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排序方式: 共有1063条查询结果,搜索用时 265 毫秒
81.
Manatt SL Elleman DD Vaughan RW Chan SI Tsay FD Huntress WT 《Science (New York, N.Y.)》1970,167(3918):709-711
Electron spin resonance searches at 9.5 gigahertz on several fines samples and portions of several rocks have yielded signals whose lineshapes and temperature dependences show that the samples are principally ferromagnetic in nature. Proton magnetic resonance searches at 60 megahertz of these samples have not revealed any signals ascribable to water or any other types of hydrogen in concentrations greater than 0.0001 percent by weight contained in narrow lines (5 oersteds wide or less) and 0.01 percent by weight in wide lines (as wide as 100 oersteds). 相似文献
82.
包头市全巴图工业污染区盐渍土特征研究 总被引:2,自引:0,他引:2
包头市西南全巴图工业污水排放地区,在水文地质、气候等因素综合作用下,形成以草甸盐土为主的盐渍土,土壤中含盐量0.32~19.02%,是中度-强度盐渍化土或盐土,盐害较重,在进行改良后才能利用。盐土盐分以表层最高,土层中下部浓度变低,尤其改良地淡化过程明显(表3)。在本区盐渍土地上,采取合理的改良措施后,可以逐步地进行防污林带营造等保护生态环境的工程。 相似文献
83.
Chan F Barth JA Lubchenco J Kirincich A Weeks H Peterson WT Menge BA 《Science (New York, N.Y.)》2008,319(5865):920
Eastern boundary current systems are among the world's most productive large marine ecosystems. Because upwelling currents transport nutrient-rich but oxygen-depleted water onto shallow seas, large expanses of productive continental shelves can be vulnerable to the risk of extreme low-oxygen events. Here, we report the novel rise of water-column shelf anoxia in the northern California Current system, a large marine ecosystem with no previous record of such extreme oxygen deficits. The expansion of anoxia highlights the potential for rapid and discontinuous ecosystem change in productive coastal systems that sustain a major portion of the world's fisheries. 相似文献
84.
85.
Changelian PS Flanagan ME Ball DJ Kent CR Magnuson KS Martin WH Rizzuti BJ Sawyer PS Perry BD Brissette WH McCurdy SP Kudlacz EM Conklyn MJ Elliott EA Koslov ER Fisher MB Strelevitz TJ Yoon K Whipple DA Sun J Munchhof MJ Doty JL Casavant JM Blumenkopf TA Hines M Brown MF Lillie BM Subramanyam C Shang-Poa C Milici AJ Beckius GE Moyer JD Su C Woodworth TG Gaweco AS Beals CR Littman BH Fisher DA Smith JF Zagouras P Magna HA Saltarelli MJ Johnson KS Nelms LF Des Etages SG Hayes LS Kawabata TT 《Science (New York, N.Y.)》2003,302(5646):875-878
Because of its requirement for signaling by multiple cytokines, Janus kinase 3 (JAK3) is an excellent target for clinical immunosuppression. We report the development of a specific, orally active inhibitor of JAK3, CP-690,550, that significantly prolonged survival in a murine model of heart transplantation and in cynomolgus monkeys receiving kidney transplants. CP-690,550 treatment was not associated with hypertension, hyperlipidemia, or lymphoproliferative disease. On the basis of these preclinical results, we believe JAK3 blockade by CP-690,550 has potential for therapeutically desirable immunosuppression in human organ transplantation and in other clinical settings. 相似文献
86.
Single-domain microcrystals of LaC(2) encapsulated within nanoscale polyhedral carbon particles have been synthesized in a carbon arc. Typical particle sizes are on the order of 20 to 40 nanometers. The stoichiometry and phase of the La-containing crystals have been assigned from characteristic lattice spacings observed by high-resolution transmission electron microscopy and energy dispersive spectroscopy (EDS). EDS spectra show that La and C are the only elements present. Characteristic interatomic distances of 3.39 and 2.78 angstroms identify the compound inside the nanoparticle cavities as alpha-LaC(2), the phase of LaC(2) that is stable at room temperature. Bulk alpha-LaC(2) is metallic and hydrolytic. Observation of crystals of pure encapsulated alpha-LaC(2) that were exposed to air for several days before analysis indicates that the LaC(2) is protected from degradation bythe carbon polyhedral shells of the nanoparticles. A high percentage of the carbon nanoparticles have encapsulated LaC(2) single crystals. These carbon-coated metal crystals form a new class of materials that can be protected in their pure or carbide forms and may have interesting and useful properties. 相似文献
87.
We report on the observation of nonclassical rotational inertia in solid helium-4 confined to an annular channel in a sample cell under torsional motion, demonstrating superfluid behavior. The effect shows up as a drop in the resonant oscillation period as the sample cell is cooled below 230 millikelvin. Measurement of 17 solid samples allows us to map out the boundary of this superfluid-like solid or supersolid phase from the melting line up to 66 bars. This experiment indicates that superfluid behavior is found in all three phases of matter. 相似文献
88.
RNA silencing genes control de novo DNA methylation 总被引:1,自引:0,他引:1
Chan SW Zilberman D Xie Z Johansen LK Carrington JC Jacobsen SE 《Science (New York, N.Y.)》2004,303(5662):1336
89.
Chan C. W. Schueller J. K. Miller W. M. Whitney J. D. Wheaton T. A. Cornell J. A. 《Precision Agriculture》2002,3(1):81-94
Spatially-variable application of inputs to agricultural fields is dependent upon accuracy of the input variables. The effects of boundary determination, interpolation method, and GPS location errors were studied for determining a variable rate nitrogen application map based upon yield maps of a 3.6 ha Florida citrus block. A general linear model for the mean absolute error approximated the error effects. 相似文献
90.
Chan FK Chun HJ Zheng L Siegel RM Bui KL Lenardo MJ 《Science (New York, N.Y.)》2000,288(5475):2351-2354
A conserved domain in the extracellular region of the 60- and 80-kilodalton tumor necrosis factor receptors (TNFRs) was identified that mediates specific ligand-independent assembly of receptor trimers. This pre-ligand-binding assembly domain (PLAD) is physically distinct from the domain that forms the major contacts with ligand, but is necessary and sufficient for the assembly of TNFR complexes that bind TNF-alpha and mediate signaling. Other members of the TNFR superfamily, including TRAIL receptor 1 and CD40, show similar homotypic association. Thus, TNFRs and related receptors appear to function as preformed complexes rather than as individual receptor subunits that oligomerize after ligand binding. 相似文献