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61.
Persistent neural activity constitutes one neuronal correlate of working memory, the ability to hold and manipulate information
across time, a prerequisite for cognition. Yet, the underlying neuronal mechanisms are still elusive. Here, we design a visuo-
spatial delayed-response task to identify the relationship between the cue-distractor spatial distance and mnemonic accuracy.
Using a shared experimental and computational test protocol, we probe human subjects in computer experiments, and subsequently
we evaluate different neural mechanisms underlying persistent activity using an in silico prefrontal network model. Five modes
of action of the network were tested: weak or strong synaptic interactions, wide synaptic arborization, cellular bistability
and reduced synaptic NMDA component. The five neural mechanisms and the human behavioral data, all exhibited a significant
deterioration of the mnemonic accuracy with decreased spatial distance between the distractor and the cue. A subsequent computational
analysis revealed that the firing rate and not the neural mechanism per se, accounted for the positive correlation between
mnemonic accuracy and spatial distance. Moreover, the computational modeling predicts an inverse correlation between accuracy
and distractibility. In conclusion, any pharmacological modulation, pathological condition or memory training paradigm targeting
the underlying neural circuitry and altering the net population firing rate during the delay is predicted to determine the
amount of influence of a visual distraction. 相似文献
62.
Application of Measurements of Transepithelial Electrical Resistance of Intestinal Epithelial Cell Monolayers To Evaluate Probiotic Activity 总被引:2,自引:0,他引:2
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Trine Dan? Klingberg Maja Herold Pedersen Avrelija Cencic Birgitte Bj?rn Budde 《Applied microbiology》2005,71(11):7528-7530
Among five potentially probiotic lactobacilli investigated, Lactobacillus plantarum MF1298 and Lactobacillus salivarius DC5 showed the highest increase in the transepithelial electrical resistance (TER) of polarized monolayers of Caco-2 cells, and this increase was shown to be dose dependent. Furthermore, preincubation with MF1298 attenuated a decrease in TER induced by Listeria monocytogenes. 相似文献
63.
Ohlsson AB Djerbi S Winzell A Bessueille L Ståldal V Li X Blomqvist K Bulone V Teeri TT Berglund T 《Protoplasma》2006,228(4):221-229
Summary. Compared to wood, cell suspension cultures provide convenient model systems to study many different cellular processes in
plants. Here we have established cell suspension cultures of Populus tremula L. × P. tremuloides Michx. and characterized them by determining the enzymatic activities and/or mRNA expression levels of selected cell wall-specific
proteins at the different stages of growth. While enzymes and proteins typically associated with primary cell wall synthesis
and expansion were detected in the exponential growth phase of the cultures, the late stationary phase showed high expression
of the secondary-cell-wall-associated cellulose synthase genes. Interestingly, detergent extracts of membranes from aging
cell suspension cultures exhibited high levels of in vitro cellulose synthesis. The estimated ratio of cellulose to callose
was as high as 50 : 50, as opposed to the ratio of 30 : 70 so far achieved with membrane preparations extracted from other
systems. The increased cellulose synthase activity was also evidenced by higher levels of Calcofluor white binding in the
cell material from the stationary-phase cultures. The ease of handling cell suspension cultures and the improved capacity
for in vitro cellulose synthesis suggest that these cultures offer a new basis for studying the mechanism of cellulose biosynthesis.
Correspondence and reprints: School of Biotechnology, Royal Institute of Technology, AlbaNova University Centre, 106 91 Stockholm,
Sweden.
Present address: Department of Biotechnology, Beijing Forestry University, Beijing, People’s Republic of China 相似文献
64.
Plankton composition and cycling of carbon during the rainy season in a tropical coastal ecosystem, Zanzibar, Tanzania 总被引:3,自引:0,他引:3
Lugomela Charles; Wallberg Petra; Nielsen Torkel Gissel 《Journal of plankton research》2001,23(10):1121-1136
Biomass, species composition and production of the planktoniccommunity were investigated during the rainy season in May andJune 1999 outside Zanzibar Island, Tanzania. In general, theplankton biomass of different organisms was uniform betweendepths as well as over time. The integrated water column primaryproduction ranged from 204 to 4142 mg C m2 day1.Bacterial production varied between 10 and 72 mg C m2day1, comprising ~5% of the total bacterial standingstock. The data obtained from these experiments are summarizedin a carbon budget. At the most 77% of the total primary productionchannelled through the heterotrophic flagellates, ciliates andheterotrophic dinoflagellates to higher trophic levels. Of theestimated carbon demand for mesozooplankton, 28% could potentiallybe met by ciliates and heterotrophic dinoflagellates. 相似文献
65.
66.
Trevor J. Trust Magdalena Kostrzynska Levente Emödy Torkel Wadström 《Molecular microbiology》1993,7(4):593-600
The surface of the fish pathogen Aeromonas salmonicida is covered by a paracrystalline array (the A-layer) which is a virulence factor for the organism. Quantification of the ability of A. salmonicida cells to bind collagen types I and IV in a 125I-radiolabelled liquid-phase assay showed that A-layer-positive cells bound high levels of collagen type IV, but significantly lower levels of collagen type I. Collagen type IV binding was confirmed using non-radiolabelled enzyme-linked immunosorbent assays. 125I-Collagen type IV binding was rapid, specific, saturable, high affinity, and essentially irreversible by unlabelled collagen type IV. The A-layer was responsible for collagen type IV binding because binding was inactivated by selective removal of the A-layer at pH 2.2, and neither isogenic A-layer-deficient A. salmonicida mutants nor strains of Aeromonas hydrophila possessing a morphologically similar paracrystalline array bound this basement membrane protein. 相似文献
67.
Association of Helicobacter pylori and gastric autoimmunity: A population-based study 总被引:1,自引:0,他引:1
Raivo Uibo Tamara Vorobjova Kaja Metsküla Kalle Kisand Torkel Wadström Tiiu Kivik 《FEMS immunology and medical microbiology》1995,11(1):65-68
Abstract Based on clinical studies, a negative association between Helicobacter pylori and autoimmune corpus gastritis is described. In the present investigation of an unselected population of 1461 adults we can state, however, that there exists a relationship between H. pylori infection and the development of gastric corpus autoimmunity. As confirmation for the gastric autoantibody development through molecular mimicry, a high homology (72% in 25 amino acid overlap) between the beta subunit of H. pylori urease and that of H + K + ATPase, the gastric parietal cell autoantigen, was revealed. 相似文献
68.
The initial adhesion of microbes to tissue and solid surfaces can be mediated by hydrophobic interaction. Expression of microbial cell surface hydrophobicity (CSH) is influenced by growth conditions, and often best expressed after growth under nutrient-poor conditions, or “starvation.” In the present study, the CSH of 133 strains of Enterobacteriaceae, Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus faecalis, group A streptococcus, Pseudomonas aeruginosa, Clostridium perfringens, Bacteroides fragilis, Peptococcus magnus, and of 8 Candida albicans strains was measured by the salt aggregation test after growth on hematin agar in a 5% CO2 atmosphere, or under anaerobiosis. Cells of all but 8 strains expressed pronounced or moderate CSH, i.e., they aggregated in 0.01-2 M ammonium sulfate. When the agar surface was covered by human serum (diluted 1:5) to mimic growth conditions in a wound, 94 strains expressed higher CSH, and 44 strains the same CSH as after growth without serum. The CSH of 12 strains of different species was measured after growth on blood, hematin and PDM agar, with or without serum, and in an aerobic or a 5% CO2 atmosphere. The highest CSH was expressed after growth in 5% CO2 with serum, and the lowest growth after on blood agar in aerobic atmosphere. Identical results were obtained with native and heat-inactivated (56 C, 20 min) serum. The reduced surface tension obtained in 5% CO2, as well as yet unidentified serum factors, promotes expression of CSH. 相似文献
69.
Hydrophobic and hemagglutinating activities of piliated enterotoxigenicEscherichia coli possessing colonization factor antigens (CFA)/I and putative CFA/II, strains with type 1 pili, and piliated strains of nonenterotoxigenicE. coli from urinary tract infections were compared. When passed through columns of hydrophobic Phenyl Sepharose in the presence of buffered ammonium sulfate, the strains with CFA adsorbed most strongly. Similarly, the CFA strains showed a tendency to autoagglutinate at a lower (NH4)2SO4 concentration than the other strains studied. The degree of hydrophobicity of the strains tested is in the order CFA/I>CFA/II>type 1 pili>urinary tract strains. Rough variants ofE. coli strains were more hydrophobic than their smooth parents. Electron microscopy showed large numbers of pili on CFA strains, whereas type 1 piliated strains possessed fewer pili. CFA-negative clones possessed few or no, pili and did not adsorb to the gel. A highly piliated mutant strain (PAK/2PfS) ofPseudomonas aeruginosa bound to the Phenyl Sepharose while the poorly piliated wild-type strains did not. Strains, lost their adsorptive capacity after blending, sonication, heating, or trypsin treatment. It is concluded that the hydrophobicity of enteric organisms, as measured by hydrophobic interaction chromatography, is a function of the type and number of pili on the cell surface. 相似文献
70.
Summary Human diploid embryonic lung fibroblasts were cultivated in Eagle's Minimum Essential Medium and labeled with3H-uridine. The release of soluble radioactive substances into the medium was used as an indicator of damage to the cell membrane. The assay method described is simple, sensitive and rapid and allows quantitative estimation of changes in membrane permeability before any morphological damage is observed microscopically. Crude commercial preparations of phospholipase C (E.C. 3.1.4.3.) (40 g/ml) were highly active on the cell membrane but most of the membrane damaging activity was found to be due to contaminating theta-toxin. However, also highly purified phospholipase C caused a membrane damage as measured by release of isotope through the plasma membrane. The release could be increased by including an optimal concentration of calcium ions in the incubation buffer, by treating the cells in a hypotonic medium and by simultaneous treatment with sublytic concentrations of Triton X-100. To our knowledge this is the first report of membrane damage on a live, intact, metabolizing human diploid cell caused by a highly purified phospholipase C. The results are in agreement with a dynamic membrane structure with the polar groups of a part of the phospholipids accessible at the membrane surface. 相似文献