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In this letter we employ high-precision Monte Carlo simulations to investigate tracer diffusion kinetics for diffusion via divacancies in the bcc lattice. We utilize the mechanisms originally identified by Mehrer in which the divacancy can move by nearest-neighbour jumps with stable first-nearest-neighbour, second-nearest-neighbour and fourth-nearest-neighbour configurations of the divacancy. The tracer correlation factor and the 'impurity-form' correlation factor were found to be some 4-6% lower than those found by the matrix method. The tracer diffusion data and isotope effect for sodium were revisited in terms of monovacancy and divacancy contributions. The main change is a revision upwards from 0.55 to 0.61 of the j K kinetic factor for divacancies. 相似文献
13.
Novel structures for multiple hydrogen atoms trapped at a monovacancy are discussed. Using atomistic simulations based on semiempirical interatomic potentials and density functional theory, we find low-energy configurations for four, five, and six hydrogen atoms around a monovacancy different than those that have been previously studied in the literature. The energetics of hydrogen binding are compared to results, both theoretical and experimental, previously published in the literature. We argue that up to four hydrogen atoms may be exothermically bound to monovacancy. 相似文献
14.
Any formal model of visual Gestalt perception requires a language for representing possible perceptual structures of visual stimuli, as well as a decision criterion that selects the actually perceived structure of a stimulus among its possible alternatives. This paper discusses an existing model of visual Gestalt perception that is based on Structural Information Theory. We investigate two factors that determine the representational power of this model: the domain of visual stimuli that can be analyzed, and the class of perceptual structures that can be generated for these stimuli. We show that the representational power of the existing model of Structural Information Theory is limited, and that some of the generated structures are perceptually inadequate. We argue that these limitations do not imply the implausibility of the underlying ideas of Structural Information Theory and introduce alternative models based on the same ideas. For each of these models, the domain of visual stimuli that can be analyzed properly is formally defined. We show that the models are conservative modifications of the original model of Structural Information Theory: for cases that are adequately analyzed in the original model of Structural Information Theory, they yield the same results. 相似文献
15.
Nannan Ren 《Philosophical Magazine Letters》2016,96(1):1-8
The electronic structures of the μ phase of Co7Mo6 were investigated by means of first-principles calculation based on the density functional theory. The calculated equilibrium lattice parameters of Co7Mo6 are in good agreement with the experimental results. The results of calculation reveal that the addition of tungsten (W) promotes the stability of the μ phase of Co7Mo6 and W tends to participate in its formation. Through analysing the calculated electronic structure (partial density of states and charge density difference), it can be noted that a strong interaction exists due to d–d hybridization. Also, the majority of the atoms may contribute their valence electrons to the formation of metallic bonds in binary and ternary systems. Furthermore, the calculated results show that the doped W atom prefers to occupy the Co site in Co7Mo6 μ phase. 相似文献
16.
Robust schemes in regression are adapted to mean and covariance structure analysis, providing an iteratively reweighted least squares approach to robust structural equation modeling. Each case is properly weighted according to its distance, based on first and second order moments, from the structural model. A simple weighting function is adopted because of its flexibility with changing dimensions. The weight matrix is obtained from an adaptive way of using residuals. Test statistic and standard error estimators are given, based on iteratively reweighted least squares. The method reduces to a standard distribution-free methodology if all cases are equally weighted. Examples demonstrate the value of the robust procedure.The authors acknowledge the constructive comments of three referees and the Editor that lead to an improved version of the paper. This work was supported by National Institute on Drug Abuse Grants DA01070 and DA00017 and by the University of North Texas Faculty Research Grant Program. 相似文献
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Elias Zafiris 《Axiomathes》2005,15(2):181-190
Using the concept of adjunction, for the comprehension of the structure of a complex system, developed in Part I, we introduce the notion of covering systems consisting of partially or locally defined adequately understood objects. This notion incorporates the necessary and sufficient conditions for a sheaf theoretical representation of the informational content included in the structure of a complex system in terms of localization systems. Furthermore, it accommodates a formulation of an invariance property of information communication concerning the analysis of a complex system. 相似文献
19.
首先,依据Elliot关于成就目标的能力界定标准和能力效价的理论构想,提出教师成就目标的理论结构。浙江省内外十多所中小学523份有效调查数据的探索性和验证性因素分析的结果表明,教师成就目标由6个因素构成,即:绝对-回避目标、个人-回避目标、参照-回避目标、个人-接近目标、参照-接近目标、绝对-接近目标。然后,利用浙江省内外另外十多所中小学625份调查问卷的结果,采用结构方程模型技术对教师成就目标和学校目标结构之间的关系进行了分析。结果表明,掌握目标结构对绝对-接近目标、个人-接近目标具有显著正效应,对绝对-回避目标具有显著负效应;成绩目标结构对绝对-接近目标、参照-接近目标、个人-回避目标和参照-回避目标具有显著正效应。 相似文献
20.
Applied Logic without Psychologism 总被引:1,自引:0,他引:1
Gregory Wheeler 《Studia Logica》2008,88(1):137-156
Logic is a celebrated representation language because of its formal generality. But there are two senses in which a logic
may be considered general, one that concerns a technical ability to discriminate between different types of individuals, and
another that concerns constitutive norms for reasoning as such. This essay embraces the former, permutation-invariance conception
of logic and rejects the latter, Fregean conception of logic. The question of how to apply logic under this pure invariantist
view is addressed, and a methodology is given. The pure invariantist view is contrasted with logical pluralism, and a methodology
for applied logic is demonstrated in remarks on a variety of issues concerning non-monotonic logic and non-monotonic inference,
including Charles Morgan’s impossibility results for non-monotonic logic, David Makinson’s normative constraints for non-monotonic
inference, and Igor Douven and Timothy Williamson’s proposed formal constraints on rational acceptance. 相似文献