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排序方式: 共有1091条查询结果,搜索用时 15 毫秒
91.
92.
Gu Y Filippi MD Cancelas JA Siefring JE Williams EP Jasti AC Harris CE Lee AW Prabhakar R Atkinson SJ Kwiatkowski DJ Williams DA 《Science (New York, N.Y.)》2003,302(5644):445-449
The Rho guanosine triphosphatases (GTPases) Rac1 and Rac2 are critical signaling regulators in mammalian cells. The deletion of both Rac1 and Rac2 murine alleles leads to a massive egress of hematopoietic stem/progenitor cells (HSC/Ps) into the blood from the marrow, whereas Rac1-/- but not Rac2-/- HSC/Ps fail to engraft in the bone marrow of irradiated recipient mice. In contrast, Rac2, but not Rac1, regulates superoxide production and directed migration in neutrophils, and in each cell type, the two GTPases play distinct roles in actin organization, cell survival, and proliferation. Thus, Rac1 and Rac2 regulate unique aspects of hematopoietic development and function. 相似文献
93.
Lung cancer and indoor air pollution in Xuan Wei, China 总被引:20,自引:0,他引:20
J L Mumford X Z He R S Chapman S R Cao D B Harris X M Li Y L Xian W Z Jiang C W Xu J C Chuang 《Science (New York, N.Y.)》1987,235(4785):217-220
In Xuan Wei County, Yunnan Province, lung cancer mortality is among China's highest and, especially in females, is more closely associated with indoor burning of "smoky" coal, as opposed to wood or "smokeless" coal, than with tobacco smoking. Indoor air samples were collected during the burning of all three fuels. In contrast to wood and smokeless coal emissions, smoky coal emission has high concentrations of submicron particles containing mutagenic organics, especially in aromatic and polar fractions. These studies suggested an etiologic link between domestic smoky coal burning and lung cancer in Xuan Wei. 相似文献
94.
Energized configurations of heart mitochondria in situ 总被引:3,自引:0,他引:3
R A Harris C H Williams M Caldwell D E Green E Valdivia 《Science (New York, N.Y.)》1969,165(894):700-703
Changes in the configurational state of the cristal membranes of rat heart mitochondria within the living cell can be induced by imposing energizing conditions. An exact correlation has been established between the configurational states of the cristal membrane and the energy states of the mitochondrion. The configurational changes observed in mitochondria in situ are comparable to those established for beef heart mitochondria in vitro and are consistent with the postulate of the conformational basis of energy transductions in membrane systems. The formation of paracrystalline arrays is one of the noteworthy features of configurational changes of mitochondria in situ. 相似文献
95.
Collagen-like fragments: excretion in urine of patients with Paget's disease of bone 总被引:2,自引:0,他引:2
Patients with Paget's disease of bone excrete, in the urine, polypeptides that have amino acid composition and other properties resembling those of fragments of collagen. The pattern of isotope incorporation in vivo suggests that these fragments are derived from collagen that has been synthesized and rapidly degraded, or that they are rapidly synthesized but not incorporated into tropocollagen molecules. 相似文献
96.
RNA and DNA synthesis in developing eggs of the milkweed bug, Oncopeltus fasciatus (Dallas) 总被引:2,自引:0,他引:2
Ribosomal RNA synthesis in developing eggs of the milkweed bug, Oncopeltus fasciatus (Dallas), is turned on at gastrulation and is essentially turned off when organogenesis begins about 72 hours later. The pattern for DNA synthesis is similar although less pronounced. 相似文献
97.
The multiple relationships within kinships of adult monozygotic twins permit incisive analyses to be made of genetic and environmental effects on behavioral traits. Data from families of 65 monozygotic twin pairs yield evidence of genetic variance on the Block Design Test, a nonverbal measure of general intelligence. 相似文献
98.
99.
PM Lundquist R Wortmann C Geletneky RJ Twieg M Jurich VY Lee CR Moylan DM Burland 《Science (New York, N.Y.)》1996,274(5290):1182-1185
The performance of amorphous organic photorefractive (PR) materials in applications such as optical data storage is generally limited by the concentration of active molecules (chromophores) that can be incorporated into the host without forming a crystalline material with poor optical quality. In polymeric PR systems described previously, performance has been limited by the necessity of devoting a large fraction of the material to inert polymer and plasticizing components in order to ensure compositional stability. A new class of organic PR materials composed of multifunctional glass-forming organic chromophores is described that have long-term stability and greatly improved PR properties. 相似文献
100.