全文获取类型
收费全文 | 133篇 |
免费 | 3篇 |
专业分类
136篇 |
出版年
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 5篇 |
2007年 | 10篇 |
2004年 | 2篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1959年 | 1篇 |
1953年 | 1篇 |
1952年 | 1篇 |
1937年 | 2篇 |
1936年 | 1篇 |
1934年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有136条查询结果,搜索用时 0 毫秒
91.
Konrad V. Miller Roberto Noguera Jordan Beaver Anita Oberholster David E. Block 《Biotechnology and bioengineering》2020,117(1):109-116
Red wine production begins with a simultaneous fermentation and solid-phase extraction process. Red wine color and mouthfeel is the result of the extraction of phenolics from grape skins and seeds during fermentation, where extraction is a strong function of temperature and ethanol concentration. During fermentation, grape solids form a porous “cap” at the top of the fermentor, resulting in a heterogeneous fermentation system with significant temperature and concentration gradients. In this work, we present a spatial, time-variant reactor engineering model for phenolic extraction during red wine fermentation, incorporating fermentation kinetics, mass transfer, heat transfer, compressible fluid flow, and phenolic extraction kinetics. The temperature and ethanol concentration profiles predicted by this model allow for the calculation of phenolic extraction rates over the course of fermentation. Phenolic extraction predictions were validated against prior experimental data to good agreement and compared to a well-mixed model's predictions to show the utility of a spatial model over well-mixed models. 相似文献
92.
CM Beaver 《Cell biology and toxicology》2012,28(5):291-301
Primary cultures and cell lines form three types of colonies, termed holoclones, meroclones and paraclones by Barrandon and Green (Proc Natl Acad Sci U S A 84:2302-2306, 1987). They suggested that the three types correspond to colonies derived from stem, transit-amplifying and terminally differentiated cells. We determined the effect of culture conditions (seeding density, serum concentration, type of medium and substrate) on the proportion of each colony type and the cell number of individual colonies, using three prostate cancer cell lines, DU145, LNCaP and PC-3. In less favourable culture conditions, stem cell (SC) colonies tended to be lost; but in more favourable conditions, only modest increases in the proportion of SC colonies were observed. Under some conditions, cell number, but not colony-forming ability, was altered, indicating that colony cell number is controlled, at least in part, by different factors to colony formation. Colony-forming ability of individual cell lines is remarkably stable and there is little evidence for clonal evolution in culture, which might be expected and would result in more aggressive, faster-growing cells. Better understanding of how colony-forming efficiency is controlled could lead to the identification of drug targets that control SC growth and modify the progression of cancer. 相似文献
93.
Laura M. Beaver Vladimir I. Klichko Eileen S. Chow Joanna Kotwica-Rolinska Marisa Williamson William C. Orr Svetlana N. Radyuk Jadwiga M. Giebultowicz 《PloS one》2012,7(11)
Circadian clocks generate daily rhythms in neuronal, physiological, and metabolic functions. Previous studies in mammals reported daily fluctuations in levels of the major endogenous antioxidant, glutathione (GSH), but the molecular mechanisms that govern such fluctuations remained unknown. To address this question, we used the model species Drosophila, which has a rich arsenal of genetic tools. Previously, we showed that loss of the circadian clock increased oxidative damage and caused neurodegenerative changes in the brain, while enhanced GSH production in neuronal tissue conferred beneficial effects on fly survivorship under normal and stress conditions. In the current study we report that the GSH concentrations in fly heads fluctuate in a circadian clock-dependent manner. We further demonstrate a rhythm in activity of glutamate cysteine ligase (GCL), the rate-limiting enzyme in glutathione biosynthesis. Significant rhythms were also observed for mRNA levels of genes encoding the catalytic (Gclc) and modulatory (Gclm) subunits comprising the GCL holoenzyme. Furthermore, we found that the expression of a glutathione S-transferase, GstD1, which utilizes GSH in cellular detoxification, significantly fluctuated during the circadian day. To directly address the role of the clock in regulating GSH-related rhythms, the expression levels of the GCL subunits and GstD1, as well as GCL activity and GSH production were evaluated in flies with a null mutation in the clock genes cycle and period. The rhythms observed in control flies were not evident in the clock mutants, thus linking glutathione production and utilization to the circadian system. Together, these data suggest that the circadian system modulates pathways involved in production and utilization of glutathione. 相似文献
94.
95.
96.
Thermal regimes of Florida lakes 总被引:3,自引:3,他引:0
Water column temperatures were determined monthly for 24 lakes and bimonthly for 5 lakes in peninsular Florida during 1979. Three geographical groups (north, central, south) were delineated from mean monthly water column temperatures for individual lakes. On a monthly basis, northern lakes were least similar to southern lakes, while central Florida lakes displayed greater affinity to the southern than to the northern lake group. Temperature differences between lake groups broke down during late summer. Subtropical lakes have been defined tentatively as those Florida lakes south of 28° latitude which possess warm monomictic circulation and a mean annual temperature of 24.2 ± 4.8 °C with minimum water column temperature rarely less than 14 °C and summer maxima rarely exceeding 31 °C. While all lakes in Florida are clearly warm monomictic annual nutrient cycling and productivity patterns may be influenced by inter-group differences in the timing and duration of water column circulation. 相似文献
97.
Havens Karl E. Ji Gaohua Beaver John R. Fulton Rolland S. Teacher Catherine E. 《Hydrobiologia》2019,829(1):43-59
Hydrobiologia - Analysis of an 18-year dataset from seven shallow lakes in Florida provides evidence of hydrologic factors controlling dynamics of cyanobacteria blooms. Depth was the most important... 相似文献
98.
Analysis of the community structure of planktonic ciliated protozoa relative to trophic state in Florida lakes 总被引:4,自引:0,他引:4
The planktonic ciliate populations of 30 Florida lakes constituting a broad trophic gradient were examined to determine the response of protozoan community structure to increasing eutrophication. Both ciliate abundance and biomass were strongly related to lake trophic state. Comparison of the Florida data base with a comparable north temperate lake group indicated that subtropical lakes generally possess higher ciliate abundance and biomass at a given trophic state than temperate lakes. However the equations derived for each data base were not significantly different. Community diversity and species richness increased with increasing lake productivity. Highly acidic lakes displayed significantly reduced diversity and numbers of species when contrasted with nonacidic oligotrophic lakes. Small-bodied (< 30 um) ciliates dominated all lakes but were proportionally less important in oligotrophic lakes. Presence-absence data produced three assemblages: an ubiquitous association of primarily small ciliate taxa, a group of large ciliates mainly restricted to eutrophic-hypereutrophic lakes, and a very large ciliate,Stentor niger, which dominated the protozoan communities of acidic oligotrophic lakes. 相似文献
99.
The shortcomings of many established toxicity criteria for metals have resulted from a simplification of bioassays performed with single metals. A more comprehensive approach was needed to diagnose the effects of metal mixtures on aquatic organisms. Using Chlorella, Ankistrodesmus and Scenedesmus as test organisms, we experimented on a number of factors which affected metal toxicity bioassays. These included metal interactions, algal competitions, species sensitivities, the ratio of an excess metal to other metals and nutrient levels. An alternative technique was finally established which involved an evaluation of individual assays of Chlorella and Ankistrodesmus in separate media and a tissue-metal analysis on Chlorella. Chlorella fusca, commonly found in lakes with high metal concentrations, showed high tolerance to mixed-metal solutions, while Ankistrodesmus proved to be very sensitive. By determining the maximum yield ratio between Ankistrodesmus and Chlorella (i.e. the A/Ch ratio) it was possible to compare the toxic strength of harmful metals according to an established standard curve of A/Ch ratio versus mixed-metal concentrations. The levels of tissue-metal analysed in Chlorella also gave some indication as to which metals were responsible for the toxicity. 相似文献
100.
Seasonality of planktonic ciliated protozoa in 20 subtropical Florida lakes of varying trophic state 总被引:2,自引:0,他引:2
The planktonic ciliate populations of 20 Florida lakes ranging from oligotrophic to hypereutrophic were examined monthly for
one year. Oligotrophic lakes displayed abundance peaks during fall mixis and biomass peaks in late winter and fall. Mesotrophic
systems exhibited a spring-fall bimodality in ciliate abundance with a biomass maxima occurring during fall. Eutrophic/hypereutrophic
lakes had pronounced abundance and biomass maxima during summer, with the large ciliates Plagiopyla nasuta and Paramecium trichium often contributing heavily to the midsummer biomass peak. Members of the Oligotrichida numerically dominated abundance and
biomass peaks in oligotrophic lakes while the Scuticociliatida dominated the communities of higher trophic states. Total ciliate
abundance and biomass were strongly correlated with chlorophyll a concentrations as were various ciliate taxonomic groups. The relationship between ciliate seasonal distribution in these
subtropical lakes with lake thermal regimes and trophic state is discussed. 相似文献