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排序方式: 共有3792条查询结果,搜索用时 15 毫秒
991.
992.
Brownlee D Tsou P Aléon J Alexander CM Araki T Bajt S Baratta GA Bastien R Bland P Bleuet P Borg J Bradley JP Brearley A Brenker F Brennan S Bridges JC Browning ND Brucato JR Bullock E Burchell MJ Busemann H Butterworth A Chaussidon M Cheuvront A Chi M Cintala MJ Clark BC Clemett SJ Cody G Colangeli L Cooper G Cordier P Daghlian C Dai Z D'Hendecourt L Djouadi Z Dominguez G Duxbury T Dworkin JP Ebel DS Economou TE Fakra S Fairey SA Fallon S Ferrini G Ferroir T Fleckenstein H Floss C Flynn G 《Science (New York, N.Y.)》2006,314(5806):1711-1716
The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales. 相似文献
993.
Zicha D Dobbie IM Holt MR Monypenny J Soong DY Gray C Dunn GA 《Science (New York, N.Y.)》2003,300(5616):142-145
Transformed rat fibroblasts expressing two variants of green fluorescent protein, each fused to beta-actin, were used to study actin dynamics during cell protrusion. The recently developed FLAP (fluorescence localization after photobleaching) method permits the tracking of one fluorophore after localized photobleaching by using the other as a colocalized reference. Here, by visualizing the ratio of bleached to total molecules, we found that actin was delivered to protruding zones of the leading edge of the cell at speeds that exceeded 5 micrometers per second. Monte Carlo modeling confirmed that this flow cannot be explained by diffusion and may involve active transport. 相似文献
994.
Germinal centers (GCs) generate memory B and plasma cells, which are essential for long-lived humoral immunity. GC B cells with high-affinity B cell receptors (BCRs) are selectively expanded. To enable this selection, BCRs of such cells are thought to signal differently from those with lower affinity. We show that, surprisingly, most proliferating GC B cells did not demonstrate active BCR signaling. Rather, spontaneous and induced signaling was limited by increased phosphatase activity. Accordingly, both SH2 domain-containing phosphatase-1 (SHP-1) and SH2 domain-containing inositol 5 phosphatase were hyperphosphorylated in GC cells and remained colocalized with BCRs after ligation. Furthermore, SHP-1 was required for GC maintenance. Intriguingly, GC B cells in the cell-cycle G(2) period regained responsiveness to BCR stimulation. These data have implications for how higher-affinity B cells are selected in the GC. 相似文献
995.
Rhesus Macaque Genome Sequencing Analysis Consortium Gibbs RA Rogers J Katze MG Bumgarner R Weinstock GM Mardis ER Remington KA Strausberg RL Venter JC Wilson RK Batzer MA Bustamante CD Eichler EE Hahn MW Hardison RC Makova KD Miller W Milosavljevic A Palermo RE Siepel A Sikela JM Attaway T Bell S Bernard KE Buhay CJ Chandrabose MN Dao M Davis C Delehaunty KD Ding Y Dinh HH Dugan-Rocha S Fulton LA Gabisi RA Garner TT Godfrey J Hawes AC Hernandez J Hines S Holder M Hume J Jhangiani SN 《Science (New York, N.Y.)》2007,316(5822):222-234
996.
997.
Croucher NJ Harris SR Fraser C Quail MA Burton J van der Linden M McGee L von Gottberg A Song JH Ko KS Pichon B Baker S Parry CM Lambertsen LM Shahinas D Pillai DR Mitchell TJ Dougan G Tomasz A Klugman KP Parkhill J Hanage WP Bentley SD 《Science (New York, N.Y.)》2011,331(6016):430-434
Epidemiological studies of the naturally transformable bacterial pathogen Streptococcus pneumoniae have previously been confounded by high rates of recombination. Sequencing 240 isolates of the PMEN1 (Spain(23F)-1) multidrug-resistant lineage enabled base substitutions to be distinguished from polymorphisms arising through horizontal sequence transfer. More than 700 recombinations were detected, with genes encoding major antigens frequently affected. Among these were 10 capsule-switching events, one of which accompanied a population shift as vaccine-escape serotype 19A isolates emerged in the USA after the introduction of the conjugate polysaccharide vaccine. The evolution of resistance to fluoroquinolones, rifampicin, and macrolides was observed to occur on multiple occasions. This study details how genomic plasticity within lineages of recombinogenic bacteria can permit adaptation to clinical interventions over remarkably short time scales. 相似文献
998.
Ecology is a synthetic discipline benefiting from open access to data from the earth, life, and social sciences. Technological challenges exist, however, due to the dispersed and heterogeneous nature of these data. Standardization of methods and development of robust metadata can increase data access but are not sufficient. Reproducibility of analyses is also important, and executable workflows are addressing this issue by capturing data provenance. Sociological challenges, including inadequate rewards for sharing data, must also be resolved. The establishment of well-curated, federated data repositories will provide a means to preserve data while promoting attribution and acknowledgement of its use. 相似文献
999.
Tennessen JA Bigham AW O'Connor TD Fu W Kenny EE Gravel S McGee S Do R Liu X Jun G Kang HM Jordan D Leal SM Gabriel S Rieder MJ Abecasis G Altshuler D Nickerson DA Boerwinkle E Sunyaev S Bustamante CD Bamshad MJ Akey JM;Broad GO;Seattle GO;NHLBI Exome Sequencing Project 《Science (New York, N.Y.)》2012,337(6090):64-69
As a first step toward understanding how rare variants contribute to risk for complex diseases, we sequenced 15,585 human protein-coding genes to an average median depth of 111× in 2440 individuals of European (n = 1351) and African (n = 1088) ancestry. We identified over 500,000 single-nucleotide variants (SNVs), the majority of which were rare (86% with a minor allele frequency less than 0.5%), previously unknown (82%), and population-specific (82%). On average, 2.3% of the 13,595 SNVs each person carried were predicted to affect protein function of ~313 genes per genome, and ~95.7% of SNVs predicted to be functionally important were rare. This excess of rare functional variants is due to the combined effects of explosive, recent accelerated population growth and weak purifying selection. Furthermore, we show that large sample sizes will be required to associate rare variants with complex traits. 相似文献
1000.