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排序方式: 共有874条查询结果,搜索用时 10 毫秒
841.
本文利用重合度理论的延拓定理及分析的技巧讨论了具有两个捕获项的比率依赖型食物链系统周期解的存在性问题,得到至少存在四个周期解的充分条件. 相似文献
842.
A novel complex fluorescent probe based on quantum dots and organic dye (QDs-TO) was designed and prepared by incorporating a benzothiazole derivative into QDs-1-(3-amidepropyl)-4-methylquinoline. The complex probe was characterized by FT-IR and TG/DTA. The emission wavelength of QDs-1-(3-amidepropyl)-4-methylquinoline was found at 475 nm and a new peak corresponding to QDs-TO appeared at 550 nm, indicating that benzothiazole derivative can react with QDs-1-(3-amidepropyl)-4-methylquinoline to afford QDs-TO. Furthermore, the emission wavelength of QDs shifted blue while the characteristic peak of TO shifted red during the reaction. This suggests that the probe may be useful for biological labeling in offering an efficient method to study the interrelation between quantum dots and organic dyes. 相似文献
843.
Zaliznyak IA Xu Z Tranquada JM Gu G Tsvelik AM Stone MB 《Physical review letters》2011,107(21):216403
Our inelastic neutron scattering study of spin excitations in iron telluride reveals remarkable thermal evolution of the collective magnetism. In the temperature range relevant for the superconductivity in FeTe(1-x)Se(x) materials, where the local-moment behavior is dominated by liquidlike correlations of emergent spin plaquettes, we observe unusual, marked increase of magnetic fluctuations upon heating. The effective spin per Fe at T ≈ 10 K, in the phase with weak antiferromagnetic order, corresponds to S ≈ 1, consistent with the recent analyses that emphasize importance of Hund's coupling [K. Haule and G. Kotliar, New J. Phys. 11, 025021 (2009).]. However, it grows to S ≈ 3/2 in the high-T disordered phase, suggestive of the Kondo-type behavior, where local magnetic moments are entangled with the itinerant electrons. 相似文献
844.
Jianhui Guo Jingwei Zhang Chuang ZhaoJiwei Zhang Zhijun Zhang 《Applied Surface Science》2011,258(2):791-799
Hydrogenated-carbon nitride (CNx:H) films were synthesized on silicon substrate in a large quantity by the pyrolysis of ethylenediamine in a temperature range of 700-950 °C. The influence of temperature on the morphology, structure, adhesion to substrate, and friction and wear behavior of CNx:H films was investigated. It has been found that CNx:H films obtained at 700 °C and 800 °C are amorphous, and those prepared at 900 °C and 950 °C consist of carbon nitride nanocrystal. Besides, CNx:H film sample obtained at 700 °C has the maximum N content of 9.1 at.% but the poorest adhesion to Si substrate, while the one prepared at 900 °C has the lower N content and the highest adhesion to substrate. As a result, nanocrystalline CNx:H (nc-CNx:H) film synthesized at 900 °C possesses the best wear resistance when slides against stainless steel counterpart. N atom is incorporated into the graphitic network in three different bonding forms, and their relative content is closely related to temperature, corresponding to different adhesion as well as friction and wear behavior of the films obtained at different temperatures. Furthermore, the friction coefficient and antiwear life of as-deposited CNx:H films vary with varying deposition temperature and thickness, and the film with thickness of 1.3 μm, obtained at 900 °C, has the longest antiwear life of over 180,000 s. 相似文献
845.
Because small molecules can be beneficial or toxic in biology and the environment, specific and sensitive detection of small molecules is one of the most important objectives of the scientific community. In this study, new signal amplification assays for detection of small molecules based on Mg2+-dependent DNAzyme were developed. A cleavable DNA substrate containing a ribonucleotide, the ends of which were labeled with black hole quencher (BHQ) and 6-carboxyfluorescein (FAM), was used for fluorescence detection. When the small molecule of interest is added to the assay solution, the Mg2+-dependent DNAzyme is activated, facilitating hybridization between the Mg2+-dependent DNAzyme and the DNA substrate. Binding of the substrate to the DNAzyme structure results in hydrolytic cleavage of the substrate in the presence of Mg2+ ions. The fluorescence signal was amplified by continuous cleavage of the enzyme substrate. Ochratoxin A (OTA) and adenosine triphosphate (ATP) were used as model analytes in these experiments. This method can detect OTA specifically with a detection limit as low as 140 pmol?L?1 and detect ATP specifically with a detection limit as low as 13 nmol?L?1. Moreover, this method is potentially extendable to detection of other small molecules which are able to dissociate the aptamer from the DNAzyme, leading to activation of the DNAzyme. 相似文献
846.
1-[^18F]Fluoro-l-deoxy-2,5-anhydro-D-mannitol (3, ^18F-FDAM) has been synthesized in 6 steps starting from 2,5-anhydro-D-mannitol (2,5-AM) and evaluated as a new radiotracer for PET imaging of MCF-7 breast tumor. The result of PET imaging study showed that 3 displayed a slightly higher uptake by breast tumor in comparison with the normal breast tissue, implying the possibility of development of PET radiotraeers based on targeting fructose transporters. 相似文献
847.
Jinling Wang Hui Zhu Gaojian Chen Zhijun Hu Yuyan Weng Xinbo Wang Weidong Zhang 《Macromolecular rapid communications》2014,35(11):1061-1067
Dopamine‐containing monomers, N‐3,4‐dihydroxybenzenethyl methacrylamide (DMA) and dimethylaminoethyl methacrylate (DMAEMA), are successfully copolymerized in a well‐controlled manner via ambient temperature single‐electron transfer initiation and propagation through the radical addition fragmentation chain transfer (SET‐RAFT) method. The controlled behaviors of the copolymerization are confirmed by the first‐order kinetic plots, the linear relationships between molecular weights, and the monomer conversions while keeping relatively narrow molecular weight distribution (Mw/Mn ≤ 1.45). Moreover, biomimetic self‐assembly of poly(N‐3,4‐dihydroxybenzenethyl methacrylamide‐co‐dimethylaminoethyl methacrylate) PDMA‐co‐PDMAEMA and inorganic particles are employed to prepare tunable honeycomb‐like porous hybrid particles (HPHPs) by regulating the predesigned chemical composition. In addition, the inorganic sacrificial templates are successfully selective etched for the formation of porous organic materials.
848.
This paper addresses the JND(Just Noticeable Difference)change of auditory perception with synchronous visual stimuli.Through psychoacoustics experimentS,loudness JND,subjective duration JND and pitch JND of pure tone were measured in auditory-only mode and visual_auditory mode with different visual stimuli which have different attributes such as color,illumination,quality and moving state.Statistical analyses of the experimental data indicare that,comparing with JND in auditory-only mode,the amount of JND with visual stimuli is often larger.The JND'S average increment of subjective duration,pitch and loudness are 45.1%,14.8%and 12.3%,respectively.The conclusion is that the ability of JNDbased auditory perception often decreases with visual stimuli.The incremental amount of JND is afiected bv the attributes of visual stimuli.If the visual stimuli make subjects feel more comfortable,the JND of auditory perception will change smaller. 相似文献
849.
850.
Fuyuan Zhang Zhijun Zhang Hongying Li Mengyu Zhu Shuo Wang 《Journal of separation science》2014,37(23):3579-3586
In the study, four different semiempirical algorithms, modified neglect of diatomic overlap, a reparameterization of Austin Model 1, complete neglect of differential overlap and typed neglect of differential overlap, have been applied for the energy optimization of template, monomer, and template‐monomer complexes of imprinted polymers. For phosmet‐, estrone‐, and metolcarb‐imprinted polymers, the binding energies of template‐monomer complexes were calculated and the docking configures were assessed in different molar ratio of template/monomer. It was found that two algorithms were not suitable for calculating the binding energy in template‐monomers complex system. For the other algorithms, the obtained optimum molar ratio of template and monomers were consistent with the experimental results. Therefore, two algorithms have been selected and applied for the preparation of enrofloxacin‐imprinted polymers. Meanwhile using a different molar ratio of template and monomer, we prepared imprinted polymers and nonimprinted polymers, and evaluated the adsorption to template. It was verified that the experimental results were in good agreement with the modeling results. As a result, the semiempirical algorithm had certain feasibility in designing the preparation of imprinted polymers. 相似文献