共查询到20条相似文献,搜索用时 484 毫秒
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TheU .S .EnvironmentalProtectionAgencyrequestedtheNationalResearchCouncil(whichistheoperatingarmoftheU .S .NationalAcademyofSciencesandtheU .S .NationalAcademyofEngineering)tocarryoutacriticalscientificevaluationofindicatorstomonitorecologicalchangesfromeit… 相似文献
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Rull V 《Die Naturwissenschaften》2004,91(3):139-142
The peculiar biogeography of the so-called Lost World, i.e. the summits of sandstone tableaux (tepuis) in the Neotropical Guyana region of Venezuela, has generated a debate regarding the factors that are thought to account for modern vegetation patterns in the region. Some argue that plant communities on these high-elevation summits reflect a long history of evolution in isolation, while others surmise that there has been substantial biotic interchange with the surrounding lowlands during glacial times. Until now, these apparently competing hypotheses have not been tested using palaeoecological methods. I used pollen analysis of Quaternary sediments and documented past vertical migrations of vegetation in response to climate changes, which supports the second hypothesis. Physiographical analysis, however, shows that about half the tableaux summits are too high for their flora to have reached the lowlands during the last glaciation, suggesting that a portion of the tableaux vegetation has always experienced some degree of biotic isolation. Thus, a component of the summit vegetation evolved in isolation, whereas other taxa experienced interchange, as reflected in endemism patterns among the tableaux summits. Biogeographical patterns on the summits are the result of complex evolutionary processes. The two hypotheses invoked to explain the vegetation patterns are not mutually exclusive, but instead complement one another. 相似文献
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Simen Vergote Francesca Maria Russo David Basurto Jan Deprest Neeltje Crombag 《黑龙江环境通报》2023,43(8):1018-1027
Objective
To explore the views and practices of maternal-fetal medicine specialists on offering fetoscopic endoluminal tracheal occlusion (FETO) for left- and right-sided congenital diaphragmatic hernia (LCDH, RCDH) in the post Tracheal Occlusion To Accelerate Lung growth (TOTAL)-trial era.Method
Cross-sectional knowledge, attitude and practice survey was conducted among 105 attendees of the 19th World Congress of Fetal Medicine.Results
On average, respondents were knowledgeable about CDH, involved in research, and provided antenatal treatment options. Four out of five (82%) agreed that neonatal survival in LCDH can be reliably predicted in the prenatal period. Few respondents considered the exact risks and benefits of FETO for severe LCDH as being unclear (16%), yet half were uncertain about this for moderate LCDH (57%) and severe RCDH (45%). Most respondents offer FETO for severe LCDH (97%) and RCDH (79%), but only 59% offer it for moderate LCDH. However, half of respondents (58%) stated that not offering FETO for moderate LCDH would be a psychological burden for parents.Conclusion
Respondents consider the risk-benefit ratio of FETO for severe LCDH clear and consistently offer FETO, but not for moderate LDCH and severe RCDH. However, not offering the option of FETO to parents was considered a psychological burden. 相似文献5.
-In order to reduce the increasingly serious environmental impact caused by wastewater from the paper industry, the municipality of Jinan plans to adopt a specialized production technology. The new technology will centralize pulp production and decentralize paper production. It is predicted that the new technology will greatly reduce the environmental effects of the paper industry. Perhaps it is a new direction for the development of the paper industry in China. 相似文献
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DevelopmentoftheprocedureforthestabilizationofrainwatersamplesYuanZhongxin;Chung-ShinYuan(DepartmentofChemicalEngineeringNati... 相似文献
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Purification function of the natural wetland in the Liaohe Delta 总被引:6,自引:0,他引:6
Li Xiu Zhen Qu Xiang rong Wang Lian ping Zhang Hai rong Xiao Du ning 《环境科学学报(英文版)》1999,11(2):236-242
1IntroductionStructure,functionandchangearethreeimportantaspectsoflandscapeecology(Forman,1986).Landscapefunctionmeanstheinte... 相似文献
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Today it is generally accepted that the Earth's magnetic field, as well as that of many other planets, is generated by buoyancy driven convection in the electrically conducting liquid cores of these rotating celestial bodies. The conversion of mechanical energy into electromagnetic energy is known as the dynamo effect. In contrast to technical dynamos, which utilize the rotational motion of a complex arrangement of wire coils and other materials of different electrical and magnetic properties, the geodynamo is based on a freely developing spiral flow in a practically homogeneous, electrically conducting liquid core domain, and is therefore termed a homogeneous dynamo. This report outlines some fundamental properties of the Earth's magnetic field. The structure of the spiral flow in the liquid interior of planets is explained with the help of some model experiments in rapidly rotating spherical shells, which were carried out by Busse and Carrigan (1974). Based on the main ideas of electromagnetism it is shown that spiral motion in well-conducting fluids, like liquid metals, can amplify seed magnetic fields to generate dynamo action. Starting from the conjectured flow structure in the Earth's interior, a conceptional and engineering design is described for a laboratory dynamo experiment. Some details of the construction of the test facility and first experimental results are presented and discussed. 相似文献
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On the study of ecosystem health:state of the art 总被引:2,自引:0,他引:2
IntroductionDuringlastdecades,theterm“ecosystemhealth”isusedwithincreasingfrequencyintheliterature.Thegrowinginterestsinthestu... 相似文献
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T. A. Persson 《Mitigation and Adaptation Strategies for Global Change》2009,14(5):399-408
It is argued that there are at least five reasons for the Northeast states of the United States to implement a regional emission
trading scheme for carbon dioxide despite the lack of federal policy regulations: goodwill, learning, political influence,
risk management and competitiveness interests. Using an energy-economy model, the carbon price to bring the firms into compliance
with a 10% reduction by 2020 is estimated to be 20-150 US$ per ton C. There have been discussions about linking the ongoing
EU Emission Trading Schemes to the Northeast state initiative. The prime argument is that such a linkage would encourage a
change of the federal US policy, which has traditionally followed action taken at the state level. Emissions trading with
binding mitigation commitments could thus be demanded and accepted also on federal level. This paper demonstrates that the
impact of linkage on permit prices depends on the reduction target in the European scheme: A low EU target results in a net
flow of permits to the Northeast scheme, while a 40% EU reduction target results in a net flow of permits from the Northeast.
Flow of permits from the Northeast state must be compensated for by the EU because the United States is not a party of the
Kyoto Protocol. The EU must therefore buy permits in allowances recognized in the Kyoto regime in an amount equal to the net
flow of permits from the Northeast states.
相似文献
T. A. PerssonEmail: |
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Amethodforcalculatingthetotalozoneamountintheclearskies¥BaiJianhui;WangGengchen(InstituteofAtmosphericPhysics,ChineseAcademyo... 相似文献
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--The micronucleus(MCN) test of
Vicia faba root tip cell 相似文献
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StudyonthewaterqualityoftheTaihuLakeusinggenotoxicologicalmethodsWuQinglong,ChenKainingNanjingInstituteofGeographyandLimnol... 相似文献
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It is thought that young homing pigeons are able to use information acquired en route for their initial homeward orientation. However, the cues involved and mechanisms utilised are under discussion. Blocking light-dependent route-specific information during the first leg of an outward journey detour, together with analysis of pigeons that were raised under different loft conditions, allowed us to correctly evaluate the functioning of this mechanism and, more generally, the navigational map of birds. Pigeons from the same stock were raised and kept in two different lofts. The birds in the experimental groups were transported to the release sites via detours, and light-dependent information was denied during the first half of the outward journey (no compass information was available). Control birds were transported by the most direct route and had access to all available information. In general, the results showed that the low-loft birds preferred to use magnetic compass cues, whereas the high-loft birds preferred to use navigational map cues to collect information of the first part of the outward journey. The impairments observed in the homing performances of the experimental groups highlight the reliability of information collected inside the map area. Relevant to an understanding of the route-reversal mechanism was the evidence that this mechanism is able to function in the absence of compass information (birds raised in a wind-exposed loft show a detour effect). In systems where directional information could be provided by multiple sources, processing and extracting accurate course trajectories through a common mechanism may prove more efficient and reliable. 相似文献
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Based on the significant enhancement of fluorescence intensity of carbaryl in inclusion complex, a spetrofluorimetric method with high sensitivity was developed for the determination of carbaryl in aqueous solution. Under the optimum conditions, the complex had excitation and emission maxima at 278 nm and 332 nm, respectively. The linear range of the method was 7.0 ng/ml-1500 ng/ml with a detection limit of 1.2 ng/ml. The proposed method was successfully used to determine quantitatively of carbaryl in cottonseeds. 相似文献
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《世界环境》2006,(2)
Central to the mission of America's environmental schools is the development of professional environmental managers. The majority of our graduate students at Yale are enrolled in our master of environmental management program. But what exactly is environmental management? When I am asked this question, I reply that environmental management is the new business of bringing our human enterprise into harmony with the natural world of which we are a part. And I add: it's the most important thing in the world. 相似文献