Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
cao hoi » cau hoi, co hoi, cao hoc
hieu va » lieu va, hieu qua
cac tuc » cac toc, cac tu, cac tac
tuc gia » tac gia, duc gia, toc gia
de khoa » da khoa, ke khoa, te khoa
de hoa » de hoan, do hoa, de hoc

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) or (thu hoach)) ky nang cao hoi. hieu va cac tuc gia thanh ((de hoa) OR (de khoa)) viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu hoach)) ky nang cao hoi. hieu va cac tuc gia thanh ((de hoa) OR (de khoa)) viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (thu hoach)) ky nang cao hoi. hieu va cac tuc gia thanh ((de hoa) OR (de khoa)) viet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (thu hoach)) ky nang cao hoi. hieu va cac tuc gia thanh ((de hoa) OR (de khoa)) viet*.