Not feasible for an unrestricted Internet site.

To restrict access, you could require authentication with a login in
order to view content or have your site on a VPN.

If the concern is only spam: do not list any email addresses on your
site. If you want to receive email as a result of you site, you could
provide online forms that generate the email and do not display email
addresses. if you need to list email address on the site, disguise the
email address in graphics, with special characters and or javascript.