关于页面打印不全的问题！

<script language="JavaScript">
function doprint()
{
b.style.display="";
b.innerText = a.value;
a.style.display="none";
window.print();
b.style.display="none";
b.innerText = "";
a.style.display="";
}
</script>
<span id="b" style="display:none"></span>
<textarea style="width:100%;height:60%;" id="a">
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asdf
saf
as
dg
asdg
asdgas
dg
asd
gas
gasgasdgasg
asdf
saf
as
dg
asdg
asdgas
dg
asd
gas
gasgasdgasg
asdf
saf
as
dg
asdg
asdgas
dg
asd
gas
gasgasdgasg
asdf
saf
as
dg
asdg
asdgas
dg
asd
gas
gasgasdgasg
asdf
saf
as
dg
asdg
asdgas
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asd
gas
gasgasdgasg
</textarea>
<input type="button" onclick="doprint();" value="打印">