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排序方式: 共有535条查询结果,搜索用时 15 毫秒
51.
P.F. Fisher 《Geoderma》1983,29(2):93-105
The properties of soils associated with the Bronze Age site near the South Lodge of Rushmore Park, Wiltshire, are described. Three primary soil types are identified: rendzinas (Rendolls), argillic brown earths (Hapludalfs) and a brown calcareous earth (Eutrochrept). The mapped distribution of these soil types is related to the archaeological landscape. The argillic brown earths are limited in extent to the deeper soils of the positive (accumulating) lynchets of the field system, whereas rendzinas occupy the negative (eroding) lynchets and the remainder of the fields. The only occurrence of a brown calcareous earth is in a positive lynchet within the enclosure. From the distribution of soil types and analogies with the soils of other prehistoric field systems on the Chalk, it is concluded that the argillic brown earths have formed from a highly calcareous colluvial deposit since abandonment of the field system in the later Bronze Age. Further, the development of this soil type appears to be controlled by lateral throughflow of soil water combined with the re-establishment of a wooded landscape. Formation of the argillic brown earth at this site appears to be more recent than at any other site in southern England for which information has been published. 相似文献
52.
53.
Fisher LW 《Science (New York, N.Y.)》1936,84(2189):534-535
54.
55.
Type-restricted neutralization of molecular clones of human immunodeficiency virus 总被引:23,自引:0,他引:23
D J Looney A G Fisher S D Putney J R Rusche R R Redfield D S Burke R C Gallo F Wong-Staal 《Science (New York, N.Y.)》1988,241(4863):357-359
In a study of the immunologic significance of the genetic diversity present within single isolates of human immunodeficiency virus type 1 (HIV-1), the neutralization of viruses derived from molecular clones of the HIV-1 strain HTLV-IIIB by an extensive panel of sera was compared. Sera from HIV-1-infected patients and from goats immunized with polyacrylamide gel-purified HIV-1 envelope glycoprotein (gp120), native gp120, or gp120-derived recombinant peptides, showed marked heterogeneity in neutralizing activity against these closely related viruses. The change of a single amino acid residue in gp120 may account for such "clonal restriction" of neutralizing activity. 相似文献
56.
Nagata T Ishikawa Y Kinoshita H Kono M Syono Y Fisher RM 《Science (New York, N.Y.)》1970,167(3918):703-704
Magnetic measurements have shown that nondiamagnetic minerals in a lunar crystalline rock of type B are (free Fe(2)+ in paramagnetic pyroxenes) : (antiferromagnetic FeSiO(3)) : (antiferromagnetic FeTiO(3)) : (ferromagnetic iron) = 4.3 : 7 : 20 : 0.08 in weight percentage. The abundance of ferromagnetic Fe in the lunar fines is about 7.5 times its abundance in the crystalline rock. The natural remanent magnetization of the crystalline rock of 7.5 x 10(-6) emu/ g in intensity may not be attributable to its thermoremanent magnetization. 相似文献
57.
Similarity of synthetic peptide from human tumor to parathyroid hormone in vivo and in vitro 总被引:18,自引:0,他引:18
N Horiuchi M P Caulfield J E Fisher M E Goldman R L McKee J E Reagan J J Levy R F Nutt S B Rodan T L Schofield 《Science (New York, N.Y.)》1987,238(4833):1566-1568
One mechanism considered responsible for the hypercalcemia that frequently accompanies malignancy is secretion by the tumor of a circulating factor that alters calcium metabolism. The structure of a tumor-secreted peptide was recently determined and found to be partially homologous to parathyroid hormone (PTH). The amino-terminal 1-34 region of the factor was synthesized and evaluated biologically. In vivo it produced hypercalcemia, acted on bone and kidney, and stimulated 1,25-dihydroxy-vitamin D3 formation. In vitro it interacted with PTH receptors and, in some systems, was more potent than PTH. These studies support a long-standing hypothesis regarding pathogenesis of malignancy-associated hypercalcemia. 相似文献
58.
Fisher WJ 《Science (New York, N.Y.)》1918,48(1244):427-433
59.
Galibert F Finan TM Long SR Puhler A Abola P Ampe F Barloy-Hubler F Barnett MJ Becker A Boistard P Bothe G Boutry M Bowser L Buhrmester J Cadieu E Capela D Chain P Cowie A Davis RW Dreano S Federspiel NA Fisher RF Gloux S Godrie T Goffeau A Golding B Gouzy J Gurjal M Hernandez-Lucas I Hong A Huizar L Hyman RW Jones T Kahn D Kahn ML Kalman S Keating DH Kiss E Komp C Lelaure V Masuy D Palm C Peck MC Pohl TM Portetelle D Purnelle B Ramsperger U Surzycki R Thebault P Vandenbol M Vorholter FJ 《Science (New York, N.Y.)》2001,293(5530):668-672
The scarcity of usable nitrogen frequently limits plant growth. A tight metabolic association with rhizobial bacteria allows legumes to obtain nitrogen compounds by bacterial reduction of dinitrogen (N2) to ammonium (NH4+). We present here the annotated DNA sequence of the alpha-proteobacterium Sinorhizobium meliloti, the symbiont of alfalfa. The tripartite 6.7-megabase (Mb) genome comprises a 3.65-Mb chromosome, and 1.35-Mb pSymA and 1.68-Mb pSymB megaplasmids. Genome sequence analysis indicates that all three elements contribute, in varying degrees, to symbiosis and reveals how this genome may have emerged during evolution. The genome sequence will be useful in understanding the dynamics of interkingdom associations and of life in soil environments. 相似文献
60.
Senthil T Vishwanath A Balents L Sachdev S Fisher MP 《Science (New York, N.Y.)》2004,303(5663):1490-1494
The theory of second-order phase transitions is one of the foundations of modern statistical mechanics and condensed-matter theory. A central concept is the observable order parameter, whose nonzero average value characterizes one or more phases. At large distances and long times, fluctuations of the order parameter(s) are described by a continuum field theory, and these dominate the physics near such phase transitions. We show that near second-order quantum phase transitions, subtle quantum interference effects can invalidate this paradigm, and we present a theory of quantum critical points in a variety of experimentally relevant two-dimensional antiferromagnets. The critical points separate phases characterized by conventional "confining" order parameters. Nevertheless, the critical theory contains an emergent gauge field and "deconfined" degrees of freedom associated with fractionalization of the order parameters. We propose that this paradigm for quantum criticality may be the key to resolving a number of experimental puzzles in correlated electron systems and offer a new perspective on the properties of complex materials. 相似文献