Perhaps you should try some spelling variations:
thu sach » thuat sach, thuoc sach, thu hoach
vat hanh » vat thanh, van hanh, va hanh
nam thuc » nam thuoc, am thuc, nam thu
tu sach » su sach, te sach, tu cach
hanh ve » hanh vi, hanh va, hanh kem
hieu va » lieu va
lang ha » long ha
ky lang » ky nang, ky dang, ky tang
so viet » hoc viet
ha hoi » hoa hoi, ha noi, xa hoi
ve so » ve su, va so, ve co

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 sach)) ky lang ha hoi. ((hieu va) OR (hieu qua)) nam thuc vat hanh ve so viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu sach)) ky lang ha hoi. ((hieu va) OR (hieu qua)) nam thuc vat hanh ve so viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (thu sach)) ky lang ha hoi. ((hieu va) OR (hieu qua)) nam thuc vat hanh ve so viet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (thu sach)) ky lang ha hoi. ((hieu va) OR (hieu qua)) nam thuc vat hanh ve so viet*.