全文获取类型
收费全文 | 1176篇 |
免费 | 53篇 |
国内免费 | 12篇 |
专业分类
化学 | 763篇 |
晶体学 | 3篇 |
力学 | 60篇 |
数学 | 233篇 |
物理学 | 182篇 |
出版年
2023年 | 14篇 |
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 27篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 18篇 |
2016年 | 46篇 |
2015年 | 46篇 |
2014年 | 31篇 |
2013年 | 54篇 |
2012年 | 77篇 |
2011年 | 90篇 |
2010年 | 55篇 |
2009年 | 50篇 |
2008年 | 66篇 |
2007年 | 75篇 |
2006年 | 70篇 |
2005年 | 73篇 |
2004年 | 75篇 |
2003年 | 48篇 |
2002年 | 31篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 16篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1909年 | 4篇 |
1908年 | 3篇 |
1899年 | 2篇 |
排序方式: 共有1241条查询结果,搜索用时 15 毫秒
121.
Lise-Lotte Gundersen Carl Henrik G?rbitz Liina Neier Heidi Roggen Toomas Tamm 《Theoretical chemistry accounts》2011,129(3-5):349-358
Density Functional Theory calculations of nine 2-substituted N-methoxy-9-methyl-9H-purin-6-amines in the amino and imino tautomeric forms, as well as the complexes of the same with dimethyl sulfoxide (DMSO), were performed using two functionals (BP86 and B3LYP) and two basis sets (SV(P) and def2-TZVP). Solid-state structures of two of the compounds were obtained from single-crystal X-ray diffraction techniques. It was found that the inclusion of both an explicit hydrogen-bonding partner (DMSO) as well as continuum solvation effects, and vibrational corrections to energy, were necessary for qualitative and reasonable quantitative agreement with observed tautomeric ratios. The solution-optimized geometries and X-ray structures were found to be in good agreement. NMR spectroscopy confirmed the dependence of the tautomeric ratios on hydrogen-bonding abilities, in addition to the dipole moment of the solvent in question. Natural Bond Orbital charges on the N-7 nitrogen, as well as the tautomeric ratios were used to explain the observed reactivities of the compounds toward N-7 alkylation. 相似文献
122.
Henrik Stetkær 《Semigroup Forum》2001,63(3):466-468
No abstract.
November 15, 1999 相似文献
123.
124.
125.
126.
Simon W. de Leeuw John W. Perram Henrik G. Petersen 《Journal of statistical physics》1990,61(5-6):1203-1222
We derive expressions for the conjugate momenta and the Hamiltonian for classical dynamical systems subject to holonomic constraints. We give an algorithm for correcting deviations of the constraints arising in numerical solution of the equations of motion. We obtain an explicit expression for the momentum integral for constrained systems. 相似文献
127.
128.
129.
The process of "evolutionary diffusion," i.e., reproduction with local mutation but without selection in a biological population, resembles standard diffusion in many ways. However, evolutionary diffusion allows the formation of localized peaks that undergo drift, even in the infinite population limit. We relate a microscopic evolution model to a stochastic model which we solve fully. This allows us to understand the large population limit, relates evolution to diffusion, and shows that independent local mutations act as a diffusion of interacting particles taking larger steps. 相似文献
130.
Dr. Vitthal N. Yadav Prof. Angiolina Comotti Prof. Piero Sozzani Dr. Silvia Bracco Prof. Tore Bonge‐Hansen Dr. Martin Hennum Prof. Carl Henrik Görbitz 《Angewandte Chemie (International ed. in English)》2015,54(52):15684-15688
Dipeptides with two hydrophobic side chains have proved to be an exceptional source of microporous organic materials, but since previous structures were limited to the incorporation of only proteinogenic residues, their full potential as adsorbents has remained unexplored. Single‐crystal XRD data for ten new compounds with non‐proteinogenic L ‐2‐aminobutanoic acid and/or L ‐2‐amino‐pentanoic acid are presented. The gas‐phase accessibility of their crystal pores, with cross‐sections of 2.3 to 5.1 Å, was monitored by CO2 and CH4 adsorption isotherms. Included CO2 was also detected spectroscopically by 2D MAS NMR. An extensive conformational analysis reveals that the use of linear rather than branched side chains (such as L ‐valine and L ‐isoleucine) affords peptides with a greater degree of conformational freedom and yields more‐flexible channel surfaces that may easily adapt to a series of potential guest molecules. 相似文献