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21.
In four experiments, we examined the effects on the affiliative preferences of 'focal' female Japanese quail given the opportunity to watch a conspecific male interact with a 'model' female. Experiments were conducted in three, 10-min phases: (1) a pretest, during which a 'focal' female chose between two males; (2) an observation phase, when each focal female watched the male she had spent less time near during the pretest (her 'nonpreferred' male) interact with a 'model' quail; and (3) a post-test, during which each focal female again chose between her nonpreferred and preferred males. Focal females increased their preferences for nonpreferred males after seeing them together with a model female (but not a model male), even if the nonpreferred male and model female were separated by an opaque barrier that prevented them from interacting. A focal female's preference for the end of the enclosure containing her nonpreferred male was not increased when she either watched him court a concealed model female or watched a model female that was being courted by him. Taken together, the present results suggest that a simple tendency for females to approach areas where they have previously seen a male and female quail, in preference to locations where they have seen only a male quail, can explain some of the effect of watching a nonpreferred male mate on a female's tendency to affiliate with him. However, focal females also showed enhanced preferences for nonpreferred males they had seen mating after we both moved those males and controlled for effects of transposition. Thus, processes akin to both 'mate choice copying' and 'conspecific cueing' remain viable explanations for the increase in a focal female quail's tendency to affiliate with a male she watched mate with another female. Copyright 1999 The Association for the Study of Animal Behaviour. 相似文献
22.
Diana P Barraja P Lauria A Montalbano A Almerico AM Dattolo G Cirrincione G 《Bioorganic & medicinal chemistry》2003,11(11):2371-2380
Pyrrolo[2,1-d][1,2,3,5]tetrazinones 10a-o, compounds that hold the deaza skeleton of the antitumor drug temozolomide, were prepared by reaction of 2-diazopyrroles 9 and isocyanates. Such a synthetic route represents, among those leading to azolotetrazinones reported so far, the only possible one since attempts to cyclize to the title ring system 2-amino-1-carbamoylpyrroles 11 or the mono substituted 2-triazenopyrrole 12 failed. Compounds 10 were screened at the National Cancer Institute (NCI) for their activity against a panel of about 60 human tumor cell lines. Most of them possess remarkable antineoplastic activity having GI(50) values in the low micromolar or sub-micromolar range and reaching, in the case of compound 10d, nanomolar concentrations. The most sensitive cell lines were MDA-N and MDA-MB-435 of the breast sub-panel, and SR, K-562, HL60 (TB) and CCRF-CEM of the leukaemia sub-panel. SAR evaluation and COMPARE computations indicate, for compounds 10, a mechanism of action different from that of temozolomide. 相似文献
23.
The Aflatoxin Biosynthesis Cluster Gene, aflX, Encodes an Oxidoreductase Involved in Conversion of Versicolorin A to Demethylsterigmatocystin 下载免费PDF全文
Jeffrey W. Cary Kenneth C. Ehrlich John M. Bland Beverly G. Montalbano 《Applied microbiology》2006,72(2):1096-1101
Biosynthesis of the toxic and carcinogenic aflatoxins by the fungus Aspergillus flavus is a complicated process involving more that 27 enzymes and regulatory factors encoded by a clustered group of genes. Previous studies found that three enzymes, encoded by verA, ver-1, and aflY, are required for conversion of versicolorin A (VA), to demethylsterigmatocystin. We now show that a fourth enzyme, encoded by the previously uncharacterized gene, aflX (ordB), is also required for this conversion. A homolog of this gene, stcQ, is present in the A. nidulans sterigmatocystin (ST) biosynthesis cluster. Disruption of aflX in Aspergillus flavus gave transformants that accumulated ~4-fold more VA and fourfold less aflatoxin than the untransformed strain. Southern and Northern blot analyses confirmed that aflX was the only gene disrupted in these transformants. Feeding ST or O-methylsterigmatocystin, but not VA or earlier precursor metabolites, restored normal levels of AF production. The protein encoded by aflX is predicted to have domains typical of an NADH-dependent oxidoreductase. It has 27% amino acid identity to a protein encoded by the aflatoxin cluster gene, aflO (avfA). Some of domains in the protein are similar to those of epoxide hydrolases. 相似文献
24.
In growing Escherichia coli K12 cells, the cryptic bgl operon is activated
98% of the time by insertions of IS1 or IS5 into the control region,
designated bglR. The activated bgl operon permits utilization of the
beta-glucoside sugar arbutin as a sole carbon and energy source. The bgl
operon is also activated by late-occurring mutations during prolonged
selection on arbutin. The late-occurring mutations that occurred during
prolonged carbon starvation in the presence of arbutin were "adaptive
mutations" because they were specific to the presence of arbutin, and they
did not occur during prolonged starvation in the absence of arbutin. The
spectrum of late-arising mutations differed from that of early-arising,
growth-dependent mutations in that 20% of the late-arising mutants resulted
from mutations at the hns locus. This provides the first direct evidence
for adaptive mutagenesis mediated by the insertion of IS elements. Because
no special genetic background is required to select Bgl+ mutants, this
affords the opportunity to study IS-element-mediated adaptive mutagenesis
in a variety of genetic backgrounds, including the backgrounds of natural
isolates of E. coli.
相似文献
25.
Jain RK; Piskorz CF; Huang BG; Locke RD; Han HL; Koenig A; Varki A; Matta KL 《Glycobiology》1998,8(7):707-717
The selectins interact in important normal and pathological situations with
certain sialylated, fucosylated glycoconjugate ligands containing sialyl
Lewisx(Neu5Acalpha2-3Galbeta1-4(Fucalpha1-3)GlcN Ac). Much effort has gone
into the synthesis of sialylated and sulfated Lewisxanalogs as competitive
ligands for the selectins. Since the natural selectin ligands GlyCAM-1 and
PSGL-1 carry sialyl Lewisxas part of a branched Core 2 O-linked structure,
we recently synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(SE-3Galbeta1++
+-3)GalNAc1alphaOMe and found it to be a moderately superior ligand for L
and P-selectin (Koenig et al. , Glycobiology 7, 79-93, 1997). Other studies
have shown that sulfate esters can replace sialic acid in some selectin
ligands (Yeun et al. , Biochemistry, 31, 9126-9131, 1992; Imai et al. ,
Nature, 361, 555, 1993). Based upon these observations, we hypothesized
that Neu5Acalpha2-3Galbeta1-3GalNAc might have the capability of
interacting with L- and P-selectin. To examine this hypothesis, we
synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(Neu5Acalpha2++
+-3Galbeta1-3)- GalNAc alpha1-OB, which was found to be 2- to 3-fold better
than sialyl Lexfor P and L selectin, respectively. We also report the
synthesis of an unusual structure GalNAcbeta1-4(Fucalpha1-
3)GlcNAcbeta1-OMe (GalNAc- Lewisx-O-methyl glycoside), which also proved to
be a better inhibitor of L- and P-selectin than sialyl Lewisx-OMe.
Combining this with our knowledge of Core 2 branched structures, we have
synthesized a molecule that is 5- to 6-fold better at inhibiting L- and
P-selectin than sialyl Lewisx-OMe, By contrast to unbranched structures,
substitution of a sulfate ester group for a sialic acid residue in such a
molecule resulted in a considerable loss of inhibition ability. Thus, the
combination of a sialic acid residue on the primary (beta1-3) arm, and a
modified Lexunit on the branched (beta1-6) arm on an O-linked Core 2
structure generated a monovalent synthetic oliogosaccharide inhibitor
superior to SLexfor both L- and P-selectin.
相似文献
26.
The role of a single N-linked glycosylation site for a functional epitope of herpes simplex virus type 1 envelope glycoprotein gC 总被引:4,自引:2,他引:2
Olofsson S; Bolmstedt A; Biller M; Mardberg K; Leckner J; Malmstrom BG; Trybala E; Bergstrom T 《Glycobiology》1999,9(1):73-81
A monoclonal antibody, B1C1, binding to an epitope of antigenic site II of
the herpes simplex virus type 1 (HSV-1) glycoprotein gC-1, is a potent
inhibitor of two important biological functions of gC-1: its binding to
cell surface heparan sulfate and its binding to the receptor for complement
factor C3b. Here, we have analyzed a B1C1-resistant HSV- 1 variant
(HSV-12762/B1C1B4.2), obtained after passage of wild type HSV- 1
(HSV-12762) in the presence of high concentrations of B1C1. The transport
of newly synthesized mutant gC-1 to the cell surface was comparable to that
of wild type glycoprotein, but no binding of surface- associated mutant
gC-1 to B1C1 was detected. However, mutant and wild type gC-1 bound equally
well to other site II Mabs. Attachment of wild type but not mutant virus
was inhibited by B1C1. Sequencing of the mutant gC-1 gene revealed only one
nucleotide change, resulting in replacement of Thr150 by an Ile, in turn
destroying an N-glycosylation site at Asn148. Loss of one complex type
N-linked glycan was confirmed by endoglycosidase digestion and subsequent
SDS-polyacrylamide gel electrophoresis. Circular dichroism analysis of
purified gC-1 from cells infected with mutant or wild type virus did not
reveal any difference in secondary structure between mutant and wild type
gC-1. It was not possible to obtain a B1C1-resistant phenotype by
nucleotide- directed mutagenesis of gC-1 where Asn148 was changed to a
glutamine. These data demonstrated that the threonine of the glycosylation
site and not the N-linked glycan in itself was essential for B1C1 binding
相似文献
27.
PksA catalyzes the formation of the polyketide backbone necessary for aflatoxin biosynthesis. Based on reporter assays and sequence comparisons of the nor1-pksA intergenic region in different aflatoxin-producing Aspergillus species, cis-acting elements for the aflatoxin pathway-specific regulatory protein, AflR, and the global-acting regulatory proteins BrlA and PacC are involved in pksA promoter activity. 相似文献
28.
29.
Barraja P Diana P Montalbano A Carbone A Viola G Basso G Salvador A Vedaldi D Dall'Acqua F Cirrincione G 《Bioorganic & medicinal chemistry》2011,19(7):2326-2341
Pyrrolo[3,4-h]quinolin-2-ones were synthesized as nitrogen isosters of the angular furocoumarin angelicin, with the aim of obtaining new photochemotherapeutic agents with increased antiproliferative activity and lower undesired toxic effects. A versatile synthetic pathway was approached to allow the isolation of derivatives of the new ring system with a good substitution pattern on the pyrrole moiety. Photobiological screenings of the new compounds revealed a potent phototoxic effect and a great UVA dose dependence, reaching IC(50) values at submicromolar level. The induced cellular photocytotoxicity was related to apoptosis with the involvement of mitochondria and lysosomes, alteration of cell cycle profile and membrane lipid peroxidation. 相似文献
30.
AFLR is a Zn2Cys6-type sequence-specific DNA-binding protein that is thought to be necessary for expression of most of the genes in the aflatoxin pathway gene cluster in Aspergillus parasiticus and A. flavus, and the sterigmatocystin gene cluster in A. nidulans. However, it was not known whether AFLR bound to the promoter regions of each of the genes in the cluster. Recently, A. nidulans AFLR was shown to bind to the motif 5′-TCGN5CGA-3′. In the present study, we examined the binding of AFLR to promoter regions of 11 genes in the A. parasiticus cluster. Based on electrophoretic mobility shift assays, the genes nor1, pksA, adhA, norA, ver1, omtA, ordA, and, vbs, had at least one 5′-TCGN5CGA-3′ binding site within 200 bp of the translation start site, and pksA and ver1 had an additional binding site further upstream. Although the promoter region of avnA lacked this motif, AFLR bound weakly to the sequence 5′-TCGCAGCCCGG-3′ at −110 bp. One region in the promoter of the divergently transcribed genes aflR/aflJ bound weakly to AFLR even though it contained a site with at most only 7 bp of the 5′-TCGN5CGA-3′ motif. This partial site may be recognized by a monomeric form of AFLR. Based on a comparison of 16 possible sites, the preferred binding sequence was 5′-TCGSWNNSCGR-3′. 相似文献