I found this answer here.
Its geared toward a single theme, but works on my theme too.
…If you want to change this so that the full posts are seen (instead of excerpts), in your WP Admin area, you’ll need to go to your “Design” tab (”Presentation” in WP 2.3.3 and earlier) and select “Theme Editor.” Then choose the file called “Archive (archive.php)” to edit it. (NOTE: don’t get confused with the file called “Archive (archives.php)” – they are named almost exactly the same – you want the one that is not plural.) In that file, look for a line that says:
<?php the_excerpt(”.__(‘Read More <span class=”meta-nav”>»</span>’, ‘ProPhoto’).”) ?>
Delete it and then paste in this line:
<?php the_content() ?>
Click “update file” to save your changes and then check your work.
You can also do this with your category pages as well. Just open up the file “Category Template (category.php)” and do the same edit.
Hope this helps you, it worked for me.
