Open Access (OA)
By 'open access' to this literature, we mean its free availability on the public internet, permitting any users to read, download, copy, distribute, print, search, or link to the full texts of these articles, crawl them for indexing, pass them as data to software, or use them for any other lawful purpose, without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself. The only constraint on reproduction and distribution, and the only role for copyright in this domain, should be to give authors control over the integrity of their work and the right to be properly acknowledged and cited.
Open archives initiative (OAI)
The Open Archives Initiative develops and promotes interoperability standards that aim to facilitate the efficient dissemination of content. OAI has its roots in the open access and institutional repository movements. Continued support of this work remains a cornerstone of the Open Archives program. Over time, however, the work of OAI has expanded to promote broad access to digital resources for eScholarship, eLearning, and eScience.
Source : http://www.openarchives.org/
The OR operator lets you retrieve records that contain any of your search terms. For example, the search “heart attack OR myocardial infarction” retrieves records that contain “heart attack”, “myocardial infarction” or both terms. Results are all inclusive
Source : OVID help. Available form: http://www.ovid.com/site/help/documentation/ospb/en/syntax.htm#operators
Image source : http://en.wikipedia.org/wiki/File:LogicGates.svg