Perhaps you should try some spelling variations:
population center » population census, population censuses, population change
5.2 communication » 3.2 communication, 6.2 communication, 2.2 communication
technology set » technology sector, technology 1, technology 2.2
set population » meet population, de population, em population
4.1 developing » 3.1 developing, 4 developing, 3.3 developing
center crec » center prcec, center area, center eric
costs 4.1 » costs 4.2, costs 4.4, costs 4.3
crec 5.2 » clsc 5.2, spec 5.2

You may be able to get more results by adjusting your search query.

• Adding a wildcard symbol may retrieve word variants: technology set population center crec 5.2 communication costs 4.1 developing _ african.*.