VOLUME 21 (5)/October 1991

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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Institute of Meteorology and Hydrology, Bulgarian Academy of Sciences, 1184 Sofia
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Institute of Meteorology and Hydrology, Bulgarian Academy of Sciences, 1184 Sofia
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University of Mining and Geology, 1156 Sofia

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
|
Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria