药物的半衰期主要用于衡量药物的（  ）。 

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SQL Error: select id,body,options from ***_enewstiku where sourceid='24975' and id < 2127553 and id<>'2127553' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='24975' and id > 2127553 and id<>'2127553' order by id asc limit 5