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"AM Radio" redirects here. For the song by Everclear, see AM Radio (song). For the American musical group, see AM Radio (band). AM broadcasting is a radio broadcasting technology, which employs amplitude modulation (AM) transmissions. It was the first method developed for making audio radio transmissions, and is still used worldwide, primarily for medium wave (also known as "AM band") transmissions, but also on the longwave and shortwave radio bands. The earliest experimental AM transmissions were begun in the early 1900s. However, widespread AM broadcasting was not established until the 1920s, following the development of vacuum tube receivers and transmitters. AM radio remained the dominant method of broadcasting for the next 30 years, a period called the "Golden Age of Radio", until television broadcasting became widespread in the 1950s and received most of the programming previously carried by radio. Subsequently, AM radio's audiences have a

  玄参科 翅茎玄参 （ Scrophularia umbrosa ） 科學分類 界： 植物界 門： 被子植物门 綱： 双子叶植物纲 目： 唇形目 科： 玄参科 Juss. 属 参见正文 玄参科 （Scrophulariaceae）原来是一个大科，包括275属约5,000种，但最新对基因分析研究进展，将许多属划出，有的独立成科，如泡桐科、蒲包花科等，有的划入其他科，如婆婆納屬劃入車前科。中国有54属约600种，分布在全国各地，在西南各省品种较多。 本科植物分布在世界的地的温带地区和热带的山区，大部分是草本，稀有木本，单叶对生，无托叶；花两性，两侧对称，花冠合瓣，常为两唇形，雄蕊生长在花冠筒上；果实为蒴果。 本科植物许多品种可以作为药用，含有甙类和生物碱，如毛地黄、玄参等，也有观赏花卉。 属 星號為APG分类法歸至別科的植物 毛麝香屬 Adenosma Agalinis Raf. 黑蒴属 Alectra Thunb. 假面花属 Alonsoa Ruiz & Pav. Aureolaria Raf. 假馬齒莧屬 Bacopa Brachystigma Pennell 來江藤屬 Brandisia 黑草属 Buchnera L. 醉鱼草属 Buddleja Capraria L. 火焰草屬 Castilleja 假胡麻草属 Centrantheropsis Dasistoma Raf. 澤番椒屬 Deinostema 毛地黄屬 * Digitalis Diplacus Nutt. 幌菊屬 Ellisiophyllum 小米草屬 Euphrasia Gerardia 水八角屬 Gratiola 珍珠草属 Hemianthus Nutt. 羊膜草屬 Hemiphragma 定经草属 Ilysanthes 兔耳草屬 Lagotis 肉果草屬 Lancea 三翅萼屬 Legazpia 九阶草属 Leptandra 方莖草屬 Leptorhabdos Le