Depending on your field of interest, you can search in a variety of our library databases to find literature reviews. Here's a tip that works across most databases: enter your keyword(s) in the first search box and then "literature review" in the second search box.
Annual Reviews are another great source for literature reviews. Each selection within a volume is a detailed essay reviewing the literature in a topic related to the field. Use advanced search to enter your keywords and find reviews within a particular time frame.
In whatever database you're searching, use filters to change the date range and find older examples of the genre.
Many of the journal articles found in library databases are empirical research reports. These include quantitative or qualitative data analyses, and often feature the following sections: introduction, methods, results, and discussion.
One way you might track changes in the genre of empirical research reports over time is to pick one scholarly journal from your discipline of choice and examine a few sample issues from the past few decades. You could look at the table of contents of sample issues, or focus on a particular section (like methods), to see if you notice any trends over time.
Find journals in your subject area with BrowZine.
Policy memos are a little trickier to find, as they are often not labeled as such, and are not often collected in one place. You can try to find them in your database of choice by adding "policy memo" to your search. Try this in ERIC, the database for studies in education, for example.
Another tool that might be useful is Harvard's Think Tank Search, which is a scoped Google search of various policy research institutions' websites.