Perhaps you should try some spelling variations:
hieu quan » hieu qua, lieu quan, thien quan
nam thuc » nam thuoc, nam thu, nam tu
danh vi » hanh vi, dinh vi, danh di
va danh » va dinh, va dan, va hanh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
lang ra » lang ha, lang xa, lang va
nang co » nang cao, nang doc, nang noi
vi cua » vai cua, di cua
cua tu » cua tuc, cua su, cua cu

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 ky ((nang co) or (lang ra)) hoi. hieu quan ((nam thuc) OR (am thuc)) va danh vi cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky ((nang co) OR (lang ra)) hoi. hieu quan ((nam thuc) OR (am thuc)) va danh vi cua tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky ((nang co) or (lang ra)) hoi. hieu quan ((nam thuc) OR (am thuc)) va danh vi cua tu".
• Adding a wildcard symbol may retrieve word variants: tu sach ky ((nang co) or (lang ra)) hoi. hieu quan ((nam thuc) OR (am thuc)) va danh vi cua tu*.