function getID(id){
    return window.document.getElementById?window.document.getElementById(id):null;
}

function fn_showTable(tid){
    for(var i=1;i<=2;i++){
        getID("b"+i).className = "chanpin";
        getID("box"+i).style.display = "none";    
    }
    getID(tid).className = "chanpin1";
    getID(tid.replace("b","box")).style.display = "";
}