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191.
Hossein Aghabozorg Zohreh Derikvand Marilyn M. Olmstead Jafar Attar Gharamaleki 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(11):m372-m374
For charge balance in the title compound, (H5O2)(C3H7N6)3[Mn(C7H3NO4)2]2(OH)·C7H5NO4·5H2O, it is assumed that the metal atom site is disordered MnII/MnIII, probably due to partial air oxidation of the starting MnII species. The formula unit of the complex contains a hydroxonium hydrate cation, H5O2+, also known as the Zundel cation, with twofold symmetry. The O...O [2.445 (10) Å] and O...H distances [1.24 (2) Å] in the H5O2+ cation indicate a strong hydrogen bond. In addition, there is a hydroxide ion that is disordered with respect to a twofold rotation axis. One of the melaminium groups and the pyridine‐2,6‐dicarboxylate (pydc) ligand also reside on crystallographic twofold axes. The coordination environment of the Mn ion is distorted octahedral. Three intermolecular C=O...π interactions are observed, with distances of 3.536 (4), 3.262 (4) and 3.750 (4) Å between carboxylate C=O groups and the centroids of the aromatic rings of pydc and melaminium. There are numerous O—H...O, O—H...N, N—H...O, N—H...N and C—H...O hydrogen bonds. Most of the components of the structure are organized into one plane. 相似文献
192.
Bergès J Varmenot N Scemama A Abedinzadeh Z Bobrowski K 《The journal of physical chemistry. A》2008,112(30):7015-7026
The mutual location of the sulfur atom and the acetyl group was found to affect significantly the (*)OH-induced oxidation mechanism of the organic sulfides containing either an alpha- or beta-positioned acetyl group. This phenomenon was reflected in formation of different intermediate products observed in pulse radiolysis experiments (Varmenot et al. J. Phys. Chem. A. 2004, 108, 6331-6346). In order to obtain a better support for the earlier interpretation of the experimental data, quantum mechanical calculations were performed using a density functional theory method (DFT-B3LYP) and the ab initio method (M?ller-Plesset perturbation theory MP2) for optimizations and energy calculations of the parent molecules and radicals and radical cations derived from them. In accordance with experiments, it was found that the alpha-positioned acetyl group in S-ethylthioacetate (SETAc) destabilizes hydroxysulfuranyl radicals and monomeric sulfur radical cations. Instead, formation of stable C-centered radicals of the alpha-(alkylthio)alkyl-type was found energetically favorable, the H3C-(*)CH-S-C(=O)CH3 radical, in particular. On the other hand, the beta-positioned acetyl group in S-ethylthioacetone (SETA) does not destabilize hydroxysulfuranyl radicals, monomeric sulfur radical cations, and dimeric sulfur radical cations. Moreover, the alpha-(alkylthio)alkyl radicals of the type -S-(*)CH-C(=O)- were found to be particularly stabilized. The calculated transition states pointed toward the efficient direct conversion of the hydroxysulfuranyl radicals derived from SETAC and SETA radicals into the respective C-centered radicals. This reaction pathway, important in neutral solutions, is responsible for the absence of the dimeric radical cations of SETAc at low and high concentrations and of the dimeric radical cations of SETA at relatively low concentrations of the solute. 相似文献
193.
The chemical composition of the essential oil obtained from the aerial parts of Betonica grandiflora Willd., growing wild in Iran, was analysed by gas chromatography-mass spectrometry for the first time. Overall, 40 volatile components were identified on the basis of their mass spectra characteristics and retention indices in which ledol (21.8%), myrtenyl acetate (21.7%), eudesm-7(11)-en-4-ol (6.5%), trans-caryophyllene (5.5%), α-bisabolol (4.9%) and isolongifolol (4.5%) were the major constituents. Oxygenated sesquiterpenes, monoterpene hydrocarbons and sesquiterpene hydrocarbons were the main groups of compounds with 45.6%, 23.1% and 18.4%, respectively. The oil was moderately active against Bacillus subtilis and Staphylococcus aureus and inactive against Enterococcus faecalis and Klebsiella pneumoniae. 相似文献
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196.
The immobilization of sulfonic acid on the surface of Fe3O4 magnetic nanoparticles (MNPs) as a novel acid nanocatalyst has been successfully reported. The morphological features, thermal stability, magnetic properties, and other physicochemical properties of the prepared superparamagnetic core–shell (Fe3O4@PFBA–Metformin@SO3H) were thoroughly characterized using Fourier transform infrared (FTIR), X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDS), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric analysis–differential thermal analysis (TGA‐DTA), atomic force microscopy (AFM), dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET), and vibrating sample magnetometer (VSM) techniques. It was applied as an efficient and reusable catalyst for the synthesis of 2‐(piperazin‐1‐yl) quinoxaline and benzimidazole derivatives via a one‐pot multiple‐component cascade reaction under green conditions. The results displayed the excellent catalytic activity of Fe3O4@PFBA–metformin@SO3H as an organic–inorganic hybrid nanocatalyst in condensation and multicomponent Mannich‐type reactions. The easy separation, simple workup, excellent stability, and reusability of the nanocatalyst and quantitative yields of products and short reaction time are some outstanding advantages of this protocol. 相似文献
197.
This article investigates an optimal preventive standby activation policy for an -out-of- redundant system. We assume that for such a system, which starts operating at time , a standby component will be activated at either the failure time of the system or at a predetermined time , whichever occurs first. We first obtain the system reliability function under this switching policy as a function of . Then, we investigate the optimal switching time so that the mean time to failure of the system is maximized. The results indicate that the existence of an optimal value of depends on the lifetime of the standby redundancy and its virtual age in the standby state. Some illustrative examples are presented to examine the theoretical outcomes. 相似文献