全文获取类型
收费全文 | 178篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
现状及发展 | 50篇 |
研究方法 | 24篇 |
综合类 | 102篇 |
自然研究 | 4篇 |
出版年
2020年 | 1篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2013年 | 6篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 11篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1970年 | 8篇 |
1969年 | 4篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1966年 | 4篇 |
1965年 | 3篇 |
1963年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有180条查询结果,搜索用时 109 毫秒
41.
The long-standing paradigm that hotspot volcanoes such as Hawaii or Iceland represent the surface expression of mantle plumes--hot, buoyant upwelling regions beneath the Earth's lithosphere--has recently been the focus of controversy. Whether mantle plumes exist or not is pivotal for our understanding of the thermal, dynamic and compositional evolution of the Earth's mantle. Here we show that uranium-series disequilibria measured in hotspot lavas indicate that hotspots are indeed associated with hot and buoyant upwellings and that weaker (low buoyancy flux) hotspots such as Iceland and the Azores are characterized by lower excess temperatures than stronger hotspots such as Hawaii. This direct link between buoyancy flux and mantle temperature is evidence for the existence of mantle plumes. 相似文献
42.
43.
Prisoner's dilemma in an RNA virus 总被引:13,自引:0,他引:13
The evolution of competitive interactions among viruses was studied in the RNA phage phi6 at high and low multiplicities of infection (that is, at high and low ratios of infecting phage to host cells). At high multiplicities, many phage infect and reproduce in the same host cell, whereas at low multiplicities the viruses reproduce mainly as clones. An unexpected result of this study was that phage grown at high rates of co-infection increased in fitness initially, but then evolved lowered fitness. Here we show that the fitness of the high-multiplicity phage relative to their ancestors generates a pay-off matrix conforming to the prisoner's dilemma strategy of game theory. In this strategy, defection (selfishness) evolves, despite the greater fitness pay-off that would result if all players were to cooperate. Viral cooperation and defection can be defined as, respectively, the manufacturing and sequestering of diffusible (shared) intracellular products. Because the low-multiplicity phage did not evolve lowered fitness, we attribute the evolution of selfishness to the lack of clonal structure and the mixing of unrelated genotypes at high multiplicity. 相似文献
44.
45.
46.
47.
Summary An acidic fraction of Panamenian variant ofCannabis sativa L., afforded upon repeated chromatography a new non-cannabinoid phenol {5-hydroxy-7-methoxy spiro-(cyclohexane-1, 1-indan)-4-one}Ia, named iso-cannabispiran.Acknowledgment. Supported in part by NIDA contract No. 271-78-3527 and by the Research Institute of Pharmaceutical Sciences. 相似文献
48.
Fish (cartilaginous: elasmobranch and bony: osteichthyan actinopterygian) and reptile (crocodile) microfossils comprising scales and teeth have been examined from a series of limestone samples in the Upper Jurassic of France and Germany to gauge the possibilities of using them for correlation between fully marine and hypo-or hyper-saline (non-marine) deposits. 相似文献
49.
Sun J Zheng SL Wiklund F Isaacs SD Purcell LD Gao Z Hsu FC Kim ST Liu W Zhu Y Stattin P Adami HO Wiley KE Dimitrov L Sun J Li T Turner AR Adams TS Adolfsson J Johansson JE Lowey J Trock BJ Partin AW Walsh PC Trent JM Duggan D Carpten J Chang BL Grönberg H Isaacs WB Xu J 《Nature genetics》2008,40(10):1153-1155
We carried out a fine-mapping study in the HNF1B gene at 17q12 in two study populations and identified a second locus associated with prostate cancer risk, approximately 26 kb centromeric to the first known locus (rs4430796); these loci are separated by a recombination hot spot. We confirmed the association with a SNP in the second locus (rs11649743) in five additional populations, with P = 1.7 x 10(-9) for an allelic test of the seven studies combined. The association at each SNP remained significant after adjustment for the other SNP. 相似文献
50.