JSTOR provides access to millions of journal articles, books, images, and primary sources in 75 disciplines. The Archive Journal Collection is included.
API available, more information here: APIs for Scholarly Research
Chapter/content section downloads
Project MUSE hosts more than 800 journals and more than 90,000 books covering the humanities and social sciences from nearly 400 leading university presses, scholarly societies, and related publishers.
Full text downloads, chapter/content section downloads
PDF, Compressed PDF
VIRGO-- The U.Va. Library Catalog
Keyword search should be "Google-like," just enter whatever terms you want; no need for connectors like and.
Will search the title, author's name or description of the item.
There are also some Subject terms that indicate primary source materials:
Archives*
Correspondence*
Diaries*
Early works to 1800
Facsimilies
Notebooks, sketchbooks, etc.
Pamphlets
Personal narratives (used in relation to specific events only)
Songs and music
Sources
Speeches, addresses, etc.*
Treaties
*Used with individuals' names,classes of persons (e.g., soldiers), and organizations.
Google Books Searches the full text of thousands of books. If used in conjunction with Amazon.com full text search of a book, can get most of the text of a book.
Searchable full text with page images of books published in 17th- and 18th-century America. Browsable by genre, subject, author, printer, place of publication, and language. See also Early English Books Online and Eighteenth Century Collections Online.
Full text downloads, page range downloads.*
*Pages may download across more than one file.
Searchable full text with page images of books published in early 19th-century America. The collection can also be browsed by genre, subject, author, printer, place of publication, and language.
Full text downloads, page range downloads.*
*Pages may download across more than one file.