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排序方式: 共有559条查询结果,搜索用时 62 毫秒
91.
92.
Androutsellis-Theotokis A Leker RR Soldner F Hoeppner DJ Ravin R Poser SW Rueger MA Bae SK Kittappa R McKay RD 《Nature》2006,442(7104):823-826
93.
The capybara Hydrochoerus hydrochaeris is one of the largest and most widely distributed herbivores in the Neotropical lowlands. However, as yet, there are no records of its occurrence in highland environments. Our aim was to evaluate the environmental variables related to the capybara’s distribution and monitor the effects of its herbivory on the individuals and on the reproductive phenology of A. polyanthus, a common and important plant species of the high-altitude grasslands. Our results show that capybaras frequently occur in the high-altitude grasslands along the Campo Belo River, but they avoid waterlogged areas, occurring more frequently on the dry rocky areas. Capybara herbivory affected the number of A. polyanthus rosettes in flower, leading to the presence of inflorescence formation anomalies. High-altitude grasslands apparently provide capybaras with the three main components (food, shelter and water) required for their occurrence. However, although they seem to present a seasonal feeding strategy, which also happens in lowlands, their avoidance of the waterlogged areas suggests that in highlands the species may present different environmental preferences from those presented in lowlands. In addition, the impact of capybaras’ herbivory on A. polyanthus individuals indicates the potential impact that capybaras can represent on the plant community of the high-altitude grasslands. This appears to be a great opportunity to study the effect of the arrival of a large herbivore in a new environment and possible impacts on plant assemblages. 相似文献
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MATOS Ver?nica Soares de CARMO Fernanda Santos do DINIZ Claudia Leite NASCIMENTO Ana Lucia Rosa PEREIRA Márcia Oliveira FERNANDES Joelma Fonseca de Oliveira SANTOS-FILHO Sebastiao David MORENO Silvana Ramos Farias BERNARDO-FILHO Mario 《科学通报(英文版)》2013,58(17):2061-2065
The Liu Wei Di Huang Wan is a formula of a traditional Chinese medicine that is used to treat asthma patients and has been shown to have several important properties,such as antioxidant and free radical scavenging activities.The influence of an extract of Liu Wei Di Huang Wan on the labeling of blood constituents with technetium-99m was investigated.Anticoagulated blood(Wistar rats) was incubated with the extract,stannous chloride and technetium-99m,as sodium pertechnetate.Samples were centrifuged and aliquots of plasma and blood cells were separated and precipitated with trichloroacetic acid,to obtain soluble and insoluble fractions of the blood constituents.The percentage of radioactivity(%ATI) in all the fractions was determined.The analysis of the results shows that the extract at the highest concentration used(70 mg/mL) decreased significantly(P<0.05) the %ATI(from 96.48 ± 1.19 to 54.46 ± 7.38) on blood cells compartment,(from 81.11 ± 4.15 to 61.33 ± 4.74) on insoluble fractions of blood cells and(from 65.91 ± 2.44 to 13.15 ± 3.62) on insoluble fractions of plasma.In conclusion,the results suggest that the substances present on this extract can alter this labeling process,probably due to(i) redox properties(antioxidant and chelator activities) and/or(ii) specific actions in the binding sites where the 99mTc would be bound on the blood constituents.As a consequence,precaution is suggested on the interpretation of the nuclear medicine results from performed with blood constituents labeled with 99m Tc in patients that have undertaken LWDHW,although the current findings were obtained in experimental animal models. 相似文献
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Marscher AP Jorstad SG D'Arcangelo FD Smith PS Williams GG Larionov VM Oh H Olmstead AR Aller MF Aller HD McHardy IM Lähteenmäki A Tornikoski M Valtaoja E Hagen-Thorn VA Kopatskaya EN Gear WK Tosti G Kurtanidze O Nikolashvili M Sigua L Miller HR Ryle WT 《Nature》2008,452(7190):966-969
Blazars are the most extreme active galactic nuclei. They possess oppositely directed plasma jets emanating at near light speeds from accreting supermassive black holes. According to theoretical models, such jets are propelled by magnetic fields twisted by differential rotation of the black hole's accretion disk or inertial-frame-dragging ergosphere. The flow velocity increases outward along the jet in an acceleration and collimation zone containing a coiled magnetic field. Detailed observations of outbursts of electromagnetic radiation, for which blazars are famous, can potentially probe the zone. It has hitherto not been possible to either specify the location of the outbursts or verify the general picture of jet formation. Here we report sequences of high-resolution radio images and optical polarization measurements of the blazar BL Lacertae. The data reveal a bright feature in the jet that causes a double flare of radiation from optical frequencies to TeV gamma-ray energies, as well as a delayed outburst at radio wavelengths. We conclude that the event starts in a region with a helical magnetic field that we identify with the acceleration and collimation zone predicted by the theories. The feature brightens again when it crosses a standing shock wave corresponding to the bright 'core' seen on the images. 相似文献
98.
Warne T Serrano-Vega MJ Baker JG Moukhametzianov R Edwards PC Henderson R Leslie AG Tate CG Schertler GF 《Nature》2008,454(7203):486-491
G-protein-coupled receptors have a major role in transmembrane signalling in most eukaryotes and many are important drug targets. Here we report the 2.7 A resolution crystal structure of a beta(1)-adrenergic receptor in complex with the high-affinity antagonist cyanopindolol. The modified turkey (Meleagris gallopavo) receptor was selected to be in its antagonist conformation and its thermostability improved by earlier limited mutagenesis. The ligand-binding pocket comprises 15 side chains from amino acid residues in 4 transmembrane alpha-helices and extracellular loop 2. This loop defines the entrance of the ligand-binding pocket and is stabilized by two disulphide bonds and a sodium ion. Binding of cyanopindolol to the beta(1)-adrenergic receptor and binding of carazolol to the beta(2)-adrenergic receptor involve similar interactions. A short well-defined helix in cytoplasmic loop 2, not observed in either rhodopsin or the beta(2)-adrenergic receptor, directly interacts by means of a tyrosine with the highly conserved DRY motif at the end of helix 3 that is essential for receptor activation. 相似文献
99.
Big data: The future of biocuration 总被引:2,自引:0,他引:2
Howe D Costanzo M Fey P Gojobori T Hannick L Hide W Hill DP Kania R Schaeffer M St Pierre S Twigger S White O Rhee SY 《Nature》2008,455(7209):47-50
100.