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排序方式: 共有2037条查询结果,搜索用时 15 毫秒
161.
Jaffe W Meisenheimer K Röttgering HJ Leinert Ch Richichi A Chesneau O Fraix-Burnet D Glazenborg-Kluttig A Granato GL Graser U Heijligers B Köhler R Malbet F Miley GK Paresce F Pel JW Perrin G Przygodda F Schoeller M Sol H Waters LB Weigelt G Woillez J De Zeeuw PT 《Nature》2004,429(6987):47-49
Active galactic nuclei (AGNs) display many energetic phenomena--broad emission lines, X-rays, relativistic jets, radio lobes--originating from matter falling onto a supermassive black hole. It is widely accepted that orientation effects play a major role in explaining the observational appearance of AGNs. Seen from certain directions, circum-nuclear dust clouds would block our view of the central powerhouse. Indirect evidence suggests that the dust clouds form a parsec-sized torus-shaped distribution. This explanation, however, remains unproved, as even the largest telescopes have not been able to resolve the dust structures. Here we report interferometric mid-infrared observations that spatially resolve these structures in the galaxy NGC 1068. The observations reveal warm (320 K) dust in a structure 2.1 parsec thick and 3.4 parsec in diameter, surrounding a smaller hot structure. As such a configuration of dust clouds would collapse in a time much shorter than the active phase of the AGN, this observation requires a continual input of kinetic energy to the cloud system from a source coexistent with the AGN. 相似文献
162.
The Madagascan fat-tailed dwarf lemur, Cheirogaleus medius, hibernates in tree holes for seven months of the year, even though winter temperatures rise to over 30 degrees C. Here we show that this tropical primate relies on a flexible thermal response that depends on the properties of its tree hole: if the hole is poorly insulated, body temperature fluctuates widely, passively following the ambient temperature; if well insulated, body temperature stays fairly constant and the animal undergoes regular spells of arousal. Our findings indicate that arousals are determined by maximum body temperatures and that hypometabolism in hibernating animals is not necessarily coupled to a low body temperature. 相似文献
163.
164.
U Siebenlist 《Nature》1979,279(5714):651-652
165.
Levamisole added to cultured calvarial bones inhibited spontaneous bone resorption, as indicated by reduced release of calcium and inorganic phosphate to the medium. In addition, levamisole reduced lactate production and release of lysosomal enzymes. 相似文献
166.
167.
U. C. Dubach 《Cellular and molecular life sciences : CMLS》1965,21(5):263-263
Zusammenfassung In den einzelnen Abschnitten des menschlichen Nephrons und in Nierenhomogenaten wurden quantitativ die Glucose-6-phosphat-dehydrogenase-und
die Isozitronens?uredehydrogenase-Aktivit?t gemessen.
This investigation was made possible by a grant from the Swiss National Foundation for the Development of Scientific Research. The technical assistance of MissD. Keller is gratefully acknowledged. 相似文献
This investigation was made possible by a grant from the Swiss National Foundation for the Development of Scientific Research. The technical assistance of MissD. Keller is gratefully acknowledged. 相似文献
168.
169.
R. Ikan U. Ravid D. Trosset E. Shulman 《Cellular and molecular life sciences : CMLS》1971,27(5):504-505
Résumé L'ecdystérone, hormone de mue des insectes a été extraite de l'Achyranthes aspera et identifiée par des méthodes chromatographiques et spectroscopiques. 相似文献
170.
Theopold U Li D Fabbri M Scherfer C Schmidt O 《Cellular and molecular life sciences : CMLS》2002,59(2):363-372
In contrast to both vertebrates and non-insect arthropods, little is known about the coagulation of hemolymph (hemostasis) in insects. We discuss the integration of the hemostatic response with other branches of the insect immune system. We also describe the present stage in the characterization of both soluble and cellular factors that contribute to hemostasis in insects. The factors of the well-characterized clotting cascades of vertebrates, primitive chelicerates and crustaceans are used to assess the implications of sequencing the whole Drosophila genome for searching candidate genes involved in hemostasis. Some striking similarities between blood clotting in vertebrates and the reaction of insect cells involved in hemolymph coagulation have implications for a phylogenetic comparison of hemostasis between divergent animal classes. 相似文献