全文获取类型
收费全文 | 76篇 |
免费 | 0篇 |
专业分类
系统科学 | 2篇 |
现状及发展 | 6篇 |
研究方法 | 2篇 |
综合类 | 56篇 |
自然研究 | 10篇 |
出版年
2012年 | 3篇 |
2011年 | 11篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有76条查询结果,搜索用时 642 毫秒
21.
Phenol stabilizes more helix in a new symmetrical zinc insulin hexamer 总被引:14,自引:0,他引:14
U Derewenda Z Derewenda E J Dodson G G Dodson C D Reynolds G D Smith C Sparks D Swenson 《Nature》1989,338(6216):594-596
SINCE insulin was first shown by Scott to crystallize in the presence of zinc ions in 1934, a variety of Zn-containing insulin crystals have been grown. The structures of insulin in the related rhombohedral crystals of 2Zn-insulin and 4Zn-insulin have been solved and reveal that the molecule is a hexamer, organized as three dimers, each containing a 2-fold symmetry axis and held together by Zn ions. In 2Zn-insulin the hexamer is nearly symmetrical with the two axial Zn ions and the two molecules of the dimer related closely by a local 2-fold axis. But in 4Zn-insulin the two molecules in the dimer differ remarkably, creating an asymmetric 4Zn-hexamer in which one trimer is essentially equivalent to that in 2Zn-insulin and the other is different by virtue of an additional stretch of N-terminal helix between residues B1 and B8 (refs 6, 7). We report here the structure of a new symmetrical hexamer, in which all six molecules have the B1-B8 helix seen in 4Zn-insulin. Phenol molecules, found bonding specifically to each molecule, evidently stabilize this new helical conformation. 相似文献
22.
Capaldi EA Smith AD Osborne JL Fahrbach SE Farris SM Reynolds DR Edwards AS Martin A Robinson GE Poppy GM Riley JR 《Nature》2000,403(6769):537-540
Cognitive ethology focuses on the study of animals under natural conditions to reveal ecologically adapted modes of learning. But biologists can more easily study what an animal learns than how it learns. For example, honeybees take repeated 'orientation' flights before becoming foragers at about three weeks of age. These flights are a prerequisite for successful homing. Little is known about these flights because orienting bees rapidly fly out of the range of human observation. Using harmonic radar, we show for the first time a striking ontogeny to honeybee orientation flights. With increased experience, bees hold trip duration constant but fly faster, so later trips cover a larger area than earlier trips. In addition, each flight is typically restricted to a narrow sector around the hive. Orientation flights provide honeybees with repeated opportunities to view the hive and landscape features from different viewpoints, suggesting that bees learn the local landscape in a progressive fashion. We also show that these changes in orientation flight are related to the number of previous flights taken instead of chronological age, suggesting a learning process adapted to changes in weather conditions, flower availability and the needs of bee colonies. 相似文献
23.
Résumé Un essai sur lamelle porte-objet a été mis au point pour la détermination quantitative du triphosphate d'adénosine. Il s'agit d'une modification de la réaction bien connue entre la luciférine et la luciférase dérivées de la luciole. Cet essai permet de déceler des quantités minuscules de l'ATP pouvant atteindre 10–13 g. 相似文献
24.
Numerical taxonomy and comparative elaborateness, with a speculation on unused genes 总被引:1,自引:0,他引:1
K A Reynolds 《Nature》1965,206(980):166-168
25.
Burrows of small mammals can impact a variety of soil processes including organic turnover, aeration, and mineralization rates. The structure of burrows, depth, length, and complexity can influence the extent of the impact burrows have on soil processes. Soil properties, in turn, are thought to affect burrow structure. To increase our understanding of burrow-soil dynamics, we compared maximum depth, total volume, total length, volume:length ratio, and complexity of burrows of five small mammal species with bulk density of soil texture in multiple regression analyses. Burrows of Wyoming ground squirrels ( Spermophilus elegans ) were deeper, longer, and more complex as percentage of silt and clay increased and percentage of sand and bulk density decreased. Average maximum depth of montane vole ( Microtus montanus ) burrows increased as soils became sandier. Length and volume of deer mice ( Peromyscus maniculatus ) burrows increased with increases in bulk density and percentage of clay. Volume, length, and complexity of kangaroo rat ( Dipodomys ordii ) burrows were greater in soils with higher amounts of clay and silt. Townsend's ground squirrel ( Spermophilus townsendii ) burrows did not appear to be affected by the soil properties measured. 相似文献
26.
The county by county distribution of the tiger salamander ( Ambystoma tigrinum ) and night snake ( Hypsiglena torquata ) in Idaho from previous reports is presented. This is augmented and expanded from recent findings. 相似文献
27.
28.
Feline sarcoma virus polyprotein P115 binds a host phosphoprotein in transformed cells 总被引:4,自引:0,他引:4
Several independent isoltes of feline sarcoma virus (FeSV) have been described. Such viruses are apparently derived by genetic recombination between feline leukaemia virus (FeLV) genomic RNA and host cellular genetic sequences with transforming potential. Two FeSV isolates, one originally described by Gardner and the second by Snyder-Theilen, have been shown to encode polyproteins of around 115,000 molecular weight. Both polyproteins contain FeLV structural components (p15, p12) at their amino terminus in addition to nonstructural carboxyl terminal components encoded by acquired sequences within the FeSV genome. We have previously shown that Gardner FeSV P115 contains multiple sites of phosphorylation within its nonstructural component and possesses an associated protein kinase activity. In the present study we describe the expression in cells derived from a number of mammalian species, of a highly conserved celklular phosphoprotein with binding affinity for Gardner FeSV P115. This protein, designated P150, exhibits an associated protein kinase activity and is immunologically and structurally distinct from polyproteins encoded by the Gardner or Snyder-Theilen strains of FeSV. 相似文献
29.
30.
The accessible chromatin landscape of the human genome 总被引:2,自引:0,他引:2
RE Thurman E Rynes R Humbert J Vierstra MT Maurano E Haugen NC Sheffield AB Stergachis H Wang B Vernot K Garg S John R Sandstrom D Bates L Boatman TK Canfield M Diegel D Dunn AK Ebersol T Frum E Giste AK Johnson EM Johnson T Kutyavin B Lajoie BK Lee K Lee D London D Lotakis S Neph F Neri ED Nguyen H Qu AP Reynolds V Roach A Safi ME Sanchez A Sanyal A Shafer JM Simon L Song S Vong M Weaver Y Yan Z Zhang Z Zhang B Lenhard M Tewari MO Dorschner RS Hansen PA Navas G Stamatoyannopoulos VR Iyer 《Nature》2012,489(7414):75-82