Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
dang xay » dang van, van xay
nam thuc » nam thuoc, am thuc, nam tu
sach ky » sac ky, sach y, sach ty
ky dang » ky nang, ky danh
xay hoi » xa hoi, tay hoi, cay phoi
dau tai » dai tai, dat tai, da tai
buu tre » cuu tre
va dau » va dao

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ky dang xay hoi. hieu qua ((nam thuc) or (nam thu)) va dau tai buu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky dang xay hoi. hieu qua ((nam thuc) OR (nam thu)) va dau tai buu tre.
• Adding a wildcard symbol may retrieve word variants: doc sach ky dang xay hoi. hieu qua ((nam thuc) or (nam thu)) va dau tai buu tre*.