The best starting point for electronic indexes is the Libraries' Electronic Resources Web page with hot links to many tools of this kind. While the overall quality of these resources is generally good, you still have to decide which tools are most relevant for your specific project . No single source covers all articles and books. Experiment and experience help too. 1994 Full text, but no content prior to 1994.
Coverage goes back farther for appropriate topics.
Possible coverage back to 1987. Humanities Abstracts 2 hits no full text 1994 Possible coverage back to 1984. History and Life 3 hits no full text 1994 Possible coverage back to 1964. No source does all these things. Therefore, good research requires you to intelligently choose your finding tools, systematically use multiple sources, and critically evaluate what you find.