I am a researcher, and I would like to scrape a list of scientific libraries sites such as Springerlink.com, ScienceDirect.com, IEEExplore digital library and so on, to analyse them for some purpose. In this task I'm interested in abstracts, and full text of publicly accessible papers, I would like to know the legal framework of this, since that I read before (but I don't remember where and how to find it again) that this is illegal, and if I do that any new request from my IP address to those sites will be rejected. It means that this task will be considered as a Denial of service attack.
To what extent this is true?