全文获取类型
收费全文 | 420篇 |
免费 | 19篇 |
专业分类
化学 | 269篇 |
晶体学 | 9篇 |
力学 | 7篇 |
数学 | 56篇 |
物理学 | 98篇 |
出版年
2024年 | 1篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 22篇 |
2014年 | 18篇 |
2013年 | 27篇 |
2012年 | 25篇 |
2011年 | 31篇 |
2010年 | 20篇 |
2009年 | 10篇 |
2008年 | 31篇 |
2007年 | 27篇 |
2006年 | 20篇 |
2005年 | 23篇 |
2004年 | 22篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1938年 | 1篇 |
1928年 | 2篇 |
排序方式: 共有439条查询结果,搜索用时 15 毫秒
101.
Pasinetti PM Romá F Riccardo JL Ramirez-Pastor AJ 《The Journal of chemical physics》2006,125(21):214705
Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior in a submonolayer lattice-gas of interacting monomers adsorbed on one-dimensional channels arranged in a triangular cross-sectional structure. Two kinds of lateral interaction energies have been considered: (1) w(L), interaction energy between nearest-neighbor particles adsorbed along a single channel and (2) w(T), interaction energy between particles adsorbed across nearest-neighbor channels. We focus on the case of repulsive transverse interactions (w(T)>0), where a rich variety of structural orderings are observed in the adlayer, depending on the value of the parameters k(B)Tw(T) (being k(B) the Boltzmann constant) and w(L)w(T). For w(L)w(T)=0, successive planes are uncorrelated, the system is equivalent to the triangular lattice, and the well-known ([square root] 3 x [square root] 3) [([square root] 3 x ([square root] 3)(*)] ordered phase is found at low temperatures and a coverage, theta, of 13. In the more general case (w(L)/w(T) not equal 0), a competition between interactions along a single channel and a transverse coupling between sites in neighboring channels leads to a three-dimensional adsorbed layer. Consequently, the ([square root] 3 x ([square root] 3) and (([square root] 3 x ([square root] 3)(*) structures "propagate" along the channels and new ordered phases appear in the adlayer. Each ordered phase is separated from the disordered state by a continuous order-disorder phase transition occurring at a critical temperature, T(c), which presents an interesting dependence with w(L)/w(T). The Monte Carlo technique was combined with the recently reported free energy minimization criterion approach (FEMCA) [F. Roma et al., Phys. Rev. B 68, 205407 (2003)] to predict the critical temperatures of the order-disorder transformation. The excellent qualitative agreement between simulated data and FEMCA results allows us to interpret the physical meaning of the mechanisms underlying the observed transitions. 相似文献
102.
Two density functional theories, the fundamental measures theory of Rosenfeld [Phys. Rev. Lett. 63, 980 (1989)] and a subsequent approximation by Tarazona [Phys. Rev. Lett. 84, 694 (2000)] are applied to the study of the hard-sphere fluid in two situations: the cylindrical pore and the spherical cavity. The results are compared with those obtained with grand canonical ensemble Monte Carlo simulations. The differences between both theories are evaluated and interpreted in the terms of the dimensional crossover from three to one and zero dimensions. 相似文献
103.
Navarro A Tauler R Lacorte S Barceló D 《Analytical and bioanalytical chemistry》2006,385(6):1020-1030
A multivariate statistical data analysis, using principal component analysis, of historical data from 1996 to 2003 concerning
the concentration of different polycyclic aromatic hydrocarbons and organochlorine compounds in sediment samples from different
sampling sites of the Ebro River Basin was performed under the UE funded project AQUATERRA. Three major contamination sources
were identified and their composition and distribution profiles were resolved. The first contamination profile was mostly
loaded by polycyclic aromatic hydrocarbons, the second contamination profile was loaded by some organochlorine compounds and
the third contamination profile was more specifically loaded by naphthalene. Samples from the different geographical regions
of the Ebro River Basin were grouped according to the contamination described by these three major profiles. 相似文献
104.
We numerically address the issue of how the ground-state topology is reflected in the finite temperature dynamics of the +/-J Edwards-Anderson spin glass model. In this system a careful study of the ground-state configurations allows us to classify spins into two sets: solidary and nonsolidary spins. We show that these sets quantitatively account for the dynamical heterogeneities found in the mean flipping time distribution at finite low temperatures. The results highlight the relevance of taking into account the ground-state topology in the analysis of the finite temperature dynamics of spin glasses. 相似文献
105.
We describe the Gerstenhaber algebra structure on the Hochschild cohomology HH?(A) when A is a quadratic string algebra. First we compute the Hochschild cohomology groups using Barzdell’s resolution and we describe generators of these groups. Then we construct comparison morphisms between the bar resolution and Bardzell’s resolution in order to get formulae for the cup product and the Lie bracket. We find conditions on the bound quiver associated to string algebras in order to get non-trivial structures. 相似文献
106.
Alexandre Monteiro Pacheco Diego Romão Gondim Luciana Rocha Barros Gonçalves 《Applied biochemistry and biotechnology》2010,161(1-8):209-217
In this work, cashew apple bagasse (CAB) was used for Saccharomyces cerevisiae immobilization. The support was prepared through a treatment with a solution of 3% HCl, and delignification with 2% NaOH was also conducted. Optical micrographs showed that high populations of yeast cells adhered to pre-treated CAB surface. Ten consecutive fermentations of cashew apple juice for ethanol production were carried out using immobilized yeasts. High ethanol productivity was observed from the third fermentation assay until the tenth fermentation. Ethanol concentrations (about 19.82–37.83 g L?1 in average value) and ethanol productivities (about 3.30–6.31 g L?1 h?1) were high and stable, and residual sugar concentrations were low in almost all fermentations (around 3.00 g L?1) with conversions ranging from 44.80% to 96.50%, showing efficiency (85.30–98.52%) and operational stability of the biocatalyst for ethanol fermentation. Results showed that cashew apple bagasse is an efficient support for cell immobilization aiming at ethanol production. 相似文献
107.
Román Salmerón José García Catalina García María del Mar López 《Computational Statistics》2018,33(3):1497-1524
Ridge estimation (RE) is an alternative method to ordinary least squares (OLS) estimation when collinearity is detected in a linear regression model. After applying RE, it is sensible to determine whether such collinearity has been mitigated. The condition number (CN) is a commonly applied measure to detect the presence of collinearity in econometric models, but to the best of our knowledge, it has not been extended to be applied after RE. In OLS estimation, Belsley et al. (Regression diagnostics: identifying influential data and sources of collinearity, Wiley, New York, 1980) established that the regressors must be of unit length and not centered to correctly calculate the CN. This paper reviews this requirement in the context of RE and presents an expression to calculate the CN in RE. 相似文献
108.
109.
Arturo Echeverría-Enríquez Jesús Marín-Solano Miguel C. Muñoz-Lecanda Narciso Román-Roy 《Acta Appl Math》2003,77(1):1-40
The time-evolution K-operator (or relative Hamiltonian vector field) in mechanics is a powerful tool which can be geometrically defined as a vector field along the Legendre map. It has been extensively used by several authors for studying the structure and properties of the dynamical systems (mainly the nonregular ones), such as the relation between the Lagrangian and Hamiltonian formalisms, constraints, and higher-order mechanics. This paper is devoted to defining a generalization of this operator for field theories, in a covariant formulation. In order to do this, we use sections along maps, in particular multivector fields (skew-symmetric contravariant tensor fields of order greater than 1), jet fields and connection forms along the Legendre map. As a relevant result, we use these geometrical objects to obtain the solutions of the Lagrangian and Hamiltonian field equations, and the equivalence among them (specially for nonregular field theories). 相似文献
110.
Abrantes M Valente AA Pillinger M Gonçalves IS Rocha J Romão CC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(12):2685-2695
The organotin-oxomolybdates [(R(3)Sn)(2)MoO(4)].n H(2)O (R=methyl, n-butyl, cyclohexyl, phenyl, benzyl) have been prepared and tested as catalysts for the oxidation of benzothiophene with aqueous hydrogen peroxide, at 35 degrees C and atmospheric pressure. In all cases, the 1,1-dioxide was the only observed product. The kinetic profiles depend on the nature of the tin-bound R group and also on the addition of a co-solvent. For the tribenzyltin derivative, the apparent activation energies for sulfoxidation as a function of the co-solvent are in the order 1,2-dichloroethane (5 kcal mol(-1))相似文献