全文获取类型
收费全文 | 632篇 |
免费 | 58篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 24篇 |
2018年 | 11篇 |
2017年 | 19篇 |
2016年 | 19篇 |
2015年 | 42篇 |
2014年 | 43篇 |
2013年 | 42篇 |
2012年 | 55篇 |
2011年 | 59篇 |
2010年 | 29篇 |
2009年 | 35篇 |
2008年 | 41篇 |
2007年 | 26篇 |
2006年 | 25篇 |
2005年 | 39篇 |
2004年 | 36篇 |
2003年 | 22篇 |
2002年 | 29篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1985年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有690条查询结果,搜索用时 725 毫秒
161.
A. R. Khomutov T. A. Keinanen N. A. Grigorenko M. T. Hyvonen A. Uimari M. Pietila M. Cerrada-Gimenez A. R. Simonian M. A. Khomutov J. Vepsalainen L. Alhonen J. Janne 《Molecular Biology》2009,43(2):249-259
Biogenic amines spermine (Spm) and spermidine (Spd) are essential for cell growth. Polyamine analogs are widely used to investigate the enzymes of polyamine metabolism and the functions of spermine and spermidine in vitro and in vivo. It was demonstrated recently that α-methylated derivatives of Spm and Spd are able to fulfill the key cellular functions of polyamines, moreover, in some cases, the effects of (R) and (S) isomers were actually different. Using these α-methylated analogs of Spm and Spd, it turned possible to prevent the development of acute pancreatitis in SSAT-transgenic rats with controllable expression of the Spm/Spd N1-acetyltransferase gene. The analogs made it possible to reveal dormant stereospecificity of polyamine oxidase, Spm oxidase, and deoxyhypusine synthase. An original approach was suggested to regulate the stereospecificity of polyamine oxidase. Depletion of the intracellular polyamine pool was found to have both hypusine-related consequences and consequences unrelated to posttranslational modification of the eukaryotic translation initiation factor eIF5A. Possible applications of a new family of C-methylated polyamine analogs for the investigation and regulation of polyamine metabolism in vitro and in vivo are discussed. 相似文献
162.
163.
Maria Kahlert Raino-Lars Albert Eeva-Leena Anttila Roland Bengtsson Christian Bigler Tiina Eskola Veronika Gälman Steffi Gottschalk Eva Herlitz Amelie Jarlman Jurate Kasperoviciene Mikołaj Kokociński Helen Luup Juha Miettinen Ieva Paunksnyte Kai Piirsoo Isabel Quintana Janne Raunio Bernt Sandell Heikki Simola Irene Sundberg Sirje Vilbaste Jan Weckström 《Journal of applied phycology》2009,21(4):471-482
The goal of this study was a harmonization of diatom identification and counting among diatomists from the Scandinavian and
Baltic countries to improve the comparison of diatom studies in this geographical area. An analysis of the results of 25 diatomists
following the European standard EN 14407 during an intercalibration exercise showed that a high similarity was achieved by
harmonization and not because of a long experience with diatoms. Sources of error were wrong calibration scales, overlooking
of small taxa, especially small Navicula s.l., misidentifications (Eunotia rhomboidea was mistaken for Eunotia incisa) and unclear separation between certain taxa in the identification literature. The latter was discussed during a workshop
with focus on the Achnanthes minutissima group, the separation of Fragilaria capucina var. gracilis from F. capucina var. rumpens, and Nitzschia palea var. palea from N. palea var. debilis. The exercise showed also that the Swedish standard diatom method tested here worked fine with acceptable error for the indices
IPS (Indice de Polluo-sensibilité Spécifique) and ACID (ACidity Index for Diatoms) when diatomists with a low similarity (Bray–Curtis
<60%) with the auditor in at least one of the samples are excluded. 相似文献
164.
Bing He Anne-May
sterholm Anna Hoverflt Carol Forsblom Eyrún Edda Hjrleifsdttir Ann-Sofie Nilsson Maikki Parkkonen Janne Pitkniemi strdur Hreidarsson Cinzia Sarti Amy Jayne McKnight A. Peter Maxwell Jaakko Tuomilehto Per-Henrik Groop Karl Tryggvason 《American journal of human genetics》2009,84(1):5-13
Diabetic nephropathy (DN) is the primary cause of morbidity and mortality in patients with type 1 diabetes mellitus (T1DM) and affects about 30% of these patients. We have previously localized a DN locus on chromosome 3q with suggestive linkage in Finnish individuals. Linkage to this region has also been reported earlier by several other groups. To fine map this locus, we conducted a multistage case-control association study in T1DM patients, comprising 1822 cases with nephropathy and 1874 T1DM patients free of nephropathy, from Finland, Iceland, and the British Isles. At the screening stage, we genotyped 3072 tag SNPs, spanning a 28 Mb region, in 234 patients and 215 controls from Finland. SNPs that met the significance threshold of p < 0.01 at this stage were followed up by a series of sample sets. A genetic variant, rs1866813, in the noncoding region at 3q22 was associated with increased risk of DN (overall p = 7.07 × 10−6, combined odds ratio [OR] of the allele = 1.33). The estimated genotypic ORs of this variant in all Finnish samples suggested a codominant effect, resulting in significant association, with a p value of 4.7 × 10−5 (OR = 1.38; 95% confidence interval = 1.18–1.62). Additionally, an 11 kb segment flanked by rs62408925 and rs1866813, two strongly correlated variants (r2 = 0.95), contains three elements highly conserved across multiple species. Independent replication will clarify the role of the associated variants at 3q22 in influencing the risk of DN. 相似文献
165.
166.
Lepidopterists have long acknowledged that many uncommon butterfly species can be extremely abundant in suitable locations. If this is generally true, it contradicts the general macroecological pattern of the positive interspecific relationship between abundance and distribution, i.e. locally abundant species are often geographically more widespread than locally rare species. Indeed, a negative abundance–distribution relationship has been documented for butterflies in Finland. Here we show, using the Finnish butterflies as an example, that a positive abundance–distribution relationship results if the geographically restricted species are missed, as may be the case in studies based on random or restricted sampling protocols, or in studies that are conducted over small spatial scales. In our case, the abundance–distribution relationship becomes negative when approximately 70 per cent of the species are included. This observation suggests that the abundance–distribution relationship may in fact not be linear over the entire range of distributions. This intriguing possibility combined with some taxonomic biases in the literature may undermine the generalization that for a given taxonomic assemblage there is a positive interspecific relationship between local abundance and regional distribution. 相似文献
167.
Jesper Sejrup Nielsen Lisbeth Kristensen Lei Tine Ebersbach Anders Steno Olsen Janne Kudsk Klitgaard Poul Valentin-Hansen Birgitte Haahr Kallipolitis 《Nucleic acids research》2010,38(3):907-919
Small trans-encoded RNAs (sRNAs) modulate the translation and decay of mRNAs in bacteria. In Gram-negative species, antisense regulation by trans-encoded sRNAs relies on the Sm-like protein Hfq. In contrast to this, Hfq is dispensable for sRNA-mediated riboregulation in the Gram-positive species studied thus far. Here, we provide evidence for Hfq-dependent translational repression in the Gram-positive human pathogen Listeria monocytogenes, which is known to encode at least 50 sRNAs. We show that the Hfq-binding sRNA LhrA controls the translation and degradation of its target mRNA by an antisense mechanism, and that Hfq facilitates the binding of LhrA to its target. The work presented here provides the first experimental evidence for Hfq-dependent riboregulation in a Gram-positive bacterium. Our findings indicate that modulation of translation by trans-encoded sRNAs may occur by both Hfq-dependent and -independent mechanisms, thus adding another layer of complexity to sRNA-mediated riboregulation in Gram-positive species. 相似文献
168.
Jani Heino Luis Mauricio Bini Satu Maaria Karjalainen Heikki Mykrä Janne Soininen Ludgero Cardoso Galli Vieira José Alexandre Felizola Diniz‐Filho 《Oikos》2010,119(1):129-137
A topic under intensive study in community ecology and biogeography is the degree to which microscopic, as well as macroscopic organisms, show spatially-structured variation in community characteristics. In general, unicellular microscopic organisms are regarded as ubiquitously distributed and, therefore, without a clear biogeographic signal. This view was summarized 75 years ago by Baas-Becking, who stated "everything is everywhere, but, the environment selects". Within the context of metacommunity theory, this hypothesis is congruent with the species sorting model. By using a broad-scale dataset on stream diatom communities and environmental predictor variables across most of Finland, our main aim was to test this hypothesis. Patterns of spatial autocorrelation were evaluated by Moran's I based correlograms, whereas partial regression analysis and partial redundancy analysis were used to quantify the relative importance of environmental and spatial factors on total species richness and on community composition, respectively. Significant patterns of spatial autocorrelation were found for all environmental variables, which also varied widely. Our main results were clear-cut. In general, pure spatial effects clearly overcame those of environmental effects, with the former explaining much more variation in species richness and community composition. Most likely, missing environmental variables cannot explain the higher predictive power of spatial variables, because we measured key factors that have previously been found to be the most important variables (e.g. pH, conductivity, colour, phosphorus, nitrogen) shaping the structure of diatom communities. Therefore, our results provided only limited support for the Baas-Becking hypothesis and the species sorting perspective of metacommunity theory. 相似文献
169.
170.