Every airline in germany has to offer parttime flying, otherwise you can just sue them for parttime with a nearly guaranteed chance on winning (companies in germany are required by law to offer parttime schemes). However in most cases you have to join as fulltimer and then bid for parttime which is allocated according seniority. Another thing is that most airlines dont take DECs so you would have to start over as an FO (one big exception is Air Berlin).
Parttime schemes are different within each company, in my outfit (dba, dont take DECs) we have 75% and 50% schemes on a monthly bases, meaning you get a certain amount of so called "parttime days" per month, those days are treated as non-touchable off days and are allocated as the same block of days each month.