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71.
72.
M. Tagami M. Sumida Ch. Krauns Y. Yamada T. Umeda Y. Shiohara 《Physica C: Superconductivity and its Applications》1995,250(3-4):240-246
Recently, we succeeded in fabricating single crystals of PrBa2Cu3O7−δ by a modified top seeded crystal pulling method called the SRL-CP (Solute Rich Liquid-Crystal Pulling) method. Y2O3 and MgO polycrystalline crucibles and a MgO single crystal crucible were used to grow the single crystals. The crystal growth temperature was set in the range of 968°C to 972°C. The grown crystals were identified as PrBa2Cu3O7−δ by X-ray diffraction. In the case of using Y2O3 crucibles the composition of the grown crystals was YxPr1−xBa2Cu3O7−δ (0.48 < x < 0.57) and in the case of using MgO crucibles a relatively small amount of Mg contamination to the grown crystals occurred at a typical concentration of approximately 1 at.% of the sum of cations. According to the crystal growth model of the SRL-CP method [1–5], a maximum growth rate of 1.7 × 10−5 cm/s was calculated with the aid of the phase diagram studies we reported earlier [6]. This value is reasonably in agreement with the experimental results. 相似文献
73.
Understanding of rhenium behavior in seawater gives an idea of the possible behavior of 99Tc, which is an important radionuclide in long-term dose assessment for humans. In this study, Re determinations in manganese
nodules, which have high Mn content, were carried out. Since Mn, Tc and Re are the member of group 7A in the periodic table,
accumulation of Tc and Re in the nodules was also expected. After alkaline fusions and chemical separations, Re concentrations
in manganese nodules were measured by ICP-MS. Total chemical recovery of the method for Re was 95% and the detection limit
was 4.5 ng/kg. Re concentrations in the manganese nodules were very low, <4.5–49 ng/kg. The results indicated that the nodules
had been mineralized under oxic conditions. This type of nodule could not be an important geochemical reservoir of Re and
99Tc in the sea. 相似文献
74.
For99Tc separation from environmental samples, liquid-liquid extraction, ion-exchange chromatography and coprecipitation, have been described. Although these methods are removing matrix elements, some combinations of them is necessary for purification and concentration of Tc. Besides, the procedures are time-consuming and generally a week or more is needed to purify Tc in the samples. In this study, a novel extraction chromatographic resin for the separation and preconcentration of Tc from several kinds of solutions is described. The material is shown to retain Tc efficiently and selectively from these solutions. Sorbed Tc is readily recovered using 5 ml of 12M HNO3 and the recoveries with95mTc are more than 97% for all sample solutions. 相似文献
75.
Analysis of the artificial radionuclide 99Tc in environmental samples requires a chemical separation due to its low concentration, and therefore the use of a chemical yield tracer is peremptory. From a practical viewpoint, Re can be used for this purpose, due to its chemical similarities with Tc. Thus, the use of a radioactive tracer for Tc recovery calculation can be avoided. However, results from a recent intercomparison exercise showed that using of Re as a chemical yield tracer appears to underestimate the Tc concentration relative to the result obtained with isotopes of Tc. In the present work, the methodology used to design a simple separation method for the measurement of 99Tc in environmental samples is described. Tc recovery is estimated throughout the Re recovery calculation by the isotope dilution technique coupled with ICP-MS (ID-ICP-MS) technique. For chemical separation, a chromatographic resin is used. Interfering elements are removed using a resin washing step carefully designed to avoid any element fractionation between Re and Tc; the care taken in this step is of major importance to assure the equivalence of the chemical recoveries for both elements. Agreement is tested using five replicates of five seaweed samples. The average recoveries for 95mTc and Re were 93±6 and 95±7%, respectively, those are within the uncertainty intervals for each other. The results explained here demonstrate the possibility of applying Re chemical recoveries to calculate the Tc concentrations with the advantage of not introducing systematic errors. 相似文献
76.
In order to compare the soil-to-plant transfer factors (TFs) of fallout 137Cs and those of native stable 133Cs, concentrations of these isotopes were determined in various crops and the associated soils collected throughout Japan.
The results showed that TF-137Cs was 11 times higher than TF-native 133Cs for brown rice, while those values were almost the same for leafy vegetables. Possibly, fallout 137Cs would be more mobile and more easily adsorbed by plants than native 133Cs in the soil because a part of the 133Cs is in a soil structure where it is hard to replace with 137Cs. However, 137Cs and native 133Cs have reached an approximately isotopic equilibrium in the bioavailable fraction in the soils, therefore, the TF-native
133Cs can be used for long-term transfer of 137Cs in the environment. 相似文献
77.
H. Seyama Y. Soma M. Soma S. Takao T. Sakurai S. Tagami 《Fresenius' Journal of Analytical Chemistry》1991,341(10):619-624
Summary Secondary ion mass spectrometry (SIMS) was applied for the analysis of asbestos fibers. It was possible to identify the asbestos fibers by the pattern of the positive secondary ion mass spectrum. The image of the asbestos fibers was measurable by use of any major positive secondary ions. The smallest size of detectable asbestos fiber was about 5 and 1 m in length and diameter, respectively. Using a fast atom bombardment (FAB) source instead of primary ion beam, asbestos fibers collected on a membrane filter were easily detected without any pretreatment. 相似文献
78.
79.
Numerical simulations based on three-dimensional discrete element model (DEM) are conducted for mono-disperse, binary and ternary systems of particles in a fluidized bed. Fluid drag force acting on each particle depending on its size and relative velocity is assigned. The drag coefficient corresponding to Ergun’s correlation is applied to the system of fluidized bed with particle size ratios of 1:1 for the mono-disperse system, 1:1.2, 1:1.4 and 1:2 for the binary system and 1:1.33:2 for the ternary system b... 相似文献
80.
This paper investigates theoretically the electronic transmission
spectra of the three terminal pyrene molecular bridge and the
quantum current distribution on each bond by the tight-binding model
based on nonequilibrium Green's function and the quantum current
density approach, in which one π molecular orbital is taken
into account per carbon atom when the energy levels and HOMO-LUMO
gap are obtained. The transmission spectra show that the electronic
transmission of the three terminal pyrene molecular bridge depends
obviously on the incident electronic energy and the pyrene
eigenenergy. The symmetrical and oscillation properties of the
transmission spectra are illustrated. A novel plus-minus energy
switching function is found. The quantum current distribution shows
that the loop currents inside the pyrene are induced, and some bond
currents are much larger than the input and the output currents. The
reasons why the loop currents and the larger bond currents are
induced are the phase difference of the atomic orbits and the
degeneracy of the molecular orbits. The calculations illustrate that
the quantum current distributions are in good agreement with
Kirchhoff quantum current conservation law. 相似文献