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101.
Multidimensional heteronuclear NMR studies have been applied to the
resonance assignment and conformational analysis of 13C-enriched
Neu5Acalpha2-3Galbeta1-4Glc. It is demonstrated that three-dimensional
ROESY-HSQC experiments provide through-space distance restraints which
cannot be observed with conventional homonuclear 1H techniques due to
resonance overlap. In particular, connectivities demonstrating the
existence of the "anti" conformation about the Galbeta1-4Glc glycosidic
linkage are unambiguously observed. It is shown that 13C isotopic
enrichment of the trisaccharide at a level >95% enables straightforward
measurement of trans-glycosidic 1H-13C and 13C-13C coupling constants and a
Karplus-type relation is derived for the latter. In total 15 conformational
restraints were obtained for the trisaccharide in aqueous solution, all of
which were in excellent agreement with theoretical parameters computed from
a 5 ns molecular dynamics simulation of the glycan.
相似文献
102.
A Mazumder J A Gerlt M J Absalon J Stubbe R P Cunningham J Withka P H Bolton 《Biochemistry》1991,30(4):1119-1126
The DNA strand cleavage reaction catalyzed by endonuclease III from Escherichia coli (endo III) on the 3'-side of aldehyde abasic sites proceeds by a syn beta-elimination involving abstraction of the 2'-pro-S proton and formation of a trans alpha,beta-unsaturated aldose product; we previously reported the same stereochemical course for the reaction catalyzed by UV endonuclease V from bacteriophage T4 (UV endo V) [Mazumder, A., Gerlt, J. A., Rabow, L., Absalon, M. J., Stubbe, J., & Bolton, P. H. (1989) J. Am. Chem. Soc. 111, 8029-8030]. Since the UV endo V does not contain an 4Fe-4S center, the 4Fe-4S center present in endo III need not be assigned a unique role in the beta-elimination reaction. The beta-elimination reactions that occur under alkaline conditions (0.1 N NaOH) and in the presence of the tripeptide Lys-Trp-Lys proceed by anti beta-elimination mechanisms involving abstraction of the 2'-pro-R proton and formation of a trans alpha,beta-unsaturated aldose product. The different stereochemical outcomes of the enzymatic and nonenzymatic beta-elimination reactions support the hypothesis that the enzyme-catalyzed reactions may involve general-base-catalyzed abstraction of the 2'-pro-S proton by the internucleotidic phosphodiester leaving group. 相似文献
103.
104.
Evolution of alcohol dehydrogenase genes in peonies (Paeonia): phylogenetic relationships of putative nonhybrid species 总被引:11,自引:0,他引:11
Alcohol dehydrogenase genes were amplified by PCR, cloned, and sequenced
from 11 putative nonhybrid species of the angiosperm genus Paeonia.
Sequences of five exons and six intron regions of the Adh gene were used to
reconstruct the phylogeny of these species. Two paralogous genes, Adh1A,
and Adh2, were found; an additional gene, Adh1B, is also present in section
Moutan. Phylogenetic analyses of exon sequences of the Adh genes of Paeonia
and a variety of other angiosperms imply that duplication of Adh1 and Adh2
occurred prior to the divergence of Paeonia species and was followed by a
duplication resulting in Adh1A and Adh1B. Concerted evolution appears to be
absent between these paralogous loci. Phylogenetic analysis of only the
Paeonia Adh exon sequences, positioning the root of the tree between the
paralogous genes Adh1 and Adh2, suggests that the first evolutionary split
within the genus occurred between the shrubby section Moutan and the other
two herbaceous sections Oneapia and Paeonia. Restriction of Adh1B genes to
section Moutan may have resulted from deletion of Adh1B from the common
ancestor of sections Oneapia and Paeonia. A relative-rate test was designed
to compare rates of molecular change among lineages based on the divergence
of paralogous genes, and the results indicate a slower rate of evolution
within the shrubby section Moutan than in section Oneapia. This may be
responsible for the relatively long branch length of section Oneapia and
the short branch length between section Moutan and the other two sections
found on the Adh, ITS (nrDNA), and matK (cpDNA) phylogenies of the genus.
Adh1 and Adh2 intron sequences cannot be aligned, and we therefore carried
out separate analyses of Adh1A and Adh2 genes using exon and intron
sequences together. The Templeton test suggested that there is not
significant incongruence among Adh1A, ITS, and matK data sets, but that
these three data sets conflict significantly with Adh2 sequence data. A
combined analysis of Adh1A, ITS, and matK sequences produced a tree that is
better resolved than that of any individual gene, and congruent with
morphology and the results of artificial hybridization. It is therefore
considered to be the current best estimate of the species phylogeny.
Paraphyly of section Paeonia in the Adh2 gene tree may be caused by longer
coalescence times and random sorting of ancestral alleles.
相似文献
105.
G Nivaler EA Zimmerman R Defendini AS Liotta DT Kreiger MJ Brownstein 《The Journal of cell biology》1979,81(1):50-58
Adrenocorticotropin and β-lipotropin (β-LPH) have been localized by immunoperoxidase methods in nerve cells and fibers of the hypothalamus and brain stem of the ewe. 6-μm sections were immunostained first for either ACTH or β-LPH. The reaction products and the antibody complexes were then eluted completely from the tissue, and the same section was immunostained for the second peptide. Absorption of the primary antisera with a variety of peptide fragments of ACTH and β-LPH demonstrated, immunocytochemically as well as by radioimmunoassay, that the ACTH and β-LPH antisera were directed to the COOH- and NH(2)-termini of the peptides, respectively. Neither antiserum recognized any portion of the heterologous peptide. In the sequential staining procedure on the same tissue section, preincubation of the antisera with the homologous peptide abolished the staining, whereas preincubation with the heterologous peptide did not affect it, regardless of the order followed. Every nerve cell in the arcuate nucleus that contained ACTH also contained β-LPH, but β-LPH cells appeared, probably falsely, to be twice as numerous as ACTH cells. β-LPH-positive fibers in and beyond the hypothalamus were also more numerous and stained more intensively than ACTH fibers. The salient exception was fibers in the infundibular zona externa, where the opposite was true. Our observations establish that ACTH and β-LPH are contained in the same nerve cells They stongly favor biosynthesis in brain, probably from a common precursor molecule, as has been demonstrated in the pituitary gland. The complexity of the cytologic distribution pattern described suggests that the two peptides are not processed in the same manner by the nerve cell. 相似文献
106.
Tracey E Toms Vasileios F Panoulas Holly John Karen MJ Douglas George D Kitas 《Arthritis research & therapy》2009,11(4):R110-10
Introduction
The metabolic syndrome (MetS) may contribute to the excess cardiovascular burden observed in rheumatoid arthritis (RA). The prevalence and associations of the MetS in RA remain uncertain: systemic inflammation and anti-rheumatic therapy may contribute. Methotrexate (MTX) use has recently been linked to a reduced presence of MetS, via an assumed generic anti-inflammatory mechanism. We aimed to: assess the prevalence of the MetS in RA; identify factors that associate with its presence; and assess their interaction with the potential influence of MTX. 相似文献107.
108.
Intraflagellar transport and functional analysis of genes required for flagellum formation in trypanosomes 总被引:1,自引:0,他引:1
Absalon S Blisnick T Kohl L Toutirais G Doré G Julkowska D Tavenet A Bastin P 《Molecular biology of the cell》2008,19(3):929-944
Intraflagellar transport (IFT) is the bidirectional movement of protein complexes required for cilia and flagella formation. We investigated IFT by analyzing nine conventional IFT genes and five novel putative IFT genes (PIFT) in Trypanosoma brucei that maintain its existing flagellum while assembling a new flagellum. Immunostaining against IFT172 or expression of tagged IFT20 or green fluorescent protein GFP::IFT52 revealed the presence of IFT proteins along the axoneme and at the basal body and probasal body regions of both old and new flagella. IFT particles were detected by electron microscopy and exhibited a strict localization to axonemal microtubules 3–4 and 7–8, suggesting the existence of specific IFT tracks. Rapid (>3 μm/s) bidirectional intraflagellar movement of GFP::IFT52 was observed in old and new flagella. RNA interference silencing demonstrated that all individual IFT and PIFT genes are essential for new flagellum construction but the old flagellum remained present. Inhibition of IFTB proteins completely blocked axoneme construction. Absence of IFTA proteins (IFT122 and IFT140) led to formation of short flagella filled with IFT172, indicative of defects in retrograde transport. Two PIFT proteins turned out to be required for retrograde transport and three for anterograde transport. Finally, flagellum membrane elongation continues despite the absence of axonemal microtubules in all IFT/PIFT mutant. 相似文献
109.
110.
A comment on D Vitkup, P Kharchenko and A Wagner: Influence of metabolic network structure and function on enzyme evolution. Genome Biol 2006, 7:R39. 相似文献