Perhaps you should try some spelling variations:
dang xay » dang van, van xay
cach hoc » cach thuc, cach thoi, dich hoc
hanh dai » hanh tai, hanh dao, vanh dai
nang ma » tang ma, sang ma, nang cao
hieu va » lieu va, hieu qua
cac hoc » cac hop, bac hoc, cac toc
va hanh » van hanh, va thanh, va danh
te sac » te sach, te cac, te san
sac ky » cac ky, sai ky
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: te sac ky ((nang ma) or (dang xay)) hoi. hieu va ((cac hoc) or (cach hoc)) va hanh dai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sac ky ((nang ma) OR (dang xay)) hoi. hieu va ((cac hoc) OR (cach hoc)) va hanh dai cua te.
• Adding a wildcard symbol may retrieve word variants: te sac ky ((nang ma) or (dang xay)) hoi. hieu va ((cac hoc) or (cach hoc)) va hanh dai cua te*.