共查询到20条相似文献，搜索用时 765 毫秒
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Williams JM 《Science (New York, N.Y.)》2002,297(5590):2207-8; author reply 2207-8
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Hotspots, basalts, and the evolution of the mantle 总被引：2，自引：0，他引：2
Anderson DL 《Science (New York, N.Y.)》1981,213(4503):82-89
The trace element concentration patterns of continental and ocean island basalts and of mid-ocean ridge basalts are complementary. The relative sizes of the source regions for these fundamentally different basalt types can be estimated from the trace element enrichment-depletion patterns. Their combined volume occupies most of the mantle above the 670 kilometer discontinuity. The source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt. The mid-ocean ridge basalts source evolved from an eclogite cumulate that lost its late-stage enriched fluids at various times to the shallower mantle and continental crust. The mid-ocean ridge basalts source is rich in garnet and clinopyroxene, whereas the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment. These relationships are consistent with the evolution of a terrestrial magma ocean. 相似文献
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Lunine JI 《Science (New York, N.Y.)》1993,261(5122):697-698
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Climate change, deforestation, and the fate of the Amazon 总被引：4，自引：0，他引：4
Malhi Y Roberts JT Betts RA Killeen TJ Li W Nobre CA 《Science (New York, N.Y.)》2008,319(5860):169-172
The forest biome of Amazonia is one of Earth's greatest biological treasures and a major component of the Earth system. This century, it faces the dual threats of deforestation and stress from climate change. Here, we summarize some of the latest findings and thinking on these threats, explore the consequences for the forest ecosystem and its human residents, and outline options for the future of Amazonia. We also discuss the implications of new proposals to finance preservation of Amazonian forests. 相似文献
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Luth RW 《Science (New York, N.Y.)》1993,261(5117):66-68
The reaction dolomite + 2 coesite --><-- diopside + 2 diamond + 2O(2) defines the coexistence of diamond and carbonate in mantle eclogites. The oxygen fugacity of this reaction is approximately 1 log unit higher at a given temperature and pressure than the oxygen fugacities of the analogous reactions that govern the stability of diamond in peridotite. This difference allows diamond-bearing eclogite to coexist with peridotite containing carbonate or carbonate + diamond. This potential coexistence of diamond-bearing eclogite and carbonate-bearing peridotite can explain the presence of carbon-free peridotite interlayered with garnet pyroxenites that contain graphitized diamond in the Moroccan Beni Bousera massif at the Earth's surface and the preferential preservation of diamond-bearing eclogitic relative to peridotitic xenoliths in the Roberts Victor kimberlite. 相似文献
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Heckenberger MJ Russell JC Fausto C Toney JR Schmidt MJ Pereira E Franchetto B Kuikuro A 《Science (New York, N.Y.)》2008,321(5893):1214-1217
The archaeology of pre-Columbian polities in the Amazon River basin forces a reconsideration of early urbanism and long-term change in tropical forest landscapes. We describe settlement and land-use patterns of complex societies on the eve of European contact (after 1492) in the Upper Xingu region of the Brazilian Amazon. These societies were organized in articulated clusters, representing small independent polities, within a regional peer polity. These patterns constitute a "galactic" form of prehistoric urbanism, sharing features with small-scale urban polities in other areas. Understanding long-term change in coupled human-environment systems relating to these societies has implications for conservation and sustainable development, notably to control ecological degradation and maintain regional biodiversity. 相似文献
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Snyder CS 《Science (New York, N.Y.)》2001,292(5521):1485-1486
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Kerr RA 《Science (New York, N.Y.)》1981,212(4500):1258
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Jeffrey Burkhardt 《Agriculture and Human Values》1988,5(3):53-60
The “new” agricultural biotechnologies are presently high-priority items on the national research agenda. The promise of increased efficiency and productivity resulting from products and processes derived from biotech is thought to justify the commitment to R&D. Nevertheless, critics challenge the environmental safety as well as political-economic consequences of particular products of biotech, notably, ice-nucleating bacteria and the bovine growth hormone. In this paper the critics' arguments are analyzed in explicitly ethical terms, and assessed as to their relative merits. In some cases, a principle of “do no foreseeable harm” as well as a clear determination of likely harms would force us to conclude that research, development, and diffusion of a product or process derived from biotechnology is ethically wrong. In all cases, one conclusion that can be reached is that everyone involved in research, development, marketing and adoption of biotech products is responsible for the results of their actions; thus, each individual has a responsibility to consider a broader range of values and goals that effect and are effected by the biotechnology effort. 相似文献
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Dean RB 《Science (New York, N.Y.)》1986,233(4762):404
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Gideonse HD 《Science (New York, N.Y.)》1968,162(3853):541-545
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There is growing evidence that the neuropeptides oxytocin and vasopressin modulate complex social behavior and social cognition. These ancient neuropeptides display a marked conservation in gene structure and expression, yet diversity in the genetic regulation of their receptors seems to underlie natural variation in social behavior, both between and within species. Human studies are beginning to explore the roles of these neuropeptides in social cognition and behavior and suggest that variation in the genes encoding their receptors may contribute to variation in human social behavior by altering brain function. Understanding the neurobiology and neurogenetics of social cognition and behavior has important implications, both clinically and for society. 相似文献
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Rubin VC 《Science (New York, N.Y.)》1980,209(4452):64-71
Our perception of the universe has been altered by recent discoveries in astronomy, discoveries of new objects and of new phenomena, coming from a wide range of observing techniques. By 1990 astronomers expect to know more about the distribution of mass in the universe, the physics of energetic sources, and the intricate interconnections of astrophysical processes on a variety of spatial and temporal scales. 相似文献
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Merton RK 《Science (New York, N.Y.)》1947,105(2717):79-84
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A key unresolved question in population ecology concerns the relationship between a population's size and its growth rate. We estimated this relationship for 1780 time series of mammals, birds, fish, and insects. We found that rates of population growth are high at low population densities but, contrary to previous predictions, decline rapidly with increasing population size and then flatten out, for all four taxa. This produces a strongly concave relationship between a population's growth rate and its size. These findings have fundamental implications for our understanding of animals' lives, suggesting in particular that many animals in these taxa will be found living at densities above the carrying capacity of their environments. 相似文献
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清真雅正是清代朝廷推行的衡文准则，包括在理、法、辞、气等方面有所要求。为了引导生徒作文步入正轨以及促进健康文风的形成，清代一些书院将清真雅正纳入八股文教育的范畴，清真雅正在书院学规、课艺甄选、课艺评点等内容中有着重要体现。为了便于生徒理解清真雅正，施教者要求研习明清时期八股文名家善本，用范文来指导习作。清代一些书院在进行清真雅正教育时，重视将为文上的开导与为人上的训迪结合起来，从而为国家培养品学兼优的科举人才，实现文学教育的崇高理想。 相似文献
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