Is there a tool for showing trend in a technical research field?
I use Scopus quite a lot and it provides the ability to analyze keywords (there is a link to 'Analyze search results'):


I was able to quickly obtain this plot for publications per year for the keyword 'wearable computing':



It can also be restricted to particular sources. For example
this one for 'wearable computing' in 'IEEE Pervasive computing':



Unfortunately you need a subscription to access Scopus.