全文获取类型
收费全文 | 188篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 2篇 |
丛书文集 | 2篇 |
教育与普及 | 1篇 |
现状及发展 | 29篇 |
研究方法 | 19篇 |
综合类 | 132篇 |
自然研究 | 5篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 12篇 |
2011年 | 18篇 |
2010年 | 4篇 |
2009年 | 10篇 |
2008年 | 7篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1967年 | 3篇 |
1966年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有190条查询结果,搜索用时 46 毫秒
181.
Complete mitochondrial genome sequences of two extinct moas clarify ratite evolution 总被引:30,自引:0,他引:30
The origin of the ratites, large flightless birds from the Southern Hemisphere, along with their flighted sister taxa, the South American tinamous, is central to understanding the role of plate tectonics in the distributions of modern birds and mammals. Defining the dates of ratite divergences is also critical for determining the age of modern avian orders. To resolve the ratite phylogeny and provide biogeographical data to examine these issues, we have here determined the first complete mitochondrial genome sequences of any extinct taxa--two New Zealand moa genera--along with a 1,000-base-pair sequence from an extinct Madagascan elephant-bird. For comparative data, we also generated 12 kilobases of contiguous sequence from the kiwi, cassowary, emu and two tinamou genera. This large dataset allows statistically precise estimates of molecular divergence dates and these support a Late Cretaceous vicariant speciation of ratite taxa, followed by the subsequent dispersal of the kiwi to New Zealand. This first molecular view of the break-up of Gondwana provides a new temporal framework for speciation events within other Gondwanan biota and can be used to evaluate competing biogeographical hypotheses. 相似文献
182.
The genetic engineering of production traits in domestic animals 总被引:1,自引:0,他引:1
183.
184.
185.
186.
187.
Flierl MA Rittirsch D Nadeau BA Chen AJ Sarma JV Zetoune FS McGuire SR List RP Day DE Hoesel LM Gao H Van Rooijen N Huber-Lang MS Neubig RR Ward PA 《Nature》2007,449(7163):721-725
It is becoming increasingly clear that the autonomic nervous system and the immune system demonstrate cross-talk during inflammation by means of sympathetic and parasympathetic pathways. We investigated whether phagocytes are capable of de novo production of catecholamines, suggesting an autocrine/paracrine self-regulatory mechanism by catecholamines during inflammation, as has been described for lymphocytes. Here we show that exposure of phagocytes to lipopolysaccharide led to a release of catecholamines and an induction of catecholamine-generating and degrading enzymes, indicating the presence of the complete intracellular machinery for the generation, release and inactivation of catecholamines. To assess the importance of these findings in vivo, we chose two models of acute lung injury. Blockade of alpha2-adrenoreceptors or catecholamine-generating enzymes greatly suppressed lung inflammation, whereas the opposite was the case either for an alpha2-adrenoreceptor agonist or for inhibition of catecholamine-degrading enzymes. We were able to exclude T cells or sympathetic nerve endings as sources of the injury-modulating catecholamines. Our studies identify phagocytes as a new source of catecholamines, which enhance the inflammatory response. 相似文献
188.
189.
引入随机子群蚁群算法的JSP仿真与研究 总被引:1,自引:0,他引:1
针对标准蚁群算法易于出现早熟停滞等缺陷,在原有算法基础上引入一定比例的随机蚁群.在优化过程中随机蚁群以一定概率做随机搜索,以扩大了解的搜索空间;在信息素更新策略上,为了兼顾当代和历代的搜索成果,采取了信息素混合更新策略,同时增强随机子群的最佳路径信息及剩余全部蚁群路径信息,有效抑制了收敛过程中的早熟停滞现象,提高了算法收敛速度.通过典型作业车间调度问题(JSP)实例进行了仿真实验,表明该算法不仅能够克服早熟现象,而且能够加快收敛速度. 相似文献
190.