全文获取类型
收费全文 | 114篇 |
免费 | 6篇 |
专业分类
化学 | 84篇 |
力学 | 1篇 |
数学 | 7篇 |
物理学 | 28篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 8篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 5篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有120条查询结果,搜索用时 171 毫秒
111.
112.
113.
Wiebke Unkrig Fu Zhe Razan Tamim Friederike Oesten Dr. Daniel Kratzert Prof. Dr. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(2):758-765
The syntheses of the homoleptic bis(arene) niobium cations [Nb(arene)2]+ (arene = C6H3Me3, C6H5Me) with 16 valence electrons and heteroleptic arene-carbonyl cations [(CO)Nb(arene)2]+ (arene = C6H3Me3, C6H5Me) and [(arene)M(CO)4]+ (arene = C6H3Me3, C6H6) obeying 18 valence electrons are described. Stabilization of these complexes was achieved by using the weakly coordinating anions [Al(ORF)4]− or [F{Al(ORF)3}2]− (RF = C(CF3)3). The limits of two synthesis routes starting from neutral Nb(arene)2 (arene = C6H3Me3, C6H5Me) or [NEt4][M(CO)6] (M = Nb, Ta) were investigated. All compounds were analyzed by single crystal X-ray determination, vibrational and NMR spectroscopy. DFT calculations were executed to support the experimental data. 相似文献
114.
Müller C Wald J Hoth-Hannig W Umanskaya N Scholz D Hannig M Ziegler C 《Analytical and bioanalytical chemistry》2011,400(3):679-689
Protein adsorption is a field of huge interest in a number of application fields. Information on protein adhesion is accessible
by a variety of methods. However, the results obtained are significantly influenced by the applied technique. The objective
of this work was to understand the role of adhesion forces (obtained by scanning force spectroscopy, SFS) in the process of
protein adsorption and desorption. In SFS, the protein is forced to and retracted from the surface, even under unfavorable
conditions, in contrast to the natural situation. Furthermore, adhesion forces are correlated with adhesion energies, neglecting
the entropic part in the Gibbs enthalpy. In this context, dynamic contact angle (DCA) measurements were performed to identify
the potential of this method to complement SFS data. In DCA measurements, the protein diffuses voluntarily to the surface
and information on surface coverage and reversibility of adsorption is obtained, including entropic effects (conformational
changes and hydrophobic effect). It could be shown that the surface coverage (by DCA) of bovine serum albumin on dental materials
correlates well with the adhesion forces (by SFS) if no hydrophobic surface is involved. On those, the entropic hydrophobic
effect plays a major role. As a second task, the reversibility of the protein adsorption, i.e., the voluntary desorption as
studied by DCA, was compared to the adhesion forces. Here, a correlation between low adhesion forces and good reversibility
could be found as long as no covalent bonds were involved. The comparative study of DCA and SFS, thus, leads to a more detailed
picture of the complete adsorption/desorption cycle. 相似文献
115.
The mechanism of hydrogen recombination on a Pd(111) single crystal and well‐defined Pd nanoparticles is studied using pulsed multi‐molecular beam techniques and the H2/D2 isotope exchange reaction. The focus of this study is to obtain a microscopic understanding of the role of subsurface hydrogen in enhancing the associative desorption of molecular hydrogen. HD production from H2 and D2 over Pd is investigated using pulsed molecular beams, and the temperature dependence and reaction orders are obtained for the rate of HD production under various reaction conditions designed to modulate the amount of subsurface hydrogen present. The experimental data are compared to the results of kinetic modeling based on different mechanisms for hydrogen recombination. We found that under conditions where virtually no subsurface hydrogen species are present, the HD formation rate can be described exceptionally well by a classic Langmuir–Hinshelwood model. However, this model completely fails to reproduce the experimentally observed high HD formation rates and the reaction orders under reaction conditions where subsurface hydrogen is present. To analyze this phenomenon, we develop two kinetic models that account for the role of subsurface hydrogen. First, we investigate the possibility of a change in the reaction mechanism, where recombination of one subsurface and one surface hydrogen species (known as a breakthrough mechanism) becomes dominant when subsurface hydrogen is present. Second, we investigate the possibility of the modified Langmuir–Hinshelwood mechanism with subsurface hydrogen lowering the activation energy for recombination of two hydrogen species adsorbed on the surface. We show that the experimental reaction kinetics can be well described by both kinetic models based on non‐Langmuir–Hinshelwood‐type mechanisms. 相似文献
116.
Menche D Arikan F Perlova O Horstmann N Ahlbrecht W Wenzel SC Jansen R Irschik H Müller R 《Journal of the American Chemical Society》2008,130(43):14234-14243
A potent novel analogue of the natural macrolide antibiotic etnangien, a structurally unique RNA polymerase inhibitor from myxobacteria, is reported. It may be readily obtained from fermentation broths of Sorangium cellulosum and shows high antibiotic activity, comparable to that of etnangien. However, it is much more readily available than the notoriously labile authentic natural product itself. Importantly, it is stable under neutral conditions, allowing for elaborate NMR measurements for assignment of the 12 hydroxyl- and methyl-bearing stereogenic centers. The full absolute and relative stereochemistries of these complex polyketides were determined by a combination of extensive high-field NMR studies, including J-based configuration analysis, molecular modeling, and synthetic derivatization in combination with an innovative method based on biosynthetic studies of this polyketide which is also presented here. A first look into the solution conformation and 3D structure of these promising macrolide antibiotics is reported. Finally, the complete biosynthetic gene cluster was analyzed in detail, revealing a highly unusual and complex trans-AT type polyketide biosynthesis, which does not follow colinearity rules, most likely performs programmed iteration as well as module skipping, and exhibits HMG-CoA box-directed methylation. 相似文献
117.
The complexes of uranium(VI) with salicylhydroxamate, benzohydroxamate, and benzoate have been investigated in a combined computational and experimental study using density functional theory methods and extended X-ray absorption fine structure spectroscopy, respectively. The calculated molecular structures, relative stabilities, as well as excitation spectra from time-dependent density functional theory calculations are in good agreement with experimental data. Furthermore, these calculations allow the identification of the coordinating atoms in the uranium(VI)-salicylhydroxamate complex, i.e. salicylhydroxamate binds to the uranyl ion via the hydroxamic acid oxygen atoms and not via the phenolic oxygen and the nitrogen atom. Carefully addressing solvation effects has been found to be necessary to bring in line computational and experimental structures, as well as excitation spectra. 相似文献
118.
The overall rate constant for the radical-radical reaction C2H5 + HO2 --> products has been determined at room temperature by means of time-resolved mass spectrometry using a laser photolysis/flow reactor combination. Excimer laser photolysis of gas mixtures containing ethane, hydrogen peroxide, and oxalyl chloride was employed to generate controlled concentrations of C2H5 and HO2 radicals by the fast H abstraction reactions of the primary radicals Cl and OH with C2H6 and H2O2, respectively. By careful adjustments of the radical precursor concentrations, the title reaction could be measured under almost pseudo-first-order conditions with the concentration of HO2 in large excess over that of C2H5. From detailed numerical simulations of the measured concentration-time profiles of C2H5 and HO2, the overall rate constant for the reaction was found to be k1(293 K) = (3.1 +/- 1.0) x 10(13) cm3 mol(-1) s(-1). C2H5O could be confirmed as a direct reaction product. 相似文献
119.
120.
Wiebke Wunderlich Nick Benfaremo Markus Klapper Klaus Müllen 《Macromolecular rapid communications》1996,17(6):433-438
Bulk polymerizations of methyl methacrylate (MMA) at 60°C initiated with 2,2′-azoisobutyronitrile are influenced by the presence of an organic π-donor such as tetrathiafulvalene (TTF). Upon addition of TTF, the ratio of weight- to number-average molecular weights M̄w/M̄n are significantly reduced and the thermal stability of the poly(methyl methacrylate) samples is increased. Kinetic investigations indicate that TTF acts as a retarder on the polymerization mechanism. 相似文献