The majority of this LibGuide has looked at Open Access from the perspective of the creator of a work. This section of the LibGuide looks at OA from the perspective of the consumer, reader and researcher: what tools are available to help you access research publications for free?
Unpaywall is a web browser extension that you can install quickly and easily from their website here. Once installed, a padlock will appear in your browser screen when you land on the page of a scholarly article with a DOI. If the work is openly accessible, the padlock will turn green - all you have to do is click and you will be redirected to the OA version of the item you are interested in. At the time of writing (January 2019) Unpaywall had harvested just under 25 million Open Access scholarly articles from 50,000 publishers and repositories around the world. Other similar tools exist, too, which you could try. These include Kopernio and the Open Access Button.
Google Scholar is the world's largest database of scholarly publications, with a recent estimate suggesting the database had close to 400 million items indexed from repositories, academic publishers, professional society webpages, and other sites. Not everything indexed is OA, and it's important to bear in mind that not all research outputs are indexed in Scholar, but it is the most comprehensive tool available in terms of providing a central location to search for resources across the web.
CORE, like Google Scholar, is a centralised search tool containing publications from repositories and journal publishers from around the world. At the time of writing (January 2019), CORE has over 130 million publications indexed in its service. CORE differs from Google Scholar in that it only indexes fully OA content and also in that it harvests fulltext versions of all indexed items (rather than linking out to other websites in the same way Google Scholar does) enabling interested researchers to text mine content aggregated by the service.
Open Access Repositories
Most repositories are indexed in the tools above, however there may be times when it is advantageous to go directly to an individual repository to search. For example, perhaps you are interested in searching for Australian higher education policy documents and related research. In this instance a stop by the Australian and New Zealand focused Analysis and Policy Observatory (APO), which contains only policy and policy research-related publications, is likely to provide you with relevant results more quickly and easily. A detailed overview of the different type of repositories and most popular platforms can be found in the Sharing Your Work Part 1 - Green OA section of this guide.
The DOAJ (or Directory of Open Access Journals) is the longest established resource on this list. Commenced in 2003, it now lists more than 12,000 fully OA journals. An advantage of using DOAJ is that it has a degree of quality control as it only indexes journals which are peer-reviewed or have a quality control process in place. You can search by journal or by article, and also by licence (particularly useful if you are interested in reusing materials for a specific reason or interested in text data mining).
Still no luck?
If you have tried the above and still cannot access what you are looking for, try emailing the author directly to obtain a copy!