ISBN stands for International Standard Book Number. You can usually find the ISBN on the Title Page, Back of the Title Page, or the Back Cover of the book.
Notice the ISBNs below. Each is to the Publication Manual of the American Psychological Association
Fifth edition - Hard Cover
Fifth edition - Paperback
If there were a digital version, it would have a different ISBN.
Books published before 1970 do not have ISBNs. Beginning in 2005 ISBNs were expanded from 10 to 13 digits. Now, most have both a 10 and a 13-digit number.
Also important to libraries is the ISSN
This is important when ordering articles through Interlibrary Loan as there are often two or more periodicals with similar, if not identical titles. Example - Journal of Cloud Computing. There is one by IBIMA Publishing and one by SpringerOpen.
Many citation styles have begun using Digital Object Identifiers at the end of the citation - when available.
DOIs are unique codes that identify an electronic document, much like a social security number identifies a person. Additionally, DOIs can be used to find the document on the internet - usually at the publisher's web site.
Unlike standard urls which can change, DOIs are permanent. This gives them an important advantage over the urls you would typically find associated with journal articles retrieved from databases.
Cancer Risk in Children and Adolescents with Birth Defects: A Population-Based Cohort Study. Full Text Available By: Botto, Lorenzo D.; Flood, Timothy; Little, Julian; Fluchel, Mark N.; Krikov, Sergey; Feldkamp, Marcia L.; Wu, Yuan; Goedken, Rhinda; Puzhankara, Soman; Romitti, Paul A. PLoS ONE. Jul2013, Vol. 8 Issue 7, p1-13. 13p. DOI: 10.1371/journal.pone.0069077
You can change the DOI found in the article above into a DOI url by inserting the following:
No. A DOI can reference any kind of electronic document, including articles, books, and book chapters.
Usually at the top or bottom of an article. Some databases provide the DOI along with the citation.
No. In fact most don't. DOIs are still new. As such they are most likely to be found in medical and scientific journals.
Usually to the publisher's website. NOT to the database you originally used. Warning! The publishers website may try to sell you access to the same article you got for free through the library's databases.
Try Google. If that doesn't work, you can turn it into a DOI.