Here simple Jquery code to do the same...
<script type="text/javascript">
$(document).ready(function(){
$("#txtwhichpart").keypress(function(e){
if (e.which == 13){
// do your custom processing here
$('#bsubmit_blist').click();
}
});
});
</script>
txtwhichpart is text box id
bsubmit_blist is button id
//code behind
protected void btnsearchhome_Click(object sender, EventArgs e)
{
}