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971.
Raegen T. MILLER Richard J. MURNANE John B. WILLETT 《Revue Internationale du Travail》2008,147(1):77-95
Partant de données relatives à 285 professeurs et 8 631 élèves d'un district scolaire économiquement désavantagé des Etats‐Unis, les auteurs testent l'hypothèse selon laquelle les absences des enseignants sont souvent discrétionnaires et réduisent leur productivité, mesurée par les résultats des élèves à un examen de mathématiques. Comme cela est courant, lorsque le remplaçant est moins qualifié, l'enseignement est moins intense et cohérent, avec une chute, limitée mais significative, des résultats des élèves, pouvant conduire à une baisse de leur classification et de leur motivation. Les auteurs proposent des mesures susceptibles de limiter cet absentéisme. 相似文献
972.
Image models are useful in quantitatively specifying natural constraints and general assumptions about the physical world and the imaging process. This review paper explains how Gibbs and Markov random field models provide a unifying theme for many contemporary problems in image analysis. Random field models permit the introduction of spatial context into pixel labeling problems, such as segmentation and restoration. Random field models also describe textured images and lead to algorithms for generating textured images, classifying textures and segmenting textured images. In spite of some impressive model-based image restoration and texture segmentation results reported in the literature, a number of fundamental issues remain unexplored, such as the specification of MRF models, modeling noise processes, performance evaluation, parameter estimation, the phase transition phenomenon and the comparative analysis of alternative procedures. The literature of random field models is filled with great promise, but a better mathematical understanding of these issues is needed as well as efficient algorithms for applications. These issues need to be resolved before random field models will be widely accepted as general tools in the image-processing community. 相似文献
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974.
A Box-Cox transformed linear model usually has the form y(λ) = μ + β1x1 +… + βpxp + oe, where y(λ) is the power transform of y. Although widely used in practice, the Fisher information matrix for the unknown parameters and, in particular, its inverse have not been studied seriously in the literature. We obtain those two important matrices to put the Box-Cox transformed linear model on a firmer ground. The question of how to make inference on β = (β1,…,βp)T when λ; is estimated from the data is then discussed for large but finite sample size by studying some parameter-based asymptotics. Both unconditional and conditional inference are studied from the frequentist point of view. 相似文献
975.
Richard D. Lamm 《Population and environment》1991,13(1):79-88
H.R. 4300, The Family Unity and Employment Opportunity Act of 1990. 相似文献
976.
Richard T. Corlett 《Urban Ecosystems》2005,8(3-4):275-283
I observed the use of exotic plant species by native birds and bats in 8 km2 of urban Hong Kong. Twenty-nine plant taxa were used repeatedly. Five species accounted for most interactions with birds:
Cinnamomum camphora (10 bird species), Ficus religiosa (6), Livistona chinensis (7) and Pyracantha crenulata (6) provided fruits, while Bombax ceiba (6) supplied nectar. Panicum maximum (2) and C. camphora (1) provided seeds for granivorous birds and Leucaena leucocephala is host to a psyllid consumed by small insectivores in winter. Most trophic interactions between exotics and fruit bats involved
the fruits or flowers of Syzygium jambos, while Livistona chinensis provided roosting sites for Cynopterus sphinx. The fruiting phenologies of the exotic species differed from the local flora, with fruit of some species available for the
majority of the year. Fruit characteristics for the most commonly eaten species are within the range for native fruit species,
although most are larger and have a lower seed load than the medians for native species. Seed dispersal by birds and/or fruit
bats is a necessary, but not sufficient, condition for the naturalization of fleshy-fruited plants in Hong Kong, but S. jambos is the only naturalizing exotic species that needs vertebrates for pollination. 相似文献
977.
Image models are useful in quantitatively specifying natural constraints and general assumptions about the physical world and the imaging process. This review paper explains how Gibbs and Markov random field models provide a unifying theme for many contemporary problems in image analysis. Random field models permit the introduction of spatial context into pixel labeling problems, such as segmentation and restoration. Random field models also describe textured images and lead to algorithms for generating textured images, classifying textures, and segmenting textured images. In spite of some impressive model-based image restoration and texture segmentation results reported in the literature, a number of fundamental issues remain unexplored, such as the specification of MRF models, modeling noise processes, performance evaluation, parameter estimation, the phase transition phenomenon, and the comparative analysis of alternative procedures. The literature of random field models is filled with great promise, but a better mathematical understanding of these issues is needed as well as efficient algorithms for applications. These issues need to be resolved before random field models will be widely accepted as general tools in the image processing community. 相似文献
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