What is a DOI number?
DOI stands for Digital Object Identifier and it is the unique number that belongs to a single scientific paper. It is structured so that if you state the DOI-number in your web-browser's address field, then you go directly to the specific article wherever it is on the internet. The DOI numbers are administered by private companies and the journals pay a fee to use DOI-numbers for their articles. Therefore, not all journals use DOI-numbers, so for now the original reference to an article is still the journal name, year of publication, volume number and page numbers.
The DOI-code is made of various elements and could par example look like this:
10.1111 is the code of Blackwell which is the company that owns the journal.
J indicates that it is a journal article.
1748-1716 is the e-issn number for the journal.
2006 is the year in which the article was accepted for publication.
0618 is the article’s unique number.
You can read much more about this system at www.doi.org.