排序方式： 共有73条查询结果，搜索用时 15 毫秒
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S. B. Sosorova A. B. Gyninova M. G. Merkusheva L. L. Ubugunov L. N. Boloneva 《Eurasian Soil Science》2012,45(4):376-385
The content of microelements (Mn, Zn, Cu, Co, Ni, Cr, Pb, and Cd) and Fe is determined in the soils and plants of the Lake
Kotokel’ basin. Their content in the soils is proved not to exceed the regional background and the existing MPC and APC. The
content of Cd is revealed to exceed its clarke value for the world soils, which is related to the natural origin of this element.
The concentrations of Mn, Co, and Pb are close to their clarke values, and those of Zn, Cu, Ni, and Cr are lower than their
clarkes. The studied soils are specified by the maximal amount of the mobile forms of microelements. The profile distribution
of the microelements differs depending on the genetic soil type. For Mn, Zn, and Cu, a significant biogenic accumulation is
pronounced in the organic soil horizons. The content of microelements in the aboveground phytomass exceeds the maximal permissible
levels for Mn, Co, Cr, and Fe. The intensity of the microelements absorption by the plants varies widely, being specified
by the high coefficient of the biological adsorption (except for Fe). Mn, Zn, and Cu are accumulated in the plant phytomass
the most intensely. 相似文献
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为了深入研究温带草原区气候变化及其对自然-社会-经济系统的影响、系统响应及适应,回顾了温带草原区气候主要要素（如温度、降雨）与旱灾的变化及未来区域气候趋势预测等方面的研究进展,重点总结了气候变化对温带草原植被影响的最新研究成果。研究发现,温带草原区呈现总体气温明显升高,降水区域差异显著,干旱年份增多、旱灾增加的变化趋势。受此影响,植物物候、生理特征、生产力、覆盖度等发生明显的变化。最后指出,在气候变化核心要素预测、研究的时空尺度等方面还不完善,今后应重视开展大尺度气候变化的时空格局,微地形下气候变化的时空异质性等方面研究,同时加强气候变化对草原植被的影响与生态系统响应以及气候变化适应等方面的研究。 相似文献
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The chemical speciation of sulfur in geological fluids is a controlling factor in a number of processes on Earth. The two major chemical forms of sulfur in crustal fluids over a wide range of temperature and pressure are believed to be sulfate and sulfide; however, we use in situ Raman spectroscopy to show that the dominant stable form of sulfur in aqueous solution above 250°C and 0.5 gigapascal is the trisulfur ion S(3)(-). The large stability range of S(3)(-) enables efficient transport and concentration of sulfur and gold by geological fluids in deep metamorphic and subduction-zone settings. Furthermore, the formation of S(3)(-) requires a revision of sulfur isotope-fractionation models between sulfides and sulfates in natural fluids. 相似文献
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Azaroff LV 《Science (New York, N.Y.)》2003,301(5633):597-598
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Complex I of respiratory chains plays a central role in bioenergetics and is implicated in many human neurodegenerative diseases. An understanding of its mechanism requires a knowledge of the organization of redox centers. The arrangement of iron-sulfur clusters in the hydrophilic domain of complex I from Thermus thermophilus has been determined with the use of x-ray crystallography. One binuclear and six tetranuclear clusters are arranged, maximally 14 angstroms apart, in an 84-angstrom-long electron transfer chain. The binuclear cluster N1a and the tetranuclear cluster N7 are not in this pathway. Cluster N1a may play a role in the prevention of oxidative damage. The structure provides a framework for the interpretation of the large amounts of data accumulated on complex I. 相似文献
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Kuznedelov K Minakhin L Niedziela-Majka A Dove SL Rogulja D Nickels BE Hochschild A Heyduk T Severinov K 《Science (New York, N.Y.)》2002,295(5556):855-857
In bacteria, promoter recognition depends on the RNA polymerase sigma subunit, which combines with the catalytically proficient RNA polymerase core to form the holoenzyme. The major class of bacterial promoters is defined by two conserved elements (the -10 and -35 elements, which are 10 and 35 nucleotides upstream of the initiation point, respectively) that are contacted by sigma in the holoenzyme. We show that recognition of promoters of this class depends on the "flexible flap" domain of the RNA polymerase beta subunit. The flap interacts with conserved region 4 of sigma and triggers a conformational change that moves region 4 into the correct position for interaction with the -35 element. Because the flexible flap is evolutionarily conserved, this domain may facilitate promoter recognition by specificity factors in eukaryotes as well. 相似文献
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生防因子螺旋毛壳ND35的细胞壁降解酶与重寄生作用 总被引：1，自引：0，他引：1
1 IntroductionSomespeciesofthesaprophyticascomycetegeneraChaetomiumKunzeexFr .arepotentialantagonistsofseveralplantpathogenicfungi ,forexampleRhizoctoniasolaniandPythiumultimumwhichcauseseedlingdamping -offandVenturiainaequaliswhichcausestheapplescabChae… 相似文献
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ML Reaves S Sinha JD Rabinowitz L Kruglyak RJ Redfield 《Science (New York, N.Y.)》2012,337(6093):470-473
A strain of Halomonas bacteria, GFAJ-1, has been claimed to be able to use arsenate as a nutrient when phosphate is limiting and to specifically incorporate arsenic into its DNA in place of phosphorus. However, we have found that arsenate does not contribute to growth of GFAJ-1 when phosphate is limiting and that DNA purified from cells grown with limiting phosphate and abundant arsenate does not exhibit the spontaneous hydrolysis expected of arsenate ester bonds. Furthermore, mass spectrometry showed that this DNA contains only trace amounts of free arsenate and no detectable covalently bound arsenate. 相似文献