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21.
Geik Ling Teoh Kong Yong Liew Wan A. K. Mahmood 《Journal of Sol-Gel Science and Technology》2007,44(3):177-186
Abstract Alumina nanofibers of high aspect ratio with surface area of >300 m2 g−1 has been prepared successfully in bulk quantities by the sol–gel method. The synthesis parameters including the binary water–alcohol
solvent system to aluminium isopropoxide ratio, pH, type of solvent and aging temperature affect the uniformity and formation
of nanofibers. It is proposed that alumina nanofibers were formed by the curling of the nanosheets upon condensation after
the hydrolysis. The phase evolution of alumina nanofibers from pseudoboehmite to α phase has been shown by XRD and FTIR. 27Al NMR investigations show that the Al atoms are six and four coordinated. The morphology of the alumina nanofibers does not
change much as the calcination temperature was increased. In addition, the average pore size increases and the BET surface
area decreases as a function of calcination temperature. The thermal behavior of alumina nanofibers was investigated by TGA.
Graphical Abstract
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The reactivity of CeO2 is determined by grain size and oxygen vacancies, which can be achieved by doping elements with less oxidation state into CeO2. In this study nanocrystalline Ca-doped CeO2 sol was synthesized from the reaction of hydrate cerium (III) nitrate and calcium nitrate tetrahydrate in alcohol solution after being calcined at 600?°C. X-ray diffraction as well as selected area electron diffraction gave evidence that the synthesized Ca-doped CeO2 samples were well crystalline and had a cubic fluorite structure. TEM observation revealed that Ca-doped CeO2 was composed by nanoparticles with grain size around 8?nm. The Raman spectrum of pure CeO2 consists of a single triple degenerate F2g model characteristic of the fluorite-like structure. In the Ca-doped CeO2 sample, two additional low-intensity Raman bands were detected, thus confirming the formation of the solid solution. The synthesized nanometric powder is expected to be used in solid oxide fuel cells as well as in the catalytic treatment of automobile exhaust fumes. 相似文献
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Wuen Yew Teoh Hooi Poay Tan Sui Kiong Ling Norhanom Abdul Wahab 《Natural product research》2016,30(4):448-451
Gynura bicolor (Compositae) is a popular vegetable in Asia and believed to confer a wide range of benefits including anti-cancer. Our previous findings showed that the ethyl acetate extract of G. bicolor possessed cytotoxicity and induced apoptotic and necrotic cell death in human colon carcinoma cells (HCT 116). A combination of column chromatography had been used to purify chemical constituents from the ethyl acetate and water extract of G. bicolor leaves. Eight chemical constituents 5-p-trans-coumaroylquinic acid (I), 4-hydroxybenzoic acid (II), rutin (III), kampferol-3-O-rutinoside (IV), 3,5-dicaffeoylquinic acid (V), kampferol-3-O-glucoside (VI), guanosine (VII) and chlorogenic acid (VIII) were isolated from G. bicolor grown in Malaysia. To our best knowledge, all chemical constituents were isolated for the first time from G. bicolor leaves except rutin (III). 3,5-dicaffeoylquinic acid (V), guanosine (VII) and chlorogenic acid (VIII) demonstrated selective cytotoxicity (selective index>3) against HCT 116 cancer cells compared to CCD-18Co human normal colon cells. 相似文献
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Chang-ting Wang Jinfan Chen Jiayuan Xu Fangfang Wei Chi Yung Yam Keith Man-Chung Wong Patrick H.-L. Sit Wey Yang Teoh 《Materials Today Chemistry》2021
The CO2 reduction reaction is an imperative piece of technology that closes the carbon cycle in many critical energy conversion and chemical manufacturing processes. Here, we report two new iridium (III) terpyridine-based photocatalysts capable of selective reduction of CO2 to CO under visible light (λ ≥ 420 nm). The first photocatalyst, [Ir–COOH], was functionalized with the carboxyl group on the phenylpyridine, whereas the second, [Ir-PhCOOH], was attached to a phenyl spacer on the terpyridine. The [Ir-PhCOOH] was characterized by a higher extinction coefficient than [Ir–COOH], thus allowing more absorption of photons. Although both photocatalysts require two-electron activation, the [Ir-PhCOOH] is more readily activated as a result of the more negatively charged Ir center. These photocatalysts show exclusive selectivities in the production of CO. The turnover frequencies for [Ir–COOH] and [Ir-PhCOOH] were 19 and 10 h?1, respectively, under visible light irradiation. The e-e-H-H pathway was identified as the most favorable, consisting of the rate-limiting step in the conversion of 1COOH to 1CO, and where the barrier is significantly lower for [Ir-PhCOOH] than for [Ir–COOH]. 相似文献
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Monte Carlo (MC) simulations were performed for systems of hard oblate spherocylinders with breadth-to-height ratios φ = 0.5–3.5 and packing fractions y = 0.25–0.45 and for Kihara oblate molecule systems of φ = 1 at reduced temperatures T* = 0.75 and 1.0 and y = 0.05–0.45. The compression factors and the dependence of the average correlation functions on the shortest surface-to-surface distance were determined for the case of hard oblate spherocylinders and the compression factors, residual internal energies and average correlation functions for the case of the generalized Kihara molecule systems. In addition, values of the third virial coefficient of the hard oblate spherocylinders were evaluated in the range of φ = 1–3. Results of the MC simulations for the hard oblate spherocylinders compare well with the available data in the literature and theoretical values; thermodynamic functions of the Kihara molecule systems were determined from the second-order perturbation theory. They agree well with our MC values at lower densities and higher reduced temperatures. 相似文献
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Abstract Using ultrapure samples of polyacrylonitrile (PAN) of 485,000 or 150,000 average molecular weight solution cast in dimethylformamide, the dc conductivity ([sgrave]) of pyrolyzed PAN (PANP) films has been studied for pyrolysis temperatures (Tp) of 280-435°C. Conductivity measurements made during pyrolysis indicate the onset of a dramatic increase in [sgrave] for Tp of 390-435°C. Conductivities as high as 5 (ohm-cm)?1 have been observed for Tp < 435°C. This situation contrasts sharply with previous literature which had indicated that a increased uniformly and monotonically with Tp for 200°C < Tp < 900°C and that values of [sgrave] > 1 (ohm-cm)?1 were observed only for Tp > 600°C. Our results indicate that the maximum value of [sgrave] obtained is not a strong function of Tp (390°C < Tp < 435°C) or of molecular weight. However, the rate of increase of [sgrave](t) is strongly dependent on Tp in this range. After pyrolysis, repeated heating and cooling below Tp do not alter [sgrave](T). IR spectra show that the sudden increase in [sgrave] is correlated to the formation of conjugated C=C and C=N bonds. The shape of [sgrave](T) suggests that conduction is probably due to hopping. 相似文献