全文获取类型
收费全文 | 135篇 |
免费 | 3篇 |
国内免费 | 9篇 |
专业分类
化学 | 143篇 |
物理学 | 4篇 |
出版年
2023年 | 6篇 |
2022年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2016年 | 1篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 4篇 |
2011年 | 7篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 12篇 |
2007年 | 4篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 3篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1993年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有147条查询结果,搜索用时 31 毫秒
101.
102.
Lewis acid promoted anomerisation has potential in O- or S-glycoside synthesis. Herein, the anomerisation kinetics of thirty-one β-d-glucopyranosides was determined to determine how particular acyl protecting groups and their location influence reactivity towards a Lewis acid promoted reaction. The replacement of acetyl groups with benzoyl groups led to reduced reactivity when located at O-3, O-4 and O-6. However a reactivity increase was observed when the acetyl group was replaced by a benzoyl group at O-2. The 2,3,4,6-tetra-O-(4-methoxy)benzoate had an?~2-fold increase in rate when compared to the tetrabenzoate. 相似文献
103.
Uta Schädel 《Tetrahedron》2005,61(5):1149-1154
Synthetic routes for linking two sugar units at the upper rim of cone calix[4]arenes, through the formation of amide bonds, have been explored. Steric effects prevent the coupling of calix[4]arene dicarboxylic acid with simple aminoglycosides, whereas the corresponding reaction with carbohydrates bearing a two or three carbon atoms spacer, terminating with a primary amino group, allows the synthesis of several difunctionalized calix[4]arene neoglycoconjugates, attractive in chemical glycobiology and supramolecular chemistry. 相似文献
104.
Mosselhi A. N. Mosselhi Elham S. Darwish Klaus Peseke 《Monatshefte für Chemie / Chemical Monthly》2008,139(7):825-834
Heating of 8-aminotheophylline with methyl (Z)-2-benzoylamino-3-(dimethylamino)propenoate in acetic acid afforded in a one-pot synthesis a new pyrimido[2,1-f]theophylline derivative. Methylation of this by using CH3I/NaH furnished in good yield the double methylated derivative. Furthermore, glycosidation of the former with 1-α-bromo-2,3,4,6-tetra-O-acetyl-d-glucose gave the β-glucoside derivative. Reaction of 8-aminotheophylline with [bis(methylthio)methylene]malonitrile, ethyl[bis(methylthio)methylene]cyanoacetate,
1,3-diphenylprop-2-en-1-one, 2-cyano-1,3-diphenylprop-2-en-1-one, 1-(4-nitrophenyl)-3-(dimethylamino)prop-2-ennitrile, 1-phenyl-3-(dimethylamino)prop-2-en-1-one,
2-substituted 3-aryl or heteroarylprop-2-ennitrile and ethyl(arylmethylene)cyanoacetate in N,N-dimethylformamide in the presence of anhydrous potassium carbonate afforded also the corresponding new derivatives of pyrimido-[2,1-f]theophylline. However, 8-aminotheophylline reacted in similar manner with 3-chloropentan-2,4-dione and 2-bromo-1-phenylethanone
to give the corresponding imidazo[2,1-f]theophyllines. Furthermore, azo-coupling of one of these with 4-methylphenyldiazonium chloride was performed. The antimicrobial
activity of the products has been evaluated. The structures of all new compounds obtained were established by their spectral
analyses.
Correspondence: Mosselhi A. N. Mosselhi, Department of Chemistry, Faculty of Science, Cairo University, Cairo, Egypt. 相似文献
105.
Jordan DB 《Applied biochemistry and biotechnology》2008,146(1-3):137-149
Catalytically efficient β-d-xylosidase from Selenomonas ruminantium (SXA) exhibits pK
as 5 and 7 (assigned to catalytic base, D14, and catalytic acid, E186) for k
cat/K
m with substrates 1,4-β-d-xylobiose (X2) and 1,4-β-d-xylotriose (X3). Catalytically inactive, dianionic SXA (D14−E186−) has threefold lower affinity than catalytically active, monoanionic SXA (D14−E186H) for X2 and X3, whereas D14−E186− has twofold higher affinity than D14−E186H for 4-nitrophenyl-β-d-xylopyranoside (4NPX), and D14−E186− has no affinity for 4-nitrophenyl-α-l-arabinofuranoside. Anomeric isomers, α-d-xylose and β-d-xylose, have similar affinity for SXA. 4-Nitrophenol competitively inhibits SXA-catalyzed hydrolysis of 4NPX. SXA steady-state
kinetic parameters account for complete progress curves of SXA-catalyzed hydrolysis reactions.
The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of
Agriculture over other firms or similar products not mentioned. 相似文献
106.
Olapeju O. Aiyelaagbe Arvind S. Negi Abdulmumeen A. Hamid Suaib Luqman Sathish B. Kumar Fatima Kaneez 《中国化学会会志》2015,62(9):751-755
Methanol extract of Alafia barteri leaves showed cytotoxic activity on leukaemia carcinoma K562, and hepatic liver cancer cells WRL (IC50 values 193.1 and 225.0 μM respectively). Isolation of the extract gave ursane triterpenoid, 28‐acety‐urs‐5,20‐dien‐2β,3β,24α‐triol, 1 , together with undecanol, 2 , stigmasterol, 3 and octadecanoic acid, 4 . The structures of these compounds were identified by spectroscopic analysis, including MS, 1D and 2D NMR, and supported with literature data. Compound 1 exhibited cytotoxic activity against K‐562 at 50 and 100 μM concentrations with IC50 74.22 μM, while compounds 2 , 3 and 4 showed low inhibition of WRL, MCF‐7 and COLO cell lines. 相似文献
107.
通过改进的Koenigs-knorr法在熊果酸3位和28位进行半乳糖苷化得到6个化合物. 通过MTT法考察了上述化合物对大鼠肝干细胞样上皮细胞WB-F344 的作用, 发现化合物12b和12e可明显提高WB-F344细胞的成活率. 体内实验结果表明, 化合物12b, 12d和12f在刀豆蛋白引起的小鼠急性免疫性肝损伤模型上, 除化合物12d对小鼠血清谷草转氨酶升高具有一定程度的降低作用外, 其余化合物均未见对谷草和谷丙转氨酶的升高表现出明显的保护作用. 相似文献
108.
109.
110.