Perhaps you should try some spelling variations:
doc sach » hoc sach, nuoc sach, dac sac
nam thuc » nam thuoc, am thuc, nam thu
toc sach » hoc sach, thuoc sach, nuoc sach
danh tai » doanh tai, dinh tai, hanh tai
hieu van » hieu va, thien van, lieu va
cam thuc » am thuc, cam thu, can thuc
tai cua » thai cua, tai cuc, tri cua
va danh » va dinh, va dan, va hanh
cua te » cua tu
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 (toc sach)) ky nang x hoi. hieu van ((cam thuc) OR (nam thuc)) va danh tai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((doc sach) OR (toc sach)) ky nang x hoi. hieu van ((cam thuc) OR (nam thuc)) va danh tai cua te*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((doc sach) or (toc sach)) ky nang x hoi. hieu van ((cam thuc) OR (nam thuc)) va danh tai cua te*".