Perhaps you should try some spelling variations:
tham thuc » nham thuc, pham thuc, tam thuc
van tham » van thanh, van tuan, van chat
nang cai » nang cao, nang cap, nang can
hanh dao » lanh dao, thanh dat, thanh dam
nang tai » hang tai, tang tai, sang tai
hanh dai » hanh tai, vanh dai, thanh dat
hieu van » hieu va, thien van, lieu va
vu sach » vu bach, su sach, vu khach
sach ky » sac ky, sach y, sach ty
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: vu sach ky ((nang cai) or (nang tai)) hoi. hieu van tham thuc vat ((hanh dai) OR (hanh dao)) cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach ky ((nang cai) OR (nang tai)) hoi. hieu van tham thuc vat ((hanh dai) OR (hanh dao)) cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu sach ky ((nang cai) or (nang tai)) hoi. hieu van tham thuc vat ((hanh dai) OR (hanh dao)) cua te".
• Adding a wildcard symbol may retrieve word variants: vu sach ky ((nang cai) or (nang tai)) hoi. hieu van tham thuc vat ((hanh dai) OR (hanh dao)) cua te*.