Most of these resources are article databases - huge collections of articles from journals, magazines, and other publications that have been digitized and linked in a searchable database. When you search a database, your results list will include links to PDF or HTML version of articles that have been previously published.
However, sometimes your results will only provide information ABOUT an article, rather than the article itself. RILM is an index that has very few full-text articles. However, you can search RILM to find out about articles on your topic, and then look for those articles in other sources.
Grove Online is actually a multi-volume set of reference books that has been digitized for easy access. The "articles" in Grove's are really encyclopedia or dictionary entries. Still, Grove's is usually the best place to start your music research!