全文获取类型
收费全文 | 2294篇 |
免费 | 180篇 |
国内免费 | 6篇 |
出版年
2022年 | 7篇 |
2021年 | 33篇 |
2020年 | 23篇 |
2019年 | 30篇 |
2018年 | 45篇 |
2017年 | 33篇 |
2016年 | 46篇 |
2015年 | 79篇 |
2014年 | 99篇 |
2013年 | 130篇 |
2012年 | 209篇 |
2011年 | 162篇 |
2010年 | 96篇 |
2009年 | 99篇 |
2008年 | 140篇 |
2007年 | 155篇 |
2006年 | 149篇 |
2005年 | 117篇 |
2004年 | 143篇 |
2003年 | 108篇 |
2002年 | 93篇 |
2001年 | 29篇 |
2000年 | 18篇 |
1999年 | 21篇 |
1998年 | 32篇 |
1997年 | 17篇 |
1996年 | 11篇 |
1995年 | 19篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1974年 | 10篇 |
1973年 | 10篇 |
1971年 | 7篇 |
1970年 | 6篇 |
1967年 | 7篇 |
排序方式: 共有2480条查询结果,搜索用时 343 毫秒
991.
992.
Characterization of an exported protease from Shiga toxin-producing Escherichia coli 总被引:2,自引:1,他引:1
Soudabeh Djafari Frank Ebel Christina Deibel Sylvia Krämer Martina Hudel & Trinad Chakraborty 《Molecular microbiology》1997,25(4):771-784
The gene for a novel, high molecular weight protein secreted by Shiga toxin-producing Escherichia coli (STEC) has been cloned, sequenced and characterized with respect to its activity. This gene, designated pssA , is localized on the large plasmid that also harbours the STEC haemolysin operon. Sequencing of a region comprising 10 630 nt revealed that the sequences flanking the pssA gene are composed of several remnants of different insertion elements. The PssA protein is produced as a 142 kDa precursor molecule that, after N- and C-terminal processing, is released into the culture supernatant as a mature polypeptide of approximately 104 kDa. The primary sequence of PssA is highly related to a family of autonomously transported putative virulence factors from different Gram-negative pathogens, which includes the Tsh protein of an avian-pathogenic E . coli strain, the SepA protein from Shigella flexneri and the EspC protein from enteropathogenic E . coli . A common motif present in all four proteins is reminiscent of the catalytic centre of certain serine proteases. PssA (protease secreted by STEC) indeed shows serine protease activity in a casein-based assay and is moreover cytotoxic for Vero cells. This activity of PssA and probably of other proteins of the Tsh family may be of functional importance during infection of the mucosal cell layer by the bacterial pathogen. 相似文献
993.
994.
995.
Sylvia Limerick 《BMJ (Clinical research ed.)》1982,285(6353):1502-1503
996.
997.
998.
Sylvia Grune Loffler Maria Elisa Pavan Bibiana Vanasco Luis Samartino Olga Suarez Carmelo Auteri Graciela Romero Bibiana Brihuega 《Memórias do Instituto Oswaldo Cruz》2014,109(2):163-167
Leptospirosis is the most widespread zoonosis in the world and significant efforts
have been made to determine and classify pathogenic Leptospira
strains. This zoonosis is maintained in nature through chronic renal
infections of carrier animals, with rodents and other small mammals serving as the
most important reservoirs. Additionally, domestic animals, such as livestock and
dogs, are significant sources of human infection. In this study, a
multiple-locus variable-number tandem repeat analysis (MLVA) was
applied to genotype 22 pathogenic Leptospira strains isolated from
urban and periurban rodent populations from different regions of Argentina. Three
MLVA profiles were identified in strains belonging to the species Leptospira
interrogans (serovars Icterohaemorrhagiae and Canicola); one profile was
observed in serovar Icterohaemorrhagiae and two MLVA profiles were observed in
isolates of serovars Canicola and Portlandvere. All strains belonging to
Leptospira borgpetersenii serovar Castellonis exhibited the same
MLVA profile. Four different genotypes were isolated from urban populations of
rodents, including both mice and rats and two different genotypes were isolated from
periurban populations. 相似文献
999.
In small shallow lakes and ponds, the clear-water state can generally be maintained at higher nutrient concentrations compared to larger shallow lakes. The main objective of this study was to identify thresholds for total phosphorus (TP), submerged vegetation cover and zooplankton size that determine biomanipulation success in peri-urban eutrophic ponds. Additionally, the relationship between transparency and TP is discussed with regard to similar relationships and thresholds reported for shallow lakes. Using classification trees, a threshold TP concentration of 0.300 mg P L?1 was determined below which a clear-water state was generally maintained after biomanipulation. When the average TP concentration was >0.300 mg P L?1, the stability of the clear-water state largely depended on the presence of sufficiently large zooplankton (>0.87 mm) or a submerged vegetation cover of >82% at some point during the year. This threshold TP concentration is considerably higher than the threshold of 0.1 mg L?1 which is generally suggested for longer-term success of biomanipulation in shallow lakes. Such threshold nutrient concentration is important when restoring ecological quality in eutrophic small lakes and ponds. Extended follow-up of biomanipulation success in eutrophic ponds could provide more insight into the feasibility of these thresholds on the longer term. 相似文献