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211.
An algorithm for calculating the partition function of a molecule with the path integral Monte Carlo method is presented. Staged thermodynamic perturbation with respect to a reference harmonic potential is utilized to evaluate the ratio of partition functions. Parallel tempering and a new Monte Carlo estimator for the ratio of partition functions are implemented here to achieve well converged simulations that give an accuracy of 0.04 kcal/mol in the reported free energies. The method is applied to various test systems, including a catalytic system composed of 18 atoms. Absolute free energies calculated by this method lead to corrections as large as 2.6 kcal/mol at 300 K for some of the examples presented. 相似文献
212.
213.
Caputo F Cattaneo C Clerici F Gelmi ML Pellegrino S 《The Journal of organic chemistry》2006,71(22):8467-8472
The synthesis of two new diastereomeric 6-amino-3-azabicyclo[3.2.1]octane-6-carboxylic acids exo- and endo-8,9 is reported using exo- and endo-norbornene amino acids as chiral building blocks. This method provides a fast access to optically pure amino acids 8 and 9 which can be considered both alpha,gamma- and alpha,delta-diamino acids containing sterical constraints and characterized by alpha,alpha-disubstitution. 相似文献
214.
Raiteri P Laio A Gervasio FL Micheletti C Parrinello M 《The journal of physical chemistry. B》2006,110(8):3533-3539
Recently, we have introduced a new method, metadynamics, which is able to sample rarely occurring transitions and to reconstruct the free energy as a function of several variables with a controlled accuracy. This method has been successfully applied in many different fields, ranging from chemistry to biophysics and ligand docking and from material science to crystal structure prediction. We present an important development that speeds up metadynamics calculations by orders of magnitude and renders the algorithm much more robust. We use multiple interacting simulations, walkers, for exploring and reconstructing the same free energy surface. Each walker contributes to the history-dependent potential that, in metadynamics, is an estimate of the free energy. We show that the error on the reconstructed free energy does not depend on the number of walkers, leading to a fully linear scaling algorithm even on inexpensive loosely coupled clusters of PCs. In addition, we show that the accuracy and stability of the method are much improved by combining it with a weighted histogram analysis. We check the validity of our new method on a realistic application. 相似文献
215.
Cristian Virdol 《Journal of Number Theory》2010,130(5):1197-1211
In this paper we compute the l-adic Lie algebra of a product of l-adic representations associated to a Hilbert modular surface and a Picard modular surface. 相似文献
216.
Cristian Lenart 《Journal of Combinatorial Theory, Series A》2010,117(7):842-856
We present a partial generalization of the classical Littlewood-Richardson rule (in its version based on Schützenberger's jeu de taquin) to Schubert calculus on flag varieties. More precisely, we describe certain structure constants expressing the product of a Schubert and a Schur polynomial. We use a generalization of Fomin's growth diagrams (for chains in Young's lattice of partitions) to chains of permutations in the so-called k-Bruhat order. Our work is based on the recent thesis of Beligan, in which he generalizes the classical plactic structure on words to chains in certain intervals in k-Bruhat order. Potential applications of our work include the generalization of the S3-symmetric Littlewood-Richardson rule due to Thomas and Yong, which is based on Fomin's growth diagrams. 相似文献
217.
Cristian Enache 《NoDEA : Nonlinear Differential Equations and Applications》2010,17(5):591-600
This paper is concerned with a class of boundary value problems for fully nonlinear elliptic PDEs involving the p-Hessian operator. We first derive a maximum principle for a suitable function involving the solution u(x) and its gradient. This maximum principle is then applied to obtain some sharp estimates for the solution and the magnitude
of its gradient. We also investigate some symmetry properties of Ω or u(x) under specific boundary condition or geometry of Ω. 相似文献
218.
Cristian Tacelli 《Applied Mathematics Letters》2010,23(9):1099-1103
In this work general quantitative estimates of Voronovskaja-type formulas in the space of functions of several variables that are twice continuously differentiable and in the space of functions with weighted second-order derivatives are established. 相似文献
219.
Alpar Pöllnitz Anca Silvestru Cristian Silvestru 《Journal of organometallic chemistry》2010,695(23):2486-2492
Diorganodiselenide [2-(Et2NCH2)C6H4]2Se2 (1) was obtained by hydrolysis/oxidation of the corresponding [2-(Et2NCH2)C6H4]SeLi derivative. The treatment of [2-(Et2NCH2)C6H4]2Se2 with elemental sodium in THF resulted in [2-(Et2NCH2)C6H4]SeNa (2). Reactions between alkali metal selenolates [2-(R2NCH2)C6H4]SeM′ (R = Me, Et; M′ = Li, Na) and MCl2 (M = Zn, Cd) in a 2:1 molar ratio resulted in the [2-(R2NCH2)C6H4Se]2M species [R = Me, M = Zn (3), Cd (4); R = Et, M = Zn (5), Cd (6)]. The new compounds were characterized by multinuclear NMR (1H, 13C, 77Se, 113Cd) and mass spectrometry. The crystal and molecular structures of 1, 3 and 4 revealed monomeric species stabilized by N → Se (for 1) and N → M (for 3 and 4) intramolecular interactions. 相似文献
220.
Mihaela Matache Cristian Dobrota Niculina D. Bogdan Lavinia L. Ruta Ileana C. Farcasanu Daniel P. Funeriu 《Tetrahedron》2009,65(31):5949-3817
A new efficient approach for the synthesis of functionalized dihydro-pyrimido[4,3-d]coumarins is described. Use of benzyl- or tert-butyl acetoacetate and various salicyl aldehydes in typical Biginelli multicomponent reactions provides esters that can be easily deprotected to yield the corresponding hydroxy acids. Annelation of the latter leads to the target dihydro-pyrimido[4,3-d]coumarins. Formation of some unexpected oxo-bridged tetrahydro-pyrimidines is also described. Spectral properties of the synthesized dihydro-pyrimido[4,3-d]coumarins indicate the necessity to revisit some compounds previously reported as products of direct one-pot Biginelli condensation involving 4-hydroxycoumarin as dicarbonyl component. 相似文献