So much of the research done today focuses on resources that can be accessed online, digital information that can be found and analyzed quickly... often from home on a snowy day while wearing pajamas.
As convenient as it is, relying solely on online information introduces a dangerous bias in research. It's true that an increasing amount of older information is being digitized every day, but that is still just a tiny sample of all the information that has been produced. Limiting your research to only online sources introduces a shortsightedness that can affect your conclusions and your decisions.
Paradoxically, I say all that as preamble to a post about yet another online resource, but the database I'm highlighting exists in part to help correct the myopia: GFDatabase.