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排序方式: 共有134条查询结果,搜索用时 15 毫秒
31.
Some multiplicity results of solutions are obtained for a class of elliptic systems which are near resonance with a nonprincipal eigenvalue by the classical saddle point theorem and a local saddle point theorem in critical point theory. 相似文献
32.
Imino sugars, sometimes called azasugars, are an important class of natural and unnatural compounds that have activity to selectively inhibit glycohydrolases responsible for the cleavage of glycosidic bonds.[1,2] In azasugars, the ring oxygen is replaced by nitrogen, which can be protonated under physiological pH, thus mimicking the glycopyranosyl cation. Because of the potential chemotherapeutic applications of such compounds, lots of chemists have continuing interests in the synthesis of imino sugars, such as deoxynojirimycin (DNJ, 1,5-dideoxy-1,5-imino-D-glucitol) and miglitol derivatives. 相似文献
33.
2,2-Bis(C-branched-chain)glucopyranosid-3-uloses, designed for the preparation of biologically active natural product iridoid derivatives, are synthesized selectively by the new reaction of butenolide-containing sugar with active methylene compounds, and the new reaction is clarified as autoxidation followed by Michael addition of carbanion. 相似文献
34.
Wang H Miao JJ Zhu JM Ma HM Zhu JJ Chen HY 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11738-11747
A facile and efficient approach for the fabrication of mesoporous spherical aggregates of anatase nanocrystals is reported in this paper. Cetyltrimethylammonium bromide was used as the structure-directing agent, and the interaction between cyclohexane microdroplets and the cetyltrimethylammonium bromide self-assemblies led to the assembly of 4-5-nm-sized anatase nanocrystals into spherical aggregates with mesoporous structures. The as-prepared anatase powders exhibited high photocatalytic activity and could be effectively used as the catalyst for the room-temperature photodegradation of a variety of organic dye pollutants in aqueous media including methyl orange, bromopyrogallol red, and methylene blue. 相似文献
35.
5-O-Benzoyl-1,2-O-isopropylidene-α-D-erythro-ketofuranose-3-ulose-3-aminothiose 3 was synthesized and characterized by spectral analysis, and its crystal structure was determined by X-ray diffraction analysis. The crystal belongs to orthorhombic, space group P212121 with a = 6.6276(13), b = 10.993(2), c = 25.027(5) , β = 90°, V = 1823.4(6)3, Z = 4, C16H20N3O5S, Mr = 366.41, Dc = 1.335 g/cm3, μ = 0.208 mm-1, F(000) = 772, S = 1.007, the final R = 0.0465 and wR = 0.1061 for 3251 observed reflections (I > 2σ(I)). Four hydrogen bonds are observed. The absolute configuration of this molecule was confirmed by comparing with that of the original material. 相似文献
36.
2,6-Diisopropylnaphthalene (2,6-DIPN), as the precursor of important monomer 2,6-naphthalene dicarboxylic acid, could be produced by the shape-selective isopropylation of naphthalene with propene resulting in an isomeric mixture having different alkylation levels. Since the boiling points of DIPNs were very close and the differences of melting points in-between isomers were quite distinctive, the static melt crystallization was applied to separate and purify 2,6-DIPN from its isomers. 2,6-DIPN with purity ≥99% was produced through a process of three stages: crystallization→sweating→melting. The phase diagram of 2,6-DIPN-2,7-DIPN binary system was plotted to opti- mize the temperature control of crystallization. By repeated crystallization of melts with different concentration levels, the yield of pure 2,6-DIPN could be enhanced to 87%. No solvent was necessary. Keywords 2,6-diisopropylnaphthalene, static melt crystallization, crystallization rate, sweating rate, eutectic temperature 相似文献
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By means of the nuclear parton distribution obtained from DGLAP equation,measured Drell-Yan production cross sections for 800 GeV proton incident on a variety of nuclear targets are analyzed within Glauber framework with takes into account energy loss of the beam proton.It is shown that the theoretical results are in good agreement with the FNAL E866. 相似文献
40.
银釉是古代铅釉陶瓷器表面较为常见一种病变。利用扫描电子显微镜能谱、X射线衍射、傅立叶红外光谱、光电子能谱等测试技术,分析了湖北黄冈地区出土宋代绿釉陶表面银釉的成分和结构。结果发现,银釉中富含钙(5.1%~9.2%)、磷(4.6%~9.2%)、铅(56.9%~70.5%)等元素,并有Pb10-xCax(PO4)(OH)2(x<2.7)物相存在。结合其出土前(弱酸性的土壤)埋藏环境,推测银釉应为土壤中羟磷灰石及各种磷酸化合物与釉陶表面Pb2 发生化学反应的产物。 相似文献