Perhaps you should try some spelling variations:
doc sach » toc sach, nuoc sach, dac sac
hoc sach » hoc sinh, hoc cac, hoc anh
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hanh hai » thanh hai, nhanh hai, hang hai
cho thue » choi thuc, cuc thue, cho he
hieu va » lieu va, hieu qua
va hanh » van hanh, va thanh, va danh
cho tre » khoe tre
x hoi » xa hoi, o hoi, x ho

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) or (hoc sach)) ky nang x hoi. hieu va cac nuoc va hanh hai ((cho tre) OR (cho thue))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((doc sach) OR (hoc sach)) ky nang x hoi. hieu va cac nuoc va hanh hai ((cho tre) OR (cho thue)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((doc sach) or (hoc sach)) ky nang x hoi. hieu va cac nuoc va hanh hai ((cho tre) OR (cho thue))".
• Adding a wildcard symbol may retrieve word variants: ((doc sach) or (hoc sach)) ky nang x hoi. hieu va cac nuoc va hanh hai ((cho tre) OR (cho thue))*.