<script>
function   showcontent(){
var   str="这里面是阅读的内容";
if(document.getElementById("td1").innerHTML==""){
document.getElementById("td1").innerHTML=str;
}
else{
document.getElementById("td1").innerHTML=""
}
}
</script><table>
<tr>
<td id="td1">
</td>
</tr>
<caption> <input   type="button"   value="点击阅读"   onclick="showcontent()"> </caption>
</table>