代码如下：

<!--<div class="head_time">北京:<span id="beijing"></span> 伦敦:<span id="lundun"></span> 纽约:<span id="niuyue"></span> 东京:<span id="dongjing"></span></div>-->
    <div   align="right">北京:<span id="beijing"></span> 伦敦:<span id="lundun"></span> 纽约:<span id="niuyue"></span> 东京:<span id="dongjing"></span>&nbsp;&nbsp;</div>
    <script language="JavaScript">
    var now,hours,minutes,seconds,timeValue;
    function showtime(){
      now = new Date();
      hours = now.getHours();
      minutes = now.getMinutes();
      seconds = now.getSeconds();
      //北京
      timeValue = "";
      timeValue += ((hours <10 ) ? "0": "")+ hours + ":";
      timeValue += ((minutes < 10) ? "0" : "") + minutes + ":";
      timeValue += ((seconds < 10) ? "0" : "") + seconds;
      //alert(timeValue);
      document.getElementById(beijing).innerHTML = timeValue;
      //伦敦
      timeValuelundun = "";
      if((hours-7)<0)
      {
        hourslundun=24-(7-hours);
      }
      else
      {
        hourslundun=hours-7;
      }
      timeValuelundun += ((hourslundun <10 ) ? "0": "")+ hourslundun + ":";
      timeValuelundun += ((minutes < 10) ? "0" : "") + minutes + ":";
      timeValuelundun += ((seconds < 10) ? "0" : "") + seconds;
      document.getElementById(lundun).innerHTML = timeValuelundun;
      
      timeValueniuyue = "";
      if((hours-13)<0)
      {
        hoursnouyue=24-(12-hours);
      }
      else
      {
        hoursnouyue=hours-12;
      }
      timeValueniuyue += ((hoursnouyue <10 ) ? "0": "")+ hoursnouyue + ":";
      timeValueniuyue += ((minutes < 10) ? "0" : "") + minutes + ":";
      timeValueniuyue += ((seconds < 10) ? "0" : "") + seconds;
      document.getElementById(niuyue).innerHTML = timeValueniuyue;
      
      timeValuedongjing = "";
      if((hours-23)<0)
      {
        hoursdongjing=24-(23-hours);
      }
      else
      {
        hoursdongjing=hours-23;
      }
      timeValuedongjing += ((hoursdongjing <10 ) ? "0": "")+ hoursdongjing + ":";
      timeValuedongjing += ((minutes < 10) ? "0" : "") + minutes + ":";
      timeValuedongjing += ((seconds < 10) ? "0" : "") + seconds;
      document.getElementById(dongjing).innerHTML = timeValuedongjing;
      setTimeout("showtime()",1000);
    }
    showtime();
</script>
</div>