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31.
Genetic algorithms are commonly used metaheuristics for global optimization, but there has been very little research done
on the generation of their initial population. In this paper, we look for an answer to the question whether the initial population
plays a role in the performance of genetic algorithms and if so, how it should be generated. We show with a simple example
that initial populations may have an effect on the best objective function value found for several generations. Traditionally,
initial populations are generated using pseudo random numbers, but there are many alternative ways. We study the properties
of different point generators using four main criteria: the uniform coverage and the genetic diversity of the points as well
as the speed and the usability of the generator. We use the point generators to generate initial populations for a genetic
algorithm and study what effects the uniform coverage and the genetic diversity have on the convergence and on the final objective
function values. For our tests, we have selected one pseudo and one quasi random sequence generator and two spatial point
processes: simple sequential inhibition process and nonaligned systematic sampling. In numerical experiments, we solve a set
of 52 continuous test functions from 16 different function families, and analyze and discuss the results. 相似文献
32.
We consider a telecommunication problem in which the objective is to schedule data transmission to be as fast and as cheap
as possible. The main characteristic and restriction in solving this multiobjective optimization problem is the very limited
computational capacity available. We describe a simple but efficient local search heuristic to solve this problem and provide
some encouraging numerical test results. They demonstrate that we can develop a computationally inexpensive heuristic without
sacrificing too much in the solution quality. 相似文献
33.
Trade-off information related to Pareto optimal solutions is important in multiobjective optimization problems with conflicting
objectives. Recently, the concept of trade-off directions has been introduced for convex problems. These trade-offs are characterized
with the help of tangent cones. Generalized trade-off directions for nonconvex problems can be defined by replacing convex
tangent cones with nonconvex contingent cones. Here we study how the convex concepts and results can be generalized into a
nonconvex case. Giving up convexity naturally means that we need local instead of global analysis.
Received: December 2000 / Accepted: October 2001?Published online February 14, 2002 相似文献
34.
35.
Markus Hartikainen Kaisa Miettinen Margaret M. Wiecek 《Mathematical Methods of Operations Research》2011,73(2):209-234
An approach to constructing a Pareto front approximation to computationally expensive multiobjective optimization problems is developed. The approximation is constructed as a sub-complex of a Delaunay triangulation of a finite set of Pareto optimal outcomes to the problem. The approach is based on the concept of inherent nondominance. Rules for checking the inherent nondominance of complexes are developed and applying the rules is demonstrated with examples. The quality of the approximation is quantified with error estimates. Due to its properties, the Pareto front approximation works as a surrogate to the original problem for decision making with interactive methods. 相似文献
36.
Markku Miettinen 《Applicable analysis》2013,92(3-4):303-326
We prove the existence of a solution of a constrained hemivariational inequality, and, develop a fully discrete approximation of it. The relation between the constrained hemivariational inequality and a problem of finding substationary points of the corresponding potential function is also studied. 相似文献
37.
M. Miettinen M. Johansson S. Suvanto J. Riikonen U. Tapper T. T. Pakkanen V.-P. Lehto J. Jokiniemi A. Lähde 《Journal of nanoparticle research》2011,13(10):4631-4645
Silicon–carbon nanoceramics have been synthesised from hexamethyldisilane (HMDS) by the atmospheric pressure chemical vapour
synthesis (APCVS). Direct aerosol phase synthesis enables continuous production of high purity materials in one-stage process.
The particle formation is based on the decomposition of the precursor in a high temperature reactor. Reaction of the gas phase
species leads to homogeneous nucleation and formation of the nanoparticles with a narrow size distribution (geometric mean
diameter range of particle number size distribution 160–200 nm with 1.5–1.6 geometric standard deviation at reaction temperatures
800–1200 °C). A systematic investigation of the influence of the process temperature on the powder characteristics, including
the particle size, crystallinity, chemical structure, surface and bulk composition and surface morphology, was carried out.
At the reactor temperature of 800 °C, the synthesised nanoparticles were amorphous preceramics containing mostly SiC4, Si–CH2–Si and Si–H units. The composition of the powder turned towards nanocrystalline 3C–SiC (crystal size under 2 nm) when the
reaction temperature was increased to 1200 °C. The reaction temperature appeared to be a key parameter controlling the structure
and properties of the synthesised powders. 相似文献
38.
Antti J. Koivisto Maija M?kinen Elina M. Rossi Hanna K. Lindberg Mirella Miettinen Ghita C.- M. Falck Hannu Norppa Harri Alenius Anne Korpi Joakim Riikonen Esa Vanhala Minnamari Vippola Pertti Pasanen Vesa-Pekka Lehto Kai Savolainen Jorma Jokiniemi Kaarle H?meri 《Journal of nanoparticle research》2011,13(7):2949-2961
This study presents a novel exposure protocol for synthesized nanoparticles (NPs). NPs were synthesized in gas phase by thermal decomposition of metal alkoxide vapors in a laminar flow reactor. The exposure protocol was used to estimate the deposition fraction of titanium dioxide (TiO2) NPs to mice lung. The experiments were conducted at aerosol mass concentrations of 0.8, 7.2, 10.0, and 28.5 mg m?3. The means of aerosol geometric mobility diameter and aerodynamic diameter were 80 and 124 nm, and the geometric standard deviations were 1.8 and 1.7, respectively. The effective density of the particles was approximately from 1.5 to 1.7 g cm?3. Particle concentration varied from 4 × 105 cm?3 at mass concentrations of 0.8 mg m?3 to 12 × 106 cm?3 at 28.5 mg m?3. Particle phase structures were 74% of anatase and 26% of brookite with respective crystallite sized of 41 and 6 nm. The brookite crystallites were approximately 100 times the size of the anatase crystallites. The TiO2 particles were porous and highly agglomerated, with a mean primary particle size of 21 nm. The specific surface area of TiO2 powder was 61 m2 g?1. We defined mice respiratory minute volume (RMV) value during exposure to TiO2 aerosol. Both TiO2 particulate matter and gaseous by-products affected respiratory parameters. The RMV values were used to quantify the deposition fraction of TiO2 matter by using two different methods. According to individual samples, the deposition fraction was 8% on an average, and when defined from aerosol mass concentration series, it was 7%. These results show that the exposure protocol can be used to study toxicological effects of synthesized NPs. 相似文献
39.
Kaisa Miettinen Julián Molina Mercedes González Alfredo Hernández-Díaz Rafael Caballero 《European Journal of Operational Research》2009
Because of the conflicting nature of criteria or objectives, solving a multiobjective optimization problem typically requires interaction with a decision maker who can specify preference information related to the objectives in the problem in question. Due to the difficulties of dealing with multiple objectives, the way information is presented plays a very important role. Questions posed to the decision maker must be simple enough and information shown must be easy to understand. For this purpose, visualization and graphical representations can be useful and constitute one of the main tools used in the literature. In this paper, we propose to use box indices to represent information related to different solution alternatives of multiobjective optimization problems involving at least three objectives. Box indices are an intelligible and easy to handle way to represent data. They are based on evaluating the solutions in a natural and rough enough scale in order to let the decision maker easily recognize the main characteristics of a solution at a glance and to facilitate comparison of two or more solutions in an easily understandable way. 相似文献
40.
The present experimental evidence for the scaling of multiplicity distributions predicted by Koba, Nielsen and Olesen is examined critically. Our results indicate that the approximate scaling observed experimentally is not necessarily connected with an “early” approach to the asymptotic limit. Some simple models are shown to predict an extremely slow approach to scaling. The possibility of distinguishing between “early” scaling ang the “quasi-scaling” exhibited by these models with experiments at ISR is discussed. 相似文献