account_search_ruc/account_search_ruc_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
   <data>
       <record model="ir.ui.view" id="account_invoice_ruc">
           <field name="name">account.invoice.ruc</field>
           <field name="model">account.invoice</field>
           <field name="inherit_id" ref="account.invoice_tree" />
           <field name="arch" type="xml">
               <field name="partner_id" position="before">
                   <field name="partner_ruc"/>
               </field>
           </field>
       </record>

       <record model="ir.ui.view" id="account_invoice_search_ruc">
           <field name="name">account.invoice.search.ruc</field>
           <field name="model">account.invoice</field>
           <field name="inherit_id" ref="account.view_account_invoice_filter" />
           <field name="arch" type="xml">
               <field name="number" position="after">
                   <field name="partner_ruc" filter_domain="[('partner_ruc','ilike',self)]"/>
               </field>
           </field>
       </record>
   </data>
</openerp>