Perhaps you should try some spelling variations:
tham thuc » nham thuc, pham thuc, tam thuc
hieu van » hieu va, thien van, lieu va
van tham » van thanh, van tuan, van chat
viet cua » viec cua, viet ca, biet cua
viet qua » vien quan, ket qua, viet ha
doc sac » doc sach, dac sac, hoc sach
nang ma » tang ma, sang ma, nang cao
thuc va » thuc vat, thuc dan, thuc day
va danh » va dinh, va dan, va hanh
sac ky » cac ky, sai ky
ma hoi » mai hoi, xa hoi, ma hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sac ky nang ma hoi. hieu van tham thuc va danh ((viet cua) or (viet qua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sac ky nang ma hoi. hieu van tham thuc va danh ((viet cua) OR (viet qua)) tre.
• Adding a wildcard symbol may retrieve word variants: doc sac ky nang ma hoi. hieu van tham thuc va danh ((viet cua) or (viet qua)) tre*.