蛋白质的二级结构指的是（）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='30525' and id < 2464965 and id<>'2464965' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='30525' and id > 2464965 and id<>'2464965' order by id asc limit 5