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排序方式: 共有253条查询结果,搜索用时 66 毫秒
1.
The surface charge of Leishmania mexicana amazonensis was evaluated by means of the binding of colloidal iron hydroxyde particles at pH 1.8 and cationized ferritin particles at pH 7.2 to the cell surface, visualizated by electron microscopy and by direct measurements of the electrophoretic mobility of cells suspended in solutions of different pH. The following forms of the parasite were analysed: amastigotes (surrounded or not by the membrane of the endocytic vacuole, isolated from lesions), transitional forms, and infective (5 passages) and noninfective (176 passages) promastigotes. The results obtained indicate that the surface of L. m. amazonensis contains both negatively and positively charged dissociating groups and that changes occur in the surface charge during amastigote-promastigote transformation. Treatment of the parasite with neuraminidase significantly reduced the electrophoretic mobility of the cells. Neuraminidase-treated cells recovered their normal electrophoretic mobility when incubated for 8 hr in fresh culture medium by a process that is inhibited by puromycin. 相似文献
2.
M. A. Blight A. L. Pimenta J. -C. Lazzaroni C. Dando L. Kotelevets S. J. Séror I. B. Holland 《Molecular & general genetics : MGG》1994,245(4):431-440
We have carried out a genetic analysis of Escherichia coli HlyB using in vitro(hydroxylamine) mutagenesis and regionally directed mutagenesis. From random mutagenesis, three mutants, temperature sensitive (Ts) for secretion, were isolated and the DNA sequenced: Glyl0Arg close to the N-terminus, Gly408Asp in a highly conserved small periplasmic loop region PIV, and Pro624Leu in another highly conserved region, within the ATP-binding region. Despite the Ts character of the Gly10 substitution, a derivative of HlyB, in which the first 25 amino acids were replaced by 21 amino acids of the Cro protein, was still active in secretion of HlyA. This indicates that this region of HlyB is dispensable for function. Interestingly, the Gly408Asp substitution was toxic at high temperature and this is the first reported example of a conditional lethal mutation in HlyB. We have isolated 4 additional mutations in PIV by directed mutagenesis, giving a total of 5 out of 12 residues substituted in this region, with 4 mutations rendering HlyB defective in secretion. The Pro624 mutation, close to the Walker B-site for ATP binding in the cytoplasmic domain is identical to a mutation in HisP that leads to uncoupling of ATP hydrolysis from the transport of histidine. The expression of a fully functional haemolysin translocation system comprising HlyC,A,B and D increases the sensitivity of E. coli to vancomycin 2.5-fold, compared with cells expressing HlyB and HlyD alone. Thus, active translocation of HlyA renders the cells hyperpermeable to the drug. Mutations in hlyB affecting secretion could be assigned to two classes: those that restore the level of vancomycin resistance to that of E. coli not secreting HlyA and those that still confer hypersensitivity to the drug in the presence of HlyA. We propose that mutations that promote vancomycin resistance will include mutations affecting initial recognition of the secretion signal and therefore activation of a functional transport channel. Mutations that do not alter HlyA-dependent vancomycin sensitivity may, in contrast, affect later steps in the transport process. 相似文献
3.
The comparative fine structure and surface glycoconjugate expression of three life stages of Leishmania major 总被引:5,自引:0,他引:5
The cellular ultrastructure and surface glycoconjugate expression of three life stages of Leishmania major were compared. Noninfective logarithmic phase promastigotes (LP) are immature cells bearing a thin cell coat, short flagellum, small and empty flagellar pocket, and a loose cytoplasm filled with profiles of ER and large Golgi complex. LP also contain subpopulations of maturing cells containing less ER and Golgi and synthesizing cytoplasmic granules of different size, number, and electron-density. Infective or metacyclic promastigotes (MP) are fully differentiated nondividing forms with a thickened, prominent cell coat, long flagellum, distended flagellar pocket filled with secretory material, and few cytoplasmic organelles other than abundant electron-dense granules. Tissue amastigotes also contain electron-dense cytoplasmic granules, their flagellar pockets are also enlarged and contain secretory material, but they lack a discernable cell coat. Immunogold labeling of GP63 on the cell surface was extensive only on amastigotes. Promastigote GP63 appeared to be masked by the presence of a densely packed lipophosphoglycan (LPG) coat which was extensively labeled on the entire surface of MP and LP. An elongated, developmentally modified form of LPG was abundantly labeled only on MP. LPG was poorly labeled on amastigotes, arguing that the promastigote cell coat is a stage-specific structure which is lost during intracellular transformation. 相似文献
4.
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6.
Denise C.O.F. Valdetaro Thomas C. Harrington Leonardo S.S. Oliveira Lúcio M.S. Guimarães Douglas L. McNew Lucas V.A. Pimenta Rivadalve C. Gonçalves Daniel A. Schurt Acelino C. Alfenas 《Fungal biology》2019,123(2):170-182
Ceratocystis fimbriata Ellis & Halsted recently was recorded causing seed and seedling blight on Carapa guianensis Aubl. (andiroba), a tree species native to the Amazon Rainforest and prized for its valuable timber and medicinal seed oil. C. fimbriata more commonly causes wilt type diseases in woody hosts, especially on non-native host trees. However, on andiroba the disease occurs on seedlings and seeds, affecting the species regeneration. We studied 73 isolates of C. fimbriata on andiroba from three regions of the Amazon Basin to see if they represented natural or introduced populations. Analysis of ITS rDNA sequences and phylogenetic analysis of mating type genes revealed new haplotypes of C. fimbriata from the Latin American Clade that were closely related to other Brazilian populations of the fungus. In mating experiments, andiroba isolates were inter-fertile with tester strains of C. fimbriata from Brazil and elsewhere, confirming that they belong to a single biological species. Using microsatellite markers, 14 genotypes and populations with intermediate levels of genetic variability were found, suggesting that the fungus is indigenous to the Amazon Basin. Inoculation tests indicated that the andiroba isolates are host-specialized on andiroba, supporting the proposition of the special form C. fimbriata f. sp. carapa. 相似文献
7.
Pimenta Larissa Langsdorff Lima Gustavo Pereira Biondi Michel Vaz Marcelo Gomes Marçal Vieira de Freitas Coelho Flávia 《Aquatic Ecology》2022,56(3):543-553
Aquatic Ecology - In epiphytic associations, cyanobacteria form the periphyton with phytoplanktonic algae and with aquatic macrophytes. In this study, we found homocytous and heterocytous... 相似文献
8.
Chen VC Chao L Pimenta DC Bledsoe G Juliano L Chao J 《The Journal of biological chemistry》2001,276(2):1276-1284
Kallistatin is a heparin-binding serine proteinase inhibitor (serpin), which specifically inhibits human tissue kallikrein by forming a covalent complex. The inhibitory activity of kallistatin is blocked upon its binding to heparin. In this study we attempted to locate the heparin-binding site of kallistatin using synthetic peptides derived from its surface regions and by site-directed mutagenesis of basic residues in these surface regions. Two synthetic peptides, containing clusters of positive-charged residues, one derived from the F helix and the other from the region encompassing the H helix and C2 sheet of kallistatin, were used to assess their heparin binding activity. Competition assay analysis showed that the peptide derived from the H helix and C2 sheet displayed higher and specific heparin binding activity. The basic residues in both regions were substituted to generate three kallistatin double mutants K187A/K188A (mutations in the F helix) and K307A/R308A and K312A/K313A (mutations in the region between the H helix and C2 sheet), using a kallistatin P1Arg variant as a scaffold. Analysis of these mutants by heparin-affinity chromatography showed that the heparin binding capacity of the variant K187A/K188A was not altered, whereas the binding capacity of K307A/R308A and K312A/K313A mutants was markedly reduced. Titration analysis with heparin showed that the K312A/K313A mutant has the highest dissociation constant. Like kallistatin, the binding activity of K187A/K188A to tissue kallikrein was blocked by heparin, whereas K307A/R308A and K312A/K313A retained significant binding and inhibitory activities in the presence of heparin. These results indicate that the basic residues, particularly Lys(312)-Lys(313), in the region between the H helix and C2 sheet of kallistatin, comprise a major heparin-binding site responsible for its heparin-suppressed tissue kallikrein binding. 相似文献
9.
HlyD has a single transmembrane domain (residues 59-80) and a large periplasmic domain, and is essential for the secretion
of haemolysin from Escherichia coli. Using an antibody raised against HlyD, the protein was localised to the cell envelope by immunofluorescence and to the cytoplasmic
membrane by sucrose gradient analysis. We have examined the stability of this protein in the presence and absence of other
putative components of the translocator, HlyB and TolC. HlyD is normally highly stable but in the absence of TolC, the steady-state
level of HlyD is greatly reduced and the protein has a half-life at 37° C of 36 min. In the absence of HlyB, HlyD is also
unstable and specific degradation products are detected, which co-fractionate with the inner membrane, indicating in this
case limited cleavage at specific sites. However, the effect of removing both HlyB and TolC is not additive. On the contrary,
in the absence of both HlyB and TolC the half-life of HlyD is approximately 110 min. This result shows that in the presence
of HlyB removal of TolC renders HlyD more unstable than it is in the absence of both HlyB and TolC. This suggests that the
presence of HlyB induces a structural change in HlyD. In addition, HlyB itself appears to be less stable in the absence of
HlyD. These results are consistent with an interaction between HlyD/TolC and HlyB/HlyD. A derivative of HlyD, HlyD22, lacking
the 40 N-terminal residues of HlyD assembles into the inner membrane displaying the same stability with and without HlyB as
wild type HlyD does. This N-terminal region therefore appears to play no role in stable localisation but is involved in secretion,
since HlyD22 is completely secretion defective. Modification of the C-terminus on the other hand completely destabilised the
molecule and HlyD was not detectable in the envelope. Secretion of active haemolysin is limited to a brief period during mid
to late exponential phase. In contrast, HlyD is apparently synthesised constitutively throughout the growth phase, demonstrating
that the production of this component of the translocator is not the limiting factor for growth phase-dependent secretion.
Received: 10 July 1998 / Accepted: 19 October 1998 相似文献
10.
Entamoeba histolytica Schaudinn, 1903 and Entamoeba dispar Brumpt. 1925 are two of eight species of Entamoeba that sometimes inhabit the human colon. The former is an invasive organism capable of causing life-threatening intestinal and extra-intestinal disease: the latter appears not to be invasive. Because the two species, when viewed by light microscopy appear morphologically similar, they were long regarded as a single species. However, recent biochemical. immunological, and genetic studies provided convincing evidence that they belong to separate species. Our ultrastructural studies revealed distinct differences in at least two features of the trophozoites. 1) The cell surfaces of the trophozoites of each species differ with regard to structures exposed on the surface, and the distribution and arrangement of intra-membranous proteins. 2) The phagocytosis of bacteria differs in respect to the formation of the phagocytic vacuoles. Loose vacuoles containing several bacteria were seen in E. histolytica whereas tight vacuoles containing a single bacterium were observed in E. dispar. Furthermore, bacteria were found only within vacuoles in E. histolytica; in E. dispar, bacteria were found within vacuoles and some were found free in the cytoplasm. 相似文献