Actually, Google does have a way of handling this. It has a feature called "First click free", where webmasters can allow a visitor to access the first article for a given site. If the user then clicks through to another page, they reach the login or registration page as usual. More information here.
Another approach would be to post a one-paragraph keyword-rich summary of each article in a separate directory. Make these summaries freely accessible to all. In each case, include a link to the login / registration page. Then, in robots.txt, make sure the relevant directory is crawlable, but disallow crawlling of the directory that holds the subscription articles.
In both cases, searchers will always find a useful result, and the website has a chance of converting them to registered users.