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排序方式: 共有8511条查询结果,搜索用时 281 毫秒
851.
852.
讨论了具有垂直传染且总人口在变化的连续预防接种SIRS传染病模型,给出了基本再生数R_0的表达式,并利用广义Bendixson-Dulac函数方法证明了无病平衡点和地方病平衡点的全局稳定性. 相似文献
853.
Shi Z Liu J Lin T Xia F Liu PN Lin N 《Journal of the American Chemical Society》2011,133(16):6150-6153
We investigated the thermodynamic processes of two-dimensional (2D) metallo-supramolecular self-assembly at molecular resolution using scanning tunneling microscopy and variable-temperature low-energy electron diffraction. On a Au(111) substrate, tripyridyl ligands coordinated with Cu in a twofold Cu-pyridyl binding mode or with Fe in a threefold Fe-pyridyl binding mode, forming a 2D open network structure in each case. The network structures exhibited remarkable thermal stability (600 K for the Cu-coordinated network and 680 K for the Fe-coordinated network). The Fe-pyridyl binding was selected thermodynamically as well as kinetically in self-assembly involving both modes. The selectivity can be effectively suppressed in a specifically designed self-assembly route. 相似文献
854.
We report the rational synthesis of α-FeOOH (goethite) nanowires following a dislocation-driven mechanism by utilizing a continuous-flow reactor and chemical equilibria to maintain constant low supersaturations. The existence of axial screw dislocations and the associated Eshelby twist in the nanowire product were confirmed using bright-/dark-field transmission electron microscopy imaging and twist contour analysis. The α-FeOOH nanowires can be readily converted into semiconducting single-crystal but porous α-Fe(2)O(3) (hematite) nanowires via topotactic transformation. Our results indicate that, with proper experimental design, many more useful materials can be grown in one-dimensional morphologies in aqueous solutions via the dislocation-driven mechanism. 相似文献
855.
The essential oils extracted from Coriandrum sativum L. were analyzed by GC-MS coupled with chemometric resolution methods. Through the chemometric resolution methods, peak clusters were uniquely resolved into the pure chromatographic profiles and mass spectra of each component. Qualitative analysis was performed by comparing the pure mass spectra with those in the NIST 05 mass spectral library. Quantitative analysis was performed using the total volume integration method. A total of 118 constituents were detected, of which 104 were identified, accounting for 97.27% of the total content. The results indicate that GC-MS combined with chemometric resolution methods can greatly enhance the capability of separation and the reliability of qualitative and quantitative results. The combined method is an economical and accurate approach for the rapid analysis of the complex essential oil samples in Coriandrum sativum L. 相似文献
856.
A fast and direct competitive biomimetic enzyme‐linked immunosorbent assay (BELISA) method was developed for the determination of methimazole (MMZ) in urine sample based on a molecularly imprinted film as an artificial antibody. This is the first example to monitor methimazole with a direct competitive biomimetic enzyme‐linked immunosorbent assay (BELISA) method. The imprinted film was directly synthesized on the well surface of MaxiSorp polystyrene 96‐well plate and characterized. The results showed that it exhibited an antibody‐like binding ability, rapid adsorption speed, high stability, which was particularly advantageous and suitable for BELISA development. The BELISA method established in this paper had a higher selectivity for MMZ than for the structurally related compounds and the IC50 (calculated as the concentration giving 50% inhibition of color development) and the detection limit values under optimized experimental conditions were 70 ± 4 μg L‐1 and 0.9 ± 0.04 μg L‐1, respectively. The method was applied to the determination of MMZ in spiked urine sample with excellent recoveries ranging from 90% to 95%, and the imprinted film was able to be reused for 20 times without loss of sensitivity. The results obtained by BELISA correlated well with that obtained by the high performance liquid chromatography (HPLC) method. 相似文献
857.
Jing Ning Ying‐Tong Di Shi‐Fei Li Zhao‐Liang Geng Hong‐Ping He Yue‐Hu Wang Yuan‐Yuan Wang Yan Li Shun‐Lin Li Xiao‐Jiang Hao 《Helvetica chimica acta》2011,94(3):376-381
A phytochemical investigation of Toona ciliata var. ciliata afforded three new polyynes, 1 – 3 . Their structures were elucidated on the basis of spectroscopic analysis and chemical methods. Only compound 3 exhibited potent cytotoxicity against the HL‐60 cell line with an IC50 value of 6.7±0.27 μM . 相似文献
858.
Yu‐Bo Liu Jiang‐Jiang Qin Xiang‐Rong Cheng Jia‐Xian Zhu Fei Zhang Hui‐Zi Jin Wei‐Dong Zhang 《Helvetica chimica acta》2011,94(9):1685-1691
Three new neolignans, (7S,8S,7′E)‐4,9‐dihydroxy‐3,7,3′,9′‐tetramethoxy‐8,4′‐oxyneolign‐7′‐ene ( 1 ), (7R,8S,7′E)‐4, 9‐dihydroxy‐3,7,3′,9′‐tetramethoxy‐8,4′‐oxyneolign‐7′‐ene ( 2 ), (7S,8S,7′E)‐5, 9‐dihydroxy‐3,7,3′,5′,9′‐pentamethoxy‐8,4′‐oxyneolign‐7′‐ene ( 3 ), and one new phenylpropanoid, threo‐5‐hydroxy‐3,7‐dimethoxyphenylpropane‐8,9‐diol ( 4 ), were isolated from the leaves and stems of Toona ciliata var. pubescens. Their structures were determined on the basis of spectroscopic analysis, especially 2D‐NMR, HR‐ESI‐MS, and CD data. The antiproliferative activities of these compounds against four tumor cell lines (A549, Colo 205, QGY‐7703, and LOVO) were also evaluated by MTT (=(3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide) method. 相似文献
859.
Yu W Zhu J Qi L Sun C Gao F Dong L Chen Y 《Journal of colloid and interface science》2011,364(2):435-442
XRD, LRS, TPR and in situ NH(3) adsorption FT-IR were used to investigate the dispersion state of the copper oxide and molybdena species of MoO(3)/CeO(2) and CuO/MoO(3)/CeO(2) catalysts as well as their surface acidity. The results showed that the molybdena monolayer modification promoted the dispersion of CuO due to the formation of new tetrahedral vacancies. Meanwhile, CuO changed the structure of molybdenum species and then influenced the surface acidity of the samples. A detail discussion about the possible model of the surface structure of the catalyst was presented. In addition, combining with the in situ NH(3) adsorption FT-IR, the relationships between the activities for 'NO + NH(3) + O(2)' reaction and surface acid properties (Br?nsted and Lewis acid sites) of the catalysts were discussed. 相似文献
860.
Low-cost and effective phenol and basic dyes trapper derived from the porous silica coated with hydrotalcite gel 总被引:1,自引:0,他引:1
Tao YF Lin WG Gao L Yang J Zhou Y Yang JY Wei F Wang Y Zhu JH 《Journal of colloid and interface science》2011,358(2):554-561
Novel low-cost and effective adsorbents of phenol and basic dyes were made by coating amorphous silica with hydrotalcite (HT) gel followed by soaking in alkaline solution, and the surface basic-acidic properties of resulting composites were evaluated by CO(2)-TPD, Hammett indicator method and NH(3)-TPD, respectively. Both BET surface area and microporous surface area of the composites were increased after they were soaked with alkaline solution; meanwhile the center of pore size distribution was changed from 9 to 3-4 nm. These composites efficiently captured phenol in gaseous and liquid phases, superior to mesoporous silica such as MCM-48 or SBA-15 and zeolite NaY, and the equilibrium data of gaseous adsorption could be well fitted to Freundlich model. These modified silicas also exhibited high adsorption capacity forward basic dyes such as crystal violet (CV) and leuco-crystal violet (LCV), reaching the adsorption equilibrium within 1 h and offering a new material for environment protection. 相似文献