function ispc() {
    var useragentinfo = navigator.useragent;
    var agents = ["android", "iphone",
                "symbianos", "windows phone",
                "ipad", "ipod"];
    var flag = true;
    for (var v = 0; v < agents.length; v++) {
        if (useragentinfo.indexof(agents[v]) > 0) {
            flag = false;
            break;
        }
    }
    return flag;
}

$(function(){
        //当滚动条的位置处于距顶部100像素以下时，跳转链接出现，否则消失
        $(function () {
            $(window).scroll(function(){
                if ($(window).scrolltop()>200){
                    $("#back-to-top").fadein(700);
                }
                else
                {
                    $("#back-to-top").fadeout(700);
                }
            });
            //当点击跳转链接后，回到页面顶部位置
            $("#back-to-top").click(function(){
                $('body,html').animate({scrolltop:0},700);
                return false;
            });
        });
    });