全文获取类型
收费全文 | 36848篇 |
免费 | 2567篇 |
国内免费 | 7篇 |
出版年
2023年 | 186篇 |
2022年 | 160篇 |
2021年 | 316篇 |
2020年 | 362篇 |
2019年 | 335篇 |
2018年 | 877篇 |
2017年 | 753篇 |
2016年 | 1208篇 |
2015年 | 1899篇 |
2014年 | 1761篇 |
2013年 | 2493篇 |
2012年 | 3000篇 |
2011年 | 2854篇 |
2010年 | 1681篇 |
2009年 | 1323篇 |
2008年 | 2309篇 |
2007年 | 2240篇 |
2006年 | 2160篇 |
2005年 | 1952篇 |
2004年 | 1879篇 |
2003年 | 1708篇 |
2002年 | 1595篇 |
2001年 | 521篇 |
2000年 | 499篇 |
1999年 | 482篇 |
1998年 | 264篇 |
1997年 | 206篇 |
1996年 | 201篇 |
1995年 | 212篇 |
1994年 | 185篇 |
1993年 | 166篇 |
1992年 | 283篇 |
1991年 | 267篇 |
1990年 | 238篇 |
1989年 | 194篇 |
1988年 | 203篇 |
1987年 | 164篇 |
1986年 | 153篇 |
1985年 | 156篇 |
1984年 | 157篇 |
1983年 | 114篇 |
1982年 | 118篇 |
1981年 | 124篇 |
1980年 | 91篇 |
1979年 | 126篇 |
1978年 | 116篇 |
1977年 | 92篇 |
1976年 | 119篇 |
1975年 | 98篇 |
1974年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 302 毫秒
51.
José Augusto Rosemberg 《Mycopathologia》1959,10(4):283-288
Riassunto E' una breve nota descrittiva diIsaria cretacea
van Beyma isolata da terreno di bosco ad Eucalipto.Trattasi di un Ifomicete non ancora segnalato presente in Italia e forse non ancora rinvenuto nel terreno.E' specie auxo-eterotrofa e presenta attività antagonista verso altre specie di funghi.
Summary The present note deals briefly withIsaria cretacea van Beyma, isolated from Eucaliptus soil. The fungus is a Hyphomycete whose presence in Italy was never noticed before and perhaps it is the first time the it is found in soil. ThisIsaria is an auxo-heterotrophic species and shows a certain antagonistic activity against some fungi.
Resumo O presente trabalho é uma nota breve descritiva deIsaria cretacea van Beyma, isolada de terreno de um bosque de Eucaliptos. Tratase de um Ifomicete cuja presença na Italia não foi ainda assinalada e talvez seja a primeira vez que é isolada de terreno.E' uma especie auxo-heterotrofica e apresenta uma certa atividade antagonista sobre outros fungos.相似文献
52.
Guaraná (Paullinia cupana) is a woody vine or sprawling shrub native to the central Amazon Basin. The seeds are commercially produced on some 6,000 ha in the state of Amazonas near Manaus. The principal article of commerce is an amber-colored, carbonated soft drink. It is also widely used as a high caffeine stimulant and in local medicines. The plant is monoecious and is damaged by a number of diseases, the most severe being anthracnose. Prospects are excellent for greatly expanded international markets. 相似文献
53.
J Ignacio Andrés Jesús Alcázar José M Alonso Adolfo Díaz Javier Fernández Pilar Gil Laura Iturrino Encarna Matesanz Theo F Meert Anton Megens Victor K Sipido 《Bioorganic & medicinal chemistry letters》2002,12(2):249-253
Following the programme started at Janssen Research Foundation searching for 5-HT(2A/2C) antagonists, we now report on the synthesis of a series of substituted 2-(Dimethylaminomethyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives. The 5-HT(2A), 5-HT(2C) and H(1) receptor affinities as well as the mCPP antagonistic activity of the compounds synthesised is described. 相似文献
54.
Administration of choline chloride i.p. to rats causes a dose-dependent increase in the brain concentration of the neurotransmitter, acetylcholine (ACh). This increase is maximal (22% after a 60-mg/kg dose) 40 minutes after injection. These observations suggest that precursor availability may influence brain ACh synthesis, just as brain tryptophan and tyrosine levels have previously been shown to control the synthesis of brain serotonin and catecholamines. 相似文献
55.
56.
57.
58.
59.
Kimberly A. Aeling Kirsty A. Salmon José M. Laplaza Ling Li Jennifer R. Headman Alex H. Hutagalung Stephen Picataggio 《Journal of industrial microbiology & biotechnology》2012,39(11):1597-1604
We have integrated and coordinately expressed in Saccharomyces cerevisiae a xylose isomerase and cellobiose phosphorylase from Ruminococcus flavefaciens that enables fermentation of glucose, xylose, and cellobiose under completely anaerobic conditions. The native xylose isomerase was active in cell-free extracts from yeast transformants containing a single integrated copy of the gene. We improved the activity of the enzyme and its affinity for xylose by modifications to the 5′-end of the gene, site-directed mutagenesis, and codon optimization. The improved enzyme, designated RfCO*, demonstrated a 4.8-fold increase in activity compared to the native xylose isomerase, with a Km for xylose of 66.7?mM and a specific activity of 1.41?μmol/min/mg. In comparison, the native xylose isomerase was found to have a Km for xylose of 117.1?mM and a specific activity of 0.29?μmol/min/mg. The coordinate over-expression of RfCO* along with cellobiose phosphorylase, cellobiose transporters, the endogenous genes GAL2 and XKS1, and disruption of the native PHO13 and GRE3 genes allowed the fermentation of glucose, xylose, and cellobiose under completely anaerobic conditions. Interestingly, this strain was unable to utilize xylose or cellobiose as a sole carbon source for growth under anaerobic conditions, thus minimizing yield loss to biomass formation and maximizing ethanol yield during their fermentation. 相似文献
60.