全文获取类型
收费全文 | 303篇 |
免费 | 30篇 |
国内免费 | 28篇 |
专业分类
化学 | 168篇 |
晶体学 | 5篇 |
力学 | 16篇 |
综合类 | 2篇 |
数学 | 69篇 |
物理学 | 101篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 31篇 |
2012年 | 23篇 |
2011年 | 21篇 |
2010年 | 11篇 |
2009年 | 19篇 |
2008年 | 20篇 |
2007年 | 30篇 |
2006年 | 18篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有361条查询结果,搜索用时 896 毫秒
331.
Interactions between Si ad-dimers on Si (001) have been studied by molecular dynamics simulations using the Stillinger–Weber potential. The interactions determine the formation of clusters from diffusing dimers. We show different pathways for the formation of multiple-dimer clusters and propose a new tetramer (TCC) structure formation by two diffusing dimers interacting. This tetramer structure has been found to be energetically stable with respect to isolated ad-dimers. Moreover, their local bonding configuration is very similar to the B-type step edge which is known to be the favoured adsorption site for epitaxial growth. The proposed tetramer may play a crucial role as the nucleus of the new epitaxial layer on Si (001). 相似文献
332.
Conformational features of palytoxin and acetylated palytoxin were investigated by detailed analyses of NOESY spectra. The conformational differences between palytoxin and acetylated palytoxin may account for the difference in the assembly state of palytoxin, which exists as an associated dimer, and the acetylated derivative, which exists as a monomer in aqueous solution. Two palytoxin units in the dimer may come in contact with each other at the hydrophobic region (C21-40) and the region around two conjugated double bonds (C60-84). The amino group of palytoxin is important for biological activities via Na/K ATPase, but it was not found to be involved in the contact faces of the two palytoxin units. This information should aid in revealing how palytoxin interacts with Na/K ATPase. 相似文献
333.
Ben Young 《Journal of Combinatorial Theory, Series A》2009,116(2):334-350
We verify a recent conjecture of Kenyon/Szendr?i by computing the generating function for pyramid partitions. Pyramid partitions are closely related to Aztec Diamonds; their generating function turns out to be the partition function for the Donaldson-Thomas theory of a non-commutative resolution of the conifold singularity {x1x2−x3x4=0}⊂C4. The proof does not require algebraic geometry; it uses a modified version of the domino shuffling algorithm of Elkies, Kuperberg, Larsen and Propp [Noam Elkies, Greg Kuperberg, Michael Larsen, James Propp, Alternating sign matrices and domino tilings. II, J. Algebraic Combin. 1 (3) (1992) 219-234]. 相似文献
334.
甲醇缩合生成二甲醚的质谱和量子化学研究 总被引:1,自引:0,他引:1
利用质谱分析结果结合量子化学abinitio方法,研究甲醇缩合脱水的反应过程.研究表明,在气相中,甲醇分子主要以二聚体和多聚体的形式存在,据此提出甲醇脱水反应的原始反应物是甲醇二聚体,而不是单个甲醇分子.研究了气相甲醇二聚体、过渡态的能量和结构、甲醇脱水生成二甲醚反应的可能反应途径和反应势垒,对甲醇缩合脱水生成二甲醚的反应性及其影响因素作了讨论. 相似文献
335.
The cluster state is an indispensable resource for one-way quantum computing (1WQC). We propose a practical scheme for constructing cluster states among nuclear spins in nitrogen-vacancy defect centres (NV centres) in different diamonds. The entanglement of nuclear spins within an NV centre is made by hyperfine coupling via electron spin, and the entanglement between remote NV centres is accomplished using the parity projection of emitted photons. We discus the possibility to build large-scale nuclear-spin cluster states with diamonds. 相似文献
336.
M. Ramos Silva A. J. F. N. Sobral J. A. Silva A. C. Santos S. M. Melo A. Matos Beja 《Journal of chemical crystallography》2007,37(10):695-698
Abstract A new substituted pyrrole, a precursor of meso-free-porphyrins, has been synthesised and characterised by single-crystal X-ray
diffraction: monoclinic, P21/c with a = 14.607(9) ?, b = 5.136(2) ?, c = 25.832(17) ?, β = 108.14(5)°, Mr = 349.41, V = 1841.6(18) ?3, Z = 4. The molecules are assembled in centrosymmetric dimers via strong N–H...O hydrogen bonds. The dimers are gathered
into chains via C–H...π intermolecular interactions.
Graphical abstract The molecules in 4-benzyl-5-methoxymethyl-3-methyl-1H-pyrrole-2-carboxylic acid benzyl ester are joined in dimmers by strong
hydrogen bonds. The dimmers are aggregated in chains running along the b axis through C-H...?€ intermoleculear interactions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
337.
密度泛函理论研究4-巯基吡啶及其二聚体的结构与振动光谱 总被引:1,自引:1,他引:0
利用B3LYP/6-311++G(d, p)方法对4-巯基吡啶及其二聚体的结构和振动光谱进行了计算,对形成二聚体后在结构和光谱上的变化及作用力做了初步分析,并对光谱做了指认。结果显示,4-巯基吡啶(4MPY)的稳定结构为Cs对称性,其二聚体是由SH基团中H原子与另一个环上的N原子靠分子间氢键形成的;相对于单体来说,二聚体形成后在结构与光谱上均有一定的变化。 相似文献
338.
339.
Ab initio (HF/3-21G*), DFT (B3LYP with basis sets 6-31G*, 6-311+G* and 6-311+G(2d)) and, in some cases, MP2/6-31G* calculations, were done on cyclic dimers, trimers, etc. and on acyclic oligomers (with OH and H on the ends) of sulfur monoxide and sulfur dioxide. The four cyclic (SO)n molecules were (S–O)2 (1,3,2,4-dioxadithietane, 1a), (S–O)3 (1,3,5,2,4,6-trioxatrithiane, 2a), (S(=O))4 (tetrathietane 1,2,3,4-tetraoxide, 1b), and (S(=O))6 (hexathiane 1,2,3,4,5,6-hexaoxide, 2b). The four cyclic (SO2)n molecules were the dioxide of 1a (1,3,2,4-dioxadithietane 2,4-dioxide, 1c), the trioxide of 2a (1,3,5,2,4,6-trioxatrithiane 2,4,6-trioxide, 2c), the tetraoxide of 1b (tetrathietane 1,1,2,2,3,3,4,4-octaoxide, 1d) and the hexaoxide of 2b (hexathiane 1,1,2,2,3,3,4,4,5,5,6,6-dodecaoxide, 2d). The 16 acyclic molecules (oxides of disulfane, trisulfane, etc. and oxides of oxadisulfane, dioxatrisulfane, etc.) were (–S–O–)n, (–S(=O)–)n, (–S(=O)O–)n, and (–S(=O)2–)n, with n from 2 to 5 and HO, H at the ends. Most of these species are relative minima on the B3LYP/6-31G* potential energy surface. In energy content, the SO dimer, etc. lie below, and the SO2 dimer, etc. above, their SOx components, at all the electron-correlated levels. 相似文献
340.
In this paper we study Banach spaces that admit weighted Chebyshev centres for finite sets. Such spaces have been extensively studied recently by Veselý using the approach of finitely intersecting balls. Following his approach we exhibit large classes of Banach spaces that have this property. Certain stability results for spaces of vector valued continuous and Bochner integrable functions are also obtained. 相似文献