What happens is as you find new technologies you earn tech points. (basically a percentage of what you just researched)

Then you are able to trade these tech points, which apply directly to the field of their type. Meaning you will get x number of points towards that type of research.

To view this in action, open your tech tree before you trade and you will see all of the un-researched techs completely empty except for the one you are currently researching. Now do the trade. Go back and look in the tree in which you just acquired research points. You'll see one of the techs is partially filled in.

It is possible that you can actually get full techs if you have already partially researched or have already acquired points in that particular tech in a previous trade and happen to get credit in that specific tech. Also, I believe the tech in that tree in which the points are applied is random.

If you trade for a high enough number of research points you can also just flat out get the new tech as well.

Hope I explained that well, and hope I got it all right as well

Feel free to ask more if that didn't quite explain it.