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1.
In this work, the NP-hard maximum clique problem on graphs is considered. Starting from basic greedy heuristics, modifications and improvements are proposed and combined in a two-phase heuristic procedure. In the first phase an improved greedy procedure is applied starting from each node of the graph; on the basis of the results of this phase a reduced subset of nodes is selected and an adaptive greedy algorithm is repeatedly started to build cliques around such nodes. In each restart the selection of nodes is biased by the maximal clique generated in the previous execution. Computational results are reported on the DIMACS benchmarks suite. Remarkably, the two-phase procedure successfully solves the difficult Brockington-Culberson instances, and is generally competitive with state-of-the-art much more complex heuristics. 相似文献
2.
Andrea Grosso Marco Locatelli Fabio Schoen 《Computational Optimization and Applications》2007,38(3):351-370
In this paper we perform a computational analysis of a population based approach for global optimization, Population Basin
Hopping (PBH), which was proven to be very efficient on very challenging global optimization problems by the authors (see
). The experimental analysis aims at understanding more deeply how the approach works and why it is successful on challenging
problems. 相似文献
3.
Arsenic(III), selenium(IV), copper(II), lead(II), cadmium(II) and zinc(II) are determined in environmental matrices. The voltammetric measurements were carried out using a conventional three-electrode cell and the ammonia-ammonium chloride buffer pH 9.3 as supporting electrolyte. The analytical procedure was verified by the analysis of the standard reference materials Estuarine Sediment BCR-CRM 277 and River Sediment BCR-CRM 320. The precision, expressed as relative standard deviation (s(r)), and the accuracy, expressed as relative error, were, in all cases, less than 5%; the detection limits, for each element and in the experimental conditions employed, were around 10(-9) M. The standard addition technique significantly improved the resolution of the voltammetric method, even in the case of very high metal concentration ratios. 相似文献
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5.
Locatelli C 《Talanta》1996,43(1):45-54
The determination of manganese in the presence of iron and chromium by differential pulse voltammetry and fundamental harmonic alternating current voltammetry was compared, including the case of very high element concentration ratios. The voltammetric measurements were carried out using a stationary mercury electrode in ammonia-ammonium chloride buffer (pH 9.6). The analytical procedure was verified by the analysis of the standard reference materials Portland Cement BCS 372, Spectrographic Zinc Spelter NBS-SRM 631, Stainless Steel (AISI 321) NBS-SRM 121d and Highly Alloyed Steel Eurostandard 281-1. Precision and accuracy, expressed as relative standard deviation and relative error respectively, were of the order of 3-5%, while the detection limit for each element was around 1 x 10(-9) M. The standard addition technique improved the resolution of the voltammetric methods, within a maximum experimental error of 5%, even in the case of very high concentration ratios, that is outside the non-interference concentration ratios 69:1 >c(Fe):c(Mn) > 1:74; 35:1 > c(Fe):c(Cr) > 1:30 and 63:1 > c(Fe):c(Mn) > 1:65; 32:1 > c(Fe):c(Cr) > 1:31 for the differential pulse and alternating current techniques respectively, extrapolating the linear section of the i(p) vs. concentration analytical calibration function for the element present at the lowest concentration. In contrast, the element with the greatest concentration was determined by the relevant calibration curve. 相似文献
6.
Aldo Andreani Alessandra Locatelli Mirella Rambaldi 《Journal of heterocyclic chemistry》1995,32(1):49-51
The reaction of 1-substituted 2-chloroindole-3-carboxaldehydes with 1-amino-2-imidazolidinone gave a series of 1-substituted 2-chloro-3-(2-oxo-1-imidazolidinyliminomethyl)indoles which were evaluated as potential herbicides. The level of biological activity was not sufficient to warrant further investigation. 相似文献
7.
Liquid sodium containing titanium nanoparticles (LSnanop) of 10-nm diameter was prepared by dispersing titanium nanoparticles (2 at.% Ti) into liquid sodium with the addition of stirring and ultrasonic sound wave. The titanium nanoparticles themselves were prepared by the vapor deposition method. This new liquid metal, LSnanop, shows a remarkable stability due to the Brownian motion of nanoparticles in liquid sodium medium. In addition, the difference of measured heat of reaction to water between this LSnanop and liquid sodium indicates the existence of cohesive energy between the liquid sodium medium and dispersed titanium nanoparticles. The origin of the cohesive energy, which serves to stabilize this new liquid metal, was explained by the model of screened nanoparticles in liquid sodium. In this model, negatively charged nanoparticles with transferred electrons from liquid sodium are surrounded by the positively charged screening shell, which may inhibit the gathering of nanoparticles by the ??Coulombic repulsion coating.?? The atomic volume of LSnanop shows the shrinkage from the linear law, which also suggests the existence of cohesive energy. The viscosity of LSnanop is almost the same as that of liquid sodium. This behavior was explained by the Einstein equation. The surface tension of LSnanop is 17?% larger than that of liquid sodium. The cohesive energy and the negative adsorption may be responsible to this increase. Titanium nanoparticles in liquid sodium seem to be free from the Coulomb fission. This new liquid metal containing nanoparticles suggests the possibility to prepare various stable suspensions with new properties. 相似文献
8.
9.
10.
Undominated d.c. Decompositions of Quadratic Functions and Applications to Branch-and-Bound Approaches 总被引:2,自引:0,他引:2
In this paper we analyze difference-of-convex (d.c.) decompositions for indefinite quadratic functions. Given a quadratic function, there are many possible ways to decompose it as a difference of two convex quadratic functions. Some decompositions are dominated, in the sense that other decompositions exist with a lower curvature. Obviously, undominated decompositions are of particular interest. We provide three different characterizations of such decompositions, and show that there is an infinity of undominated decompositions for indefinite quadratic functions. Moreover, two different procedures will be suggested to find an undominated decomposition starting from a generic one. Finally, we address applications where undominated d.c.d.s may be helpful: in particular, we show how to improve bounds in branch-and-bound procedures for quadratic optimization problems. 相似文献