Researches are split into four categories:
Economy - Will give you bonuses pertaining to the economic side of your Base
Military - Will unlock new units and will give them attack and defense bonuses
Combat - Will unlock new features which give both economic and military bonuses
Supplies - Will unlock the supplies feature and give some extra economic and military bonuses
Available researches:
Construction Speed
Food Production
Cement Production
Steel Production
Oil Production
Unit Load
March Speed
Gathering Speed
Gold Gathering Speed
Scouting
Production Speed
Fighter Attack
Tank Attack
AAA Attack
Fighter Defense
Tank Defense
AAA Defense
T-34
P-51D Mustang
Möbelwagen
Lancaster
Bomber Attack
Bomber Defense
IS-2
Spitfire Mk. XIV
M16 MGMC
B-17
Unit Hitpoints
Unit Defence
Tiger II
Me 262
M19 MGMC
B-29
Advanced Vault
Gathering March Speed
Rebel March Speed
Unit Attack
March Slot
Equipment Slot
Commander Preset
March Preset
Enemy Defense Debuff
Enemy Attack Debuff
Enemy Hitpoints Debuff
Atomic Facility Rally Capacity
Attack Rally Capacity
Unlock Supply Slot 1
Unit Hitpoints
Unit Attack
Unit Defense
Supplies Active Time
Gathering March Speed
Rebel March Speed
Rally March Speed Debuff
Enemy Hitpoints Debuff
Enemy Attack Debuff
Enemy Defense Debuff
Unlock Supply Slot 2
Supplies Active Time 2