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排序方式: 共有167条查询结果,搜索用时 546 毫秒
1.
Construction of isogenic gonococci with variable porin structure: effects on susceptibility to human serum and antibiotics 总被引:11,自引:2,他引:9
Protein I (PI) is the most abundant protein on the gonococcal cell surface and besides its porin function it may have important properties contributing to pathogenicity. By allelic exchange using cloned PI genes from FA19 (PIA) and MS11 (PIB) and a selectable marker introduced closely downstream of these genes, we constructed sets of isogenic gonococcal strains that differ only in their PI gene. Analysis revealed that PI has a major effect on stable resistance to normal human serum, and a slight effect on low-level resistance to antibiotics. All PIA/B hybrids were hypersusceptible to serum, suggesting a possible explanation for why such hybrids do not occur in nature. 相似文献
2.
Aerobactin utilization by Neisseria gonorrhoeae and cloning of a genomic DNA fragment that complements Escherichia coli fhuB mutations. 总被引:18,自引:8,他引:10
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Aerobactin, a dihydroxamate siderophore produced by many strains of enteric bacteria, stimulated the growth of Neisseria gonorrhoeae FA19 and F62 in iron-limiting medium. However, gonococci did not produce detectable amounts of aerobactin in the Escherichia coli LG1522 aerobactin bioassay. We probed gonococcal genomic DNA with the cloned E. coli aerobactin biosynthesis (iucABCD), aerobactin receptor (iutA), and hydroxamate utilization (fhuCDB) genes. Hybridization was detected with fhuB sequences but not with the other genes under conditions which will detect 70% or greater homology. Similar results were obtained with 21 additional strains of gonococci by colony filter hybridization. A library of DNA from N. gonorrhoeae FA19 was constructed in the phasmid vector lambda SE4, and a clone was isolated that complemented the fhuB mutation in derivatives of E. coli BU736 and BN3307. These results suggest that fhuB is a conserved gene and may play a fundamental role in iron acquisition by N. gonorrhoeae. 相似文献
3.
Stringfellow DA Gray BW Sparling PH Panangala VS Galik PA Young-White RR 《Theriogenology》1985,23(4):701-710
Uterine flushings were collected three times at predetermined intervals from 11 mixed-breed beef cows and cultured for Brucella abortus . Prior to sampling, all cows had aborted fetuses from which brucellae had been isolated. Initial collections were made between 21 and 34 days following abortion. The second flushing was conducted at the onset of injections used for inducing superovulation and the third flushing was conducted 6 to 8 days after the ensuing estrus. The latter two flushes were conducted between 60 and 120 days following abortion. Brucellae were isolated from uterine flushings collected from 6 of the 11 cows on the initial round of sampling. Cultures of all subsequent uterine flushings collected before and after injections for superovulation were negative. It was concluded that the superovulatory treatment is not likely to reactivate the release of brucellae into the uterine lumen during the period when embryos are normally collected. 相似文献
4.
immunocytochemical localization of urokinase-type plasminogen activator in lewis lung carcinoma 总被引:1,自引:0,他引:1
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L Skriver LI Larsson V Kielberg LS Nielsen PB Andresen P Kristensen K Dano 《The Journal of cell biology》1984,99(2):753-758
The invasively growing and metasizing Lewis lung carcinoma consistently contained urokinase-type plasminogen activator (u-PA) enzyme activity. When investigated immunocytochemically with antibodies against u-PA, different parts of individual tumors showed a pronounced heterogeneity in staining intensity. Strong staining was found in areas with invasive growth and degradation of surrounding normal tissue, while other areas were completely devoid of staining. Immunoreactivity occurred both with a perinuclear cytoplasmic localization in tumor cells and associated with apparently extracellular material. SDS PAGE of tumor extracts, under both reducing and nonreducing conditions, followed by immunoblotting, showed only one immunocytochemically stainable band with an electrophoretic mobility corresponding to that of purified proenzyme to u-PA, while no two-chain u-PA was detected. This indicates that the major part of the activator in Lewis lung carcinoma is present as one-chain pro-u-PA. 相似文献
5.
Methanococcus thermolithotrophicus is a methanogenic archaebacterium that can use either H2 or formate as its source of electrons for reduction of CO2 to methane. Growth and suspended-whole-cell experiments show that H2 plus CO2 methanogenesis was constitutive, while formate methanogenesis required adaptation time; selenium was necessary for formate utilization. Cells grown on formate had 20 to 100 times higher methanogenesis rates on formate than cells grown on H2-CO2 and transferred into formate medium. Enzyme assays with crude extracts and with F420 or methyl viologen as the electron acceptor revealed that hydrogenase was constitutive, while formate dehydrogenase was regulated. Cells grown on formate had 10 to 70 times higher formate dehydrogenase activity than cells grown on H2-CO2 with Se present in the medium; when no Se was added to H2-CO2 cultures, even lower activities were observed. Adaptation to and growth on formate were pH dependent, with an optimal pH for both about one pH unit above that optimal for H2-CO2 (pH 5.8 to 6.5). When cells were grown on H2-CO2 in the presence of formate, formate (greater than or equal to 50 mM) inhibited both growth and methanogenesis at pH 5.8 to 6.2, but not at pH greater than 6.6. Both acetate and propionate produced similar inhibition. Formate inhibition was also observed in Methanospirillum hungatei. 相似文献
6.
7.
Seven transformation-deficient mutants of piliated, competent Neisseria gonorrhoeae were isolated by screening them for their inability to be transformed by chromosomal DNA after chemical mutagenesis. Three distinct classes of mutants were obtained, each of which was piliated, as determined by electron microscopy. One class exhibited abnormal colony morphology and was unable to take up DNA into a DNase-resistant state. A second class was morphologically normal and took up DNA into a DNase-resistant state normally, but was deficient in both chromosomal and plasmid transformation; mutations in these mutants may affect entry of DNA into the cell proper. A third class was similar to the second but was fully competent for plasmid transformation, suggesting that there was a defect in a late stage of chromosomal transformation. 相似文献
8.
The pathogenic Neisseria spp. produce a number of iron-regulated gene products that are thought to be important in virulence. Iron-responsive regulation of these gene products has been attributed to the presence in Neisseria spp. of the Fur (ferric uptake regulation) protein. Evidence for the role of Fur in neisserial iron regulation has been indirect because of the inability to make fur null mutations. To circumvent this problem, we used manganese selection to isolate missense mutations of Neisseria gonorrhoeae fur. We show that a mutation in gonococcal fur resulted in reduced modulation of expression of four well-studied iron-repressed genes and affected the iron regulation of a broad range of other genes as judged by two-dimensional polyacrylamide gel electrophoresis (PAGE). All 15 of the iron-repressed spots observed by two-dimensional PAGE were at least partially derepressed in the fur mutant, and 17 of the 45 iron-induced spots were affected by the fur mutation. Thus, Fur plays a central role in regulation of iron-repressed gonococcal genes and appears to be involved in regulation of many iron-induced genes. The size and complexity of the iron regulons in N. gonorrhoeae are much greater than previously recognized. 相似文献
9.
10.
Expression of gonococcal transferrin-binding protein 1 causes Escherichia coli to bind human transferrin. 总被引:10,自引:4,他引:6
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The gene for gonococcal transferrin-binding protein 1 (TBP1) was cloned behind an inducible promoter in Escherichia coli. The resultant strain was capable of binding human transferrin with the same specificity as that of the gonococcus. E. coli expressing TBP1 did not internalize transferrin-bound iron or grow on transferrin as a sole iron source. 相似文献