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191.
192.
193.
A new regioselective synthesis of 6-amino-6-deoxycellulose with a DS 1.0 (degree of substitution) at C-6, and its 6-N-sulfonated and its 6-N-carboxymethylated derivatives, without using protecting groups is described in this paper. The reaction conditions were optimized for preparing cellulose tosylate with full tosylation at C-6 and partial tosylation at C-2 and C-3. The nucleophilic substitution (S(N)) reaction of the tosyl group by NaN(3) at low temperature of 50 degrees C in Me(2)SO was achieved completely at C-6, whereas the tosyl groups at C-2 and C-3 were not displaced. In contrast to this, at 100 degrees C the tosyl groups at C-6, and also those at C-2 and C-3, were replaced by azido groups. This regioselective reaction that depends on temperature makes it possible to reach a selective and quantitative S(N) reaction at C-6 at low temperatures. In the subsequent reduction step with LiAlH(4), the azido group at C-6 was reduced to the amino group, and the tosyl groups at C-2 and C-3 were simultaneously completely removed. Also reported is a temperature-dependent, regioselective and complete iodination by nucleophilic substitution of the tosyl group at C-6 at 60 degrees C. At higher temperatures from 75 to 130 degrees C, substitution is also observed to occur at C-2. The selective iodination at 60 degrees C was employed to confirm the complete tosylation at C-6 of cellulose. The reaction products were identified by four different independent quantitative methods, namely 13C NMR, elemental analysis, ESCA, and fluorescence spectroscopy. 6-N-Sulfonated and 6-N-carboxymethylated cellulose derivatives were also synthesized. The new derivatives are potent candidates for structure-function studies, e.g., studies in relation to regioselectively 2-N-sulfonated and 2-N-carboxymethylated chitosan derivatives. 相似文献
194.
Simultaneous regioselective protection of phenyl 1-thioglucosides at the C-3 and C-6 or at the C-2 and C-6 hydroxy groups 总被引:1,自引:0,他引:1
Simultaneous regioselective 3,6- or 2,6-selective protection of 1-thio-beta- or alpha-D-glucopyranosides is described. The C-3 and C-6 hydroxy groups of the beta-thioglucoside were selectively protected with triisopropylsilyl or tert-butyldiphenylsilyl trifluoromethanesulfonate. The C-2 and C-6 hydroxy groups of the alpha-thioglucoside were selectively protected with tert-butyldiphenylsilyl trifluoromethanesulfonate. 相似文献
195.
Regioselective glycosylation with allyl 4,6-O-benzylidene-alpha,beta-D-glucopyranoside or methyl 4,6-O-benzylidene-alpha,beta-D-glucopyranoside as the acceptor was investigated. It was found that the regioselectivity depends upon donor size and anomeric configuration of the acceptor, i.e., with a monosaccharide donor and an alpha-form acceptor, the (1-->3)-linked product was obtained predominantly or exclusively, while with disaccharide or trisaccharide donors and either an alpha or beta form acceptor, the (1-->2)-linked oligosaccharides were the only products. 相似文献
196.
Diana I. Roncaglia Alejandro M. Schmidt Luis E. Iglesias Adolfo M. Iribarren 《Biotechnology letters》2001,23(17):1439-1443
Base-labile 6-chloro-2,3,5-tri-O-acetylpurine riboside (1c) and 2-amino-6-chloro-2,3,5-tri-O-acetylpurine riboside (1d) were fully deacetylated through Candida antarctica B lipase hydrolysis, affording respectively 6-chloropurine riboside (2c) and 2-amino-6-chloro-purine riboside (2d). Quantitative results were found at pH 7 and 60 °C in 24 h for 1c and 72 h for 1d. This mild and simple enzymatic technique represents a convenient procedure for the removal of acetyl groups from such base labile halogenated nucleosides. 相似文献
197.
198.
《Bioscience, biotechnology, and biochemistry》2013,77(10):2000-2007
An esterase catalyzing the hydrolysis of acetyl ester moieties in poly(vinyl alcohol) was purified 400-fold to electrophoretic homogeneity from the cytoplasmic fraction of Pseudomonas vesicularis PD, which was capable of assimilating poly(vinyl alcohol) as the sole carbon and energy source. The purified enzyme was a homodimeric protein with a molecular mass of 80 kDa and the isoelectric point was 6.8. The pH and temperature optima of the enzyme were 8.0 and 45°C. The enzyme catalyzed the hydrolysis of side chains of poly(vinyl alcohol), short-chain p-nitrophenyl esters, 2-naphthyl acetate, and phenyl acetate, and was slightly active toward aliphatic esters. The enzyme was also active toward the enzymatic degradation products, acetoxy hydroxy fatty acids, of poly(vinyl alcohol). The K m and V max of poly(vinyl alcohol) (degree of polymerization, 500; saponification degree, 86.5-89.0 mol%) and p-nitrophenyl acetate were 0.381% (10.6 mM as acetyl content in the polymer) and 2.56 μM, and 6.52 and 12.6 μmol/min/mg, respectively. The enzyme was strongly inhibited by phenylmethylsulfonyl fluoride and diisopropyl fluorophosphate at a concentration of 5 mM, which indicated that the enzyme was a serine esterase. The pathway for the metabolism of poly(vinyl alcohol) is also discussed. 相似文献
199.
Mta1, a representative of the MTA gene family, is believed to be involved in the metastasis of malignant tumors. However, a systematic
study of its physiological function has not been performed. It has been found in normal mouse organs at relatively low levels,
except for in testis, suggesting a potential function in the male reproductive system. In order to explore the role of Mta1
protein during spermatogenesis, its expression in adult mouse testis was compared with that in developing mouse testis and
in testis from adult mice treated with methoxyacetic acid, which selectively depletes primary spermatocytes. Quantitative
analysis revealed that Mta1 protein gradually increased in the testis from 14 days postnatally. Immunolocalization analysis
demonstrated strong signals in the seminiferous tubules, and Mta1 was predominantly present in the nucleus of primary spermatocytes
and spermatogonia from 14 days postnatally. The most intensive staining was located in the nucleus of pachytene spermatocytes
in mature testes. The expression pattern of Mta1 during spermatogenesis was also shown to be stage-specific by immunohistochemistry
analysis. Finally, dramatic loss of Mta1 expression from pachytene spermatocytes was observed in the spermatogenic-arrested
adult mouse testis. These results collectively demonstrate that Mta1 appears during postnatal testis development and suggest
that this expression may be crucial for spermatogenesis.
This study was supported by the Natural Science Foundation of China (2006: 30570982; 2003: 30370750; 2003: 30371584). 相似文献
200.
Thung S. Lai Christopher Davies Charles S. Greenberg 《Protein science : a publication of the Protein Society》2010,19(2):229-235
Human tissue transglutaminase (TGM2) is implicated in the pathogenesis of several neurodegenerative disorders including Alzheimer's, Parkinson's and expanded polyglutamine (polyQ) diseases. TGM2 promotes formation of soluble and insoluble high molecular weight aggregates by catalyzing a covalent linkage between peptide‐bound Q residues in polyQ proteins and a peptide‐bound Lys residue. Therapeutic approaches to modulate the activity of TGM2 are needed to proceed with studies to test the efficacy of TGM2 inhibition in disease processes. We investigated whether acetylation of Lys‐residues by sulfosuccinimidyl acetate (SNA) or aspirin (ASA) would alter the crosslinking activity of TGM2. Acetylation by either SNA and/or ASA resulted in a loss of >90% of crosslinking activity. The Lys residues that were critical for inhibition were identified by mass spectrometry as Lys444, Lys468, and Lys663. Hence, acetylation of Lys‐residues may modulate the enzymatic function of TGM2 in vivo and offer a novel approach to treatment of TGM2 mediated disorders. 相似文献