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排序方式: 共有399条查询结果,搜索用时 546 毫秒
381.
Chambers JQ Fisher JI Zeng H Chapman EL Baker DB Hurtt GC 《Science (New York, N.Y.)》2007,318(5853):1107
Hurricane Katrina's impact on U.S. Gulf Coast forests was quantified by linking ecological field studies, Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS) image analyses, and empirically based models. Within areas affected by relatively constant wind speed, tree mortality and damage exhibited strong species-controlled gradients. Spatially explicit forest disturbance maps coupled with extrapolation models predicted mortality and severe structural damage to approximately 320 million large trees totaling 105 teragrams of carbon, representing 50 to 140% of the net annual U.S. forest tree carbon sink. Changes in disturbance regimes from increased storm activity expected under a warming climate will reduce forest biomass stocks, increase ecosystem respiration, and may represent an important positive feedback mechanism to elevated atmospheric carbon dioxide. 相似文献
382.
Zipfel B DeSilva JM Kidd RS Carlson KJ Churchill SE Berger LR 《Science (New York, N.Y.)》2011,333(6048):1417-1420
A well-preserved and articulated partial foot and ankle of Australopithecus sediba, including an associated complete adult distal tibia, talus, and calcaneus, have been discovered at the Malapa site, South Africa, and reported in direct association with the female paratype Malapa Hominin 2. These fossils reveal a mosaic of primitive and derived features that are distinct from those seen in other hominins. The ankle (talocrural) joint is mostly humanlike in form and inferred function, and there is some evidence for a humanlike arch and Achilles tendon. However, Au. sediba is apelike in possessing a more gracile calcaneal body and a more robust medial malleolus than expected. These observations suggest, if present models of foot function are correct, that Au. sediba may have practiced a unique form of bipedalism and some degree of arboreality. Given the combination of features in the Au. sediba foot, as well as comparisons between Au. sediba and older hominins, homoplasy is implied in the acquisition of bipedal adaptations in the hominin foot. 相似文献
383.
Green fluorescent protein (GFP) and its derivatives have transformed the use and analysis of proteins for diverse applications. Like proteins, RNA has complex roles in cellular function and is increasingly used for various applications, but a comparable approach for fluorescently tagging RNA is lacking. Here, we describe the generation of RNA aptamers that bind fluorophores resembling the fluorophore in GFP. These RNA-fluorophore complexes create a palette that spans the visible spectrum. An RNA-fluorophore complex, termed Spinach, resembles enhanced GFP and emits a green fluorescence comparable in brightness with fluorescent proteins. Spinach is markedly resistant to photobleaching, and Spinach fusion RNAs can be imaged in living cells. These RNA mimics of GFP provide an approach for genetic encoding of fluorescent RNAs. 相似文献
384.
Glycans are attractive targets for molecular imaging but have been inaccessible because of their incompatibility with genetically encoded reporters. We demonstrated the noninvasive imaging of glycans in live developing zebrafish, using a chemical reporter strategy. Zebrafish embryos were treated with an unnatural sugar to metabolically label their cell-surface glycans with azides. Subsequently, the embryos were reacted with fluorophore conjugates by means of copper-free click chemistry, enabling the visualization of glycans in vivo at subcellular resolution during development. At 60 hours after fertilization, we observed an increase in de novo glycan biosynthesis in the jaw region, pectoral fins, and olfactory organs. Using a multicolor detection strategy, we performed a spatiotemporal analysis of glycan expression and trafficking and identified patterns that would be undetectable with conventional molecular imaging approaches. 相似文献
385.
Ma'ayan A Jenkins SL Neves S Hasseldine A Grace E Dubin-Thaler B Eungdamrong NJ Weng G Ram PT Rice JJ Kershenbaum A Stolovitzky GA Blitzer RD Iyengar R 《Science (New York, N.Y.)》2005,309(5737):1078-1083
We developed a model of 545 components (nodes) and 1259 interactions representing signaling pathways and cellular machines in the hippocampal CA1 neuron. Using graph theory methods, we analyzed ligand-induced signal flow through the system. Specification of input and output nodes allowed us to identify functional modules. Networking resulted in the emergence of regulatory motifs, such as positive and negative feedback and feedforward loops, that process information. Key regulators of plasticity were highly connected nodes required for the formation of regulatory motifs, indicating the potential importance of such motifs in determining cellular choices between homeostasis and plasticity. 相似文献
386.
Banks JA Nishiyama T Hasebe M Bowman JL Gribskov M dePamphilis C Albert VA Aono N Aoyama T Ambrose BA Ashton NW Axtell MJ Barker E Barker MS Bennetzen JL Bonawitz ND Chapple C Cheng C Correa LG Dacre M DeBarry J Dreyer I Elias M Engstrom EM Estelle M Feng L Finet C Floyd SK Frommer WB Fujita T Gramzow L Gutensohn M Harholt J Hattori M Heyl A Hirai T Hiwatashi Y Ishikawa M Iwata M Karol KG Koehler B Kolukisaoglu U Kubo M Kurata T Lalonde S Li K Li Y Litt A Lyons E Manning G Maruyama T Michael TP 《Science (New York, N.Y.)》2011,332(6032):960-963
387.
Pandolfi JM Bradbury RH Sala E Hughes TP Bjorndal KA Cooke RG McArdle D McClenachan L Newman MJ Paredes G Warner RR Jackson JB 《Science (New York, N.Y.)》2003,301(5635):955-958
Degradation of coral reef ecosystems began centuries ago, but there is no global summary of the magnitude of change. We compiled records, extending back thousands of years, of the status and trends of seven major guilds of carnivores, herbivores, and architectural species from 14 regions. Large animals declined before small animals and architectural species, and Atlantic reefs declined before reefs in the Red Sea and Australia, but the trajectories of decline were markedly similar worldwide. All reefs were substantially degraded long before outbreaks of coral disease and bleaching. Regardless of these new threats, reefs will not survive without immediate protection from human exploitation over large spatial scales. 相似文献
388.
Damsté JS Muyzer G Abbas B Rampen SW Massé G Allard WG Belt ST Robert JM Rowland SJ Moldowan JM Barbanti SM Fago FJ Denisevich P Dahl J Trindade LA Schouten S 《Science (New York, N.Y.)》2004,304(5670):584-587
The 18S ribosomal DNA molecular phylogeny and lipid composition of over 120 marine diatoms showed that the capability to biosynthesize highly branched isoprenoid (HBI) alkenes is restricted to two specific phylogenetic clusters, which independently evolved in centric and pennate diatoms. The molecular record of C25 HBI chemical fossils in a large suite of well-dated marine sediments and petroleum revealed that the older cluster, composed of rhizosolenid diatoms, evolved 91.5 +/- 1.5 million years ago (Upper Turonian), enabling an accurate dating of the pace of diatom evolution that is unprecedented. The rapid rise of the rhizosolenid diatoms probably resulted from a major reorganization of the nutrient budget in the mid-Cretaceous oceans, triggered by plate tectonics. 相似文献
389.
Greaves SJ Rose RA Oliver TA Glowacki DR Ashfold MN Harvey JN Clark IP Greetham GM Parker AW Towrie M Orr-Ewing AJ 《Science (New York, N.Y.)》2011,331(6023):1423-1426
Solvent collisions can often mask initial disposition of energy to the products of solution-phase chemical reactions. Here, we show with transient infrared absorption spectra obtained with picosecond time resolution that the nascent HCN products of reaction of CN radicals with cyclohexane in chlorinated organic solvents exhibit preferential excitation of one quantum of the C-H stretching mode and up to two quanta of the bending mode. On time scales of approximately 100 to 300 picoseconds, the HCN products undergo relaxation to the vibrational ground state by coupling to the solvent bath. Comparison with reactions of CN radicals with alkanes in the gas phase, known to produce HCN with greater C-H stretch and bending mode excitation (up to two and approximately six quanta, respectively), indicates partial damping of the nascent product vibrational motion by the solvent. The transient infrared spectra therefore probe solvent-induced modifications to the reaction free energy surface and chemical dynamics. 相似文献
390.