Perhaps you should try some spelling variations:
"khoa hoc va thanh khac" » "khoa hoc va khoanh khac", "khoa hoc va thanh hai", "khoa hoc va thanh phan", "hoa hoc va thanh khac", "khoa hoc gia thanh khac", "khoa hoc ban thanh khac", "khoa hoc va tinh khac"
"khoa hoc va cham khac" » "khoa hoc va pham khac", "khoa hoc va tham khao", "khoa hoc va ham khai", "hoa hoc va cham khac", "khoa hoc va chat khac", "khoa hoc va tham khac"
"khoa hoc va phap khac" » "khoa hoc va nhap khau", "khoa hoc va phap phat", "khoa hoc va phap phan", "hoa hoc va phap khac", "khoa hoc va phat khac", "khoa hoc ban phap khac"

Try widening your search to All Fields.

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 thanh khac") or ((("khoa hoc va cham khac") OR ("khoa hoc va phap khac"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("khoa hoc va thanh khac") OR ((("khoa hoc va cham khac") OR ("khoa hoc va phap khac")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"khoa hoc va thanh khac\") or (((\"khoa hoc va cham khac\") OR (\"khoa hoc va phap khac\"))))".
• Removing quotes may allow a broader search: (( khoa hoc va thanh khac ) or ((( khoa hoc va cham khac ) OR ( khoa hoc va phap khac )))).
• Adding a wildcard symbol may retrieve word variants: (("khoa hoc va thanh khac") or ((("khoa hoc va cham khac") OR ("khoa hoc va phap khac"))))*.