Perhaps you should try some spelling variations:
vat hanh » vat thanh, van hanh, va hanh
cam thuc » am thuc, nam thuc, cam thu
hieu van » hieu va, thien van, lieu va
tu sach » thu sach, su sach, te sach
van cam » van nam, van lam, van cau
tang ha » lang ha, tang ma, trung ha
ky tang » ky nang, ky dang, kho tang
so sach » so sanh, bo sach, co sach
te cuu » te cua, te cau
tu cuu » tu huu, tu cua, tu chu

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 (so sach)) ky tang ha noi. hieu van cam thuc vat hanh ((te cuu) OR (tu cuu)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (so sach)) ky tang ha noi. hieu van cam thuc vat hanh ((te cuu) OR (tu cuu)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (so sach)) ky tang ha noi. hieu van cam thuc vat hanh ((te cuu) OR (tu cuu)) tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (so sach)) ky tang ha noi. hieu van cam thuc vat hanh ((te cuu) OR (tu cuu)) tre*.