Columbia subject headings:
Energy conservation--Spain--Periodicals.
Energy policy--Spain--Periodicals.
Power resources--Spain--Periodicals.
Harvard subject headings:
Energy conservation--Spain--Periodicals.
Energy policy--Spain--Periodicals.
Power resources--Spain--Periodicals.
Princeton subject headings:
Energy conservation--Spain--Periodicals.
Energy policy--Spain--Periodicals.
Periodicals.
Power resources--Spain--Periodicals.