function nowtime(){//将当前时间转换成yyyymmdd格式
    var mydate = new Date();
    var str = "" + mydate.getFullYear();
    var mm = mydate.getMonth()+1
    if(mydate.getMonth()>9){
     str += mm;
    }
    else{
     str += "0" + mm;
    }
    if(mydate.getDate()>9){
     str += mydate.getDate();
    }
    else{
     str += "0" + mydate.getDate();
    }
    return str;
  }