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51.
52.
Gideonse HD 《Science (New York, N.Y.)》1970,170(3962):1054-1059
A policy framework for analyzing educational research and development has been proposed. The framework consists of five primary elements focusing on the contexts in which educational R & D operates, its goals, its characteristics, its manpower, and its decision structures. These five primary elements interact to produce two secondary elements concerned with priorities and objectives, and strategies and tactics. The framework was applied to three current policy proposals in educational R & D including directed R & D programming in the U.S. Office of Education, the request for funds for experimental schools, and the proposed National Institute of Education. Rigorous application of the framework to major policy questions such as these three can help us examine issues before they arise. It can help prevent errors. Its application can provide greater assurance that primary, secondary, and tertiary consequences-those that arise from the interaction of the consequences we most directly perceive-will receive examination. This kind of consideration can help produce the desirable and intended effects and avoid the detrimental consequences of unanticipated impacts in unintended areas. 相似文献
53.
Yellow nutsedge (Cyperus esculentus L.) is a serious weed problem in the United States and other countries. An indigenous rust fungus [Puccinia canaliculata (Schw.) Lagerh.], pathogenic on yellow nutsedge, was released in early spring as a potential biological control agent. The fungus inhibited nutsedge flowering and new tuber formation. The fungus also dehydrated and killed nutsedge plants. The successful control of yellow nutsedge by a rust epiphytotic under experimental conditions demonstrates the potential use of the rust in an integrated weed management system. 相似文献
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Calculations and some preliminary experiments suggest that an early methane atmosphere would have been polymerized by solar ultraviolet radiation in geologically short periods of time. An oil slick 1 to 10 meters thick could have been produced in this way and might well have been of considerable importance in the development of life. 相似文献
57.
Silicate melts were equilibrated with aqueous chloride solutions at temperatures between 770 degrees and 880 degrees C and a total pressure of 1.4 to 2.4 kilobars. The ratio of potassium to sodium in the aqueous phase was (0.74 +/- 0.06) times the corresponding ratio in the coexisting melt over the entire range of temperature and pressure for all chloride concentrations between 0.2 and 4.2 moles per kilogram. 相似文献
58.
The pulse structure of the four known pulsars is given. The pulse is about 38 milliseconds for the two pulsars of longest period, and within the pulsewidth three subpulses typically appear. The pulsar of next longest period typically radiates two pulses separated about 23 milliseconds in time. The one short-period pulsar emits single pulses of constant shape. The first subpulses of all pulsars have nearly the same shape. The shape of the first subpulse agrees well with the pulse shape expected from a radio-emitting sphere which is excited by a spherically expanding disturbance, and in which the radio emission, once excited, decays exponentially. 相似文献
59.
Horneck G Bücker H Reitz G Requardt H Dose K Martens KD Mennigmann HD Weber P 《Science (New York, N.Y.)》1984,225(4658):226-228
Preliminary results of the Spacelab 1 experiment on the response of Bacillus subtilis spores to conditions of free space are presented. Exposure to the vacuum of space on the Spacelab pallet reduced viability counts about 50 percent and increased mutation frequencies by a factor of about 10. Interpretation of apparent differences in the photobiological and photochemical data between flight and ground simulation experiments will require more statistical analyses and data from actual fluence measurements. 相似文献
60.
The photolysis of methyl iodide on a porous glass surface has been studied by electron paramagnetic resonance. A large number of methyl radicals can be stabilized over a wide range of temperature. The surface of porous Vycor glass is an excellent host for trapping free radicals. 相似文献