Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
nam thuc » nam thuoc, am thuc, nam tu
sach ky » sac ky, sach y, sach ty
ky dang » ky nang, ky danh
xay hoi » tay hoi, cay phoi, gay thoi
hieu va » lieu va, hieu qua
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) OR (xa hoi)). hieu va ((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) OR (xa hoi)). hieu va ((nam thuc) OR (nam thu)) va dau tai buu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky dang ((xay hoi) OR (xa hoi)). hieu va ((nam thuc) or (nam thu)) va dau tai buu tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ky dang ((xay hoi) OR (xa hoi)). hieu va ((nam thuc) or (nam thu)) va dau tai buu tre*.