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排序方式: 共有897条查询结果,搜索用时 578 毫秒
891.
892.
893.
Andrew Bakun Elizabeth A. Babcock Salvador E. Lluch-Cota Christine Santora Christian J. Salvadeo 《Reviews in Fish Biology and Fisheries》2010,20(1):9-29
The Gulf of California system presents major challenges to the still developing frameworks for ecosystem-based management
(EBM). It is very much an open system and is intermittently subject to important influxes of migratory visitors, including large pelagic predatory fishes and small
pelagic forage fishes. These migrants include the more tropical species from the coastal ecosystems to the south and perhaps
subtropical sardines and anchovies from the California Current upwelling system. In addition to the multi-annual ENSO-scale
and what may seem to be rather erratic episodes of major population incursions, the Gulf presents nonstationary, transient
aspects on a variety of longer time scales. Moreover, the removal of top predators by commercial and sport fisheries has introduced
trends that must be affecting the entire ecosystem, and certainly the forage fishes that are their major prey base. In addition
to size limits, fishing seasons, area closures and license limitations, the fishery is managed by an ad hoc adaptive management
system, in which the fishing season can be shortened or additional areas closed to fishing if pre-season exploratory fishing
surveys indicate a shortage of small pelagic fishes on the fishing grounds. Whether this system is likely to be sustainable
in the long term is difficult to determine, given the potential for rapid changes in the system because of environmental changes
and/or feedbacks within the food web. Thus it appears that innovative management frameworks, among other things utilizing
the comparative method, may be required in order to determine defensible tradeoffs between precaution and resource utilization. 相似文献
894.
Zachary N Russ 《Journal of biological engineering》2009,3(1):7-3
The following essay was written by a sophomore undergraduate student majoring in Bioengineering at the University of Maryland,
Mr. Zachary Russ. Mr. Russ was one of 174 students who submitted a 1000–1200 word essay to the 4th Annual Bioethics Contest
sponsored by the Institute of Biological Engineering (IBE). A group of professionals in Biological Engineering assessed and
ranked the essays in a blinded process. Five semi-finalists were invited to present their essays at a session at the annual
meeting of IBE in Santa Clara, CA on March 21, 2009. Five judges scored all the presentation at the annual meeting and selected
Mr. Russ's contribution as the overall winner (1st Place). 相似文献
895.
A rapid, light-induced reversible component in Signal II is observed upon inhibition of oxygen evolution in broken spinach chloroplasts. The inhibitory treatments used include Tris washing, heat, treatment with chaotropic agents, and aging. This new Signal II component is in a 1 : 1 ratio with Signal I (P700). Its formation corresponds to a light-induced oxidation which occurs in less than 500 μs. The subsequent decay of the radical results from a reduction which occurs more rapidly as the reduction potential of the chloroplast suspension is decreased. The formation of this free radical component is complete following a single 10-μs flash, and it occurs with a quantum efficiency similar to that observed for Signal I formation. Red light is more effective than far-red light in the generation of this species, and, in preilluminated chloroplasts, 3-(3,4-dichlorophenyl)-1,1-dimethylurea blocks its formation. Inhibition studies show that the decline in oxygen evolution parallels the activation of this Signal II component.These results are interpreted in terms of a model in which two pathways, one involving water, the other involving the rapid Signal II component, compete for oxidizing equivalents generated by Photosystem II. In broken chloroplasts this Signal II pathway is deactivated and water is the principal electron donor. However, upon inhibition of oxygen evolution, the Signal II pathway is activated. 相似文献
896.
Merrill S. Babcock Maria R. Marino William T. Gunning III Gary D. Stoner 《In vitro cellular & developmental biology. Plant》1983,19(5):403-415
Summary The clonal growth and serial propagation of rat esophageal epithelial cells in low serum-containing medium has been achieved
without feeder layers or conditioned medium. To date, a total of four lines have been developed and maintained for as many
as 40 passages in culture. Growth of the cells was possible only after modifying the culture medium (PFMR-4) by reducing the
calcium concentration from 1 to 0.1 mM, and by adding low levels of dialyzed fetal bovine serum and seven growth factors; i.e. epidermal growth factor, hydrocortisone,
ethanolamine, phosphoethanolamine, insulin, transferrin, and cholera toxin. Cell lines have been developed from both explant
outgrowths and enzyme dissociated esophagi. The epithelial nature of the cells was confirmed by electron microscopy and immunological
methods. Clonal growth studies revealed that optimal cell growth occurred in medium containing 2.4% dialyzed fetal bovine
serum and 0.1 mM calcium. Calcium levels of 0.3 mM or higher caused the cells to stratify and undergo terminal differentiation. Coating the culture dishes with collagen, or
a combination of collagen, fibronectin, and bovine serum albumin, increased both the cell growth rate and the colony forming
efficiency. The successful long term culture of rat esophageal epithelial cells permits their use as models in studies concerned
with esophageal differentiation and carcinogenesis.
This investigation was supported by U.S. Public Health Service Grant CA 28950, awarded by the National Cancer Institute, Bethesda,
MD. 相似文献
897.
Reflex modulation of airflow dynamics through the upper airway 总被引:2,自引:0,他引:2
Seelagy M. M.; Schwartz A. R.; Russ D. B.; King E. D.; Wise R. A.; Smith P. L. 《Journal of applied physiology》1994,76(6):2692-2700