We first review some results on the search for an L-minimax estimator in this neighbourhood, i.e. a linear combination of order statistics whose maximum variance in Kt() is a minimum in the class of L-estimators. The natural candidate – the L-estimate which is efficient for that member of Kt,() with minimum Fisher information – is known not to be a saddlepoint solution to the minimax problem. We show here that it is not a solution at all. We do this by showing that a smaller maximum variance is attained by an appropriately trimmed mean. We argue that this trimmed mean, as well as being computationally simple – much simpler than the efficient L-estimate referred to above, and simpler than the minimax M- and R-estimators – is at least “nearly” minimax. 相似文献
66.
Robert H. Lyles Cynthia M. Lyles & Douglas J. Taylor 《Journal of the Royal Statistical Society. Series C, Applied statistics》2000,49(4):485-497
Objectives in many longitudinal studies of individuals infected with the human immunodeficiency virus (HIV) include the estimation of population average trajectories of HIV ribonucleic acid (RNA) over time and tests for differences in trajectory across subgroups. Special features that are often inherent in the underlying data include a tendency for some HIV RNA levels to be below an assay detection limit, and for individuals with high initial levels or high ranges of change to drop out of the study early because of illness or death. We develop a likelihood for the observed data that incorporates both of these features. Informative drop-outs are handled by means of an approach previously published by Schluchter. Using data from the HIV Epidemiology Research Study, we implement a maximum likelihood procedure to estimate initial HIV RNA levels and slopes within a population, compare these parameters across subgroups of HIV-infected women and illustrate the importance of appropriate treatment of left censoring and informative drop-outs. We also assess model assumptions and consider the prediction of random intercepts and slopes in this setting. The results suggest that marked bias in estimates of fixed effects, variance components and standard errors in the analysis of HIV RNA data might be avoided by the use of methods like those illustrated. 相似文献
67.
68.
Louise Curran Lars Nilsson Douglas Brew 《Development policy review : the journal of the Overseas Development Institute》2008,26(5):529-553
The European Union and the African, Caribbean and Pacific (ACP) countries entered a new era in 2008. The Cotonou trade regime and the WTO waiver legitimising it have expired, and the long anticipated, and much debated, move to Economic Partnership Agreements (EPAs) has begun. This article explains the background and analyses the ‘alternatives’ to EPAs, in order to tackle common misperceptions. Moving on from what has been the focus of debates, namely, the reciprocal liberalisation required under WTO rules, it sheds some light on the non‐goods trade aspects of EPAs which, while integral to economic policy, are inherently hard to quantify and often skimmed over in existing studies or addressed in ideological terms. 相似文献
69.
Peter P. Mollinga Ruth S. Meinzen‐Dick Douglas J. Merrey 《Development policy review : the journal of the Overseas Development Institute》2007,25(6):699-719
Starting from the assessment that past efforts at reform in agricultural water management in developing countries have achieved very little, this article argues that a fundamental change is required in the approach to policy and institutional transformation if the present deadlock in the internalisation of ecological sustainability, human development/poverty alleviation and democratic governance into the ‘core business’ of water bureaucracies is to be overcome. ‘Social engineering’ approaches need to be replaced by ‘strategic action’ approaches that acknowledge the inherently political character and the plurality of actors, institutions and objectives of water management — a perspective operationalised here around the notions of ‘problemshed’ and ‘issue network’. 相似文献
70.
Douglas P. Wiens 《Revue canadienne de statistique》1990,18(1):47-57
We consider the problem of minimax-variance, robust estimation of a location parameter, through the use of L- and R-estimators. We derive an easily checked necessary condition for L-estimation to be minimax, and a related sufficient condition for R-estimation to be minimax. Those cases in the literature in which L-estimation is known not to be minimax, and those in which R-estimation is minimax, are derived as consequences of these conditions. New classes of examples are given in each case. As well, we answer a question of Scholz (1974), who showed essentially that the asymptotic variance of an R-estimator never exceeds that of an L-estimator, if both are efficient at the same strongly unimodal distribution. Scholz raised the question of whether or not the assumption of strong unimodality could be dropped. We answer this question in the negative, theoretically and by examples. In the examples, the minimax property fails both for L-estimation and for R-estimation, but the variance of the L-estimator, as the distribution of the observation varies over the given neighbourhood, remains unbounded. That of the R-estimator is unbounded. 相似文献