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361.
Lear BJ Glover SD Salsman JC Londergan CH Kubiak CP 《Journal of the American Chemical Society》2007,129(42):12772-12779
We relate the solvent and temperature dependence of the rates of intramolecular electron transfer (ET) of mixed valence complexes of the type {[Ru3O(OAc)6(CO)(L)]2-BL}-1, where L = pyridyl ligand and BL = pyrazine. Complexes were reduced chemically or electrochemically to obtain the mixed valence anions in seven solvents: acetonitrile, methylene chloride, dimethylformamide, tetrahydrofuran, dimethylsulfoxide, chloroform, and hexamethylphosphoramide. Rate constants for intramolecular ET were estimated by simulating the observed degree of nu(CO) IR band shape coalescence in the mixed valence state. Correlations between rate constants for ET and solvent properties including static dielectric constant, optical dielectric constant, the quantity 1/epsilonop - 1/epsilonS, microscopic solvent polarity, viscosity, cardinal rotational moments of inertia, and solvent relaxation times were examined. In the temperature study, the complexes displayed a sharp increase in the ket as the freezing points of the solvents methylene chloride and acetonitrile were approached. The solvent phase transition causes a localized-to-delocalized transition in the mixed valence ions and an acceleration in the rate of ET. This is explained in terms of decoupling the slower solvent motions involved in the frequency factor nuN which increases the value of nuN. The observed solvent and temperature dependence of the ket for these complexes is used in order to formulate a new definition for Robin-Day class II-III mixed valence compounds. Specifically, it is proposed that class II-III compounds are those for which thermodynamic properties of the solvent exert no control over ket, but the dynamic properties of the solvent still influence ket. 相似文献
362.
In this paper, we present an in-depth analysis of neighborhood relations for local search algorithms. Using a curriculum-based
course timetabling problem as a case study, we investigate the search capability of four neighborhoods based on three evaluation
criteria: percentage of improving neighbors, improvement strength and search steps. This analysis shows clear correlations
of the search performance of a neighborhood with these criteria and provides useful insights on the very nature of the neighborhood.
This study helps understand why a neighborhood performs better than another one and why and how some neighborhoods can be
favorably combined to increase their search power. This study reduces the existing gap between reporting experimental assessments
of local search-based algorithms and understanding their behaviors. 相似文献
363.
Fred Glover Lawrence H. Cox Rahul Patil James P. Kelly 《Annals of Operations Research》2011,183(1):47-73
A vital task facing government agencies and commercial organizations that report data is to represent the data in a meaningful
way and simultaneously to protect the confidentiality of critical components of this data. The challenge is to organize and
disseminate data in a form that prevents such critical components from being inferred by groups bent on corporate espionage,
to gain competitive advantages, or having a desire to penetrate the security of the information underlying the data. Controlled
tabular adjustment is a recently developed approach for protecting sensitive information by imposing a special form of statistical
disclosure limitation on tabular data. The underlying model gives rise to a mixed integer linear programming problem involving
both continuous and discrete (zero-one) variables. We develop stratified ordered (s-ordered) heuristics and a new meta-heuristic
learning approach for solving this model, and compare their performance to previous heuristics and to an exact algorithm embodied
in the state-of-the-art ILOG- CPLEX software. Our new approaches are based on partitioning the problem into its discrete and
continuous components, first creating an s-ordered heuristic that reduces the number of binary variables through a grouping
procedure that combines an exact mathematical programming model with constructive heuristics. To gain further advantages we
then replace the mathematical programming model with an evolutionary scatter search approach that makes it possible to extend
the method to large problems with over 9000 entries. Finally, we introduce a new metaheuristic learning method that significantly
improves the quality of solutions obtained. 相似文献
364.
Thorogood GJ Zhang Z Hester JR Kennedy BJ Ting J Glover CJ Johannessen B 《Dalton transactions (Cambridge, England : 2003)》2011,40(41):10924-10926
The structure of TcCo(2)O(4) has been determined using a combination of synchrotron X-ray and neutron powder diffraction methods. It has an inverse spinel structure where the Tc occupies the octahedral sites. Both the refined Tc-O distance and X-ray absorption spectra suggest the Tc is predominantly trivalent. 相似文献
365.
Glover SA White JM Rosser AA Digianantonio KM 《The Journal of organic chemistry》2011,76(23):9757-9763
The first X-ray structures of two anomeric N,N-dialkoxyamides (2 and 3) have been obtained, which confirm that they are highly pyramidalized at nitrogen and have long N-CO bonds, a characteristic of other anomeric amides and a consequence of drastically reduced amidicity. The crystals also demonstrate chirality at the amide nitrogen in the solid state. The structures are well-predicted by density functional calculations using N,N-dimethoxyacetamide as a model. The amidicity of N,N-dimethoxyacetamide has been estimated by two independent methods, COSNAR and a new transamidation method, which give almost identical resonance stabilization energies of -8.6 kcal mol(-1) and only 47% that of N,N-dimethylacetamide computed at the same level. The total destabilization is composed of a resonance and an inductive contribution, which we have evaluated separately. The electronegative oxygens at nitrogen are responsible for localization of the nitrogen lone pair on the amide nitrogen, a factor that contributes to a loss of resonance over and above the impact of pyramidalization at nitrogen, as well as the fact that N,N-dimethoxyacetamide is predicted to protonate on the carbonyl oxygen in preference to nitrogen. 相似文献
366.
T.?Gehrmann E.?W.?N.?Glover T.?Huber N.?Ikizlerli C.?Studerus 《Journal of High Energy Physics》2010,2010(6):94
We describe the calculation of the three-loop QCD corrections to quark and gluon form factors. The relevant three-loop Feynman diagrams are evaluated and the resulting three-loop Feynman integrals are reduced to a small set of known master integrals by using integration-by-parts relations. Our calculation confirms the recent results by Baikov et al. for the three-loop form factors. In addition, we derive the subleading \( \mathcal{O}\left( \varepsilon \right) \) terms for the fermion-loop type contributions to the three-loop form factors which are required for the extraction of the fermionic contributions to the four-loop quark and gluon collinear anomalous dimensions. The finite parts of the form factors are used to determine the hard matching coefficients for the Drell-Yan process and inclusive Higgs-production in soft-collinear effective theory. 相似文献
367.
A. Gehrmann-De Ridder E.W.N. Glover 《The European Physical Journal C - Particles and Fields》1999,7(1):29-48
We present a detailed study of photon production in hadronic events in electron-positron annihilation at LEP energies. We
show that estimates of the inclusive photon spectrum using the quark-to-photon fragmentation function determined using the
ALEPH ‘photon’ + 1 jet data agree well with the observations of the OPAL collaboration. This agreement shows that the photon
fragmentation function determined in this way can be used for inclusive observables. We also compare next-to-leading order
and beyond leading logarithm predictions obtained using the numerically resummed solutions of the fragmentation function evolution
equation of Bourhis, Fontannaz and Guillet and Glück, Reya and Vogt with the data. Moreover, in order to check the general
behaviour of the fragmentation function, we consider an analytic series expansion in the strong coupling. We find that the
parameterizations are inaccurate at large x values. While the OPAL data is in broad agreement with estimates based on any of these approaches, the ALEPH data prefers
the resummed BFG parameterization. Finally, there is some ambiguity as to whether the fragmentation function is treated as
or . We show that at present this ambiguity affects mainly the prediction for the ‘photon’ + 1 jet rate at large z.
Received: 9 June 1998 / Published online: 21 August 1998 相似文献