全文获取类型
收费全文 | 59篇 |
免费 | 0篇 |
国内免费 | 3篇 |
专业分类
系统科学 | 1篇 |
现状及发展 | 4篇 |
研究方法 | 12篇 |
综合类 | 44篇 |
自然研究 | 1篇 |
出版年
2013年 | 1篇 |
2012年 | 3篇 |
2011年 | 5篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 4篇 |
2007年 | 1篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 6篇 |
2003年 | 1篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有62条查询结果,搜索用时 16 毫秒
21.
22.
23.
24.
25.
26.
The boundaries between prokaryotes, unicellular eukaryotes and multicellular eukaryotes are accompanied by orders-of-magnitude reductions in effective population size, with concurrent amplifications of the effects of random genetic drift and mutation. The resultant decline in the efficiency of selection seems to be sufficient to influence a wide range of attributes at the genomic level in a non-adaptive manner. A key remaining question concerns the extent to which variation in the power of random genetic drift is capable of influencing phylogenetic diversity at the subcellular and cellular levels. Should this be the case, population size would have to be considered as a potential determinant of the mechanistic pathways underlying long-term phenotypic evolution. Here we demonstrate a phylogenetically broad inverse relation between the power of drift and the structural integrity of protein subunits. This leads to the hypothesis that the accumulation of mildly deleterious mutations in populations of small size induces secondary selection for protein-protein interactions that stabilize key gene functions. By this means, the complex protein architectures and interactions essential to the genesis of phenotypic diversity may initially emerge by non-adaptive mechanisms. 相似文献
27.
Ann M. Lynch 《西北部美国博物学家》2011,64(1)
Spruce aphid, Elatobium abietinum (Walker), is a new invasive pest in high-elevation forests of southwestern USA. Plots in the White Mountains of Arizona were evaluated over several years to assess the extent and severity of damage in high-elevation forests and to identify tree and site characteristics associated with defoliation and mortality. Large areas were defoliated in each of 4 recent outbreaks. Impact from a single defoliation episode included an overall mortality of 10.3% to Picea engelmannii Parry, 24%-41% in severely defoliated trees. Defoliation severity was much greater on P. engelmannii than on P. pungens Engelm. and was more severe in the lower canopy layers. Retention of foliage in the upper-crown third of individual trees was a critical factor in tree survivorship. Mortality was associated with defoliation severity and severe infection by Arceuthobium microcarpum (Engelmann) Hawksworth & Wiens. Picea pungens was much more susceptible to A. microcarpum more than was P. engelmannii . The combined effects of high levels of defoliation and mistletoe infection were lethal, resulting in almost 70% mortality. Mortality continued to occur at 3 years after defoliation. This aphid will affect natural disturbance regimes and tree population dynamics in mixed-conifer and spruce-fir forests of the American Southwest. 相似文献
28.
Neutral metacommunity models predict fish diversity patterns in Mississippi-Missouri basin 总被引:1,自引:0,他引:1
Muneepeerakul R Bertuzzo E Lynch HJ Fagan WF Rinaldo A Rodriguez-Iturbe I 《Nature》2008,453(7192):220-222
River networks, seen as ecological corridors featuring connected and hierarchical dendritic landscapes for animals and plants, present unique challenges and opportunities for testing biogeographical theories and macroecological laws. Although local and basin-scale differences in riverine fish diversity have been analysed as functions of energy availability and habitat heterogeneity, scale-dependent environmental conditions and river discharge, a model that predicts a comprehensive set of system-wide diversity patterns has been hard to find. Here we show that fish diversity patterns throughout the Mississippi-Missouri River System are well described by a neutral metacommunity model coupled with an appropriate habitat capacity distribution and dispersal kernel. River network structure acts as an effective template for characterizing spatial attributes of fish biodiversity. We show that estimates of average dispersal behaviour and habitat capacities, objectively calculated from average runoff production, yield reliable predictions of large-scale spatial biodiversity patterns in riverine systems. The success of the neutral theory in two-dimensional forest ecosystems and here in dendritic riverine ecosystems suggests the possible application of neutral metacommunity models in a diverse suite of ecosystems. This framework offers direct linkage from large-scale forcing, such as global climate change, to biodiversity patterns. 相似文献
29.
Liu J O'Brien KL Lynch DM Simmons NL La Porte A Riggs AM Abbink P Coffey RT Grandpre LE Seaman MS Landucci G Forthal DN Montefiori DC Carville A Mansfield KG Havenga MJ Pau MG Goudsmit J Barouch DH 《Nature》2009,457(7225):87-91
A recombinant adenovirus serotype 5 (rAd5) vector-based vaccine for HIV-1 has recently failed in a phase 2b efficacy study in humans. Consistent with these results, preclinical studies have demonstrated that rAd5 vectors expressing simian immunodeficiency virus (SIV) Gag failed to reduce peak or setpoint viral loads after SIV challenge of rhesus monkeys (Macaca mulatta) that lacked the protective MHC class I allele Mamu-A*01 (ref. 3). Here we show that an improved T-cell-based vaccine regimen using two serologically distinct adenovirus vectors afforded substantially improved protective efficacy in this challenge model. In particular, a heterologous rAd26 prime/rAd5 boost vaccine regimen expressing SIV Gag elicited cellular immune responses with augmented magnitude, breadth and polyfunctionality as compared with the homologous rAd5 regimen. After SIV(MAC251) challenge, monkeys vaccinated with the rAd26/rAd5 regimen showed a 1.4 log reduction of peak and a 2.4 log reduction of setpoint viral loads as well as decreased AIDS-related mortality as compared with control animals. These data demonstrate that durable partial immune control of a pathogenic SIV challenge for more than 500 days can be achieved by a T-cell-based vaccine in Mamu-A*01-negative rhesus monkeys in the absence of a homologous Env antigen. These findings have important implications for the development of next-generation T-cell-based vaccine candidates for HIV-1. 相似文献
30.
The genomic and transcriptomic architecture of 2,000 breast tumours reveals novel subgroups 总被引:1,自引:0,他引:1
Curtis C Shah SP Chin SF Turashvili G Rueda OM Dunning MJ Speed D Lynch AG Samarajiwa S Yuan Y Gräf S Ha G Haffari G Bashashati A Russell R McKinney S;METABRIC Group Langerød A Green A Provenzano E Wishart G Pinder S Watson P Markowetz F Murphy L Ellis I Purushotham A Børresen-Dale AL Brenton JD Tavaré S Caldas C Aparicio S 《Nature》2012,486(7403):346-352