This have a 6 minute memory time window.
available.packagesMem(contriburl, method, fields, type, filters, repos)URL(s) of the contrib sections of the repositories.
    Specify this argument only if your repository mirror is incomplete,
    e.g., because you burned only the contrib section on a CD.
download method, see download.file.
a character vector giving the fields to extract from
    the PACKAGES file(s) in addition to the default ones, or
    NULL (default).  Unavailable fields result in NA
    values.
character string, indicate which type of packages: see
    install.packages.
If type = "both" this will use the source repository.
a character vector or list or NULL (default). See ‘Details’.
character vector, the base URL(s) of the repositories to use.