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排序方式: 共有563条查询结果,搜索用时 15 毫秒
41.
The impact of stochastic lead time reduction on inventory cost under order crossover 总被引:1,自引:0,他引:1
Jack C. Hayya Terry P. Harrison X. James He 《European Journal of Operational Research》2011,211(2):274-281
We use exponential lead times to demonstrate that reducing mean lead time has a secondary reduction of the variance due to order crossover. The net effect is that of reducing the inventory cost, and if the reduction in inventory cost overrides the investment in lead time reduction, then the lead time reduction strategy would be tenable.We define lead time reduction as the process of decreasing lead time at an increased cost. To date, decreasing lead times has been confined to deterministic instances. We examine the case where lead times are exponential, for when lead times are stochastic, deliveries are subject to order crossover, so that we must consider effective lead times rather than the actual lead times. The result is that the variance of these lead times is less than the variance of the original replenishment lead times.Here we present a two-stage procedure for reducing the mean and variance for exponentially distributed lead times. We assume that the lead time is made of one or several components and is the time between when the need of a replenishment order is determined to the time of receipt. 相似文献
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Dr. Carmen E. Castillo Dr. Ilaria Gamba Laia Vicens Dr. Martin Clémancey Prof. Dr. Jean-Marc Latour Prof. Dr. Miquel Costas Prof. Dr. Manuel G. Basallote 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(15):4946-4954
Oxoiron(IV) complexes bearing tetradentate ligands have been extensively studied as models for the active oxidants in non-heme iron-dependent enzymes. These species are commonly generated by oxidation of their ferrous precursors. The mechanisms of these reactions have seldom been investigated. In this work, the reaction kinetics of complexes [FeII(CH3CN)2L](SbF6)2 ( [1](SbF6)2 and [2](SbF6)2 ) and [FeII(CF3SO3)2L] ( [1](OTf)2 and [2](OTf)2 ( 1 , L=Me,HPytacn; 2 , L=nP,HPytacn; R,R′Pytacn=1-[(6-R′-2-pyridyl)methyl]-4,7- di-R-1,4,7-triazacyclononane) with Bu4NIO4 to form the corresponding [FeIV(O)(CH3CN)L]2+ ( 3 , L=Me,HPytacn; 4 , L=nP,HPytacn) species was studied in acetonitrile/acetone at low temperatures. The reactions occur in a single kinetic step with activation parameters independent of the nature of the anion and similar to those obtained for the substitution reaction with Cl− as entering ligand, which indicates that formation of [FeIV(O)(CH3CN)L]2+ is kinetically controlled by substitution in the starting complex to form [FeII(IO4)(CH3CN)L]+ intermediates that are converted rapidly to oxo complexes 3 and 4 . The kinetics of the reaction is strongly dependent on the spin state of the starting complex. A detailed analysis of the magnetic susceptibility and kinetic data for the triflate complexes reveals that the experimental values of the activation parameters for both complexes are the result of partial compensation of the contributions from the thermodynamic parameters for the spin-crossover equilibrium and the activation parameters for substitution. The observation of these opposite and compensating effects by modifying the steric hindrance at the ligand illustrates so far unconsidered factors governing the mechanism of oxygen atom transfer leading to high-valent iron oxo species. 相似文献
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Hans Toftlund 《Monatshefte für Chemie / Chemical Monthly》2001,132(11):1269-1277
Summary. The newer literature on spin equilibria of Fe(II) complexes in solution is reviewed. The thermodynamics as well as the kinetics
in different solvents are discussed. 相似文献
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Tongtao Wang Caishun Lin Feng Ye Yong Fang Jingjing Li Xindong Wang 《Electrochemistry communications》2008,10(9):1261-1263
Methanol permeation is one of the key problems for direct methanol fuel cell (DMFC) applications. It is necessary to change the structure of the cathode of membrane electrode assembly (MEA). Therefore, a novel MEA with double-layered catalyst cathode was prepared in this paper. The double-layered catalyst consists of PtRu black as inner catalyst layer and Pt black as outer catalyst layer. The inner catalyst layer is prepared for oxidation of the methanol permeated from anode. The results indicate that this double-layered catalyst reduced the effects of methanol crossover and assimilated mixed potential losses. The performance of MEA with double-layered catalyst cathode was 52.2 mW cm−2, which was a remarkable improvement compared with the performance of MEA with traditional cathode. The key factor responsible for the improved performance is the optimization of the electrode structure. 相似文献
49.
《Journal of computational chemistry》2017,38(4):224-227
Molecules exhibiting a spin‐crossover transition have been proposed for a number of applications such as molecular switches, spintronic tunable interfaces, and single molecule gates. Both the rational design of new spin‐crossover systems and the improvement of the properties of the already existing ones require a theoretical understanding of the relative energy of the high (HS) and low spin state (LS) molecules in the solid‐state. This has proved to be very challenging so far. Here, we shed some light on the importance of considering the symmetry and the geometry of the crystallographic cell to correctly evaluate the influence of the dipolar interactions on the relative energies of the molecular complex in both different spin states. Moreover, in the case of Fe(SCN)2(phen)2 dipolar interactions are found to play an important role for the stabilization of the LS complex. © 2016 Wiley Periodicals, Inc. 相似文献
50.
John W. Goodby 《Liquid crystals》2017,44(12-13):1755-1763
ABSTRACTIn this article, the relationship between molecular architecture and the formation of twist-bend phases is reviewed under the context of shape dependency. We conclude that the twist-bend phase is a universal phenomenon, which occurs in a wide variety of materials, for dimers through to main chain polymers. In the process, the chemical information on molecular design is effectively lost or irrelevant, and molecular topology takes precedence over electrostatic interactions in mesophase formation. As a consequence of this macro-scale material, engineering by shape alone becomes a possibility, potentially more phases may be realised, and entropy is anisotropic. 相似文献