PubMed Central (http://www.pubmedcentral.nih.gov/): PubMed Central is provided by the US National Center for Biotechnological Information and is a free digital archive of biomedical and life sciences journal literature (do not Caspase pathway confuse this with ‘PubMed’, which is the citation database mentioned above. For more on the different databases available from the National Library of Medicine see http://www.ncbi.nlm.nih.gov/About/tools/restable_lit.html). PubMedCentral provides free access to over 700 biomedical journals. The currency and age of content available for free varies by journal. Many journals make their content available as soon as it is published, where others

delay release of content for anywhere from a few months to more than a year after publication. However, most journals provide free access to full text within a year of publication.

For issues of major journals before the early 1990s, much content has been digitized (scanned), with the contents of some available as far back as the 1800s. PubMed Central also archives the content of the BiomedCentral open access journals. Visit http://www.pubmedcentral.nih.gov/about/faq.html for more information about what is available. Highwire Press (highwire.stanford.edu/lists/freeart.dtl) offers free access to online journals published by Highwire Press. Typically this CT99021 cost contains (but is not limited to) the journals of professional societies. The only restrictive factor is that some journals have a 12-month embargo, only allowing Thymidylate synthase full free text access one year from publication, which means the latest full-text issues may not be available beyond the titles and abstracts. The Cochrane Library (follow the link from http://www.cochrane.org) is a very useful resource, which provides access to several databases. As well as the full text

of systematic reviews and protocols produced by the Cochrane Collaboration in the Cochrane Database of Systematic Reviews (CDSR), The Cochrane Library also contains the Cochrane Central Register of Controlled Trials (known as CENTRAL), the Database of Abstracts of Reviews of Effects (DARE), which contains systematic reviews undertaken outside the Cochrane collaboration, the Cochrane Methodology Register (CMR) which contains a bibliography of publications which report on methods used in the conduct of controlled trials, the Health Technology Assessment database, which brings together details of completed and ongoing health technology assessments (studies of the medical, social, ethical and economic implications of healthcare interventions) from around the world, and the NHS Economic Evaluation Database, which contains quality-assessed economic evaluations from around the world. Residents in many countries can access The Cochrane Library online for free through a ‘provision’ or a special scheme.