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排序方式: 共有203条查询结果,搜索用时 15 毫秒
191.
van Tiggelen BA Lagendijk A van Albada MP Tip A 《Physical review. B, Condensed matter》1992,45(21):12233-12243
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用化学共沉淀法一次煅烧工艺制备Ce,Pr:GAGG粉体,利用XRD、SEM、荧光光谱仪等对样品表面形貌及发光性能进行表征,研究煅烧温度、沉淀剂引入草酸根对粉体发光性能的影响。结果表明,前驱体经950℃煅烧3 h后全部转变为GAGG相,Pr3+、Ce3+共掺未改变基质的物相结构;沉淀剂引入草酸铵后,粉体发射光谱积分强度由333 573 a.u上升至420 894 a.u,沉淀剂引入草酸根能提高粉体的发光性能。荧光寿命测试表明,在Ce:GAGG中掺入Pr3+可使Ce3+的荧光寿命降低,衰减时间为35.43 ns。 相似文献
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Metallic triflates M(OTf)(3) (M = Bi, Sc, Yb), immobilized in imidazolium ionic liquids [BMIM][BF(4)], [BMIM][PF(6)] and [BMIM][OTf] are efficient systems for one-pot reactions of propargylic alcohols 1,3-diphenyl-2-propyn-1-ol Ia, 1-methyl-3-phenyl-2-propyn-1-ol Ib, and 2-pentyn-1-ol Ic, with a wide range of arenes bearing activating substituents, under mild conditions. The [BMIM][PF(6)]/B(C(6)F(5))(3) and [BMIM][PF(6)]/TfOH systems were superior in propargylation with Ib and Ic, while reaction of 3-phenyl-2-propyn-1-ol Id with activated aromatics resulted in the formation of diaryl-propanones instead. Propargylation of anisole with Ib under M(OTf)(3) catalysis is highly para selective, but with TfOH or B(C(6)F(5))(3) as catalyst the ortho isomer was also formed. Steric influence of the propargylic moiety on substrate selectivity is reflected in the lack of ortho propargylation for phenol and ethylbenzene by using propargylic alcohol Ia, and notable formation of the ortho isomer employing alcohol Ib. In the later case para selectivity could be increased by running the reaction at r. t. for 10 h. The Bi(OTf)(3)-catalyzed reaction of 1,3-dimethoxybenzene with Ia led to minor formation of dipropargylated derivative, along with the monopropargyl product. Propargylation of the less reactive arenes (mesitylene, ethylbenzene, toluene), using Sc(OTf)(3) as catalyst, led increasingly to the formation of dipropargylic ethers and propargyl ketones, with no ring propargylation product with toluene. Concomitant formation of dipropargylic ether was also observed in Yb(OTf)(3)-catalyzed propargylation of β-naphthol, whereas propargylation of 2-nitro and 4-nitro-aniline led to N-propargylation. The recycling/reuse of the IL was demonstrated in representative cases with no appreciable decrease in the conversions over 3 cycles. It was also shown that recycled IL could be used to propargylate a different aromatic compound. The efficacy of IL/M(OTf)(3) and IL/TfOH systems for cross-breeding two propargylic alcohols or a propargylic alcohol with a non-propargylic alcohol and/or self-coupling, to form a wide variety of functionalized ethers is also demonstrated. 相似文献
197.
为探究重金属污泥高值资源化利用途径, 研究了含重金属污泥高温处理渣料磨细粉(简称磨细粉)对改性硫氧镁(MMOS)水泥基材料的工作性能、力学性能、早期自由收缩变形及其重金属浸出行为的影响. 结果表明: 随着磨细粉掺量的增加, MMOS水泥基材料的净浆流动度呈现逐渐增大趋势; 早期(3d)力学性能则呈现明显的降低趋势, 90d后磨细粉掺量对MMOS水泥基材料的力学性能的影响程度降低; 磨细粉可以显著降低MMOS水泥基材料早期的自由收缩变形值, 其中含10%磨细粉的MMOS水泥基材料早期的自由收缩变形比未掺加磨细粉MMOS水泥基材料的自由收缩变形值降低了57.1%. 微观分析结果表明: 掺加30%磨细粉后MMOS水泥基材料中水化产物5Mg(OH)2?MgSO4?7H2O(517相)的相对含量降低, MMOS水泥基材料硬化体的平均孔径提高了31.0%, 表明磨细粉降低了MMOS水泥基材料的力学性能. 当磨细粉掺量增加至40%时MMOS水泥基材料硬化体中重金属Ni、Cr、Zn和Cu的浸出浓度指标均能满足GB 30760-2014的浸出要求. 相似文献
198.
从心理活动功能角度建构人际沟通能力沟通技能、沟通认知和沟通倾向三元结构.采用国内学者编制的测量量表,运用探索性因子分析,筛选出了人际沟通能力言语表达、非言语表达、倾听、沟通认知和沟通倾向5个因子,可解释总体方差的74.23%.通过因子分析筛选出沟通技能的言语表达、非言语表达和倾听三项技能特质,人际沟通能力三元结构在人际沟通能力问卷测量中得以证实. 相似文献
199.
The dynamics of an atom coupling to a quantized cavity field have been studied. The atom is treated as a two-level system with a spontaneous emission rate. The transition probabilities have been given for both adiabatic and non-adiabatic situations. For a special Λ-type atom with dark state, the problem of momentum transfer is discussed in details. The influence of spontaneous emission on validity of the adiabatic approximation is also discussed. 相似文献
200.
A total synthesis of the thromboxane A2 analog () is described. 相似文献