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1.
Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state 总被引:6,自引:1,他引:5
The genes for cellobiose utilization are normally cryptic in Escherichia
coli. The cellobiose system was used as a model to understand the process
by which silent genes are maintained in microbial populations. Previously
reported was (1) the isolation of a mutant strain that expresses the
cellobiose-utilization (Cel) genes and (2) that expression of those genes
allows utilization of three beta- glucoside sugars: cellobiose, arbutin,
and salicin. The Cel gene cluster has now been cloned from that mutant
strain. In the course of locating the Cel genes within the cloned DNA
segment, it was discovered that inactivation of the Cel-encoded hydrolase
rendered the host strain sensitive to all three beta-glucosides as potent
inhibitors. This sensitivity arises from the accumulation of the
phosphorylated beta- glucosides. Because even the fully active genes
conferred some degree of beta-glucoside sensitivity, the effects of
cellobiose on a series of five Cel+ mutants of independent origin were
investigated. Although each of those strains utilizes cellobiose as a sole
carbon and energy source, cellobiose also acts as a potent inhibitor that
reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand,
wild-type strains that cannot utilize cellobiose are not inhibited. The
observation that the same compound can serve either as a nutrient or as an
inhibitor suggests that, under most conditions in which cellobiose will be
present together with other resources, there is a strong selective
advantage to having the cryptic (Cel0) allele. In those environments in
which cellobiose is the sole, or the best, resource, mutants that express
the genes (Cel+) will have a strong selective advantage. It is suggested
that temporal alternation between these two conditions is a major factor in
the maintenance of these genes in E. coli populations. This alternation of
environments and fitnesses was predicted by the model for cryptic-gene
maintenance that was previously published.
相似文献
2.
It has been found that tissues fixed for electron microscopy and dehydrated in acetone can be embedded in mixtures of n-butyl methacrylate and polyester resin. Activation with 1 per cent tert-butyl hydroperoxide followed by 12 to 48 hours at 60°C produces blocks that section well with glass knives. The ribbons are cleared of methacrylate by heat (200–250°C for 1 hour) and/or immersion in organic solvents (CCL4, acetone-ether). After removal of the methacrylate the residual polyester matrix provides thermostable and insoluble support for the tissue. Its insolubility permits staining by immersion of cleared preparations in organic solvents carrying heavy metal compounds in solution. Clearing by heat stabilizes section-grid relationships. The removal of volatile materials by clearing substantially reduces contamination of both specimen and microscope. Tissue fine structure is well preserved in these preparations. 相似文献
3.
Anthony P. Clevenger 《Ecography》1994,17(3):257-263
Eurasian pine martens are considered habitat specialists, associated primarily with mature stands of mesic mixed wood forest habitats, and avoid areas without overhead cover The species is found throughout the temperate and boreal regions of the continent but on the Mediterranean island of Minorca, introduced pine martens thrive in a competitor- and predator-free environment I test the prediction that because of evolved prey-capture and predator avoidance strategies Minorcan martens should select habitats most similar to temperate and northern parts of their range Scat index routes were used to quantify pine marten habitat selection Marten did not demonstrate any habitat type preferences although observed use of pine forests and coastal shrublands was slighly greater than expected Marten were indifferent to overhead cover whereas mesic sites and areas of tall high shrub density were favored Small mammal trap indices and preferred prey suggested that martens commonly used non-forested areas My results demonstrated that on Minorca pine martens were habitat generalists In the absence of predators open non-forested habitats were equally important to pine marten as were forested ones 相似文献
4.
Sarah Clevenger 《Biochemical Systematics and Ecology》1978,6(4):279-281
17 strains of New Guinea Impatiens belonging to the I. schlecteri—linearifolia group and to the I. hawkeri—mooreana—nivea group were analysed for the anthocyanidin pigments. Pelargonidin predominated in the schlecteri group white malvidin was most common in the mooreana group. 相似文献
5.
6.
Anthony P. Clevenger John Paczkowski John P. Volpe Jason T. Fisher 《Ecology and evolution》2016,6(5):1493-1503
Understanding a species’ behavioral response to rapid environmental change is an ongoing challenge in modern conservation. Anthropogenic landscape modification, or “human footprint,” is well documented as a central cause of large mammal decline and range contractions where the proximal mechanisms of decline are often contentious. Direct mortality is an obvious cause; alternatively, human‐modified landscapes perceived as unsuitable by some species may contribute to shifts in space use through preferential habitat selection. A useful approach to tease these effects apart is to determine whether behaviors potentially associated with risk vary with human footprint. We hypothesized wolverine (Gulo gulo) behaviors vary with different degrees of human footprint. We quantified metrics of behavior, which we assumed to indicate risk perception, from photographic images from a large existing camera‐trapping dataset collected to understand wolverine distribution in the Rocky Mountains of Alberta, Canada. We systematically deployed 164 camera sites across three study areas covering approximately 24,000 km2, sampled monthly between December and April (2007–2013). Wolverine behavior varied markedly across the study areas. Variation in behavior decreased with increasing human footprint. Increasing human footprint may constrain potential variation in behavior, through either restricting behavioral plasticity or individual variation in areas of high human impact. We hypothesize that behavioral constraints may indicate an increase in perceived risk in human‐modified landscapes. Although survival is obviously a key contributor to species population decline and range loss, behavior may also make a significant contribution. 相似文献
7.
Rycyzyn MA Reilly SC O'Malley K Clevenger CV 《Molecular endocrinology (Baltimore, Md.)》2000,14(8):1175-1186
The pleiotropic actions of PRL are necessary for mammary growth and differentiation and in vitro lymphoid proliferation. The proximal action of this ligand is mediated by its cell surface receptor via associated networks. PRL action, however, is also associated with the internalization and translocation of this hormone into the nucleus. To delineate the mechanism of this retrotranslocation, a yeast two-hybrid screen was performed and revealed an interaction between PRL and cyclophilin B (CypB). CypB is a peptidyl prolyl isomerase (PPI) found in the endoplasmic reticulum, extracellular space, and nucleus. The interaction between CypB and PRL was subsequently confirmed in vitro and in vivo through the use of recombinant proteins and coimmunoprecipitation studies. The exogenous addition of CypB potentiated the 3H-thymidine incorporation of PRL-dependent cell lines up to 18-fold. CypB by itself was nonmitogenic and did not potentiate the action of GH or other interleukins. CypB did not alter the affinity of the PRL receptor (PRLr) for its ligand, or increase the phosphorylation of PRLr-associated Jak2 or Stat5a. The potentiation of PRL-action by CypB, however, was accompanied by a dramatic increase in the nuclear retrotranslocation of PRL. A CypB mutant, termed CypB-NT, was generated that lacked the wild-type N-terminal nuclear localization sequence. Although CypB-NT demonstrated levels of PRL binding and PPI activity equivalent to wild-type CypB, it was incapable of mediating the nuclear retrotranslocation of PRL or enhancing PRL-driven proliferation. These studies reveal CypB as an important chaperone facilitating the nuclear retrotransport and action of the lactogenic hormones. 相似文献
8.
Stoichiometric Structure-Function Analysis of the Prolactin Receptor Signaling Domain by Receptor Chimeras 总被引:1,自引:0,他引:1 下载免费PDF全文
The intracellular domain of the prolactin (PRL) receptor (PRLr) is required for PRL-induced signaling and proliferation. To identify and test the functional stoichiometry of those PRLr motifs required for transduction and growth, chimeras consisting of the extracellular domain of either the α or β subunit of human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (GM-CSFr) and the intracellular domain of the rat PRLr were synthesized. Because the high-affinity binding of GM-CSF results from the specific pairing of one α- and one β-GM-CSFr, use of GM-CSFr/PRLr chimera enabled targeted dimerization of the PRLr intracellular domain. To that end, the extracellular domains of the α- and β-GM-CSFr were conjugated to one of the following mutations: (i) PRLr C-terminal truncations, termed α278, α294, α300, α322, or β322; (ii) PRLr tyrosine replacements, termed Y309F, Y382F, or Y309+382F; or, (iii) PRLr wild-type short, intermediate, or long isoforms. These chimeras were cotransfected into the cytokine-responsive Ba/F3 line, and their expression was confirmed by ligand binding and Northern and Western blot analyses. Data from these studies revealed that heterodimeric complexes of the wild type with C-terminal truncation mutants of the PRLr intracellular domain were incapable of ligand-induced signaling or proliferation. Replacement of any single tyrosine residue (Y309F or Y382F) in the dimerized PRLr complex resulted in a moderate reduction of receptor-associated Jak2 activation and proliferation. In contrast, trans replacement of these residues (i.e., αY309F and βY382F) markedly reduced ligand-driven Jak2 activation and proliferation, while cis replacement of both tyrosine residues in a single intracellular domain (i.e., αY309+382F) produced an inactive signaling complex. Analysis of these GM-CSFr–PRLr complexes revealed equivalent levels of Jak2 in association with the mutant receptor chains, suggesting that the tyrosine residues at 309 and 382 do not contribute to Jak association, but instead to its activation. Heterodimeric pairings of the intracellular domains from the known PRLr receptor isoforms (short-intermediate, short-long, and intermediate-long) also yielded inactive receptor complexes. These data demonstrate that the tyrosine residues at 309 and 382, as well as additional residues within the C terminus of the dimerized PRLr complex, contribute to PRL-driven signaling and proliferation. Furthermore, these findings indicate a functional requirement for the pairing of Y309 and Y382 in trans within the dimerized receptor complex. 相似文献
9.
Clevenger T Wu Y DeGruson E Brazos B Banerji S 《Journal of applied microbiology》2007,103(6):2285-2290
AIMS: To compare the disinfection ability of two widely used electrolytic generation systems (ClorTec and MIOX) and the conventional chlorine disinfectant (sodium hypochlorite) using three strains of Bacillus subtilis spores and MS2 bacteriophage. METHODS AND RESULTS: Three B. subtilis aerobic spore strains (ATCC1A1, 35021 and 35946) and the bacteriophage MS2 (ATCC 15597-B1) were propagated and sporulated. Four indicator organisms were exposed to four disinfectant treatments for comparing the effectiveness of inactivation: hypochlorite, ClorTec, MIOX and MIOX-anode. The results indicated that the two electrolytic generation systems were as effective as the conventional chlorination for the inactivation of micro-organisms used. Some data points showed the variation using anova analysis, in which the inactivation of MIOX and ClorTec was higher than that of hypochlorite. CONCLUSIONS: The ClorTec and MIOX systems are quite similar to hypochlorite in the inactivation-effectiveness for aerobic spores and bacteriophage in drinking water. SIGNIFICANCE AND IMPACT OF THE STUDY: Laboratory-scale investigation proved that gaseous chlorine could be replaced by either ClorTec or MIOX systems for the drinking water treatment utilities, which still could maintain the same disinfection efficiency. 相似文献
10.
Elisabeth APM Romme Piet Geusens Willem F Lems Erica PA Rutten Frank WJM Smeenk Joop PW van den Bergh Peter ThW van Hal Emiel FM Wouters 《Respiratory research》2015,16(1)
Although osteoporosis and its related fractures are common in patients with COPD, patients at high risk of fracture are poorly identified, and consequently, undertreated. Since there are no fracture prevention guidelines available that focus on COPD patients, we developed a clinical approach to improve the identification and treatment of COPD patients at high risk of fracture. We organised a round-table discussion with 8 clinical experts in the field of COPD and fracture prevention in the Netherlands in December 2013. The clinical experts presented a review of the literature on COPD, osteoporosis and fracture prevention. Based on the Dutch fracture prevention guideline, they developed a 5-step clinical approach for fracture prevention in COPD. Thereby, they took into account both classical risk factors for fracture (low body mass index, older age, personal and family history of fracture, immobility, smoking, alcohol intake, use of glucocorticoids and increased fall risk) and COPD-specific risk factors for fracture (severe airflow obstruction, pulmonary exacerbations and oxygen therapy). Severe COPD (defined as postbronchodilator FEV1 < 50% predicted) was added as COPD-specific risk factor to the list of classical risk factors for fracture. The 5-step clinical approach starts with case finding using clinical risk factors, followed by risk evaluation (dual energy X-ray absorptiometry and imaging of the spine), differential diagnosis, treatment and follow-up. This systematic clinical approach, which is evidence-based and easy-to-use in daily practice by pulmonologists, should contribute to optimise fracture prevention in COPD patients at high risk of fracture. 相似文献