As far as I know, Matlab does not support reading of RINEX observation/navigation files. I created functions and classes to read RINEX and other GNSS-related files (see GNSS-toolbox). You can load RINEX to Matlab OBSRNX object as following:
addpath(genpath('path_to_GNSS-toolbox/src')); % Add path to toolbox functionality
obs = OBSRNX('your_rinex_filepath');
When the OBSRNX object is created in Matlab you can querry observations and perform slicing as you want. I do not test it under R2009a, but I guess it should work.