全文获取类型
收费全文 | 258篇 |
免费 | 6篇 |
专业分类
化学 | 157篇 |
晶体学 | 3篇 |
力学 | 8篇 |
数学 | 21篇 |
物理学 | 75篇 |
出版年
2023年 | 3篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 7篇 |
2012年 | 14篇 |
2011年 | 15篇 |
2010年 | 3篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 14篇 |
2004年 | 8篇 |
2003年 | 11篇 |
2002年 | 12篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1966年 | 3篇 |
1955年 | 1篇 |
1947年 | 1篇 |
1937年 | 2篇 |
1935年 | 1篇 |
排序方式: 共有264条查询结果,搜索用时 15 毫秒
201.
An Integrated Inventory-Routing System for Multi-item Joint Replenishment with Limited Vehicle Capacity 总被引:4,自引:0,他引:4
Sombat?SindhuchaoEmail author H.?Edwin.?Romeijn Elif?Ak?ali Rein?Boondiskulchok 《Journal of Global Optimization》2005,32(1):93-118
In this paper, we develop a mathematical programming approach for coordinating inventory and transportation decisions in an inbound commodity collection system. In particular, we consider a system that consists of a set of geographically dispersed suppliers that manufacture one or more non-identical items, and a central warehouse that stocks these items. The warehouse faces a constant and deterministic demand for the items from outside retailers. The items are collected by a fleet of vehicles that are dispatched from the central warehouse. The vehicles are capacitated, and must also satisfy a frequency constraint. Adopting a policy in which each vehicle always collects the same set of items, we formulate the inventory-routing problem of minimizing the long-run average inventory and transportation costs as a set partitioning problem. We employ a column generation approach to determine a lower bound on the total costs, and develop a branch-and-price algorithm that finds the optimal assignment of items to vehicles. We also propose greedy constructive heuristics, and develop a very large-scale neighborhood (VLSN) search algorithm to find near-optimal solutions for the problem. Computational tests are performed on a set of randomly generated problem instances.The work of this author was supported by a scholarship of the Faculty of Engineering of Ubonratchathani University, Ubonratchathani, Thailand., The work of this author was supported in part by the National Science Foundation under Grant No. DMI-0085682. 相似文献
202.
Robert Rein Pierre Claverie Michael Pollak 《International journal of quantum chemistry》1968,2(1):129-144
Methods for calculating intermolecular interaction energies are evaluated in a specific application to double-stranded DNA-like configurations between bases. The total interaction is decomposed in such a way, that existing methods can be hybridized so that each method can be utilized to its best advantage. In addition, a new method is suggested for the computation of the dispersion interaction between the σ-electron system of one molecule and the π-electron system of the other. Results of various approaches applied to base pairs and double-stranded dimers are summarized and compared in a number of tables. 相似文献
203.
By taking advantage of the reversibility of the thermolysin-catalysed amide synthesis-hydrolysis reaction on a solid support, both L,L and L,D diastereoisomers of dipeptides and L-amino acids are accessible in good yields starting from enantiomeric mixtures of amino acids. 相似文献
204.
205.
206.
It is proven that in a neutral two-component plasma with space homogeneous positively charged background, which is governed by the Vlasov-Poisson system and for which Poisson's equation is considered on a cube inR
3 with periodic boundary conditions, the space homogeneous stationary solutions g with energy gradient g/ 0 and compact support are (nonlinearly) stable in the L1-norm with respect to weak solutions of the initial value problem. 相似文献
207.
[structure: see text] A stereocontrolled convergent synthesis of the annonaceous acetogenin pyragonicin (1) is presented. The key intermediates were accessed using asymmetric Horner-Wadsworth-Emmons (HWE) methodology. A reagent controlled zinc-mediated stereoselective coupling, joining the two highly functionalized intermediates 3 and 4, then provided the core structure. 相似文献
208.
In the philosophy of chemistry a view is developed according to which laws of nature and scientific theories are peculiar in chemistry. This view was criticized in an earlier issue of the Foundations of Chemistry (Vihalemm, Foundation of Chemistry 5(1): 7–22, 2003) referring to an essay by Maureen and John Christie (Christie and Christie, in N. Bushan and S. Rosenfeld (Eds.), Of Minds and Molecules: New Philosophical Perspectives on Chemistry. Oxford University Press, New York, 2000, pp. 34–50). This criticism was responded by the Christies (Christie and Christie, Foundations of Chemistry 5(2): 165–177, 2003). In the present article the debate is continued. The main issues which need to be elucidated in order to carry the analysis forward are pointed out and discussed. The relevance of a theoretical model of science for the philosophy of chemistry is stressed. 相似文献
209.
The volatile components of fresh leaves and roots from Anthriscus sylvestris (L.) Hoffm., obtained through hydrodistillation, were analysed by GC and GC-MS. This was compared to dichloromethane extracts of both fresh and dried leaf and root material. The monoterpene fraction (69-70%) dominated, while beta-phellandrene (39-45%) was the main component in both the leaf and the root oil. Other components in the leaf oil were beta-myrcene (17%), sabinene (6.2%), Z-beta-ocimene (5.4%) and benzene acetaldehyde (4.1%). In the roots we found Z-beta-ocimene (16.9%) and alpha-pinene (4.6%) as other major components. These principle constituents of both essential oils were also present in the dichloromethane extracts of the fresh and dried leaves and the roots, although in much smaller percentages. Comparing hydrodistillation of fresh plant material with a dichloromethane extract, the latter yielded a considerably lower amount of constituents. In addition, air drying and freeze drying resulted in a significant loss of volatile constituents as compared to fresh material (dichloromethane extract). 相似文献
210.
[reaction: see text]An approach to chiral tetrahydrofuran and tetrahydropyran derivatives is reported which is based on the sequential use of an asymmetric Horner-Wadsworth-Emmons desymmetrization of a meso-dialdehyde and a palladium-catalyzed intramolecular allylic substitution. The strategy is versatile in that either a cis- or a trans-relation between the stereocenters adjacent to the ring oxygen can be obtained. 相似文献