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71.
Abstract Abstract. Theory of constraints (TOC) and optimized production technology (OPT) are frequently presented as the better options for production control systems. Despite this enthusiasm, there is very little literature on how these principles can be implemented in practice without having to resort to the expensive proprietary software. In this paper we present a case study in which the OPT/TOC ideas were implemented without using the software. Management's major concern was reduction of work in process and increased delivery performance. It was decided to test whether the ideas of OPT/TOC were applicable in this environment and more importantly to which extent these two performance measures could be improved. The paper reports on the methodology used to test the OPT/TOC ideas in this shop and presents some early results of improvement, as well as some new problems which arose due to the new approach. 相似文献
72.
Since Kuhn claimed that scientific controversies are not always settled by means of rational evaluations of the intrinsic merits of competing theories, the view that the history of science should be recounted by examining the background of scientific controversies and how these controversies came to be settled has become a real heuristic maxim for the historian of science. We take issue with this view by arguing that controversies are not relevant by themselves but only insofar as one can make something out of them. Two important questions then arise: what did one come to learn from a given controversy and what came out of this apprenticeships. We compare Pauline Mazumdar's and Alfred Tauber's approaches to the history of immunology and argue that only the latter addressed these questions. In so doing, he was able to show the extension in which modern immunology is an outcome of Metchnikoff's success in correcting Haeckel's “fundamental biogenetic law”. 相似文献
73.
JÜRG SCHELLDORFER PETER BÜHLMANN SARA VAN DE GEER 《Scandinavian Journal of Statistics》2011,38(2):197-214
Abstract. We propose an ?1‐penalized estimation procedure for high‐dimensional linear mixed‐effects models. The models are useful whenever there is a grouping structure among high‐dimensional observations, that is, for clustered data. We prove a consistency and an oracle optimality result and we develop an algorithm with provable numerical convergence. Furthermore, we demonstrate the performance of the method on simulated and a real high‐dimensional data set. 相似文献
74.
75.
MARK A. LUKAS FRANK R. DE HOOG ROBERT S. ANDERSSEN 《Scandinavian Journal of Statistics》2012,39(1):97-115
Abstract. While it is a popular selection criterion for spline smoothing, generalized cross‐validation (GCV) occasionally yields severely undersmoothed estimates. Two extensions of GCV called robust GCV (RGCV) and modified GCV have been proposed as more stable criteria. Each involves a parameter that must be chosen, but the only guidance has come from simulation results. We investigate the performance of the criteria analytically. In most studies, the mean square prediction error is the only loss function considered. Here, we use both the prediction error and a stronger Sobolev norm error, which provides a better measure of the quality of the estimate. A geometric approach is used to analyse the superior small‐sample stability of RGCV compared to GCV. In addition, by deriving the asymptotic inefficiency for both the prediction error and the Sobolev error, we find intervals for the parameters of RGCV and modified GCV for which the criteria have optimal performance. 相似文献
76.
77.
Abstract. The paper proposes a method of deconvolution in a periodic setting which combines two important ideas, the fast wavelet and Fourier transform-based estimation procedure of Johnstone et al . [ J. Roy. Statist. Soc. Ser. B 66 (2004) 547] and the multichannel system technique proposed by Casey and Walnut [ SIAM Rev . 36 (1994) 537]. An unknown function is estimated by a wavelet series where the empirical wavelet coefficients are filtered in an adapting non-linear fashion. It is shown theoretically that the estimator achieves optimal convergence rate in a wide range of Besov spaces. The procedure allows to reduce the ill-posedness of the problem especially in the case of non-smooth blurring functions such as boxcar functions: it is proved that additions of extra channels improve convergence rate of the estimator. Theoretical study is supplemented by an extensive set of small-sample simulation experiments demonstrating high-quality performance of the proposed method. 相似文献
78.
ANTONIO GARCÍA DE LE
N 《Journal of historical sociology》1995,8(4):430-477
The clauses of this [social] contract are so determined by the nature of the act that the slightest modification would make them vain and ineffective; so that, although they have perhaps never been formally set forth, they are everywhere the same and everywhere tacitly admitted and recognized, until, on the violation of the social compact, each regains his original rights and resumes his natural liberty, while losing the conventional liberty in favour of which he renounced it. 相似文献
79.
If localized knowledge spillovers are present in the university setting, higher rates of both start‐up and/or survival would be observed in areas that are geographically proximate to the university. Using a detailed industry data set for Texas for 1999:3–2005:2, we analyze start‐up and exit rates for high‐tech firms. Based on a Poisson quasi‐maximum likelihood estimation, we find evidence that the level of R&D and proximity of a research institution positively affects the likelihood of technology start‐ups. However, using both the Cox proportional hazards model and Kaplan–Meier approach, our results suggest that geographic proximity to knowledge centers does not reduce hazard rates. (JEL R12, R53, O18) 相似文献
80.
UMBERTO PICCHINI REA DE GAETANO SUSANNE DITLEVSEN 《Scandinavian Journal of Statistics》2010,37(1):67-90
Abstract. Stochastic differential equations have been shown useful in describing random continuous time processes. Biomedical experiments often imply repeated measurements on a series of experimental units and differences between units can be represented by incorporating random effects into the model. When both system noise and random effects are considered, stochastic differential mixed-effects models ensue. This class of models enables the simultaneous representation of randomness in the dynamics of the phenomena being considered and variability between experimental units, thus providing a powerful modelling tool with immediate applications in biomedicine and pharmacokinetic/pharmacodynamic studies. In most cases the likelihood function is not available, and thus maximum likelihood estimation of the unknown parameters is not possible. Here we propose a computationally fast approximated maximum likelihood procedure for the estimation of the non-random parameters and the random effects. The method is evaluated on simulations from some famous diffusion processes and on real data sets. 相似文献