British Library Direct is a reissue of British Library Inside.
You can search the latest 5 years of the 20,000 journals in the British Library’s collection for free via British Library Direct You can register, order articles directly and pay by credit card. However, as long as you are connected with Princeton University, the Library will obtain anything/everything needed at no charge — through our Document Delivery Service and Interlibrary Loan.
A disadvantage of this database is that there are no links to Princeton holdings, but many articles are freely available. For example, an advanced search on "fuel cells" (in title) yielded a total of 3199, and 1708 are immediately available (free). The emphasis is on science & technology.
About British Library Direct Something to keep in mind when/if you are unaffiliated with academia!
British Library Direct Plus is a subscription-based service with 67,000 titles and goes back to the 1940′s.