Perhaps you should try some spelling variations:
vat thanh » dat thanh, gat thanh, tat thanh
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, am thuc, nam thu
tu cach » tu cac
su sach » so sach, vu sach
vai cua » dai cua, hai cua, bai cua
lai cua » dai cua, hai cua, lai chau
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu cach) or (su sach)) ky nang o hoi. hieu van nam thuc vat thanh ((vai cua) OR (lai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu cach) OR (su sach)) ky nang o hoi. hieu van nam thuc vat thanh ((vai cua) OR (lai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu cach) or (su sach)) ky nang o hoi. hieu van nam thuc vat thanh ((vai cua) OR (lai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: ((tu cach) or (su sach)) ky nang o hoi. hieu van nam thuc vat thanh ((vai cua) OR (lai cua)) tre*.