How to find size of academic literature in a given discipline? The question is related to the trend of research and focus on different disciplines. 

Is there some trend assesment which shows the number of articles or conferences on a specific disciplines? 

If someone would like to see the trend of research on let's say Nano Technology or Semantic Technology is there some source of information which shows the number of conferences related to the discipline and the number of articles tagged for these disciplines?
It is not that easy to determine the current trend. Many search engines for publications give the number of the search query.

It is important to continuously dealing with your area of ​​expertise. The best way to identify the current trend is to go to conferences and read professional journals. In addition, one also needs a lot of expertise to be able to assess as something.