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排序方式: 共有423条查询结果,搜索用时 15 毫秒
31.
Xiangjiu HeJiankuan Li Hao GaoFeng Qiu Ke HuXiangmin Cui Xinsheng Yao 《Tetrahedron》2003,59(34):6603-6607
Four new sulfonate metabolites of andrographolide, 14-deoxy-12(R)-sulfo andrographolide (Metabolite 1), 14-deoxy-12(S)-sulfo andrographolide (Metabolite 2), 14-deoxy-12(R)-sulfo-9(S)-andrographolide (Metabolite 3) and 14-sulfo isoandrographolide (Metabolite 4), were isolated from urine and feces in rats. Their structures were elucidated by chemical and spectroscopic analyses. These four metabolites were formed through a rare metabolic reaction and were all new compounds. 相似文献
32.
Roman Luis J. Zhang Xinsheng Zheng Weian 《Mathematical Physics, Analysis and Geometry》2003,6(2):113-124
We consider the solutions to /tu
(n)=a
(n)(x)u
(n) where {a
(n)(x)}
n=1,2,... are random fields satisfying a well-mixing condition (which is different to the usual strong mixing condition). In this paper we estimate the rate of convergence of u
(n) to the solution of a heat equation. Since our equation is of simple form, we get quite strong result which covers the previous homogenization results obtained on this equation. 相似文献
33.
Strength characteristics of the self-sustained wave in grooved channels with different groove length
Faming Sun Yongning Bian Hirofumi Arima Yasuyuki Ikegami Xinsheng Xu 《Heat and Mass Transfer》2010,46(11-12):1229-1237
The self-sustained oscillations arising in a series of grooved channels are investigated experimentally. Pressure drop, time-averaged and time-various local pressure in the grooved channels with six kinds of groove length are measured with the differential transducer and the pressure sensor, respectively, and the flow structures are visualized using the aluminum dust method. The local pressure signal shows that the self-sustained wave appears in the first or second frequency, and the Strouhal number, based on the nature frequency of the self-sustained wave, is almost equivalent for the first or second frequency in the same channel. Meanwhile, the Strouhal number for each channel decreases monotonously with the groove length. Furthermore, it is found that increasing pressure will result in higher amplitude of the self-sustained wave, this behavior is significant for the efficient heat transfer in practical engineering. 相似文献
34.
Dr. Zhicheng Yang Dr. Xiaoxiao Fan He Li Xinsheng Li Sifan Li Prof. Zhiyun Zhang Prof. Hui Lin Prof. Jun Qian Prof. Jianli Hua 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(57):14240-14249
Organic small-molecule fluorophores with near-infrared IIa (NIR-IIa) emission have great potential in pre-clinical detection and inoperative imaging due to the high-spatial resolution and deep penetration. However, developments of the NIR-IIa fluorophores are still facing considerable challenges. In this work, a series of diketopyrrolopyrrole (DPP)-based fluorophores were designed and synthesized. Subsequently, nanomaterial T25@F127 with significant NIR-IIa emission properties was rationally prepared by encapsulating DPP-based fluorophore T25 , and was selected for fluorescence angiography and cerebral vascular microscopic imaging with nearly 800 μm penetrating depth and excellent signal-background ratio of 4.07 and 2.26 (at 250 and 400 μm), respectively. Furthermore, the nanomaterial T25@cRGD with tumor targeting ability can image tiny metastatic tumor on intestine with a small size of 0.3 mm×1.0 mm and high-spatial resolution (SBR=3.84). This study demonstrates that the nanomaterials which encapsulated T25 behave as excellent NIR-IIa fluorescence imaging agents and have a great potential for in vivo biological application. 相似文献
35.
合成了三种新型含噻吩环大环Schiff碱及其中一种与镧,钍的配合物。它们的结构均经IR,HNMR和元素分析表征。 相似文献
36.
Xinsheng Zhu Kwang-Ho Choo 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,312(2-3):231-237
The overlapping of charged polymers (e.g., polyelectrolyte) in the liquid phase is one of the key parameters affecting the processing of the macromolecular solutions. This work focused on the development of a novel method for determining the overlap concentration of polyelectrolytes with stirred cell ultrafiltration (UF) techniques. A new, simplified equation that incorporated the resistance-in-series UF model into the osmosis phenomenon caused by polymers was developed, and then applied to estimate the threshold concentration for macromolecular overlap. The overlap concentrations of model polymers, such as poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine) and poly(diallyldimethylammonium chloride), were evaluated with different, initial polymer concentrations and membrane pore sizes. In the correlation between ln Rt/Cr and ln Cr, the concentration where ln Rt/Cr had the minimal value was referred to as the overlap concentration. The gyration radius of polyelectrolytes was calculated using the overlap concentration, which can provide insight into the understanding of the size of polymers and their rejections by membranes. Determining the overlap concentration of polymers with a UF membrane appeared to be viable and practical. 相似文献
37.
Xinsheng Xu Lixia Jia Lei Shi Xuehan Ji Zhifeng Cui 《Research on Chemical Intermediates》2010,36(3):269-275
Chemically induced dynamic electron polarization (CIDEP) is one of the important research fields of dynamic spin chemistry.
In the present work, with ethylene glycol, 1,2-propanol and their mixtures with different ratios in volume as solvents and
duroquinone as photosensitive molecule, the influence of solvent viscosity on the CIDEP of photolyzed duroquinone radicals
has been studied experimentally. In each solvent, duroquinone neutral radicals are observed. Duroquinone neutral radicals
are generated through hydrogen transfer reaction from hydrogen-donor solvent molecules to excited duroquinone triplet. The
CIDEP mechanism is mainly triplet mechanism. The CIDEP intensity of duroquinone neutral radicals decreases with the increase
in the solvent viscosity, and the variation was rapid in low-viscosity range and slow in high-viscosity range. 相似文献
38.
采用液相沉淀法制备了Ce0.6Zr0.3La0.05Y0.05O2固溶体。通过BET,XRD,SEM,程序升温还原和氧脉冲吸附等方法对合成产品性能进行了表征。研究了前驱体的形态、高温水热处理、表面处理以及后期固溶体的还原处理对固溶体性能的影响。其中前驱体的高温水热处理和固溶体的还原处理对固溶体的催化性能有很大的影响。200℃水热处理制得的固溶体经1000℃老化4 h后,比表面积为25.3 m2.g-1,孔容为0.21 cm3.g-1,经800℃还原处理3 h后储氧量为478.3μmol.g-1,显示了较高的比表面积和储氧能力的高温稳定性。 相似文献
39.
40.
本文考虑轴向应力波效应,利用分叉理论研究各种支承半无限长弹塑性梁的动态屈曲问题。在轴向阶梯载荷和脉冲载荷冲击下得到了梁的临界屈曲载荷及初始屈曲模态。其结果与实验现象相一致。同时也为研究结构动态屈曲问题提供了有效途径。 相似文献