To hide / unhide content selectively on web pages, you will need to write javascript code. But even if you were to write such a code, it most likely not work in an email client. Most email clients will have javascript turned off.
You can have
a> Use anchor tags in email so you can show summary at the top with 'Read more' links which link to the full articles which will be further down in the email.
b> You can use these 'Read more' links point to a landing page with appropriate anchor tags.
See if http://help.typepad.com/anchor-tags.html can help.
Rajesh