Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
thuc can » thuc chan, thuc dan, thuc van
hieu van » hieu va, thien van, lieu va
cau treo » cau theo, cau tren, cau triet
ky dang » ky nang, ky danh
thuc ca » thuc cua, thuc cao, thuc va
ky tang » ky nang, kho tang, ky trong
dan vai » dan va, dan tai, dan vat
vai cau » va cau, van cau, vai cac

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 tang) OR (ky dang)) xa hoi. hieu van nam ((thuc ca) or (thuc can)) dan vai cau treo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ((ky tang) OR (ky dang)) xa hoi. hieu van nam ((thuc ca) OR (thuc can)) dan vai cau treo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ((ky tang) OR (ky dang)) xa hoi. hieu van nam ((thuc ca) or (thuc can)) dan vai cau treo".
• Adding a wildcard symbol may retrieve word variants: doc sach ((ky tang) OR (ky dang)) xa hoi. hieu van nam ((thuc ca) or (thuc can)) dan vai cau treo*.