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211.
The protonation of pyridine in water clusters as a function of the number of water molecules was theoretically analyzed as a prototypical case for the protonation of organic bases. We determined the variation of structural, bonding, and energetic properties on protonation, as well as the stabilization of the ionic species formed. Thus, we used supermolecular models in which pyridine interacts with clusters of up to five water molecules. For each complex, we determined the most stable unprotonated and protonated structures from a simulated annealing at the semi ab initio level. The structures were optimized at the B3LYP/cc-pVDZ level. We found that the hydroxyl group formed on protonation of pyridine abstracts a proton from the ortho-carbon atom of the pyridine ring. The "atoms in molecules" theory showed that this C-H group loses its covalent character. However, starting with clusters of four water molecules, the C-H bond recovers its covalent nature. This effect is associated with the presence of more than one ring between the water molecules and pyridine. These rings stabilize, by delocalization, the negative charge on the hydroxyl oxygen atom. Considering the protonation energy, we find that the protonated forms are increasingly stabilized with increasing size of the water cluster. When zero-point energy is included, the variation follows closely an exponential decrease with increasing number of water molecules. Analysis of the vibrational modes for the strongest bands in the IR spectra of the complexes suggests that the protonation of pyridine occurs by concerted proton transfers among the different water rings in the structure. Symmetric water stretching was found to be responsible for hydrogen transfer from the water molecule to the pyridine nitrogen atom. 相似文献
212.
The present work reports on key factors that influence the degree of order in anodic TiO2 nanotube layers. We show that the anodization voltage and the Ti purity are of crucial importance for the ideality of self‐organization within the nanotube layers and that repeated anodization can significantly improve hexagonal ordering. Optimizing each factor significantly reduces the variation in the average pore diameter and strongly reduces the areal density of polygon ordering/packing errors. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
213.
Wisbey D Feng D Bremer MT Borca CN Caruso AN Silvernail CM Belot J Vescovo E Ranno L Dowben PA 《Journal of the American Chemical Society》2007,129(19):6249-6254
The metal-organic molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (Cu(CNdpm)2) (C24H36N2O4Cu, Cu(II)) is a copper spin-1/2 system with a magnetic moment of 1.05 +/- 0.04 muB/molecule, slightly smaller than the 1.215+/-0.02 muB/molecule for the larger size copper spin-1/2 system C36H48N4O4Cu.C4H8O (bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) 4,4'-bipyridylethene-THF). There is generally good agreement between photoemission from vapor-deposited thin films of the C24H36N2O4Cu on Cu(111) and Co(111) and model calculations. Although this molecule is expected to have a gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, the molecule remains surprisingly well screened in the photoemission final state. 相似文献
214.
Palladium complexes incorporating ligands based on a 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantanyl scaffold were used to catalyze the arylation of ethyl cyanoacetate, malononitrile, and various ketones. The products from these reactions can be elaborated to substituted β-arylethylamines and used in microwave-assisted Pictet-Spengler reactions. The protocol developed is suitable for the synthesis of libraries of substituted isoquinolines. 相似文献
215.
Builes S Roussel T Ghimbeu CM Parmentier J Gadiou R Vix-Guterl C Vega LF 《Physical chemistry chemical physics : PCCP》2011,13(35):16063-16070
In this study we attempt to investigate the potential use of two zeolite template carbon (ZTC), EMT-ZTC and FAU-ZTC, to capture CO(2) at room temperature. We report their high pressure CO(2) adsorption isotherms (273 K) that show for FAU-ZTC the highest carbon capture capacity among published carbonaceous materials and competitive data with the best organic and inorganic adsorbing frameworks ever-known (zeolites and mesoporous silicas, COFs and MOFs). The importance of these results is discussed in light of mitigation of CO(2) emissions. In addition to these new experimental CO(2) adsorption data, we also present new insight into the adsorption process of the two structures by Monte Carlo simulations: we propose that two separate effects are responsible for the apparent similarity of the adsorption behaviour of the two structures: (i) pore blocking occurring on EMT-ZTC, and (ii) the change of the carbon polarizability due to the extreme curvature of FAU-ZTC. 相似文献
216.
Victor Bulacovschi Camelia Mihǎilescu Silvia Ioan Bogdan C. Simionescu 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7):613-622
The kinetics of phase-transfer-agent-aided free radical polymerization of methyl methacrylate was investigated by using K2S2O8 as the initiator and cetyltrimethyl ammonium chloride (Arquad) as the phase transfer agent. The rate of polymerization was found to be proportional to [M]1.23[K2S2O8]0.8 [Arquad]0.25 and almost independent of the volume of water (V w)/volume of organic solvent (V o) (benzene) ratio for V w/V o < 0.33. A reaction mechanism is proposed. 相似文献
217.
Monica Dan Adriana Vulcu Sebastian A. Porav Cristian Leostean Gheorghe Borodi Oana Cadar Camelia Berghian-Grosan 《Molecules (Basel, Switzerland)》2021,26(13)
Four N-doped graphene materials with a nitrogen content ranging from 8.34 to 13.1 wt.% are prepared by the ball milling method. This method represents an eco-friendly mechanochemical process that can be easily adapted for industrial-scale productivity and allows both the exfoliation of graphite and the synthesis of large quantities of functionalized graphene. These materials are characterized by transmission and scanning electron microscopy, thermogravimetry measurements, X-ray powder diffraction, X-ray photoelectron and Raman spectroscopy, and then, are tested towards the oxygen reduction reaction by cyclic voltammetry and rotating disk electrode methods. Their responses towards ORR are analysed in correlation with their properties and use for the best ORR catalyst identification. However, even though the mechanochemical procedure and the characterization techniques are clean and green methods (i.e., water is the only solvent used for these syntheses and investigations), they are time consuming and, generally, a low number of materials can be prepared, characterized and tested. In order to eliminate some of these limitations, the use of regression learner and reverse engineering methods are proposed for facilitating the optimization of the synthesis conditions and the materials’ design. Thus, the machine learning algorithms are applied to data containing the synthesis parameters, the results obtained from different characterization techniques and the materials response towards ORR to quickly provide predictions that allow the best synthesis conditions or the best electrocatalysts’ identification. 相似文献
218.
A TPD-MS study of the adsorption of ethanol/cyclohexane mixture on activated carbons 总被引:1,自引:0,他引:1
Camelia Matei Ghimbeu Roger Gadiou Joseph Dentzer Lo?c Vidal Cathie Vix-Guterl 《Adsorption》2011,17(1):227-233
The adsorption of ethanol/cyclohexane binary mixtures on different types of activated carbons was studied in this work by
temperature programmed desorption coupled with mass spectroscopy (TPD-MS). The texture, morphology and surface chemistry of
the carbons were evaluated by N2 adsorption, scanning electron microscopy (SEM) and TPD-MS techniques. The ethanol and cyclohexane TPD-MS desorption profiles
showed that specific interactions between the carbon material and the adsorbate are involved during the adsorption. Most of
the activated carbons adsorb strongly ethanol on the surface, leading to desorption temperatures above 100 °C. Only one carbon
exhibits an affinity for cyclohexane. These observations were correlated to the different surface chemistry of the materials. 相似文献
219.
Florea Dumitrascu Ana-Maria Udrea Mino R. Caira Diana Camelia Nuta Carmen Limban Mariana Carmen Chifiriuc Marcela Popa Coralia Bleotu Anamaria Hanganu Denisa Dumitrescu Speranta Avram 《Molecules (Basel, Switzerland)》2022,27(9)
The efficient regioselective bromination and iodination of the nonsteroidal anti-inflammatory drug (NSAID) carprofen were achieved by using bromine and iodine monochloride in glacial acetic acid. The novel halogenated carprofen derivatives were functionalized at the carboxylic group by esterification. The regioselectivity of the halogenation reaction was evidenced by NMR spectroscopy and confirmed by X-ray analysis. The compounds were screened for their in vitro antibacterial activity against planktonic cells and also for their anti-biofilm effect, using Gram-positive bacteria (Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212) and Gram-negative bacteria (Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853). The cytotoxic activity of the novel compounds was tested against HeLa cells. The pharmacokinetic and pharmacodynamic profiles of carprofen derivatives, as well as their toxicity, were established by in silico analyses. 相似文献