The full text of over two million English-language dissertations dating back to 1861 is available through ProQuest's Dissertations & Theses database. Often the most useful aspect of this massive collection of material is the ability to look at the sources other researchers have used to write their dissertations (by consulting the bibliographies at the end, which are often quite extensive).  Dissertations that are somehow related to your topic or that focus on a particular aspect of it can be invaluable in pointing you toward monographs, journals, newspapers, and archival sources that you may never encounter otherwise.

The Central and Eastern European Online Library (CEEOL) is by far the most efficient way to search recent publications in Eastern European scholarly journals in the humanities and social sciences, regardless of language and discipline.  Search results can be refined using subject, language, and other filters.  A search for "Zrównoważony rozwój" (= "sustainable development" in Polish), for example, yields 4,726 results, which can be limited to those having to do with "rural areas" only (= 43 results).

While Integrum mostly consists of material published after 2009, the ambition and scope of this full-text database are nevertheless astounding.  For recent articles from Russian-language newspapers, magazines, news services and websites across the post-Soviet space, Integrum is hard to beat.  Full text from over 40,000 individual sources is being added to the database on a regular basis.  

That being said, its interface takes some getting used to.  You have to click through two pages to get to the search interface ("Enter (no registration)" on the first page, and "Artefact : search documents by query" on the second page), and even then, the enormous scope of the database is not apparent, unless you click on one of the categories to see what sources are included.  There are literally thousands of websites, for example, in the "Regional Online Media" category, and articles from them are preserved in Integrum after they have disappeared from the open Web.  Below is a tiny piece of the alphabetical listing of titles in the category "Non-Russian Newspapers and Magazines."

Historical Abstracts

Sociological Abstracts

Worldwide Political Science Abstracts

Anthropology Plus

Women's Studies International

Urban Studies Abstracts

Scopus

JSTOR

EconLit

Environmental Issues Online

GEOBASE

AGRICOLA

GreenFile

History of Science, Technology & Medicine

Index Islamicus

...and many others

ABSEEES (the American Bibliography of Slavic, East European & Eurasian Studies) is the most comprehensive database of English-language scholarship on the REEE region, so there is no better place to see what has already been written on your topic in the United States, Canada, Great Britain, and (to a somewhat lesser extent) by English-speaking scholars around the world.  Its great advantage is that everything in it has something to do with the REEE region, so you can do a general search for "climate" or "agriculture" or "gender" or "islam" and not have to filter out hundreds or thousands of results pertaining to other parts of the world.  Below are the first three of 400 results from a search for " biolog* " (i.e., biology, biologist, biologists, biological, etc.):

The name of the database changed fairly recently (adding an extra "E" for "Eurasian"), so you may have to search for the old acronym (ABSEES) in order to find it in our catalog.