function checkforminfox(){
  if (document.frm_searchinfo.keyword.value==""){
      alert("请输入关键字!");
      document.frm_searchinfo.keyword.focus();
      return false;
      }
  else
      return true;
}

str="<div class='search'><span class=mail><a href=http://mail.cuaps.com target='_blank'>进入企业邮箱</a></span><form name=frm_searchinfo method=post action=/info/searchin.asp onsubmit='javascript:return checkforminfox();'><strong>搜索：</strong><input name=keyword class='s_t' size=20><input type=submit value='' name=Submit class='s_b' hidefocus ></form></div>"

document.write(str)