Questel has Markush structure searching available in the WPIM and MPharm files. These are databases of Markush structures which can be searched by generic structure input. MPharm covers US and European pharmaceutical patents from 1985 to the present, and WPIM has all of the Derwent chemical and pharmaceutical patents from 1987 onward. Derwent also has the Derwent Patents Citation Index covering US Examiner's citations from 1984 and EPO and PCT Examiner citations from 1978. Both of these companies have US chemical patent image databases.
European patents are available on CD-ROM as well.
The full text is available on their Chemical Patent Images CD-ROM set. MicroPatent has the full text images on the Web for a fee. Here are links to printed and Internet sources for this topic.