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331.
Marcela Rizzotto Sandra Signorella Maria Inés Frascaroli Verónica Daier Luis F. Sala 《Journal of carbohydrate chemistry》2013,32(1):45-51
Abstract A rate law for the oxidation of 2-deoxy-d-glucose (2DG) by Cr(VI) in perchloric acid has been derived. This rate law corresponds to the reaction leading to the formation of 2-deoxy-d-gluconic acid (2DGA). No cleavage to carbon dioxide takes place when a twenty-fold or higher excess of aldose over Cr(VI) is employed. Kinetic constants are interpreted in terms of the absence of an hydroxyl group at C-2 on the stability of the chromic ester formed in the first reaction step. Free radicals formed during the reaction convert Cr(VI) to Cr(V). The latter species was detected by EPR measurements. 相似文献
332.
Irene Prat Dr. Anna Company Verònica Postils Dr. Xavi Ribas Prof. Lawrence Que Jr. Dr. Josep M. Luis Dr. Miquel Costas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(21):6724-6738
A detailed mechanistic study of the hydroxylation of alkane C? H bonds using H2O2 by a family of mononuclear non heme iron catalysts with the formula [FeII(CF3SO3)2(L)] is described, in which L is a tetradentate ligand containing a triazacyclononane tripod and a pyridine ring bearing different substituents at the α and γ positions, which tune the electronic or steric properties of the corresponding iron complexes. Two inequivalent cis‐labile exchangeable sites, occupied by triflate ions, complete the octahedral iron coordination sphere. The C? H hydroxylation mediated by this family of complexes takes place with retention of configuration. Oxygen atoms from water are incorporated into hydroxylated products and the extent of this incorporation depends in a systematic manner on the nature of the catalyst, and the substrate. Mechanistic probes and isotopic analyses, in combination with detailed density functional theory (DFT) calculations, provide strong evidence that C? H hydroxylation is performed by highly electrophilic [FeV(O)(OH)L] species through a concerted asynchronous mechanism, involving homolytic breakage of the C? H bond, followed by rebound of the hydroxyl ligand. The [FeV(O)(OH)L] species can exist in two tautomeric forms, differing in the position of oxo and hydroxide ligands. Isotopic‐labeling analysis shows that the relative reactivities of the two tautomeric forms are sensitively affected by the α substituent of the pyridine, and this reactivity behavior is rationalized by computational methods. 相似文献
333.
In this paper, we prove the maximal regularity property of an abstract fractional differential equation with finite delay on periodic Besov and Triebel–Lizorkin spaces and use these results to guarantee the existence and uniqueness of periodic solution of a neutral fractional differential equation with finite delay. The main tool used to achieve our goal is an operator-valued version of Miklhin’s Fourier multiplier theorem and fixed-point argument. 相似文献
334.
Patricio Hermosilla-Ibáñez Juan Costamagna Andrés Vega Verónica Paredes-García Eric Le Fur 《Journal of Coordination Chemistry》2014,67(23-24):3940-3952
In the present work, the synthesis and structural characterization of two new polyoxovanadoborate (BVO) frameworks, based on the [V12B18O60H6]10? polyanion, are reported, K(H3O)(enH2)4[V12B18O60H6]·9.60H2O (1) and Li8(NH4)2[V12B18O60H6]·8.02H2O (2). Both compounds are obtained in a mixed valence ratio of 10VIV/2VV. Framework 1 is characterized by potassium ions coordinated by the BVO cluster and ethylenediammonium and hydronium ions as charge-compensating agents. In framework 2, the BVO clusters are coordinating lithium ions and the charge is compensated by ammonium ions. Using the SHAPE 2.1 program, it was possible to calculate the best geometry for the existing lithium and potassium ions. For 2, the lithium ions are five-coordinate, best described by a square pyramid (SPY-5), while the coordination sphere around the potassium ions in 1 are six-coordinate. For 1, the coordination sphere of the existing potassium ions in the framework can be described as trigonal prism (TPR-6). Calculations were also done for a previously reported cluster [Na10[(H2O)V12B18O60H6]·18H2O] (3), in which the sodium ions are six-coordinate but in two different geometries, these being octahedral and TPR-6. The influence of the interactions of the alkali ions with the [V12B18O60H6]10? polyanion, on the vanadate and borate absorption bands observed in the infrared spectra, is discussed. 相似文献
335.
A method to extract PAHs from sediments is carried out using aqueous solutions containing aggregates of the ionic liquid (IL) 1-hexadecyl-3-methylimidazolium bromide (HDMIm-Br) as the extracting medium. Focused microwave-assisted extraction has been used to accelerate the extraction step, followed by HPLC with fluorescence detection without clean-up steps to remove the IL prior to injection. The method has been applied to certified reference sediment BCR-535 and marine sediments from Tenerife (Canary Islands) with successful results. The optimized method gave average absolute recoveries of 91.1% for six of the seven PAHs studied, with relative standard deviations lower than 10.4%. The overall method is characterized for presenting low extraction times (6min), low amounts of the sediment (0.1g), low amounts of IL (45mM), and low volumes of aqueous extractant solution (9mL). The use of small amounts of both IL and aqueous extractant solution allows the method to be considered environmental-friendly. 相似文献
336.
Dr. Haijun Peng Senhe Huang Dr. Verónica Montes-García Dr. Dawid Pakulski Dr. Haipeng Guo Dr. Fanny Richard Prof. Xiaodong Zhuang Prof. Paolo Samorì Dr. Artur Ciesielski 《Angewandte Chemie (International ed. in English)》2023,62(10):e202216136
Two-dimensional covalent organic frameworks (COFs) have emerged as promising materials for energy storage applications exhibiting enhanced electrochemical performance. While most of the reported organic cathode materials for zinc-ion batteries use carbonyl groups as electrochemically-active sites, their high hydrophilicity in aqueous electrolytes represents a critical drawback. Herein, we report a novel and structurally robust olefin-linked COF-TMT-BT synthesized via the aldol condensation between 2,4,6-trimethyl-1,3,5-triazine (TMT) and 4,4′-(benzothiadiazole-4,7-diyl)dibenzaldehyde (BT), where benzothiadiazole units are explored as novel electrochemically-active groups. Our COF-TMT-BT exhibits an outstanding Zn2+ storage capability, delivering a state-of-the-art capacity of 283.5 mAh g−1 at 0.1 A g−1. Computational and experimental analyses reveal that the charge-storage mechanism in COF-TMT-BT electrodes is based on the supramolecularly engineered and reversible Zn2+ coordination by the benzothiadiazole units. 相似文献
337.
Céderic Ver Elst Dr. Robby Vroemans Mathias Bal Dr. Sergey Sergeyev Dr. Carl Mensch Prof. Dr. Bert U. W. Maes 《Angewandte Chemie (International ed. in English)》2023,62(46):e202309597
Levulinic acid is a key biorenewable platform molecule. Its current chemical production from sugars is plagued by limited yields, char formation and difficult separations. An alternative and selective route starting from muconic acid via simple heating in water at high temperature (180 °C) has been developed. Muconic acid can be obtained from sugars or catechol fermentation. Chemical oxidation of catechol is another possibility which advantageously can also be applied on substituted catechols, hereby providing substituted muconic acids. When applying the disclosed hydrothermal protocol on these substrates hitherto unknown substituted levulinic acids were accessed. In particular, 3-propyllevulinic acid has been synthesized from 4-propylcatechol, prepared from pine wood. This propylated derivative has been used for the synthesis of a 3-propyllevulinate diester, i.e. butane-1,4-diyl bis(4-oxo-3-propylpentanoate), via esterification with 1,4-butanediol. The diester showed superior performance as plasticizer in comparison to the corresponding levulinate diester in both PVC (polyvinyl chloride) and PLA (polylactic acid). It plasticizes equally effective as the notorious commercial phthalate-based benchmark DEHP (di-2-ethylhexyl phthalate) in PVC. 相似文献
338.
Electrochemical oxidation of Paracetamol (PAR), Acetylsalicylic acid (ASA) and Caffeine (CAF) was investigated employing square wave stripping voltammetry (SWSV) using screen–printed carbon electrodes (SPCE). Determinations were performed in 0.1 mol L−1 BR buffer (pH 2.0) without accumulation step. SWV were obtained by scanning the potential from 0.00 to 1.40 V employing a scan increment of 4 mV, pulse amplitude 25 mV and frequency of 25 Hz. PAR, ASA and CAF presents oxidation signals at 0.45, 1.03 and 1.32 V. The detection limits were 1.2, 1.7 and 1.7 mg L−1, respectively. The method was applied in the PAR-ASA-CAF determination on pharmaceutical formulations. 相似文献
339.
Amelia Bilbao-Terol Mar Arenas-Parra Verónica Cañal-Fernández Mariano Jiménez 《The Journal of the Operational Research Society》2016,67(10):1259-1273
Sustainable and responsible (SR) investors have to address two criteria types: both financial ones and those pertaining to sustainability and social responsibility. We present a comfortable tool for SR investors that allow them to express their preferences at two levels: first, by comparing criteria of the same nature, and second, via the comparison between the two superior level criteria (the financial and the SR objectives). Owing to the difficulty involved in determining a precise preference between the conflicting objectives, we address this by goal programming with fuzzy hierarchies (GPFH) modelling. This methodology is a modification of the lexicographic GP approach whereby the relative importance relations among the criteria are modelled by fuzzy relations. The proposed sequential handling for the SR portfolios selection provides information to the investors on the best result they can achieve in regard to their goals. An application to a set of UK-SR mutual funds is presented. 相似文献
340.
López-Darias J Pino V Ayala JH González V Afonso AM 《Analytical and bioanalytical chemistry》2008,391(3):735-744
An environmentally friendly method to extract endocrine-disrupting phenols (EDPs) from seawaters was realized using nonionic
surfactant mixtures and micelle-mediated extractions. The preconcentration step was achieved directly in the seawater matrix,
and was followed by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection without any clean-up steps
to remove the surfactant mixture prior to injection. Various nonionic surfactant mixtures were used, and polyoxyethylene-10-laurylether
(POLE) with polyoxyethylene-4-laurylether (Brij 30) was found to be the best to work with. Method optimization involved maximizing
the preconcentration factor using the studied mixtures. The proposed method gave extraction recoveries ranging from 83.3 to
114.4% for an EDP spiking level of 46.7 μg L−1, and from 63.4 to 112.4% for a spiking level of 4.7 μg L−1 for EDPs studied in real seawater matrices, with relative standard deviations of <12.1%. The detection limits of the method
varied from 0.18 μg L−1 for bisphenol A (BPA) to 1.17 μg L−1 for 4-cumylphenol (4-CP). The method was applied to seawaters from the Canary Islands with successful results.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献