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排序方式: 共有1349条查询结果,搜索用时 968 毫秒
121.
Hall LJ Coluci VR Galvão DS Kozlov ME Zhang M Dantas SO Baughman RH 《Science (New York, N.Y.)》2008,320(5875):504-507
Most materials shrink laterally like a rubber band when stretched, so their Poisson's ratios are positive. Likewise, most materials contract in all directions when hydrostatically compressed and decrease density when stretched, so they have positive linear compressibilities. We found that the in-plane Poisson's ratio of carbon nanotube sheets (buckypaper) can be tuned from positive to negative by mixing single-walled and multiwalled nanotubes. Density-normalized sheet toughness, strength, and modulus were substantially increased by this mixing. A simple model predicts the sign and magnitude of Poisson's ratio for buckypaper from the relative ease of nanofiber bending and stretch, and explains why the Poisson's ratios of ordinary writing paper are positive and much larger. Theory also explains why the negative in-plane Poisson's ratio is associated with a large positive Poisson's ratio for the sheet thickness, and predicts that hydrostatic compression can produce biaxial sheet expansion. This tunability of Poisson's ratio can be exploited in the design of sheet-derived composites, artificial muscles, gaskets, and chemical and mechanical sensors. 相似文献
122.
Hall EH 《Science (New York, N.Y.)》1903,18(468):787-788
123.
124.
Hall MC 《Science (New York, N.Y.)》1911,33(860):974-976
125.
Visual pigment renewal in the mature frog retina 总被引:6,自引:0,他引:6
It has been demonstrated by autoradiography that radioactive amino acids serve as precursors for proteins which are subsequently incorporated into retinal rod outer segment discs in mature animals. By the isolation and purification of visual pigment from retinas of adult frogs after injection of tritiated leucine and phenylalanine, it has been shown that at least part of this labeled protein consists of visual pigment (rhodopsin). 相似文献
126.
Siridechadilok B Fraser CS Hall RJ Doudna JA Nogales E 《Science (New York, N.Y.)》2005,310(5753):1513-1515
Protein synthesis in mammalian cells requires initiation factor eIF3, a approximately 750-kilodalton complex that controls assembly of 40S ribosomal subunits on messenger RNAs (mRNAs) bearing either a 5'-cap or an internal ribosome entry site (IRES). Cryo-electron microscopy reconstructions show that eIF3, a five-lobed particle, interacts with the hepatitis C virus (HCV) IRES RNA and the 5'-cap binding complex eIF4F via the same domain. Detailed modeling of eIF3 and eIF4F onto the 40S ribosomal subunit reveals that eIF3 uses eIF4F or the HCV IRES in structurally similar ways to position the mRNA strand near the exit site of 40S, promoting initiation complex assembly. 相似文献
127.
The heat transported by currents across 25 degrees N in the Atlantic Ocean is estimated from oceanographic measurements to be 1.1 x 10(15) watts northward. This figure agrees, within estimated error, with the value obtained from charts of energy exchange between ocean and atmosphere but is smaller by a factor of 2 than the recent value derived from satellite radiation measurements. 相似文献
128.
Hall SS 《Science (New York, N.Y.)》2002,297(5580):322-324
129.
Deleted HTLV-I provirus in blood and cutaneous lesions of patients with mycosis fungoides. 总被引:12,自引:0,他引:12
W W Hall C R Liu O Schneewind H Takahashi M H Kaplan G R?upe A Vahlne 《Science (New York, N.Y.)》1991,253(5017):317-320
Mycosis fungoides, a rare form of cutaneous T cell leukemia/lymphoma, is suspected of having a viral etiology on the basis of certain similarities to adult T cell leukemia, which is associated with human T cell leukemia/lymphoma virus type I (HTLV-I) infection. Cell lines were established from peripheral blood mononuclear cells (PBMC) of an HTLV-I-seronegative patient with mycosis fungoides. DNA hybridization analysis revealed the presence of HTLV-I-related sequences with unusual restriction endonuclease sites. Sequence analysis of subcloned fragments demonstrated the presence of a monoclonally integrated provirus with a 5.5-kilobase deletion involving large regions of gag and env and all of pol. Additional evidence for the presence of deleted proviruses was found by polymerase chain reaction (PCR) amplification of DNA from cutaneous lesions of five other HTLV-I-seronegative patients. The findings suggest that HTLV-I infection may be involved in the etiology of at least certain cases of mycosis fungoides. 相似文献
130.
Reexamination of the Mawson "Tillite" (Jurassic) of Antarctica indicates that the deposit is of volcanic origin and consists largely of both primary and reworked volcanic materials. No evidence diagnostic of a glacial origin was found. 相似文献