If you are looking for journal articles available at large, to everyone on the Internet, check out these sites.

Directory of Open Access Journals (DOAJ)

DOAJ indexes open access scientific and scholarly journals using a quality control system to guarantee the content.

CORE  

CORE offers access to over 131 million open access articles and research papers. This extensive database offers articles on a number of different academic subjects. 

OAISter (WorldCat)

OAISter is a combined catalog (in OCLC's WorldCat) of more than 25 million records representing digital resources from more than 1,100 institutions. Many full text-archive, depository and governmental publications, covering many different topics

Google Scholar

Although this is not a full-text directory, Google Scholar indexes scholarly publications, and can identify full-text respository holdings.  NOTE: If you are using Google Scholar on campus, or have signed in as a student before searching Google Scholar while off-campus, you will receive notices of Full-Text availability. For adding the "Full-Text" feature to your home computer, go to Google Scholar Preferences.

The CU Libraries have many databases, which students may use free of charge.  These databases list many full text articles from scholarly journals, and other publications.