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791.
Ziółkowski M Grabowski SJ Leszczynski J 《The journal of physical chemistry. A》2006,110(20):6514-6521
The H(2)CO...(HF)(n) (n = 1, ..., 9) complexes were investigated using the MP2 method and the following basis sets: 6-311++G(d,p), aug-cc-pVDZ and aug-cc-pVTZ. It was found that the cooperativity effect enhances significantly the F-H...O hydrogen bond; in some of cases one can detect the covalent nature of hydrogen bonding. To deepen the nature of the interactions investigated, the scheme of decomposition of the interaction energy was applied; for stronger H-bonds where the cooperativity is more important, the delocalization energy term increases. The ratio of delocalization energy to electrostatic energy increases for stronger hydrogen bonds where the proton...acceptor distance is shorter. The Bader theory was also applied, and it was found that for stronger H-bonds the electronic energy density at the proton...acceptor bond critical point is negative and may be attributed to the partly covalent interaction. 相似文献
792.
Forde GK Forde AE Hill G Ford A Nazario A Leszczynski J 《The journal of physical chemistry. B》2006,110(31):15564-15571
Minor tautomers of nucleic acid bases can result by intramolecular proton transfer. These rare tautomers could be stabilized through the addition of methyl groups to DNA bases. A comprehensive theoretical study of tautomers of methylated derivatives of guanine, adenine, cytosine, thymine, and uracil was performed. Molecular geometries of all tautomers were obtained at the density functional theory and MP2 levels with the 6-31G(d,p) basis set, and single-point calculations were performed at the CCSD(T)/6-311G(d,p) level. Tautomers obtained by protonation at the preferred protonation site for methylated isolated bases were compared to their nonmethylated counterparts. The effects of methylation on the relative stabilities of nucleic acid base tautomers are also studied and discussed in this work. The results suggest that some sites on the bases may not be mutagenic and may even stabilize the canonical Watson-Crick form. The results also indicate that a number of methylation sites can stabilize the tautomers, suggesting possible mechanisms for mutagenic changes. 相似文献
793.
Catalytic cross-metathesis of commercial divinyl sulfone allowed direct access to novel (E)-alkenylvinyl sulfones and (E,E)-dialkenyl sulfones with excellent stereoselectivity. These compounds are useful building blocks, e.g., in the synthesis of substituted thiomorpholine 1,1-dioxide derivatives. [reaction: see text] 相似文献
794.
Benzene dimer configurations namely T-shaped, parallel-displaced, sandwich, and V-shaped that were proposed by experimental studies are investigated using second- and fourth-order Møller–Plesset perturbation theory. The MP2 method with aug-cc-pVDZ and aug-cc-pVTZ basis sets unequivocally shows that the parallel-displaced configuration is considerably more stable than T-shaped structure. On the other hand, the MP4(SDTQ)/aug-cc-pVDZ level predicts that the T-shaped and parallel-displaced configurations are nearly isoenergetic, which is parallel to the previous results of estimated CCSD(T)/CBS level reported recently. The lowest energy T-shaped configuration is stabilized by 0.17 kcal/mol over the parallel-displaced configuration at the MP4(SDTQ)/aug-cc-pVDZ level. Although the structures of all the four different types of configurations are found to be stable at both MP2 and full MP4 methods, the V-shaped configuration is the least stable among them. The calculated interaction energy of ?2.3 kcal/mol for the lowest energy T-shaped structure at the MP4(SDTQ)/aug-cc-pVDZ level is in good agreement with the experimental value of ?2.4 ± 0.4 kcal/mol. We conclude that the MP4(SDTQ) with a reasonably good basis set can be used for systems involving π–π interactions to obtain qualitative and quantitative results. 相似文献
795.
We prove an Ekeland’s type vector variational principle for monotonically semicontinuous mappings with perturbations given
by a convex bounded subset of directions multiplied by the distance function. This generalizes the existing results where
directions of perturbations are singletons. 相似文献
796.
The affine group of a homogeneous tree is the group of all its isometries fixing an end of its boundary. We consider a random
walk with law μ on this group and the associated random processes on the tree and its boundary. In the drift-free case there exists on the
boundary of the tree a unique μ-invariant Radon measure. In this paper we describe its behaviour at infinity. 相似文献
797.
2-Phosphonothiophenes are prepared via the reaction of β-chloroacroleins with diethyl mercaptomethylphosphonate. 相似文献
798.
The paper deals with the two-dimensional stationary temperature distribution in a composite layer. The nonhomogenous body is assumed to be composed of periodically repeated two-layered laminae. The layering is inclined with an arbitrary angle to the boundary planes. The lower and upper boundary planes are assumed to be kept at given temperatures. The considered problem is solved within the framework of the homogenized model with microlocal parameters, where the continuity thermal conditions on interfaces are satisfied. 相似文献
799.
800.