There are a large number of online, freely available digitized books, periodicals, and other digitized materials. Most digitized books and periodicals online are in PDF file format. There are a number of free dedicated PDF search engines that you can use to search for such items. But you can also search in Google for a PDF of a title you are interested in by putting the title, or a known portion of the title, in quotes and then adding "filetype:PDF" to the search box, without quotes. This method can be used to sarch for PDFs of books, other monographs, whole periodicals, and articles.
Searching for the book title in quotes without the addition of "PDF" may also give full-text sources of the book; But this also show books and articles that have that book in its bibliography, and that will give leads to other books and articles of interest on the same topic.
In addition, there are many more digitized books, periodicals, and other materials that can be accessed via public library and university library subscription services. The University of Pennsylvania has an ongoing project to identify all freely available digitized publications worldwide, and provides direct links to each database that they have been able to identify. The Univ. of Pennsylvania database of digitial databases is located at:
http://onlinebooks.library.upenn.edu/archives.html
This is the largest listing of freely available digitized books and periodicals in the world, but there are undoubtedly many other sources that the Univ. of Penn. has not yet discovered. So if you know of any such resources that are not on the Univ. of Penn. list, please write to me, John H. Reed, M.D., at joreed43 at gmail, and I will add the digital resource you have discovered to the list below, in alphabetical order:
Academic Databases and Search Engines - This is a listing of all major academic databases and search engines, many of which are freely available. Those that are available only by subscription, may be found at you local public, college, of university library.
https://en.wikipedia.org/wiki/List_of_academic_databases_and_search_engines
Academic Journal Online Publishing Services - Several of these provide freely available, digitized journals and other periodicals:
https://en.wikipedia.org/wiki/Category:Academic_journal_online_publishing_services
Aggregation Based Digital Libraries - These are Digital libraries that are primarily based on the aggregation or harvesting of other digital libraries or repositories:
https://en.wikipedia.org/wiki/Category:Aggregation-based_digital_libraries
Biodiversity Heritage Library: Over 60,000 books on biomedical subjects alone;
http://www.biodiversitylibrary.org/
Digital Libraries - Several of these are not shown on the Univ. of Penn. list noted above: https://en.wikipedia.org/wiki/Category:Digital_libraries
Digital Library of India: http://www.dli.ernet.in/
Full Text Scholarly Online Databases -
https://en.wikipedia.org/wiki/Category:Full_text_scholarly_online_databases
Gallica (The French Bibliotheque Nationale de France): http://gallica.bnf.fr/?lang=EN
Google Books: Millions of books have been digitized, many of which are full text. But many have only snippets available:
http://books.google.com/bkshp?hl=en&tab=wp&ei=_MGeUtC6DoXNkQe-joCAAQ&ved=0CBAQqS4oDQ
HathiTrust: HathiTrust has 11,149,491 total digitized volumes in its database, including 5,807,271 book titles and 291,153 serial titles. Approximately 3,759,503 volumes(~34% of total) are in the public domain, and hence freely available.
Ibiblio: http://www.ibiblio.org Claims to be one of the largest free information databases online;
India: Digital Library of India: http://www.dli.ernet.in/
Internet Archive: Over 5.5 million books are said to be avaialble:
ISHAR ( Integrative Studies Historical Archive & Repository ) is a Deepak Chopra Foundation Initiative: http://isharonline.org/ There is also a large list of biomedical Journals here: http://isharonline.org/content/journal-portal
Online Databases - This is a link to over 300 online databases covering many different subjects:
https://en.wikipedia.org/w/index.php?title=Category:Online_databases&pageuntil=Scitopia#mw-pages
Open Access Archives - This is a list of open-access archives world-wide:
https://en.wikipedia.org/wiki/Category:Open-access_archives
Open Access Journals -
https://en.wikipedia.org/wiki/List_of_open_access_journals
Open Edition Books: http://books.openedition.org/
Project Gutenberg: over 42,000 books:
U-Penn Copyright Registration and Renewal Database:
http://onlinebooks.library.upenn.edu/cce/
Other Online Sources to verify:
Public domain Free books documents listed at: https://sites.google.com/site/themetalibrary/public-domain
Download Genius: Claims over 3 million files, but you have to sign up, so sign up with your secure email account: http://www.download-genius.com
Vi-Play: https://www.vi-play.com Claims 40 million games, movies, books, etc. But it is a subscription service like Scribd
Zeobooks.org: http://zeobooks.org/
This is a website that lists hundreds of e-books, and says they are freely avaiable, but it is not clear how to access them, or how zeobooks.org fits into the picture. It is clear that the website is run by someone whose native language is not English, by reading the following write-up for one of the books it listed, as quoted:
"In case you might be looking to understand how to have Managing Higher Education in Colleges eBooks, you have to go thorough study on common search engines with all the keywords and phrases download William A. Kaplin PDF eBooks in order for you personally to only get PDF formatted books to download which are safer and virus-free you'll find an array of web sites catering for your demands.
Most of these web sites possess a large collection of PDF eBooks which you'll be able to use to your advantage. A few of them call for you to pay a paltry sum at the time of registration. After the sum is paid, you get an unlimited access to some of the most searched-for eBooks on the net.
Again, you'll find web sites, exactly where you do not need any payment, but you can access a huge collection of Managing Higher Education in Colleges eBooks.
Free Books, no matter whether Managing Higher Education in Colleges PDF eBooks or in other format, are accessible inside a heap around the web.
Finally, the following techniques for obtaining free of charge ebooks are all legal. We know along with the following geek that anybody and their brother can fire up a BitTorrent client and download entire ebook libraries or just hunt and peck in zeobooks.org search benefits for PDF files; this roundup, nonetheless, is focused on reputable channels for acquiring new reading material. Downloading these cost-free Managing Higher Education in Colleges ebooks might make book publishers sad over their lost income but they won't send an armada of lawyers following you."