全文获取类型
收费全文 | 1110篇 |
免费 | 73篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 36篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 37篇 |
2017年 | 28篇 |
2016年 | 36篇 |
2015年 | 64篇 |
2014年 | 61篇 |
2013年 | 87篇 |
2012年 | 96篇 |
2011年 | 91篇 |
2010年 | 54篇 |
2009年 | 48篇 |
2008年 | 72篇 |
2007年 | 83篇 |
2006年 | 64篇 |
2005年 | 52篇 |
2004年 | 55篇 |
2003年 | 36篇 |
2002年 | 40篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 13篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1950年 | 2篇 |
1943年 | 2篇 |
1942年 | 1篇 |
1936年 | 1篇 |
1934年 | 1篇 |
1930年 | 1篇 |
1929年 | 1篇 |
1928年 | 1篇 |
1927年 | 1篇 |
1913年 | 1篇 |
1904年 | 1篇 |
排序方式: 共有1183条查询结果,搜索用时 156 毫秒
51.
Evidence for recombination of mtDNA in the marine mussel Mytilus trossulus from the Baltic 总被引:4,自引:0,他引:4
A number of studies have claimed that recombination occurs in animal mtDNA, although this evidence is controversial. Ladoukakis and Zouros (2001) provided strong evidence for mtDNA recombination in the COIII gene in gonadal tissue in the marine mussel Mytilus galloprovincialis from the Black Sea. The recombinant molecules they reported had not however become established in the population from which experimental animals were sampled. In the present study, we provide further evidence of the generality of mtDNA recombination in Mytilus by reporting recombinant mtDNA molecules in a related mussel species, Mytilus trossulus, from the Baltic. The mtDNA region studied begins in the 16S rRNA gene and terminates in the cytochrome b gene and includes a major noncoding region that may be analogous to the D-loop region observed in other animals. Many bivalve species, including some Mytilus species, are unusual in that they have two mtDNA genomes, one of which is inherited maternally (F genome) the other inherited paternally (M genome). Two recombinant variants reported in the present study have population frequencies of 5% and 36% and appear to be mosaic for F-like and M-like sequences. However, both variants have the noncoding region from the M genome, and both are transmitted to sperm like the M genome. We speculate that acquisition of the noncoding region by the recombinant molecules has conferred a paternal role on mtDNA genomes that otherwise resemble the F genome in sequence. 相似文献
52.
Ontogenic changes in the construction cost of leaves, stems fruits and roots of tomato plants 总被引:2,自引:0,他引:2
The construction cost of a plant tissue, i.e. the amount of
photoassimilates used in the synthesis of a unit weight, varies with its
biochemical composition. Crop modellers use standard values published for a
few groups of cultivated species. Yet, there are also intraspecific
variations in the construction cost in relation with the development of the
plant or organ. This research aimed at analysing the ontogenic changes in
the construction cost of leaves, stems, roots, and fruits of tomato plants
and the specific contribution of the mineral content to these changes. For
that purpose, samples were harvested from the vegetative phase to the
beginning of fruit production. The estimation of the construction cost was
based on the contents of carbon, nitrogen and ash. In leaves, the
construction cost decreased with the physiological age whereas, in stem
internodes, it varied with the sympod number. These ontogenic changes could
partly be explained by different accumulations of minerals. In contrast,
the construction cost and the mineral content of fruits and roots remained
fairly stable. On a whole plant basis, the construction cost of the bulk of
each category of organs varied much less. Most of the increase in the mean
construction cost of the whole plant during the experiment was due to
changes in the allocation ratio between the vegetative parts and the
fruits. Attention of crop modellers is drawn to the importance of a precise
estimation of the construction cost and to the existence of ontogenic
changes at the whole plant and organ levels.Key words:
Lycopersicon esculentum Mill., construction cost, mineral
content, ontogeny, carbon content
相似文献
53.
54.
Plants have a long history as therapeutics in the treatment of human diseases and have been used as source of medicines for ages. Searching for new biologically active natural products, many plants and herbs are screened for natural products with pharmacological activities. In this field, the genus Inula, which comprises more than 100 species, several of them being used in traditional medicine, is very important, especially due to the finding that several of the isolated pure secondary metabolites proved to possess important biological activities. Inula species have been reported as rich sources of sesquiterpene lactones, including eudesmanes, germacranes, guaianes, and dimeric structures, and since 2006 ca. 400 secondary metabolites, including more than 100 new natural products, some of them with relevant pharmacological activities, have been identified. Herein, we critically compile and update the information regarding the types of secondary metabolites found in the genus Inula and the progress in their isolation. 相似文献
55.
Agnieszka Tur?o Anna Cywińska Micha? Czopowicz Lucjan Witkowski Artur Nied?wied? Malwina S?owikowska Hieronim Borowicz Anna Ja?kiewicz Anna Winnicka 《PloS one》2015,10(10)
BackgroundTraining-induced muscle, skeletal and joint trauma may result in acute phase response reflected by the changes in the blood concentration of serum amyloid A (SAA) in racehorses. It remains yet unclear if such systemic reaction could be triggered by sport injuries and what is the impact of different types of musculoskeletal trauma on SAA concentrations in racehorses. This study aimed to determine changes in the SAA blood concentration in racehorses with different types of injuries of musculoskeletal system.ResultsMean SAA concentration within the first 4 days of the injury of muscle and tendon was significantly higher than in bone fractures, dorsal metacarpal disease, joint trauma or in the healthy horses (p<0,001). There were no significant differences between the other groups.ConclusionsStrain injuries of muscle and tendons can cause a moderate increase in SAA blood concentration in racehorses, reflecting the occurrence of the acute phase response. Similar reaction is not observed in the stress-related bone injuries. 相似文献
56.
During neural circuit development, attractive or repulsive guidance cue molecules direct growth cones (GCs) to their targets by eliciting cytoskeletal remodeling, which is reflected in their morphology. The experimental power of in vitro neuronal cultures to assay this process and its molecular mechanisms is well established, however, a method to rapidly find and quantify multiple morphological aspects of GCs is lacking. To this end, we have developed a free, easy to use, and fully automated Fiji macro, Conographer, which accurately identifies and measures many morphological parameters of GCs in 2D explant culture images. These measurements are then subjected to principle component analysis and k-means clustering to mathematically classify the GCs as “collapsed” or “extended”. The morphological parameters measured for each GC are found to be significantly different between collapsed and extended GCs, and are sufficient to classify GCs as such with the same level of accuracy as human observers. Application of a known collapse-inducing ligand results in significant changes in all parameters, resulting in an increase in ‘collapsed’ GCs determined by k-means clustering, as expected. Our strategy provides a powerful tool for exploring the relationship between GC morphology and guidance cue signaling, which in particular will greatly facilitate high-throughput studies of the effects of drugs, gene silencing or overexpression, or any other experimental manipulation in the context of an in vitro axon guidance assay. 相似文献
57.
Arash Mehdiani Anatol Maier Antonio Pinto Mareike Barth Payam Akhyari Artur Lichtenberg 《Journal of visualized experiments : JoVE》2015,(95)
Although the biological importance of exosomes has recently gained an increasing amount of scientific and clinical attention, much is still unknown about their complex pathways, their bioavailability and their diverse functions in health and disease. Current work focuses on the presence and the behavior of exosomes (in vitro as well as in vivo) in the context of different human disorders, especially in the fields of oncology, gynecology and cardiology.Unfortunately, neither a consensus regarding a gold standard for exosome isolation exists, nor is there an agreement on such a method for their quantitative analysis. As there are many methods for the purification of exosomes and also many possibilities for their quantitative and qualitative analysis, it is difficult to determine a combination of methods for the ideal approach. Here, we demonstrate nanoparticle tracking analysis (NTA), a semi-automated method for the characterization of exosomes after isolation from human plasma by ultracentrifugation. The presented results show that this approach for isolation, as well as the determination of the average number and size of exosomes, delivers reproducible and valid data, as confirmed by other methods, such as scanning electron microscopy (SEM). 相似文献
58.
Artur Yakimovich Vardan Andriasyan Robert Witte I-Hsuan Wang Vibhu Prasad Maarit Suomalainen Urs F. Greber 《PloS one》2015,10(9)
Classical plaque assay measures the propagation of infectious agents across a monolayer of cells. It is dependent on cell lysis, and limited by user-specific settings and low throughput. Here, we developed Plaque2.0, a broadly applicable, fluorescence microscopy-based high-throughput method to mine patho-biological clonal cell features. Plaque2.0 is an open source framework to extract information from chemically fixed cells by immuno-histochemistry or RNA in situ hybridization, or from live cells expressing GFP transgene. Multi-parametric measurements include infection density, intensity, area, shape or location information at single plaque or population levels. Plaque2.0 distinguishes lytic and non-lytic spread of a variety of DNA and RNA viruses, including vaccinia virus, adenovirus and rhinovirus, and can be used to visualize simultaneous plaque formation from co-infecting viruses. Plaque2.0 also analyzes clonal growth of cancer cells, which is relevant for cell migration and metastatic invasion studies. Plaque2.0 is suitable to quantitatively analyze virus infections, vector properties, or cancer cell phenotypes. 相似文献
59.
Melanie Brügger Thomas Dmoulins G. Tuba Barut Beatrice Zumkehr Blandina I. Oliveira Esteves Kemal Mehinagic Quentin Haas Aline Schgler Marie-Anne Rameix-Welti Jean-Franois Elouët Ueli Moehrlen Thomas M. Marti Ralph A. Schmid Artur Summerfield Horst Posthaus Nicolas Ruggli Sean R. R. Hall Marco P. Alves 《PLoS pathogens》2021,17(7)