全文获取类型
收费全文 | 187篇 |
免费 | 5篇 |
国内免费 | 32篇 |
专业分类
化学 | 200篇 |
物理学 | 24篇 |
出版年
2023年 | 4篇 |
2021年 | 7篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2015年 | 11篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2009年 | 12篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 16篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 10篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有224条查询结果,搜索用时 0 毫秒
221.
The structures and the conformational energies of nonprotonated, monoprotonated and diprotonated 1,2-ethanediamine have been
investigated through density functional theory. The relative performance of local and gradient-corrected functionals is discussed.
The existence of hydrogen-bond formation has been determined with electron localisation function calculations. Proton affinities
for nonprotonated and monoprotonated 1,2-ethanediamine have been calculated and are in agreement with experimental data. The
influence of solvation has been accounted for through the self-consistent isodensity polarisable continuum model. The results
for the nonprotonated conformers show that solvation stabilises those conformers which have the lone pair in an antiperiplanar
conformation. Solvation of the monoprotonated conformer stabilises significantly the “anti” conformation, which is unstable
in the gas phase. For the di-protonated species, solvation stabilises slightly the gauche conformer, which is unstable in
the gas phase.
Received: 28 September 1999 / Accepted: 2 May 2000 / Published online: 27 September 2000 相似文献
222.
经不同pH值不同时间酸处理的DNA溶液拉曼光谱分析 总被引:1,自引:1,他引:0
小牛胸腺DNA被配制成pH 3.0,pH 2.0,pH 1.0的酸性溶液,在其进行水合的过程中分别测试了样品经过1,2,12和24 h后的拉曼谱图。实验结果表明,DNA分子内部发生了明显的质子化作用,其拉曼特征频率和强度均发生了不同程度的变化,而且随着不同的pH值和不同时间的酸处理它们的变化程度也不同。在pH 3.0的DNA溶液中仅在1 h处理后的拉曼谱图出现了微弱的A构型DNA的特征峰,溶液中主要以存在B构型为主,并有C构型特征峰的出现且随着水合时间的延长,该峰强增加。在pH 2.0的DNA溶液中仅见B构型和C构型特征峰,随着时间的增加,B型特征峰峰强逐渐减弱且伴随着C型特征峰峰强的增加。在pH 1.0的DNA溶液中B,C构型特征峰基本消失,出现了强度很大的891 cm-1峰以及1 265和1 418 cm-1峰,它们是Z构型的特征峰,891和1 265 cm-1峰随时间的延长峰强增加而1 418 cm-1随时间延长峰强减弱。从pH 3.0开始,随着酸性的增强和时间的延长,DNA溶液质子化程度逐渐加深,直到pH 1.0时其双螺旋结构遭到严重的修饰和发生变化。 相似文献
223.
pH Dependence of Photochemical Kinetics of Thioxanthen-9-one from Nanosecond Time-Resolved Laser Flash Photolysis 下载免费PDF全文
pH dependent fluorescence emission of a thioxanthone-based probe has been reported recently. The potential determinant factors of pH dependence may provide important clues to design novel thioxanthone-based probes in the future. pH dependence of photochemical kinetics of thioxanthone itself was investigated in this work using nanosecond time-resolved laser flash photolysis. The nanosecond time-resolved transient absorption spectra and kinetics of TX in aqueous acetonitrile were recorded, as well as for a model reaction system including TX with diphenylamine (DPA) as a co-initiator. Besides the well-known absorption peak of \begin{document}$ ^3 $\end{document} TX\begin{document}$ ^* $\end{document} , other peaks at 417, 518, 673 and 780 nm, have been reliably attributed to major intermediates in the overall reaction between TX and DPA with photolysis, which has been confirmed to occur along a multistep process. In the strong acidic solution (pH\begin{document}$ \approx $\end{document} 3.0), TX and protonated TX ions (TXH\begin{document}$ ^+ $\end{document} ) coexist due to protonated equilibrium. Consequently, high proton concentration promotes the predominant decay pathway after photolysis from electron transfer to proton affinity. Subsequently, the different primary products, \begin{document}$ ^3 $\end{document} TXH\begin{document}$ ^{+*} $\end{document} or TX\begin{document}$ ^{\bullet-} $\end{document} , proceed different secondary reaction channels. In addition, within the wide pH range from weak acid (pH = 5.0) to alkaline solution (pH = 13.0), the overall reaction mechanism and rates do not show visible changes. 相似文献
224.
Dr. Conor T. Kelly Sean Dunne Dr. Irina A. Kühne Dr. Andrew Barker Dr. Kane Esien Dr. Solveig Felton Dr. Helge Müller-Bunz Dr. Yannick Ortin Prof. Grace G. Morgan 《Angewandte Chemie (International ed. in English)》2023,62(18):e202217388
Reversible proton-induced spin state switching of an FeIII complex in solution is observed at room temperature. A reversible magnetic response was detected in the complex, [FeIII(sal2323)]ClO4 ( 1 ), using Evans’ method 1H NMR spectroscopy which indicated cumulative switching from low-spin to high-spin upon addition of one and two equivalents of acid. Infrared spectroscopy suggests a coordination-induced spin state switching (CISSS) effect, whereby protonation displaces the metal-phenoxo donors. The analogous complex, [FeIII(4-NEt2-sal2323)]ClO4 ( 2 ), with a diethylamino group on the ligand, was used to combine the magnetic change with a colorimetric response. Comparison of the protonation responses of 1 and 2 reveals that the magnetic switching is caused by perturbation of the immediate coordination sphere of the complex. These complexes constitute a new class of analyte sensor which operate by magneto-modulation, and in the case of 2 , also yield a colorimetric response. 相似文献