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排序方式: 共有451条查询结果,搜索用时 593 毫秒
61.
Scientometrics - In this paper we extend the perspective of the scholarly impact from the traditional citations to other forms of scientific communication among scholars in the mirror of the PlumX... 相似文献
62.
63.
Rolf Trettin Klaus Freyer Gerhard Strauch Hanns-Christian Treutler Walter Gläßer 《Grundwasser》1999,4(1):3-10
Environmental isotopes such as 3 H, 2 H, 18 O, 34 S and 222 Rn were applied to characterize relationships within and between ground and surface waters in two developing mining lakes. Using a two-component-model the portion of saline waters ascending through the lake bottom into the lakes was estimated. Similarly the contribution of pyritic sulphur participating in the lake sulfate has been assessed. Locally, the lakes are hydrochemically stratified. Mixing processes are reflected by all isotopes mentioned above. δ 13 C DIC values of the most mineralized lake water did not correspond with those of deep groundwater from Zechstein strata revailing additional effects such as CO 2 production. 222 Rn was checked for assessing groundwater fluxes through the lake bottom. 222 Rn was found in lake water regions with elevated salt contens but being always in an equilibrium with radium (excepting the sediment-lake water interface). Thus, radium must be taken in consideration in order to interprete radon values in saline groundwaters. 相似文献
64.
Roger Gläser Ruifeng Li Michael Hunger Stefan Ernst Jens Weitkamp 《Catalysis Letters》1998,50(3-4):141-148
The synthesis of the high-silica zeolite NU-87 and its physicochemical characterization are reported. The catalytic properties
of zeolite HNU-87 were investigated in the conversion of 1- and 2-methylnaphthalene. Both isomerization to the corresponding
methylnaphthalene and transalkylation to naphthalene and dimethylnaphthalenes are observed. The influence of reaction temperature
and the modified residence time on the product distributions is reported and discussed in terms of shape selectivity effects
in the peculiar pore system of NU-87. For comparison, typical results obained with zeolite HMCM-22, which possesses a similar
pore architecture, are also included. The results of methylnaphthalene conversion over HNU-87 are compared to those obtained
in the alkylation of naphthalene with methanol on the same zeolite catalyst.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
65.
66.
Estimation of water absorbed by expanding clay aggregates during structural lightweight concrete production 总被引:1,自引:1,他引:0
The estimation of water absorption in aggregates is still one of the major challenges related to the production of structural lightweight aggregate concrete (SLWAC). At present these predictions are only based on common practice and a more soundly based approach is required. Aggregate absorption is mainly affected by its microstructure, surface characteristics, percentage of broken particles, initial water content and characteristics of the surrounding mortar. These are the key parameters taken into account in this paper, where the absorption of different types of Iberian aggregates with varying initial water content is analysed in detail. Based on experimental tests, and by introducing new parameters which take into account the microstructure and water content of the aggregates, a new procedure for predicting absorption by aggregates in concrete is suggested. This procedure will make it possible to more accurately specify the amount of mixing water to be used in SLWAC production, and it is almost independent of the type of aggregate. Therefore, the proposed method should be easily extended to other types of aggregate. Finally, the proposed method was checked experimentally by producing several concrete mixtures, and the results were promising. 相似文献
67.
Paulo Autran Leite Lima Cristiane Xavier Resende Glória Dulce de Almeida Soares Karine Anselme Luís Eduardo Almeida 《Materials science & engineering. C, Materials for biological applications》2013,33(6):3389-3395
This work describes the preparation and characterization of porous 3D-scaffolds based on chitosan (CHI), chitosan/silk fibroin (CHI/SF) and chitosan/silk fibroin/hydroxyapatite (CHI/SF/HA) by freeze drying. The biomaterials were characterized by X-ray diffraction, attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy and energy dispersive spectroscopy. In addition, studies of porosity, pore size, contact angle and biological response of SaOs-2osteoblastic cells were performed. The CHI scaffolds have a porosity of 94.2 ± 0.9%, which is statistically higher than the one presented by CHI/SF/HA scaffolds, 89.7 ± 2.6%. Although all scaffolds were able to promote adhesion, growth and maintenance of osteogenic differentiation of SaOs-2 cells, the new 3D-scaffold based on CHI/SF/HA showed a significantly higher cell growth at 7 days and 21 days and the level of alkaline phosphatase at 14 and 21 days was statistically superior compared to other tested materials. 相似文献
68.
Helmut Glünder 《Journal of Modern Optics》2013,60(10):1365-1374
Abstract It is shown that a rotating sinusoidal grating is a useful sweep signal for the analysis of the temporal behaviour of linear imaging systems. For a suitably chosen angular velocity and spatial frequency, the spatial a.c. component of the grating appears modulated in one dimension at the output of the system. The profile of this modulation is the temporal transfer function (TTF) of the system. A quantitative analysis of this effect is presented, and results from experiments with a photographic camera are shown. It is proposed to use this method in the field of vision research since it is presently the only way to demonstrate the complex-valued TTF of the visual system for suprathreshold grating stimuli. The main consequence of the first psycho-physical investigations was the discovery of a phase reversal at the origin of the TTF of the human visual system for gratings of low spatial frequency. 相似文献
69.
The contribution deals with the comparison of microwave heating and conventional oil bath heating. Silicon dioxide nanoparticles were grafted with MPTMS under acid conditions. Those particles contain a polysiloxane shell with physically adsorbed and chemically bound fractions which can be separated by Soxhlet extraction. The resulting fractions were analyzed with TGA and MALDI‐TOF MS; one to determine the amount of physically adsorbed and chemically bound fractions and the other to get deeper insight into the polysiloxane structures. Furthermore, it was our aim to clarify which fraction can be visualized using MALDI‐TOF MS. Our results show that the ratio of chemically bound MPTMS is higher when using microwave heating, but the same structures in the physically adsorbed fraction were built in both cases.
70.
Wolfgang Glänzel 《Scientometrics》2008,77(1):187-196
In this paper some new fields of application of Hirsch-related statistics are presented. Furthermore, so far unrevealed properties
of the h-index are analysed in the context of rank-frequency and extreme-value statistics. 相似文献