Lexis+ and Westlaw contain full text journal articles for almost all of their titles from about the mid-1990s and for select journals to 1980 and even earlier. 

Use HeinOnline for comprehensive coverage of law journals including bar journals to date of inception of the journal. 

Use Index to Legal Periodicals and Books for sophisticated field searching. 

Finally, use Google Scholar as an easier searching tool for law journal articles on HeinOnline and other sources.