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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
J. F. WEBBER 《Plant pathology》1987,36(4):531-538
A particular form of mycovirus, the d2 factor, which attacks the elm pathogen Ophiostoma ulmi, was found to be extremely deleterious to this fungus both in vitro and in vivo. Most significantly, d2 -infected conidia were poor at persisting in feeding grooves, the usual infection court of the pathogen, and also showed a 50-fold reduction in successful xylem infection compared with their healthy counterparts. In addition, transmission of the d2 factor from diseased to healthy isolates of O. ulmi was found to take place in feeding grooves, indicating that the fungus exists in a mycelial phase prior to invading xylem vessels. 相似文献
992.
Service RF 《Science (New York, N.Y.)》2001,294(5549):2080-2082
993.
Service RF 《Science (New York, N.Y.)》2001,292(5518):825-826
994.
Sixty-five million years ago, massive volcanism produced on the India-Seychelles landmass the largest continental lava deposit (Deccan Traps) of the past 200 million years. Using a molecular clock-independent approach for inferring dating information from molecular phylogenies, we show that multiple lineages of frogs survived Deccan Traps volcanism after millions of years of isolation on drifting India. The collision between the Indian and Eurasian plates was followed by wide dispersal of several of these lineages. This "out-of-India" scenario reveals a zoogeographical pattern that might reconcile paleontological and molecular data in other vertebrate groups. 相似文献
995.
996.
997.
Texture evolution governs many of the physical, chemical, and mechanical properties of polycrystalline materials, but texture models have only been tested on the macroscopic level, which makes it hard to distinguish between approaches that are conceptually very different. Here, we present a universal method for providing data on the underlying structural dynamics at the grain and subgrain level. The method is based on diffraction with focused hard x-rays. First results relate to the tensile deformation of pure aluminum. Experimental grain rotations are inconsistent with the classical Taylor and Sachs models. 相似文献
998.
Service RF 《Science (New York, N.Y.)》2001,291(5505):805-806
999.
1000.
Elongation factor Tu (EF-Tu) binds all elongator aminoacyl-transfer RNAs (aa-tRNAs) for delivery to the ribosome during protein synthesis. Here, we show that EF-Tu binds misacylated tRNAs over a much wider range of affinities than it binds the corresponding correctly acylated tRNAs, suggesting that the protein exhibits considerable specificity for both the amino acid side chain and the tRNA body. The thermodynamic contributions of the amino acid and the tRNA body to the overall binding affinity are independent of each other and compensate for one another when the tRNAs are correctly acylated. Because certain misacylated tRNAs bind EF-Tu significantly more strongly or weakly than cognate aa-tRNAs, EF-Tu may contribute to translational accuracy. 相似文献