全文获取类型
收费全文 | 512篇 |
免费 | 3篇 |
国内免费 | 3篇 |
专业分类
系统科学 | 12篇 |
教育与普及 | 1篇 |
理论与方法论 | 5篇 |
现状及发展 | 204篇 |
研究方法 | 97篇 |
综合类 | 189篇 |
自然研究 | 10篇 |
出版年
2022年 | 2篇 |
2019年 | 2篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 14篇 |
2012年 | 47篇 |
2011年 | 56篇 |
2010年 | 23篇 |
2009年 | 9篇 |
2008年 | 36篇 |
2007年 | 24篇 |
2006年 | 35篇 |
2005年 | 26篇 |
2004年 | 32篇 |
2003年 | 23篇 |
2002年 | 23篇 |
1999年 | 3篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 9篇 |
1972年 | 7篇 |
1971年 | 6篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1966年 | 3篇 |
1965年 | 3篇 |
1964年 | 3篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1955年 | 5篇 |
1954年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有518条查询结果,搜索用时 0 毫秒
511.
Dislocation multi-junctions and strain hardening 总被引:2,自引:0,他引:2
Bulatov VV Hsiung LL Tang M Arsenlis A Bartelt MC Cai W Florando JN Hiratani M Rhee M Hommes G Pierce TG de la Rubia TD 《Nature》2006,440(7088):1174-1178
At the microscopic scale, the strength of a crystal derives from the motion, multiplication and interaction of distinctive line defects called dislocations. First proposed theoretically in 1934 (refs 1-3) to explain low magnitudes of crystal strength observed experimentally, the existence of dislocations was confirmed two decades later. Much of the research in dislocation physics has since focused on dislocation interactions and their role in strain hardening, a common phenomenon in which continued deformation increases a crystal's strength. The existing theory relates strain hardening to pair-wise dislocation reactions in which two intersecting dislocations form junctions that tie the dislocations together. Here we report that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed 'multi-junctions'. We first predict the existence of multi-junctions using dislocation dynamics and atomistic simulations and then confirm their existence by transmission electron microscopy experiments in single-crystal molybdenum. In large-scale dislocation dynamics simulations, multi-junctions present very strong, nearly indestructible, obstacles to dislocation motion and furnish new sources for dislocation multiplication, thereby playing an essential role in the evolution of dislocation microstructure and strength of deforming crystals. Simulation analyses conclude that multi-junctions are responsible for the strong orientation dependence of strain hardening in body-centred cubic crystals. 相似文献
512.
513.
514.
Einwögerer T Friesinger H Händel M Neugebauer-Maresch C Simon U Teschler-Nicola M 《Nature》2006,444(7117):285
Decorations on the bodies of newborns indicate that they were probably important in their community. Several adult graves from the Stone Age (Upper Palaeolithic period) have been found but child burials seem to be rare, which has prompted discussion about whether this apparently different treatment of infants could be significant. Here we describe two recently discovered infant burials from this period at Krems-Wachtberg in Lower Austria, in which the bodies were covered with red ochre and decorated with ornaments and were therefore probably ritually buried. These findings indicate that even newborns were considered to be full members of these hunter-gatherer communities about 27,000 years ago. 相似文献
515.
Kleinman ME Yamada K Takeda A Chandrasekaran V Nozaki M Baffi JZ Albuquerque RJ Yamasaki S Itaya M Pan Y Appukuttan B Gibbs D Yang Z Karikó K Ambati BK Wilgus TA DiPietro LA Sakurai E Zhang K Smith JR Taylor EW Ambati J 《Nature》2008,452(7187):591-597
Clinical trials of small interfering RNA (siRNA) targeting vascular endothelial growth factor-A (VEGFA) or its receptor VEGFR1 (also called FLT1), in patients with blinding choroidal neovascularization (CNV) from age-related macular degeneration, are premised on gene silencing by means of intracellular RNA interference (RNAi). We show instead that CNV inhibition is a siRNA-class effect: 21-nucleotide or longer siRNAs targeting non-mammalian genes, non-expressed genes, non-genomic sequences, pro- and anti-angiogenic genes, and RNAi-incompetent siRNAs all suppressed CNV in mice comparably to siRNAs targeting Vegfa or Vegfr1 without off-target RNAi or interferon-alpha/beta activation. Non-targeted (against non-mammalian genes) and targeted (against Vegfa or Vegfr1) siRNA suppressed CNV via cell-surface toll-like receptor 3 (TLR3), its adaptor TRIF, and induction of interferon-gamma and interleukin-12. Non-targeted siRNA suppressed dermal neovascularization in mice as effectively as Vegfa siRNA. siRNA-induced inhibition of neovascularization required a minimum length of 21 nucleotides, a bridging necessity in a modelled 2:1 TLR3-RNA complex. Choroidal endothelial cells from people expressing the TLR3 coding variant 412FF were refractory to extracellular siRNA-induced cytotoxicity, facilitating individualized pharmacogenetic therapy. Multiple human endothelial cell types expressed surface TLR3, indicating that generic siRNAs might treat angiogenic disorders that affect 8% of the world's population, and that siRNAs might induce unanticipated vascular or immune effects. 相似文献
516.
Today, the time-to-market for plastic products ar e getting shorter, thus the lead-time for making the injection mould is decreasin g. There is potential in timesavings in the mould design stage because the design process that is repeatable for every mould design can be standardized. T he preliminary work of any final plastic injection mould design is to always pro vide an initial design of the mould assembly for product designers (customers) p rior to receiving the final product CAD data. Traditiona... 相似文献
517.
518.
Velásquez-Rodríguez Camilo Payán-Durán Luisa 《Systemic Practice and Action Research》2022,35(1):33-53
Systemic Practice and Action Research - An organizational design proposal is made for Creo en el Agro, an organization made up of small coffee growers who were victims of the armed conflict in the... 相似文献