ON THE 37-DAY VARIATION OF GEOMAGNETIC ACTIVITY INDEX AP.APOSTOLOV EM.1977; C.R. ACAD. BULG. SCI.; BULG.; DA. 1977; VOL. 30; NO 6; PP. 825-828; BIBL. 7 REF.Article

PERIODICITIES IN IONIZATION STATE OF THE UPPER PART OF THE DAILY D REGION.APOSTOLOV EM.1975; C.R. ACAD. BULG. SCI.; BULG.; DA. 1975; VOL. 28; NO 4; PP. 465-467; BIBL. 9 REF.Article

RELATIVE INCREASE OF RECOMBINATION COEFFICIENT IN MESOSPHERE DURING SID-EFFECTS.APOSTOLOV EM.1974; C.R. ACAD. BULG. SCI.; BULG.; DA. 1974; VOL. 27; NO 10; PP. 1359-1361; BIBL. 10 REF.Article

AMPLITUDE VARIATION OF 27-DAY PERIOD IN GEOMAGNETIC ACTIVITY DURING 19TH AND 20TH SOLAR CYCLES.APOSTOLOV EM.1977; C.R. ACAD. BULG. SCI.; BULG.; DA. 1977; VOL. 30; NO 1; PP. 33-35; BIBL. 8 REF.Article

INTERPLANETARY MAGNETIC FIELD SECTOR STRUCTURE AND LOWER IONOSPHERE IONIZATIONAPOSTOLOV EM.1978; C.R. ACAD. BULG. SCI.; BGR; DA. 1978; VOL. 31; NO 11; PP. 1397-1400; BIBL. 5 REF.Article

A MODEL OF NON-MONOTONICALLY GROWING N(H) PROFILES OF THE LOWER IONOSPHERE UNDER NON-FLORE CONDITIONS.APOSTOLOV EM.1974; PURE APPL. GEOPHYS.; SWITZ.; DA. 1974; VOL. 112; NO 4; PP. 635-645; BIBL. 33 REF.Article

ENERGY-SPECTRUM DISTRIBUTION OF THE SOLAR X-RADIATION OF LESS THAN 8 A AND ITS RELATION TO THE SOLAR RADIO EMISSION ON 2800 MHZ.APOSTOLOV EM.1974; BULL. ASTR. INST. CZECHOSL.; CZECHOSL.; DA. 1974; VOL. 25; NO 5; PP. 268-271; ABS. RUSSE; BIBL. 10 REF.Article

CONTRIBUTION OF HARD SOLAR X-RAY RADIATION TO D-REGION IONIZATIONNESTOROV GT; APOSTOLOV EM.1972; C. R. ACAD. BULG. SCI.; BULG.; DA. 1972; VOL. 25; NO 10; PP. 1343-1346; BIBL. 11 REF.Serial Issue

SOLAR CYCLE AND SEASONAL VARIATIONS IN THE EFFICIENCY OF SOLAR FLARES IN PRODUCING SUDDEN IONOSPHERIC DISTURBANCESLETTUS V; APOSTOLOV EM.1982; J. ATMOS. TERR. PHYS.; ISSN 0021-9169; GBR; DA. 1982; VOL. 44; NO 4; PP. 359-362; BIBL. 4 REF.Article

COMPLEX TIME ANALYSIS OF RECURRENT ACTIVITY OF CORONAL INDEX 1971-1976LETFUS V; APOSTOLOV EM.1982; BULL. ASTRON. INST. CZECH.; ISSN 0004-6248; CSK; DA. 1982; VOL. 33; NO 5; PP. 294-302; ABS. RUS; BIBL. 12 REF.Article

LONGITUDINAL DISTRIBUTION OF RECURRENT SOLAR ACTIVITY SOURCES AND ITS REFLECTION IN GEOMAGNETIC VARIATIONSLETFUS V; APOSTOLOV EM.1980; BULL. ASTR. INST. CZECHOSL.; CSK; DA. 1980; VOL. 31; NO 2; PP. 119-122; ABS. RUS; BIBL. 11 REF.Article

CONTRIBUTION OF THE X-RAY EMISSION LINES TO IONIZATION OF LOWER IONOSPHERE.LETFUS V; APOSTOLOV EM.1974; PURE APPL. GEOPHYS.; SWITZ.; DA. 1974; VOL. 112; NO 4; PP. 647-653; BIBL. 11 REF.Article

TEMPORARY VARIATIONS OF CRITICAL FREQUENCIES OF F2 LAYER IN 9-DAY TO 1-YEAR PERIODS.APOSTOLOV EM; COHEN MM.1977; C.R. ACAD. BULG. SCI.; BULG.; DA. 1977; VOL. 30; NO 2; PP. 221-224; BIBL. 6 REF.Article

SPECTRAL ANALYSIS OF THE TIME VARIATIONS OF SOLAR X-RAYS IN THE 1-8 A AND 8-20 A REGIONS.APOSTOLOV EM; LETFUS V.1975; BULL. ASTR. INST. CZECHOSL.; CZECHOSL.; DA. 1975; VOL. 26; NO 4; PP. 193-198; ABS. RUSSE; BIBL. 11 REF.Article

IONIZING RADIATION AND AFTER EFFECTS OF SOLAR PROTON FLARES ON AUGUST 4 AND 7, 1972NESTOROV GT; APOSTOLOV EM.1973; WORLD DATA CENTER A SOLAR-TERRESTR. PHYS., REP. U.A.G.; U.S.A.; DA. 1973; NO 28; PP. 603-608; BIBL. 10 REF.Serial Issue

ON THE SOURCE OF SUNRISE EFFECTS IN THE LOW IONOSPHERENESTOROV GT; APOSTOLOV EM.1972; C. R. ACAD. BULG. SCI.; BULG.; DA. 1972; VOL. 25; NO 3; PP. 313-316; BIBL. 10 REF.Serial Issue

SOLAR CONTROL OF TIME VARIATIONS OF CRITICAL FREQUENCIES OF F2 LAYER.APOSTOLOV EM; CANDER LR; COHEN MM et al.1978; C.R. ACAD. BULG. SCI.; BGR; DA. 1978; VOL. 31; NO 4; PP. 413-416; BIBL. 10 REF.Article

TYPE VARIATION OF SOLAR SUDDEN FIELD ANOMALY (SFA) ON 164 KHZ AS AN INDICATOR OF SEASONAL STRUCTURE CHANGES IN THE D-REGIONLETFUS V; APOSTOLOV EM; NESTOROV G et al.1973; J. ATMOSPH. TERRESTR. PHYS.; G.B.; DA. 1973; VOL. 35; NO 3; PP. 571-576; BIBL. 11 REF.Serial Issue

EXPERIMENTAL EXAMINATION OF THE POSSIBLE INFLUENCE OF THE 1.87 A LINE EMISSION ON THE FINE STRUCTURE OF THE LOWER IONOSPHERE IONIZATION.LETFUS V; APOSTOLOV EM; NESTOROV GT et al.1978; PURE APPL. GEOPHYS.; SWITZ.; DA. 1978; VOL. 116; NO 1; PP. 1-7; BIBL. 16 REF.Article

PERIODICITIES IN TIME VARIATIONS OF IONIZATION STATE OF NIGHT LOWER IONOSPHERE.APOSTOLOV EM; LETFUS V; NESTOROV GT et al.1976; C.R. ACAD. BULG. SCI.; BULG.; DA. 1976; VOL. 29; NO 3; PP. 343-345; BIBL. 6 REF.Article

THE CONTRIBUTION OF THE SOLAR DISCRETE X-RAY SOURCES TO THE D-REGION IONIZATION DURING THE SOLAR ECLIPSE ON 20 MAY 1966.LETFUS V; APOSTOLOV EM; NESTOROV GT et al.1974; BULL. ASTR. INST. CZECHOSL.; CZECHOSL.; DA. 1974; VOL. 25; NO 5; PP. 262-267; ABS. RUSSE; BIBL. 7 REF.Article

SUNRISE EFFECT ON ATMOSPHERICS AND ITS RELATION TO THE DIRECTION OF THE NIGHT NOISE SOURCELETFUS V; APOSTOLOV EM; KLIMES J et al.1982; STUD. GEOPHYS. GEOD.; ISSN 0039-3169; CSK; DA. 1982; VOL. 26; NO 3; PP. 281-294; ABS. RUS; BIBL. 15 REF.Article

A STATISTICAL STUDY OF SUN-CROP YIELD RELATIONSHIPRAICHEV TK; RALCHOVSKI TM; APOSTOLOV EM et al.1979; DOKL. BOLG. AKAD. NAUK; ISSN 0366-8681; BGR; DA. 1979; VOL. 32; NO 9; PP. 1211-1214; BIBL. 6 REF.Article