[CODE]
<script type="text/javascript">
    $(function () {
      $('input:text').keydown(
      function (event) {
        if (event.keyCode == 13)
          $(this).onTextChanged(); <--funzione da lanciare
      });
    });
  </script>
<asp:Panel CssClass="ricerca" runat="server" ID="pnl_ricerca">
    <table style="border-collapse: collapse;" cellpadding="10px">
      <tbody>
        <tr class="standard-row">
          <td>
            <span class="testo">Cognome o Nome :</span>
          </td>
          <td>
            <asp:TextBox runat="server" ID="txt_nome_cognome" TabIndex="1" Columns="10" OnTextChanged="miaFunzione" />
          </td>
        </tr>
        <tr class="alternative-row">
          <td>
            <span class="testo">Telefono :</span>
          </td>
          <td>
            <asp:TextBox runat="server" ID="txt_telefono" TabIndex="2" Columns="10" OnTextChanged="miaFunzione" />
          </td>
        </tr>
......
<div><asp:GridView ...></asp:GridView>
<asp:SqlDataSource ID="sds_ricerca" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" />

-------------------------------------------------------------------------------
lato server
protected void miaFunzione(object sender, EventArgs e)
  {
    string select_query = "SELECT [MATRICOLA].....
               ......varie elucubrazioni....
sds_ricerca.SelectCommand = select_query;
    sds_ricerca.DataBind();
          
[/CODE]