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51.
Résumé Une méthode pour vider et examiner des microélectrodes de verre au microscope électronique est décrite. On a trouvé une corrélation entre le diamètre du bout et la résistance électrique. Le diamètre de l'extrémité des électrodes dépend du procédé de remplissement et les meilleurs résultats sont obtenus par la méthode deTasaki modifiée. 相似文献
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Acute lowering of blood pH between 7.4 and 6.9 in rats by ventilation with 10 or 20% CO2 does not increase the passage of ferritin molecules across the aortic endothelium. These results do not rule out alteration of endothelial permeability to anionic macromolecules in local circulatory disturbances when blood pH drops to levels much lower than 6.9. 相似文献
54.
Science Policy News
United Kingdom: Report on the research programme on AIDS supported by the Medical Research Council [MRC] 相似文献55.
Marilda M. de Oliveira 《Cellular and molecular life sciences : CMLS》1963,19(11):586-587
Résumé Nous avons utilisé, de préférence, des méthodes chromatographiques pour isoler le principe actif dePalicourea marcgravii St. Hil. (Rubiaceae), un végétal extrêmement toxiques des pâturages du Brésil. Ce principe a été identifié comme étant l'acide monofluoroacétique. 相似文献
56.
Human dynamics: Darwin and Einstein correspondence patterns 总被引:2,自引:0,他引:2
In an era when letters were the main means of exchanging scientific ideas and results, Charles Darwin (1809-82) and Albert Einstein (1879-1955) were notably prolific correspondents. But did their patterns of communication differ from those associated with the instant-access e-mail of modern times? Here we show that, although the means have changed, the communication dynamics have not: Darwin's and Einstein's patterns of correspondence and today's electronic exchanges follow the same scaling laws. However, the response times of their surface-mail communication is described by a different scaling exponent from e-mail communication, providing evidence for a new class of phenomena in human dynamics. 相似文献
57.
Summary An adaptation of the aceto-iron-haematoxylin-chloral hydrate staining solution is described for chromosome counting of dried seaweeds. The chromosome number ofPorphyra leucosticta (Rhodophyta) collected recently and fixed in ethanol-acetic acid compares well with material of the same species collected and dried in 1897. The significance of this new source of data, allowing the study of the old type material, is stressed in the paper.Under a CNPq fellowship No. 5503/74.We thank Prof.C. Pavan for valuable suggestions. 相似文献
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Alexandrou MA Oliveira C Maillard M McGill RA Newton J Creer S Taylor MI 《Nature》2011,469(7328):84-88
Until recently, the study of negative and antagonistic interactions (for example, competition and predation) has dominated our understanding of community structure, maintenance and assembly. Nevertheless, a recent theoretical model suggests that positive interactions (for example, mutualisms) may counterbalance competition, facilitating long-term coexistence even among ecologically undifferentiated species. Müllerian mimics are mutualists that share the costs of predator education and are therefore ideally suited for the investigation of positive and negative interactions in community dynamics. The sole empirical test of this model in a Müllerian mimetic community supports the prediction that positive interactions outweigh the negative effects of spatial overlap (without quantifying resource acquisition). Understanding the role of trophic niche partitioning in facilitating the evolution and stability of Müllerian mimetic communities is now of critical importance, but has yet to be formally investigated. Here we show that resource partitioning and phylogeny determine community structure and outweigh the positive effects of Müllerian mimicry in a species-rich group of neotropical catfishes. From multiple, independent reproductively isolated allopatric communities displaying convergently evolved colour patterns, 92% consist of species that do not compete for resources. Significant differences in phylogenetically conserved traits (snout morphology and body size) were consistently linked to trait-specific resource acquisition. Thus, we report the first evidence, to our knowledge, that competition for trophic resources and phylogeny are pivotal factors in the stable evolution of Müllerian mimicry rings. More generally, our work demonstrates that competition for resources is likely to have a dominant role in the structuring of communities that are simultaneously subject to the effects of both positive and negative interactions. 相似文献
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de Oliveira T Pybus OG Rambaut A Salemi M Cassol S Ciccozzi M Rezza G Gattinara GC D'Arrigo R Amicosante M Perrin L Colizzi V Perno CF;Benghazi Study Group 《Nature》2006,444(7121):836-837
In 1998, outbreaks of human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) infection were reported in children attending Al-Fateh Hospital in Benghazi, Libya. Here we use molecular phylogenetic techniques to analyse new virus sequences from these outbreaks. We find that the HIV-1 and HCV strains were already circulating and prevalent in this hospital and its environs before the arrival in March 1998 of the foreign medical staff (five Bulgarian nurses and a Palestinian doctor) who stand accused of transmitting the HIV strain to the children. 相似文献