querystring without page load

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ASP.NET

i have 4 image button through which i pass querystring and one datalist in update pannel which show data according to those image button selection..my problem is that i want to show data in datalist without refreshing page..
my page is xyz.aspx

onload()
{
if(Request.QueryString["var"] != null)
{

.....}
else
(
show data according to var;
}
}
imageclick(){
string abc;
response.redirect("xyz.aspx?var=" + abc)
}

i know becuse of this response.redirect my page load..but i don't know other option as i am new in asp.net..please help..

thank you in advance