全文获取类型
收费全文 | 4143篇 |
免费 | 762篇 |
出版年
2021年 | 56篇 |
2019年 | 37篇 |
2018年 | 52篇 |
2016年 | 63篇 |
2015年 | 120篇 |
2014年 | 127篇 |
2013年 | 175篇 |
2012年 | 197篇 |
2011年 | 199篇 |
2010年 | 106篇 |
2009年 | 97篇 |
2008年 | 133篇 |
2007年 | 154篇 |
2006年 | 201篇 |
2005年 | 204篇 |
2004年 | 206篇 |
2003年 | 197篇 |
2002年 | 189篇 |
2001年 | 199篇 |
2000年 | 114篇 |
1999年 | 105篇 |
1998年 | 42篇 |
1997年 | 51篇 |
1996年 | 39篇 |
1995年 | 46篇 |
1994年 | 48篇 |
1993年 | 37篇 |
1992年 | 83篇 |
1991年 | 85篇 |
1990年 | 78篇 |
1989年 | 61篇 |
1988年 | 80篇 |
1987年 | 72篇 |
1986年 | 85篇 |
1985年 | 67篇 |
1984年 | 58篇 |
1983年 | 53篇 |
1982年 | 37篇 |
1981年 | 42篇 |
1980年 | 48篇 |
1979年 | 66篇 |
1978年 | 43篇 |
1977年 | 38篇 |
1976年 | 39篇 |
1975年 | 63篇 |
1974年 | 46篇 |
1973年 | 55篇 |
1972年 | 46篇 |
1971年 | 48篇 |
1970年 | 34篇 |
排序方式: 共有4905条查询结果,搜索用时 109 毫秒
1.
2.
3.
Plasma concentrations of adrenaline and noradrenaline were measured at rest from cannulated fish and following net capture. Adrenaline and noradrenaline concentrations in capture-stressed fish averaged 36,740 pmol l-1 and 38,860 pmol l-1 respectively, whereas resting values were less than 200 pmol l-1 for both amines. Erythrocyte swelling and raised blood lactate were evident in stressed fish. In vitro effects of 5 mmol l-1 adrenaline on erythrocyte suspensions suggested that the catecholamine had a direct effect on erythrocyte volume. The significance of these results is discussed in relation to the oxygen transport properties of the blood. 相似文献
4.
Laura W. Pomeroy Jacob M. Aaronson Samuel Handelman Jori Hardman Kevin Kawalec Thomas Bitterman Ward C. Wheeler 《Cladistics : the international journal of the Willi Hennig Society》2012,28(5):483-488
We have reported previously on use of a web‐based application, Supramap ( http://supramap.org ) for the study of biogeographic, genotypic, and phenotypic evolution. Using Supramap we have developed maps of the spread of drug‐resistant influenza and host shifts in H1N1 and H5N1 influenza and coronaviruses such as SARS. Here we report on another zoonotic pathogen, H7 influenza, and provide an update on the implementation of Supramap as a web service. We find that the emergence of pathogenic strains of H7 is labile with many transitions from high to low pathogenicity, and from low to high pathogenicity. We use Supramap to put these events in a temporal and geospatial context. We identify several lineages of H7 influenza with biomarkers of high pathogenicity in regions that have not been reported in the scientific literature. The original implementation of Supramap was built with tightly coupled client and server software. Now we have decoupled the components to provide a modular web service for POY ( http://poyws.org ) that can be consumed by a data provider to create a novel application. To demonstrate the web service, we have produced an application, Geogenes ( http://geogenes.org ). Unlike in Supramap, in which the user is required to create and upload data files, in Geogenes the user works from a graphical interface to query an underlying dataset. Geogenes demonstrates how the web service can provide underlying processing for any sequence and metadata database. © The Willi Hennig Society 2012. 相似文献
5.
6.
7.
8.
9.
Summary The carbon cycle of a loblolly pine plantation in North Carolina was examined during its 12th through 16th years from planting. Net primary production during the study period averaged 2056 g C m-2 year-1. With autotrophic respiration equal to 2068 g C, the calculated gross production was 4124 g C m-2 year-1. Heterotrophic respiration of 694 g C m-2 year-1 resulted in net ecosystem production of 1362 g C m-2 year-1. In carbon cycle comparisons between forest ecosystems, autotrophic respiration rates were found to be closely coupled to regional temperature. 相似文献
10.
To determine whether the bicyclic monoterpene olefins (-)-alpha-pinene and (-)-beta-pinene arise biosynthetically from the same monoterpene cyclase by alternate deprotonations of a common carbocationic intermediate, the product distributions arising from the acyclic precursor [10-2H3,1-3H]geranyl pyrophosphate were compared with those resulting from incubation of [1-3H]geranyl pyrophosphate with (-)-pinene cyclase from Salvia officinalis. Alteration in proportions of the olefinic products generated by the partially purified pinene cyclase resulted from the suppression of the formation of (-)-beta-pinene (C10 deprotonation) by a primary deuterium isotope effect with a compensating stimulation of the formation of (-)-alpha-pinene (C4 deprotonation). (-)-Pinene cyclase as well as (+)-pinene cyclase also exhibited a decrease in the proportion of the acyclic olefin myrcene generated from the deuteriated substrate, accompanied by a corresponding increase in the commitment to cyclized products. The observation of isotopically sensitive branching, in conjunction with quantitation of the magnitude of the secondary deuterium isotope effect on the overall rate of product formation by the (+)- and (-)-pinene cyclases as well as two other monoterpene cyclases from the same tissue, supports the biosynthetic origin of (-)-alpha-pinene and (-)-beta-pinene by alternative deprotonations of a common enzymatic intermediate. A biogenetic scheme consistent with these results is presented, and alternate proposals for the origin of the pinenes are addressed. 相似文献