Perhaps you should try some spelling variations:
quoc sang » buoc sang, quoc quang, quoc thang
hieu van » hieu va, thien van, lieu va
quoc san » nuoc san, quoc ban, quoc lan
nang ma » tang ma, sang ma, nang cao
vai cua » dai cua, hai cua, lai cua
ma hoi » mai hoi, xa hoi, ma hoa
vi cua » di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu cac ky nang ma hoi. hieu van ban ((quoc san) OR (quoc sang)) benh ((vi cua) or (vai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu cac ky nang ma hoi. hieu van ban ((quoc san) OR (quoc sang)) benh ((vi cua) OR (vai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu cac ky nang ma hoi. hieu van ban ((quoc san) OR (quoc sang)) benh ((vi cua) or (vai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: tu cac ky nang ma hoi. hieu van ban ((quoc san) OR (quoc sang)) benh ((vi cua) or (vai cua)) tre*.