Clients like Feeder[1] and self-hosted services like Tiny Tiny RSS[2] (through its Readability plugin) can extract the full text from the source URL.

[1] https://f-droid.org/en/packages/com.nononsenseapps.feeder/

[2] https://tt-rss.org

I work on a project intended to help people produce full text feeds from partial ones. It's essentially a web service that produces a new feed URL and handles article extraction when the feed gets requested by your feed reader: http://ftr.fivefilters.org/