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排序方式: 共有479条查询结果,搜索用时 15 毫秒
61.
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Zarnecki JC Leese MR Hathi B Ball AJ Hagermann A Towner MC Lorenz RD McDonnell JA Green SF Patel MR Ringrose TJ Rosenberg PD Atkinson KR Paton MD Banaszkiewicz M Clark BC Ferri F Fulchignoni M Ghafoor NA Kargl G Svedhem H Delderfield J Grande M Parker DJ Challenor PG Geake JE 《Nature》2005,438(7069):792-795
The surface of Saturn's largest satellite--Titan--is largely obscured by an optically thick atmospheric haze, and so its nature has been the subject of considerable speculation and discussion. The Huygens probe entered Titan's atmosphere on 14 January 2005 and descended to the surface using a parachute system. Here we report measurements made just above and on the surface of Titan by the Huygens Surface Science Package. Acoustic sounding over the last 90 m above the surface reveals a relatively smooth, but not completely flat, surface surrounding the landing site. Penetrometry and accelerometry measurements during the probe impact event reveal that the surface was neither hard (like solid ice) nor very compressible (like a blanket of fluffy aerosol); rather, the Huygens probe landed on a relatively soft solid surface whose properties are analogous to wet clay, lightly packed snow and wet or dry sand. The probe settled gradually by a few millimetres after landing. 相似文献
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Interest in mapping the global distribution of malaria is motivated by a need to define populations at risk for appropriate resource allocation and to provide a robust framework for evaluating its global economic impact. Comparison of older and more recent malaria maps shows how the disease has been geographically restricted, but it remains entrenched in poor areas of the world with climates suitable for transmission. Here we provide an empirical approach to estimating the number of clinical events caused by Plasmodium falciparum worldwide, by using a combination of epidemiological, geographical and demographic data. We estimate that there were 515 (range 300-660) million episodes of clinical P. falciparum malaria in 2002. These global estimates are up to 50% higher than those reported by the World Health Organization (WHO) and 200% higher for areas outside Africa, reflecting the WHO's reliance upon passive national reporting for these countries. Without an informed understanding of the cartography of malaria risk, the global extent of clinical disease caused by P. falciparum will continue to be underestimated. 相似文献
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Résumé La microscopie électronique a permis d'observer des lésions du glomérule et du tube proximal, après administration intraveineuse d'inuline chez les lapins: nombreux macrophages dans les anses glomérulaires, tuméfaction endothéliale, tuméfaction épithéliale avec soudure des pédicelles; nécrose des cellules épithéliales du tube proximal.La poursuite de cette étude devrait établir définitivement si l'emploi de l'inuline est contre-indiqué dans l'exploration fonctionnelle rénale. 相似文献
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ABSTRACT The genus Tanaostigma is newly recorded from the Afrotropical region and three new species are described: Tanaostigma lasallei van Noort sp. nov. (South Africa), Tanaostigma mulu van Noort sp. nov. (Kenya) and Tanaostigma ukumbusho van Noort sp. nov. (Kenya). We provide comprehensive images of the holotypes and an illustrated identification key to the African species. New country distribution records are provided for Tanaostigmodes tambotis Prinsloo & LaSalle, 1995. All images presented here as well as supplementary images and online keys are available on www.waspweb.org www.zoobank.org/urn:lsid:zoobank.org:pub:61D1A59D-3702-480A-B146-73067C29CD82 相似文献
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Xi Chen ? Simon P. Ellingsen ? Conggui Gan ? Ye Xu ? Zhiqiang Shen 《科学通报(英文版)》2014,59(11):1066-1077
Class I methanol masers are important tools for investigations of star formation throughout the Universe. Recently, a series of surveys for class I methanol masers at the 95 GHz transition toward samples of young stellar objects have been undertaken. These surveys have resulted in the detection of about 200 new class I methanol masers and combined with previous increased the number of known observations they have class I methanol masers in our Galaxy to ~400. From analysis of the relationship between class I methanol maser emission and associated astrophysical objects, it has been shown that the intensity of the class I methanol maser emission is closely correlated with the properties of the 1.1 mm Bolocam Galactic Plane Survey (BGPS) dust continuum sources and outflow properties. This further supports the hypothesis that class I methanol masers are collisionally pumped and excited in shocked regions. Based on these observations, it can be inferred that the BGPS catalog is likely to provide more reliable samples for targeting further class I methanol maser searches. A new survey for class I methanol masers toward a larger size sample of BGPS sources to test this is currently underway. The prospects for detecting class I methanol megamasers in extragalactic sources is discussed, and observations constituting the first sensitive search have been proposed. 相似文献