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排序方式: 共有106条查询结果,搜索用时 15 毫秒
31.
In this paper we report a versatile and effective strategy to attain strong surface-enhanced infrared absorption by employing a sandwich system consisting of metal island films and self-assembled monolayers (SAMs) of 4-pyridinethiol. The observed larger enhancement factor stems from coupling of the electric fields induced by excitation of the surface plasmon resonance of the overlayer and underlayer Au island films, and from enhanced chemical interactions of the Au island films and the pyridine molecule in the sandwiched structures, compared to the corresponding SAM-Au configuration. Copyright 2001 Academic Press. 相似文献
32.
Ito H Imae T Nakamura T Sugiura M Oshibe Y 《Journal of colloid and interface science》2004,276(2):290-298
The self-association of the fluorinated diblock copolymer, poly(methacrylic acid)-block-poly(perfluorooctylethyl methacrylate) (PMAA-b-PFMA), in water has been investigated by light scattering, potentiometry, atomic force microscopy, and transmission electron microscopy. The size of the polymer micelles increases, as the degree of dissociation of the PMAA blocks increases. Since the charged PMAA block takes the stretched structure, PMAA-b-PFMA can easily form large micelles due to the low steric hindrance of PMAA blocks. Addition of NaCl shielded electrostatic repulsion in the PMAA chain and induced the formation of smaller micelles than water without NaCl did because of the bulky structure of the PMAA chain in the shell of the micelles. The micelle of PMAA-b-PFMA in ethanol is larger than that of poly(t-butyl methacrylate)-block-poly(perfluorooctylethyl methacrylate) (PtBMA-b-PFMA) in ethanol as a result of the higher steric hindrance of the PtBMA block. The dimensions of the core and shell of the micelles were estimated. The micelle of PMAA-b-PFMA in water possesses a rather thick shell and a large volume per molecule, consistent with the extended PMAA chain. On the other hand, the shell of the micelle in an ethanol solution of PtBMA-b-PFMA is thin but has a large surface area. Facts are consistent with the shrunk structure of the PtBMA block in poor solvent. 相似文献
33.
Selective uptake of various dyes into an aggregate of amphiphilic copolymer consisting of a hydrophilic linear polyelectrolyte block and hydrophobic block carrying pendant dendritic moiety has been investigated in water. The copolymer associated into an aggregate with a hydrophobic interior at concentrations above 0.2 mg cm(-3). The uptake (23 and 36 molecules per aggregate, respectively) of pyrene and Oil Yellow in an aggregate was one order higher than that of benzo[a]pyrene and SudanIII. The hydrophobic dyes are always doped in the interior of the aggregate, but the difference in uptake among dyes may depend on their structure. Even if a large number of guest molecules was doped into the interior of an aggregate, the size of the sphere-like aggregate was conserved. It is suggested that guest molecules are encapsulated into the persisting cavity within and between hydrophobic dendron moieties in an aggregate. Structure-selective uptake reported in this investigation is a unique character of an aggregate of copolymer with dendron moiety because the dendron moiety offers a large void for doping. 相似文献
34.
Interplay between nonlinearity,scan speed,damping, and electronics in frequency modulation atomic-force microscopy 总被引:1,自引:0,他引:1
Numerical simulations of the frequency modulation atomic force microscope, including the whole dynamical regulation by the electronics, show that the cantilever dynamics is conditionally stable and that there is a direct link between the frequency shift and the conservative tip-sample interaction. However, a soft coupling between the electronics and the nonlinearity of the interaction may significantly affect the damping. A resonance between the scan speed and the response time of the system can provide a simple explanation for the spatial shift and contrast inversion between topographical and damping images, and for the extreme sensitivity of the damping to a tip change. 相似文献
35.
Kana Tamano Toshiyuki Tanaka Kunio Awaga Toyoko Imae Shin‐ichi Yusa Yoshihiko Shimada 《Macromolecular rapid communications》2006,27(20):1764-1768
Summary: A water‐insoluble organic 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical is solubilized in aqueous solutions of aggregates of amphiphilic block copolymers with hydrophobic dendritic pendants. The number (100–200) of DPPH molecules solubilized in an aggregate, which is evaluated from UV‐visible absorption spectra, is in agreement with that of the DPPH radicals determined from electron paramagnetic resonance (EPR) spectroscopy. The DPPH radicals are stably solubilized without decomposition in the polymer aggregates. The radicals exhibit a single‐line EPR absorption, which is narrowed by the interspin interaction, and indicates the assembly formation of DPPH radicals in polymer aggregates. These results suggest the effective utilization of the DPPH radical as a spin‐probe indicator in aqueous solutions.
36.
Non-noble metal-based bifunctional electrocatalysts may be a promising new resource for electrocatalytic water-splitting devices. In this work, transition metal (cobalt)-incorporated graphitic carbon nitride was synthesized and fabricated in electrodes for use as bifunctional catalysts. The optimum catalytic activity of this bifunctional material for the hydrogen evolution reaction (HER), which benefitted at a cobalt content of 10.6 wt%, was promoted by the highest surface area and conductivity. The activity achieved a minimum overpotential of ~85 mV at 10 mA/cm2 and a Tafel slope of 44.2 mV/dec in an acidic electrolyte. These values of the HER were close to those of a benchmark catalyst (platinum on carbon paper electrode). Moreover, the kinetics evaluation at the optimum catalyst ensured the catalyst flows (Volmer–Heyrovsky mechanism), indicating that the adsorption step is rate-determining for the HER. The activity for the oxygen evolution reaction (OER) indicated an overpotential of ~530 mV at 10 mAcm−2 and a Tafel slope of 193.3 mV/dec, which were slightly less or nearly the same as those of the benchmark catalyst. Stability tests using long-term potential cycles confirmed the high durability of the catalyst for both HER and OER. Moreover, the optimal bifunctional catalyst achieved a current density of 10 mAcm−2 at a cell voltage of 1.84 V, which was slightly less than that of the benchmark catalyst (1.98 V). Thus, this research reveals that the present bifunctional, non-noble metallic electrocatalyst is adequate for use as a water-splitting technology in acidic media. 相似文献
37.
Yutaka Ohsedo Ichiro Imae Yasuhiko Shirota 《Journal of Polymer Science.Polymer Physics》2003,41(21):2471-2484
A new family of methacrylate polymers containing pendant terthiophene, quaterthiophene, quinquethiophene, and sexithiophene was synthesized by the radical polymerization of the corresponding methacrylate monomers, and the electrochemical and electrochromic properties were investigated. The anodic oxidation of these polymers in the presence of tetra‐n‐butylammonium perchlorate as a supporting electrolyte produced radical‐cation salts of pendant oligothiophenes with ClO as a dopant. The electrochemically oxidized polymers had partially crosslinked structures resulting from the coupling reaction of pendant oligothiophene radical cations, the extent of crosslinking significantly decreasing with the increasing conjugation length of the pendant oligothiophenes. Comparative spectroelectrochemical studies of the monomers in solution and the polymers as solid films showed that π‐dimer formation of oligothiophene radical cations took place more readily for the polymer films than for the monomers in solution. This new family of methacrylate polymers containing pendant oligothiophenes constitutes a new class of potential electrochromic materials, undergoing reversible, clear color changes on electrochemical oxidation and reduction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2471–2484, 2003 相似文献
38.
Fabrication and self-assembly of hydrophobic gold nanorods 总被引:1,自引:0,他引:1
Hydrophobic gold nanorods were fabricated from hydrophilic gold nanorods coated with hexadecyltrimethylammonium bromide by treating with mercaptopropyltrimethoxysilane (MPS) and subsequently octadecyltrimethoxysilane (ODS). The fabrication of the hydrophobic shell went through the process of (1) binding MPS onto the nanorods, (2) hydrolysis of methoxysilanes, and (3) immobilization of ODS by dehydration condensation. The 2- or 3-D ordered structures of hydrophobic nanorods were self-assembled by the evaporation of solvent on a substrate. The aspects of 2-D assemblies were dependent on the concentration of the nanorods, as was seen in transmission electron microscopic images. At a low concentration, the nanorods assembled parallel to the substrate, whereas they stood on the substrate at a high concentration. On the other hand, in a solid of the gold nanorods, the formation of the 3-D assembly was confirmed by small-angle X-ray scattering. The assembly consisted of hexagonal arrays of the gold nanorods and their lamellar accumulation. 相似文献
39.
Mitamura K Imae T Tian S Knoll W 《Langmuir : the ACS journal of surfaces and colloids》2008,24(6):2266-2270
Thin functional organic films on a gold substrate were fabricated by adsorbing tetrakis(carboxyphenyl)porphyrin (TCPP) on a spacer layer, which was prepared by the layer-by-layer adsorption of a dendrimer and a linear polymer. The thickness and photoluminescence of the films were investigated by surface plasmon resonance and surface plasmon fluorescence techniques, respectively. TCPP adsorbed on the spacer layer in aqueous solutions of different ionic strengths resulted in a thick TCPP adlayer at high ionic strength and a shrunk spacer layer at low ionic strength. The fluorescence was quenched at high ionic strength but could be observed at low ionic strength. The effects are explained by the states of dye aggregation. This study shows the control of energy transfer from a metal surface to a dye layer by changing the dye adlayer. It can contribute to the development of molecular devices involving energy-transfer systems. 相似文献
40.
Angular dependence of light scattering from aqueous NaCl solutions of dimethyloleylamine oxide has been measured in the presence of NaCl from 5×10–4 M to 10–1 M at 25 °C. The molecular weight and radius of gyration of micelles increase with increasing micelle concentration and reach constant values, suggesting occurrence of the sphere-rod equilibrium dependent on the micelle concentration. With increasing NaCl concentration, rodlike micelles are larger in molecular weight and become longer. The micelles formed at NaCl concentrations higher than 10–3 M are nearly monodisperse when the micelle concentration is high.Rodlike micelles of dimethyloleylamine oxide in 10–2 M and 5 × 10–2 M NaCl solutions have molecular weights of 4,760,000 and 6,900,000, respectively, and behave as semi-flexible or wormlike chains. In 5×10–2 M NaCl they have a contour length of 5750 Å and a persistence length of 1760 Å. These micelle parameters correspond to the end-to-end distance of 3780 Å and the number of Kuhn's statistical segments of 1.64. The large aggregation number of the rodlike micelles is induced by the strong cohesion of long hydrocarbon chains in solution, and their flexibility is caused by the hydration of amine oxide groups. 相似文献