You can access the Numeric Search by clicking on the Numeric Search tab on the Advanced Search screen.
If you are familiar with the MARC standard, you may search by tag in the Expert Search. Enter the three-digit tag number, the subfield (if relevant), and the value or text that corresponds to the tag. For example, to search by publisher name, enter 260 b Random House. To search several tags simultaneously, use the Add Row option. Click Search to run the search.