Thanks to a number of major digitization initiatives, MANY published sources (books, journals, etc.) are now freely available via digital web repositories. Most of these materials are in the public domain - i.e. not copyright-protected. For the U.S. this means titles published prior to 1922; copyright "cutoff" dates vary for other countries. Googling by title or author will likely retrieve materials in these digital repositories, but you can also search their contents individually. Notable examples: