霜霉病是莴笋、生菜生产中的主要病害,分布广泛,不论是露地栽培还是保护地栽培,几乎都有发生。病害严重时,大量叶片变黄或变褐枯死,植株长势弱,造成减产。除危害莴笋、生菜外,还能侵染油麦菜、菊苣及数种野生菊科植物。 一、症状识别 莴笋、生菜霜霉病的症状相同,唯莴笋初发病时病斑常出现在主脉两侧,而生菜则不明显。幼苗和成株期均可受害,主要危害叶片,中后期发病重,留种株受害也重。初从植株下部叶片发
The EC (electrical conductivity), pH and concentrations of major anions, cations and dissolved silica were determined in the stream meltwater draining from the
诱惑以外是疑惑"两年前东菱还是完全做外销的小家电企业,但从去年开始我们决定开拓庞大的国内市场.拥有13亿人口的中国,经济在高速增长,居民生活水平在快速提高,中国的小家电
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Heavy tamping is one of the important methods for ground treatment. But the vibration is often a problem that restricts the application during heavy tamping. On
We derive formulae of correction for multi-wave geometric spreading and absorption in layered viscoelastic media, this provides the theoretical foundation for t
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This paper presents a preliminary summary of the applied sequence stratigraphy in nonmarine basins in China. The geological and geophysical data show that the n
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