全文获取类型
收费全文 | 1239篇 |
免费 | 76篇 |
国内免费 | 15篇 |
专业分类
化学 | 975篇 |
晶体学 | 8篇 |
力学 | 24篇 |
数学 | 135篇 |
物理学 | 188篇 |
出版年
2022年 | 12篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 11篇 |
2018年 | 21篇 |
2017年 | 16篇 |
2016年 | 38篇 |
2015年 | 38篇 |
2014年 | 40篇 |
2013年 | 73篇 |
2012年 | 94篇 |
2011年 | 98篇 |
2010年 | 62篇 |
2009年 | 54篇 |
2008年 | 100篇 |
2007年 | 69篇 |
2006年 | 83篇 |
2005年 | 85篇 |
2004年 | 55篇 |
2003年 | 61篇 |
2002年 | 40篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 5篇 |
排序方式: 共有1330条查询结果,搜索用时 0 毫秒
1.
Laurence A. Wolsey 《Mathematical Programming》2003,97(1-2):423-447
We examine progress over the last fifteen years in finding strong valid inequalities and tight extended formulations for
simple mixed integer sets lying both on the ``easy' and ``hard' sides of the complexity frontier. Most progress has been
made in studying sets arising from knapsack and single node flow sets, and a variety of sets motivated by different lot-sizing
models. We conclude by citing briefly some of the more intriguing new avenues of research.
Received: January 15, 2003 / Accepted: April 10, 2003
Published online: May 28, 2003
Key words. mixed integer programming – strong valid inequalities – convex hull – extended formulations – single node flow sets – lot-sizing
This paper presents research results of the Belgian Program on Interuniversity Poles of Attraction initiated by the Belgian
State, Prime Minister's Office, Science Policy Programming. The scientific responsibility is assumed by the authors.
Research carried out with financial support of the project TMR-DONET nr. ERB FMRX–CT98–0202 of the European Union. 相似文献
2.
We performed ab initio quantum-chemical studies for the development of intra- and intermolecular interaction potentials for formic acid for use in molecular-dynamics simulations of formic acid molecular crystal. The formic acid structures considered in the ab initio studies include both the cis and trans monomers which are the conformers that have been postulated as part of chains constituting liquid and crystal phases under extreme conditions. Although the cis to trans transformation is not energetically favored, the trans isomer was found as a component of stable gas-phase species. Our decomposition scheme for the interaction energy indicates that the hydrogen-bonded complexes are dominated by the Hartree-Fock forces while parallel clusters are stabilized by the electron correlation energy. The calculated three-body and higher interactions are found to be negligible, thus rationalizing the development of an atom-atom pair potential for formic acid based on high-level ab initio calculations of small formic acid clusters. Here we present an atom-atom pair potential that includes both intra- and inter molecular degrees of freedom for formic acid. The newly developed pair potential is used to examine formic acid in the condensed phase via molecular-dynamics simulations. The isothermal compression under hydrostatic pressure obtained from molecular-dynamics simulations is in good agreement with experiment. Further, the calculated equilibrium melting temperature is found to be in good agreement with experiment. 相似文献
3.
The preferred conformations of the tripeptide glutathione have been investigated by performing quantum mechanical calculations using the PCILO method. A series of model compounds representing fragments of the tripeptide has been studied as well as the complete molecule. The results are compared with the available experimental data. 相似文献
4.
Haes AJ Zhao J Zou S Own CS Marks LD Schatz GC Van Duyne RP 《The journal of physical chemistry. B》2005,109(22):11158-11162
A novel method to produce solution-phase triangular silver nanoparticles is presented. Ag nanoparticles are prepared by nanosphere lithography and are subsequently released into solution. The resulting nanoparticles are asymmetrically functionalized to produce either single isolated nanoparticles or dimer pairs. The structural and optical properties of Ag nanoparticles have been characterized. Mie theory and the Discrete Dipole Approximation method (DDA) have been used to model and interpret the optical properties of the released Ag nanoparticles. 相似文献
5.
Six proficiency tests have now been completed in an ongoing program of the UK Food Analysis Performance Assessment Scheme (FAPAS) for the analysis of acrylamide in a range of food matrixes. Homogeneous test material samples were requested by laboratories throughout the world, with 29 to 45 submitting results for each test. Results were analyzed by appropriate statistical procedures, and z-scores were awarded for reported values. In the absence of both legislation and collaborative trial data, the target standard deviation was derived from the Horwitz equation, although it is acknowledged that there is a need to establish a "fit for purpose" target standard deviation specifically for acrylamide analysis. Participants were encouraged to use the analytical method routinely used in their own laboratory and to provide details of their procedure. Close examination of the data submitted indicates that performance is generally acceptable in terms of accuracy. There is no significant difference between results submitted by gas chromatography and liquid chromatography (GC and LC) methods, and no method dependency on the use of internal standards or sample size. However, choice of extraction solvent may be important, with indications that plain water is an acceptable extraction method. There is evidence from the most recent test that direct (underivatized) GC methodology may present problems, but more data are required and this aspect will be monitored in the continuing proficiency testing program. 相似文献
6.
Grandjean C Boutonnier A Guerreiro C Fournier JM Mulard LA 《The Journal of organic chemistry》2005,70(18):7123-7132
[reaction: see text] The nature of a linker used for preparing glycoconjugate vaccines is of utmost importance as it may lead to immunogenic biomolecules. We report the conjugation of carbohydrate haptens to protein carriers leading to potential vaccines using the traceless Staudinger ligation. The ligation relies on the selective transfer of a phosphane substituent to an azide to form a native amide bond in the final product upon release of an oxidized phosphane byproduct. We designed new phosphino-functionalized cross-linkers suitable for protein carrier derivatization. We evaluated their utility in preparing conjugates using both synthetic and purified bacterial carbohydrates. The use of a borane-protected phosphane which is deprotected at the time of the ligation reaction led to the best results observed thus far in terms of stability toward oxidation and reactivity. 相似文献
7.
Peter LM Riley DJ Tull EJ Wijayantha KG 《Chemical communications (Cambridge, England)》2002,(10):1030-1031
CdS quantum dots can be self-assembled on high surface area nanocrystalline TiO2 electrodes; spectroscopic and photoelectrochemical studies indicate that the size, and hence the absorption edge, of the CdS particles can be controlled; efficient photosensitization of the TiO2 electrode by the Q-particles has been achieved. 相似文献
8.
9.
High nuclearity paramagnetic, spin-coupled transition metal clusters and grids are fascinating chemists and physicists partly because of their structural beauty, and the challenge of creating them, but also because of their novel physical properties. Magnetic interactions between the spin centers are a primary focus. This review will examine a selection of Mn(II) polynuclear grids and clusters, with nuclearities in the range Mn4 to Mn9. Theoretical treatments of the magnetic properties are discussed, and approaches to solving the exchange problem for ‘large’ spin systems related to computational difficulties. A freely available software package (MAGMUN4.1) is presented as a means of dealing simply with spin-coupled clusters in general, and symmetry reduction methods are discussed briefly as a means of dealing with ‘large’ spin systems. 相似文献
10.
R. L. Laurence J. C. Slattery 《Journal of polymer science. Part A, Polymer chemistry》1967,5(6):1327-1340
A study of sorption in a copolymer of ethylene and propylene is presented. Long-time sorption and desorption measurements provided the actual diffusion coefficient in the limit of zero concentration gradient. An analysis of the diffusion–sorption data reinforced the Frisch hypothesis about diffusion in a polymer matrix. The better solvent deforms the microstructure, allowing a more marked dependence of the diffusivity upon concentration. 相似文献