Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
nam truc » nam truoc, nam thuc, nam trung
hanh tai » thanh tai, hang tai, han tai
ky dang » ky danh
nam tuc » nam thuc, nam tu, nam thuoc
va hanh » van hanh, va thanh, va danh
tai cua » thai cua, tai cuc, tri cua
cua tu » cua tuc, cua su, cua cu

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ((ky dang) or (ky nang)) xa hoi. hieu van ((nam tuc) OR (nam truc)) va hanh tai cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky dang) OR (ky nang)) xa hoi. hieu van ((nam tuc) OR (nam truc)) va hanh tai cua tu*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky dang) or (ky nang)) xa hoi. hieu van ((nam tuc) OR (nam truc)) va hanh tai cua tu*".