Perhaps you should try some spelling variations:
"khoa hoc va thuat khao" » "khoa hoc va thuat kham", "khoa hoc va thuat thao", "khoa hoc va thuat giao", "hoa hoc va thuat khao", "khoa hoc ky thuat khao", "khoa hoc ki thuat khao", "khoa hoc va thuc khao"
"khoa hoc va tham khao" » "hoa hoc va tham khao", "khoa hoc van tham khao", "khoa hoc va cham khao"
"khoa hoc va thanh pho" » "hoa hoc va thanh pho", "khoa hoc gia thanh pho", "khoa hoc ban thanh pho", "khoa hoc va tinh pho"

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

• Performing a fuzzy search may retrieve terms with similar spellings: (((("khoa hoc va tham khao") OR ("khoa hoc va thuat khao"))) or ("khoa hoc va thanh pho"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("khoa hoc va tham khao") OR ("khoa hoc va thuat khao"))) OR ("khoa hoc va thanh pho"))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"khoa hoc va tham khao\") OR (\"khoa hoc va thuat khao\"))) or (\"khoa hoc va thanh pho\"))*".
• Removing quotes may allow a broader search: (((( khoa hoc va tham khao ) OR ( khoa hoc va thuat khao ))) or ( khoa hoc va thanh pho ))*.