You almost certainly don't want to have the complete text on the list page as well as the page of the full text.
Let me explain that:
Say you are writing a blog and you have a one page for each article and you also have a homepage showing the last 10 articles. On your homepage you want to show only a snippet of each article and a "read more" link.
Where do you want to drive the traffic to? Presumably you want people to go read the full article? The only place the full text of the article should exist in on the URL that displays the full article, not the homepage. If you repeat the fulltext of each article on the homepage then it can potentially look like duplicate content to search engines. If you try and hide the full text using Javascript that is even worse as you are "cloaking" your content and Google doesn't like that.
What I would do: Show the snippet on the list page with the "read more" link and nothing more. Your keywords/SEO/content will be on the page with the full text. Push the users to the article page if they want to read the article - it's a static, linkable URL that should have a unique title and meta tags for full SEO potential. Your list page changes when new stuff is added.