Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
ky sang » ky nang, ky dang, duy sang
ky tang » ky nang, ky dang, kho tang
hieu ve » hieu va, hieu van
va danh » va dinh, va dan, va hanh
ve dat » de dat, va dat, ve dao
vi cau » va cau, di cau, viet cau
ve cau » ke cau, va cau, ve cac
nuoc » quoc, duoc, ngoc

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 sang) or (ky tang)) xa hoi. hieu ve dat nuoc va danh ((vi cau) or (ve cau)) tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky sang) OR (ky tang)) xa hoi. hieu ve dat nuoc va danh ((vi cau) OR (ve cau)) tren.
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky sang) or (ky tang)) xa hoi. hieu ve dat nuoc va danh ((vi cau) or (ve cau)) tren*.