Perhaps you should try some spelling variations:
thuat sach » thuat lanh, thuat san
vat hanh » vat thanh, van hanh, va hanh
cam thuc » am thuc, nam thuc, cam thu
tu sach » thu sach, su sach, te sach
hanh va » hang va, hanh vi
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
nang ma » tang ma, sang ma, nang cao
ve cam » ve cham, ve cac, va cam
va cua » va chua, via cua, ca cua

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 (thuat sach)) ky ((nang x) or (nang ma)) hoi. hieu ve cam thuc vat hanh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thuat sach)) ky ((nang x) OR (nang ma)) hoi. hieu ve cam thuc vat hanh va cua tre.
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (thuat sach)) ky ((nang x) or (nang ma)) hoi. hieu ve cam thuc vat hanh va cua tre*.