提取自discuz并做了一些小修改.

$(document).ready(function setscreendiv() {
    var clientHeight = 768;
    var clientWidth=600;
    var iframe = document.getElementById("main");
    if (navigator.userAgent.toLowerCase().indexOf('opera') != -1) {
        clientHeight = document.documentElement.clientHeight + 190;
        clientWidth = document.documentElement.clientWidth - 180;
    }
    else {
        clientHeight = document.documentElement.clientHeight - 55;
        clientWidth=document.documentElement.clientWidth-180;
    }
    iframe.style.height = clientHeight + 'px';
    iframe.style.width=clientWidth+'px';
    document.documentElement.style.overflow = "hidden";
    window.onresize = function () { setscreendiv(); }
    window.onscroll = function () { setscreendiv(); }
}
)

ps:框架实在难以驾驭,目前项目后台已不采用框架方式。