Perhaps you should try some spelling variations:
dua tren » dung tren
thu sach » thuat sach, thuoc sach, thu hoach
cam thuc » am thuc, nam thuc, cam thu
hieu van » hieu va, thien van, lieu va
cu tren » tu tren
thuc va » thuc vat, thuc dan, thuc day
tu sach » su sach, te sach, tu cach
nang co » nang cao, nang doc, nang noi
van cam » van nam, van lam, van cau
co hoi » co hoc, co loi
va dan » ca dan, va dao, va dau

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 nang co hoi. hieu van cam thuc va dan ca ((cu tren) or (dua tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu sach)) ky nang co hoi. hieu van cam thuc va dan ca ((cu tren) OR (dua tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) OR (thu sach)) ky nang co hoi. hieu van cam thuc va dan ca ((cu tren) or (dua tren))".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) OR (thu sach)) ky nang co hoi. hieu van cam thuc va dan ca ((cu tren) or (dua tren))*.