Perhaps you should try some spelling variations:
sach tranh » canh tranh
tranh kki » tranh cai
kki thuat » ki thuat, khoi thuat, ky thuat
sach day » sach dao, sach dat, sach dau
tu sach » thu sach, su sach, te sach
y thuat » ky thuat, my thuat, kxy thuat
day y » day _, dan y
o hoc » mo hoc, so hoc, y hoc
toan » tran

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( tu sach day y thuat ((o hoc) or (co hoc)) ) or ( tu sach tranh kki thuat toan khoa ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu sach day y thuat ((o hoc) OR (co hoc)) ) OR ( tu sach tranh kki thuat toan khoa )).
• Adding a wildcard symbol may retrieve word variants: (( tu sach day y thuat ((o hoc) or (co hoc)) ) or ( tu sach tranh kki thuat toan khoa ))*.