导体横截面上（    ）不随时间变化的电流称为直流电流。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69490' and id < 4501414 and id<>'4501414' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69490' and id > 4501414 and id<>'4501414' order by id asc limit 5