While you can’t pick and choose which papers to review, you do choose when you will and won’t be assigned to review

Setting your availability. Nobody likes getting a review assignment while they are on holiday. To avoid this, let the system know when you expect to be unavailable to serve as on the Board as a reviewer. If for an extended period you will be unavailable to act as Reviewer, change your availability status in your ISI profile. (‘Sign On’ to your ISI account at http://My.InformingScience.org, click Profile and indicate in the Reviewing tab the period of your unavailability.) Letting the system know you are not available ensures that the EiC will not assign a paper to you during that time. During this period when you are not available to review, you will not be a member of the journal’s review board.

Setting the maximum number of reviews per year. You can also set in your Profile the maximum number of reviews you will do for the journal in a year. (Log in at http://My.InformingScience.org, click Profile, and click Reviewing Options to see these options (Figure 3).)

Figure 3. When you first log in at http://My.InformingScience.org, you will see the dashboard on your personal page. Here you can see all your editorial tasks and manage your reviewing options. 
Set times when you will be unavailable to review and max reviews/yr

Withdrawing from reviewing a given paper. Of course, there are times when we unexpectedly become unavailable to review, such as during illness. If this happens, immediately click the Withdraw link shown in Figure 7. While you may withdraw from a review because of some unexpected life event, there is no picking and choosing which papers to review.