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41.
An additive procedure (SIBFA) is developed for the rapid computation of conformational energy variations in very large molecules. The macromolecule is built out of constitutive molecular fragments and the intramolecular energy is computed as a sum of interaction energies between the fragments. The electrostatic and the polarization components are calculated using multicenter multipole expansions of theab initio SCF electron density of the fragments. The repulsion component is obtained as a sum of bond and lone pair interactions.Tests of the procedure on a series of model compounds containing ether oxygens and pyridine-like nitrogens are reported and compared with the results of correspondingab initio SCF calculations. The resulting methodology is compatible with the simultaneous computation of intermolecular interactions. 相似文献
42.
A discrete variable representation (DVR) made from distributed Gaussians gn(x) = e, (n = ?∞, …, ∞) and its infinite grid limit is described. The infinite grid limit of the distributed Gaussian DVR (DGDVR) reduces to the sinc function DVR of Colbert and Miller in the limit c → 0. The numerical performance of both finite and infinite grid DGDVRs and the sinc function DVR is compared. If a small number of quadrature points are taken, the finite grid DGDVR performs much better than both infinite grid DGDVR and sinc function DVR. The infinite grid DVRs lose accuracy due to the truncation error. In contrast, the sinc function DVR is found to be superior to both finite and infinite grid DGDVRs if enough grid points are taken to eliminate the truncation error. In particular, the accuracy of DGDVRs does not get better than some limit when the distance between Gaussians d goes to zero with fixed c, whereas the accuracy of the sinc function DVR improves very quickly as d becomes smaller, and the results are exact in the limit d → 0. An analysis of the performance of distributed basis functions to represent a given function is presented in a recent publication. With this analysis, we explain why the sinc function DVR performs better than the infinite grid DGDVR. The analysis also traces the inability of Gaussians to yield exact results in the limit d → 0 to the incompleteness of this basis in this limit. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
43.
The comparison of a pure electrostatic approximation and complete supermolecule SCF ab initio computations on the hydration scheme of uracil and cytosine shows that the electrostatic procedure is capable to reproduce the general aspects of the results of the supermolecule treatment provided that different distances of shortest approach be adopted for the distances between the oxygen of water and the nitrogen of NH2 or NH groups or the oxygen of C-O groups on the one hand and the oxygen of water and pyridine-type nitrogens on the other hand. 相似文献
44.
Simple methods of analysis of first-order kinetic processes controlled by distributions of parameters (activation energies and/or frequency factors) are presented. Both the isothermal and nonisothermal regimes are considered. The procedures make use of numerically calculated time derivatives of the concentrations of decaying species (reactants in the case of chemical reactions). They do not require any adjustable initial or boundary values of parameters (like concentration at the infinite time) being thus more accurate and reliable than earlier methods in which kinetic parameters were determined from the concentration, and not from its time derivative. The methods were successfully employed in analysis of the thermally driven cis–trans isomerization of a photochromic crown ether containing the azobenzene moiety incorporated in the crown. 相似文献
45.
Continuing the recent work of the second author, we prove that the diophantine equation
for has exactly 12 solutions except when , when it has 16 solutions. If denotes one of the zeros of , then for we also find all with .
46.
Zbigniew Michalewicz 《Journal of Heuristics》1996,1(2):177-206
Evolutionary computation techniques, which are based on a powerful principle of evolution—survival of the fittest, constitute an interesting category of heuristic search. In other words, evolutionary techniques are stochastic algorithms whose search methods model some natural phenomena: genetic inheritance and Darwinian strife for survival.Any evolutionary algorithm applied to a particular problem must address the issue of genetic representation of solutions to the problem and genetic operators that would alter the genetic composition of offspring during the reproduction process. However, additional heuristics should be incorporated in the algorithm as well; some of these heuristic rules provide guidelines for evaluating (feasible and infeasible) individuals in the population. This paper surveys such heuristics and discusses their merits and drawbacks.An abridged version of this paper appears in the volume entitled META-HEURISTICS: Theory & Application, edited by Ibrahim H. Osman and James P. Kelly, to be published by Kluwer Academic Publishers in March 1996. 相似文献
47.
Emanuele Galligani 《Numerical Algorithms》1993,5(11):549-555
Givenn pairwise distinct and arbitrarily spaced pointsP
i in a domainD of thex–y plane andn real numbersf
i, consider the problem of computing a bivariate functionf(x, y) of classC
1 inD whose values inP
i are exactlyf
i,i=1,,n, and whose first or second order partial derivatives satisfy appropriate equality and inequality constraints on a given set ofp pointsQ
l inD.In this paper we present a method for solving the above problem, which is designed for extremely large data sets. A step of this method requires the solution of a large scale quadratic programming (QP) problem.The main purpose of this work is to analyse an iterative method for determining the solution of this QP problem: such a method is very efficient and well suited for parallel implementation on a multiprocessor system.Work supported by MURST Project of Computational Mathematics, Italy. 相似文献
48.
S. Filipek J. Rzeszotarska M. K. Kalinowski 《Monatshefte für Chemie / Chemical Monthly》1994,125(8-9):801-809
Summary The stability constants,K
sof monensin complexes with Li+, Na+, K+ and Cs+ ions were studied by a competitive polarographic method using the Tl+/Tl(Hg) redox couple as a sensitive electrochemical probe. TheK
svalues are strongly influenced by the solvents (acetonitrile, propionitrile, acetone, N,N-dimethylformamide, N-methyl pyrolidinone, N,N-dimethylacetamide, dimethylsulfoxide, N,N-diethylformamide and N,N-diethylacetamide were used in experiments) and vary inversely with the Gutmann donicity scale. Molecular mechanics computations revealed the probable structures of the complexes.
Polarographische Untersuchung von Tl+-, Li+-, Na+- und Cs+-Komplexen mit Monesin-Anion in dipolaren aprotischen Lösungsmitteln
Zusammenfassung Es wurden die StabilitätskonstantenK svon Monesin-Komplexen mit Li+-, Ma+- und Cs+-Ionen mittels einer competitiven polarographischen Methode unter Verwendung der Tl+/Tl(Hg)-Redoxelektrode als sensitiver elektrochemischer Sonde bestimmt. DieK s-Werte werden stark vom Lösungsmittel (Acetonitril, Propionitril, Aceton, N,N-Dimethylformamid, N-Methylpyrrolidinon, N,N-Dimethylacetamid, Dimethylsulfoxid, N,N-Diethylformamid und N,N-Diethylacetamid) beeinflußt, wobei sie invers zurGutmann schen Donizitätsskala variieren. Die wahrscheinliche Struktur der Komplexe wurde mittels molekularmechanischer Berechnungen ermittelt.相似文献
49.
This paper presents in detail a robust, efficient and accurate methodology for the computation of equilibrium composition in gaseous mixtures. The methodology is founded on the concept of the chemical basis, which is defined and formalized using a powerful matricial approach. The method is specially designed to be general, thus providing basic thermodynamic data in several areas, such as combustion, plasma chemistry and, more generally speaking, computational fluid dynamics. The performance of the method is given in terms of CPU usage and the computed results are compared with those in the published literature. The method is shown to yield results of very high quality in terms of accuracy and smoothness. 相似文献
50.
首次将微量热用于亚细胞层次的研究,测定了鲤鱼肝脏线粒体和亚线粒体代谢的热谱及其漆树漆酶的影响,并用MTD方程和演化计算技术对它们的代谢热动力学参数进行了全局优化。 相似文献