Perhaps you should try some spelling variations:
thuat sach » thuat lanh, thuat san
hieu van » hieu va, thien van, lieu va
cac nuoc » cap nuoc, hoc nuoc, cua nuoc
dang tai » dang thai, dung tai, hang tai
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, nang cao
va dang » van dang, va nang, va lang
cuc te » cua te, cuc thue, cuc tieu

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

• Performing a fuzzy search may retrieve terms with similar spellings: thuat sach ky ((mang may) or (nang ma)) hoi. hieu van ((cac nuoc) or (dat nuoc)) va dang tai cuc te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuat sach ky ((mang may) OR (nang ma)) hoi. hieu van ((cac nuoc) OR (dat nuoc)) va dang tai cuc te.
• Adding a wildcard symbol may retrieve word variants: thuat sach ky ((mang may) or (nang ma)) hoi. hieu van ((cac nuoc) or (dat nuoc)) va dang tai cuc te*.