Hi there,
Yes, most of the abstracts just detail what I would say are the most important points etc. Some as you say will allow the reader to view the whole thing for free and others, probably most of them will charge a fee to read the full piece. Usually the copyright protected ones want you to pay for them.
Personally if I were you I would not bother paying for them and just read what the abstract says etc. We do have money that was donated to us by Percy before he passed away with his instructions to purchase some if we thought they were worthy but we have to be selective about the ones we would pay for. Marion will correct me if I am wrong on this.
But my 2p worth is just read the abstracts that are free that I post.
Hope that helps.
Gavin