全文获取类型
收费全文 | 158篇 |
免费 | 11篇 |
专业分类
化学 | 104篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 26篇 |
物理学 | 36篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 7篇 |
2012年 | 7篇 |
2011年 | 11篇 |
2010年 | 7篇 |
2009年 | 3篇 |
2008年 | 12篇 |
2007年 | 2篇 |
2006年 | 5篇 |
2005年 | 11篇 |
2004年 | 1篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有169条查询结果,搜索用时 46 毫秒
101.
Mechanistic Aspects of Aryl–Halide Oxidative Addition,Coordination Chemistry,and Ring‐Walking by Palladium
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Olena V. Zenkina Dr. Ori Gidron Dr. Linda J. W. Shimon Dr. Mark A. Iron Prof. Milko E. van der Boom 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):16113-16125
This contribution describes the reactivity of a zero‐valent palladium phosphine complex with substrates that contain both an aryl halide moiety and an unsaturated carbon–carbon bond. Although η2‐coordination of the metal center to a C?C or C?C unit is kinetically favored, aryl halide bond activation is favored thermodynamically. These quantitative transformations proceed under mild reaction conditions in solution or in the solid state. Kinetic measurements indicate that formation of η2‐coordination complexes are not nonproductive side‐equilibria, but observable (and in several cases even isolated) intermediates en route to aryl halide bond cleavage. At the same time, DFT calculations show that the reaction with palladium may proceed through a dissociation–oxidative addition mechanism rather than through a haptotropic intramolecular process (i.e., ring walking). Furthermore, the transition state involves coordination of a third phosphine to the palladium center, which is lost during the oxidative addition as the C?halide bond is being broken. Interestingly, selective activation of aryl halides has been demonstrated by adding reactive aryl halides to the η2‐coordination complexes. The product distribution can be controlled by the concentration of the reactants and/or the presence of excess phosphine. 相似文献
102.
A rapid, easy, and reliable method was developed for the characterization of jet fuel with minimal sample preparation. A standard solution of 13 aliphatic n-alkanes in hexane was used to evaluate and validate the separation using cold-electron ionization gas chromatography–mass spectrometry. The method was evaluated and validated by the linearity, accuracy, and precision for all analytes. The limits of detection and quantification for each n-alkane were also evaluated. Nine major n-alkanes from n-octane to n-hexadecane were positively identified and quantified in jet fuel due to the enhanced molecular ion in the mass spectra. Major n-alkanes and their corresponding isomers in jet fuel were also identified from the extracted ion chromatograms. n-Undecane, n-dodecane, n-tridecane, and n-tetradecane were present at the highest concentrations in jet fuel at approximately 7% (v/v). The total concentrations of total straight chain alkanes were 34–37% in jet fuel that was comparable with the standard value of 32%. 相似文献
103.
Dennis Sheberla Snehangshu Patra Yair H. Wijsboom Sagar Sharma Yana Sheynin Abd-Elrazek Haj-Yahia Adva Hayoun Barak Ori Gidron Michael Bendikov 《Chemical science》2015,6(1):360-371
Polyfurans have never been established as useful conjugated polymers, as previously they were considered to be inherently unstable and poorly conductive. Here, we show the preparation of stable and conducting polyfuran films by electropolymerization of a series of oligofurans of different chain lengths substituted with alkyl groups. The polyfuran films show good conductivity in the order of 1 S cm–1, good environmental and electrochemical stabilities, very smooth morphologies (roughness 1–5 nm), long effective conjugation lengths, well-defined spectroelectrochemistry and electro-optical switching (in the Vis-NIR region), and have optical band-gaps in the range of 2.2–2.3 eV. A low oxidation potential needed for polymerization of oligofurans (compared to furan) is a key factor in achievement of improved properties of polyfurans reported in this work. DFT calculations and experiments show that polyfurans are much more rigid than polythiophenes, and alkyl substitution does not disturb backbone planarity and conjugation. The obtained properties of polyfuran films are similar or superior to the properties of electrochemically prepared poly(oligothiophene)s under similar conditions. 相似文献
104.
Ori Davidov 《商业与工业应用随机模型》1999,15(1):55-63
There is a growing interest in planning and implementing broad‐scale clinical trials with a focus on prevention and screening. Often, the data‐generating mechanism for such experiments can be viewed as a semi‐Markov process. In this communication, we develop general expressions for the steady‐state probabilities for regenerative semi‐Markov processes. Hence, the probability of being in a certain state at the time of recruitment to a clinical trial can be calculated. An application to breast cancer prevention is demonstrated. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
105.
The reaction of ω‐acylamino ketones with Lawesson's reagent (=2,4‐bis(4‐methoxyphenyl)‐1,3,2,4‐dithiadiphosphetane 2,4‐disulfide; LR ) is described. Treatment of 2‐acylamino ketones 1 (n=0) with LR gave 1,3‐thiazole derivatives 3 in good yields (Scheme 1 and Table 1). The 4H‐1,3‐thiazines 4 were obtained as main products by treatment of 3‐acylamino ketones 2 (n=1) with an equimolar amount of LR , while mainly the corresponding 3‐(thioacyl)amino ketones 5 were isolated when 0.5 equiv. of LR was used. The 3‐acylamino esters 7 also reacted with LR to give the corresponding 3‐(thioacyl)amino esters 8 (Scheme 3 and Table 2). 相似文献
106.
Dr. Anjan Bedi Dr. Ori Gidron 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(13):3279-3285
Acenes that are twisted out of planarity are expected to display chiroptical properties. However, the effect of twisting on the chiroptical properties of acenes has not been investigated computationally or experimentally. Herein, we present a computational investigation of the chiroptical properties of anthracenes to pentacenes, combined with an experimental study using a series of helically locked acenes, twisted to different torsional angles in their enantiopure form. The lowest energy transition, which is relatively weak in acenes, becomes dominant in their circular dichroism spectra upon twisting. We find that the rotational strength of acenes consistently increases with increasing twist. The experimental data obtained from enantiopure tethered twistacenes show the same trend as the calculated result, with a strong Cotton effect and anisotropy factor, rendering twisted acenes as excellent chiroptical materials. 相似文献
107.
Kalid O Mense M Fischman S Shitrit A Bihler H Ben-Zeev E Schutz N Pedemonte N Thomas PJ Bridges RJ Wetmore DR Marantz Y Senderowitz H 《Journal of computer-aided molecular design》2010,24(12):971-991
Folding correctors of F508del-CFTR were discovered by in silico structure-based screening utilizing homology models of CFTR. The intracellular segment of CFTR was modeled and three cavities were identified at inter-domain interfaces: (1) Interface between the two Nucleotide Binding Domains (NBDs); (2) Interface between NBD1 and Intracellular Loop (ICL) 4, in the region of the F508 deletion; (3) multi-domain interface between NBD1:2:ICL1:2:4. We hypothesized that compounds binding at these interfaces may improve the stability of the protein, potentially affecting the folding yield or surface stability. In silico structure-based screening was performed at the putative binding-sites and a total of 496 candidate compounds from all three sites were tested in functional assays. A total of 15 compounds, representing diverse chemotypes, were identified as F508del folding correctors. This corresponds to a 3% hit rate, ~tenfold higher than hit rates obtained in corresponding high-throughput screening campaigns. The same binding sites also yielded potentiators and, most notably, compounds with a dual corrector-potentiator activity (dual-acting). Compounds harboring both activity types may prove to be better leads for the development of CF therapeutics than either pure correctors or pure potentiators. To the best of our knowledge this is the first report of structure-based discovery of CFTR modulators. 相似文献
108.
Andrea Fedorková Renáta Oriňáková Andrej Oriňák Hans-Dieter Wiemhöfer Dušan Kaniansky Martin Winter 《Journal of Solid State Electrochemistry》2010,14(12):2173-2178
In this work, we studied LiFePO4 particles coated with thin films of highly conductive polypyrrole (PPy) and their electrochemical performance in cathode
layers of lithium cells. Carbon-free LiFePO4 particles were synthesized by a solvothermal method. Besides this, a part of the experiments were carried out on commercial
carbon-coated LiFePO4 for comparison. Polypyrrole coated LiFePO4 particles (PPy-LiFePO4) were obtained by a straightforward oxidative polymerization of dissolved pyrrole on LiFePO4 particles dispersed in water. The use of polyethylene glycol (PEG) as an additive during the polymerization was decisive
to achieve high electronic conductivities in the final cathode layers. The carbon-free and carbon-coated LiFePO4 particles were prepared with PPy and with PPy/PEG coating. The obtained PPy-LiFePO4 and PPy/PEG-LiFePO4 powders were characterized by SEM, EIS, cyclic voltammetry, and galvanostatic charge/discharge measurements in lithium-ion
cells with lithium metal as counter and reference electrode. Carbon-free LiFePO4 coated with PPy/PEG hybrid films exhibited very good electrode kinetics and a stable discharge capacity of 156 mAh/g at a
rate of C/10. Impedance measurements showed that the PPy/PEG coating decreases the charge-transfer resistance of the corresponding
LiFePO4 cathode material very effectively, which was attributed to a favorable mixed ionic and electronic conductivity of the PPy/PEG
coatings. 相似文献
109.
Andrea Fedorková Hans-Dieter Wiemhöfer Renáta Oriňáková Andrej Oriňák Dušan Kaniansky 《Solid State Sciences》2010,12(5):924-928
Polypyrrole–FePO4 powder was synthesized by an oxidative polymerization of pyrrole monomer on the surface of FePO4 powder. The polymerization reaction was initiated using hydrogen peroxide in an acidified solution and catalysed with Fe3+. The samples were investigated by light microscopy (LM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). These methods confirmed the presence of polypyrrole on FePO4 particles and its homogeneous distribution in the composite material. To determine the PPy content in the PPy–FePO4 composites a thermogravimetric analysis was used. Cyclic voltammetry curves (CV) were measured and compared in a non-aqueous lithium salt solution for electrodes consisting of pellets made from pure FePO4 and FePO4/PPy. Electrochemical impedance spectroscopy (EIS) showed that coating of PPy significantly decreases the charge transfer resistance of PPy–FePO4 electrodes. 相似文献
110.
C. Masoller M. Oriá 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,58(2):191-196
In this paper we discuss the spectral behavior of monomode semiconductor laser systems whose output amplitude is constant,
but whose frequency may be bistable, multistable, locked or present instabilities. The explored configurations are: (i) a
laser diode (Fabry-Pérot) under orthogonal filtered optical feedback; and (ii) an extended-cavity diode laser with an intracavity
strongly-saturated resonant vapor. Starting from rate equations for the carrier density and for the radiation field oscillating
in the cavity of these systems we describe spectral features which are in very good quantitative agreement with experimental
observations. 相似文献