Perhaps you should try some spelling variations:
nang hoa » nang hoat, hang hoa, nang ho
nang hoc » nang doc, nang luc, dong hoc
nam thuc » nam thuoc, am thuc, nam tu
vat hanh » vat thanh, van hanh, va hanh
su triet » su viet, su tien, ve triet
tu sach » thu sach, su sach, te sach
hieu ve » hieu va, hieu van
vi su » va su, ve su, ki su

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 y ((nang hoa) or (nang hoc)) hoi. hieu ve ((nam thuc) OR (nam thu)) vat hanh vi su triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y ((nang hoa) OR (nang hoc)) hoi. hieu ve ((nam thuc) OR (nam thu)) vat hanh vi su triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y ((nang hoa) or (nang hoc)) hoi. hieu ve ((nam thuc) OR (nam thu)) vat hanh vi su triet".
• Adding a wildcard symbol may retrieve word variants: tu sach y ((nang hoa) or (nang hoc)) hoi. hieu ve ((nam thuc) OR (nam thu)) vat hanh vi su triet*.