Easy way to see historical trend in keywords in publications?

If you have access to it, you can very easily do that with Thomson Reuters’ Web of Science portal. Run any query you want, probably starting with the simplest one: Topic=XXXX. Then, select “Analyze results” at the top-right bottom-left of the results list, and sort them by year of publication:

Edit: I though I would update this answer with a tool I recently discovered--trends.google.com

It's not specific to peer-reviewed publications, but allows one to search keywords by country, category (e.g., science), and web/image/news/.

Google's Ngram viewer is also useful. It's quick and easy for seeing trends as far back as the 1800's.

I've written a small Python tool for this purpose. It scrapes Google scholar for each year in a given time span, extracts the occurrences and saves them to a CSV file. The tool is located at: https://github.com/Pold87/academic-keyword-occurrence