全文获取类型
收费全文 | 534篇 |
免费 | 22篇 |
专业分类
556篇 |
出版年
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 5篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 10篇 |
2016年 | 25篇 |
2015年 | 30篇 |
2014年 | 37篇 |
2013年 | 23篇 |
2012年 | 44篇 |
2011年 | 48篇 |
2010年 | 24篇 |
2009年 | 14篇 |
2008年 | 23篇 |
2007年 | 23篇 |
2006年 | 13篇 |
2005年 | 11篇 |
2004年 | 21篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 8篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1971年 | 5篇 |
1970年 | 6篇 |
1969年 | 2篇 |
1968年 | 6篇 |
1965年 | 2篇 |
1960年 | 2篇 |
排序方式: 共有556条查询结果,搜索用时 15 毫秒
191.
Petra Matou?ková Hana Bártíková Iva Bou?ová Veronika Hanu?ová Barbora Szotáková Lenka Skálová 《PloS one》2014,9(1)
Obesity and metabolic syndrome is increasing health problem worldwide. Among other ways, nutritional intervention using phytochemicals is important method for treatment and prevention of this disease. Recent studies have shown that certain phytochemicals could alter the expression of specific genes and microRNAs (miRNAs) that play a fundamental role in the pathogenesis of obesity. For study of the obesity and its treatment, monosodium glutamate (MSG)-injected mice with developed central obesity, insulin resistance and liver lipid accumulation are frequently used animal models. To understand the mechanism of phytochemicals action in obese animals, the study of selected genes expression together with miRNA quantification is extremely important. For this purpose, real-time quantitative PCR is a sensitive and reproducible method, but it depends on proper normalization entirely. The aim of present study was to identify the appropriate reference genes for mRNA and miRNA quantification in MSG mice treated with green tea catechins, potential anti-obesity phytochemicals. Two sets of reference genes were tested: first set contained seven commonly used genes for normalization of messenger RNA, the second set of candidate reference genes included ten small RNAs for normalization of miRNA. The expression stability of these reference genes were tested upon treatment of mice with catechins using geNorm, NormFinder and BestKeeper algorithms. Selected normalizers for mRNA quantification were tested and validated on expression of NAD(P)H:quinone oxidoreductase, biotransformation enzyme known to be modified by catechins. The effect of selected normalizers for miRNA quantification was tested on two obesity- and diabetes- related miRNAs, miR-221 and miR-29b, respectively. Finally, the combinations of B2M/18S/HPRT1 and miR-16/sno234 were validated as optimal reference genes for mRNA and miRNA quantification in liver and 18S/RPlP0/HPRT1 and sno234/miR-186 in small intestine of MSG mice. These reference genes will be used for mRNA and miRNA normalization in further study of green tea catechins action in obese mice. 相似文献
192.
Andrej?Godány Katarína?Majzlová Viera?Horváthová Barbora?Vidová ?tefan?Jane?ekEmail author 《Biologia》2010,65(3):408-415
The presented work is focused on the naturally thermostable α-amylase from the archaebacterium Thermococcus hydrothermalis. From the evolutionary point of view, the archaeal α-amylases are most closely related to plant α-amylases. In a wider sense, especially when the evolutionary trees are based on the less conserved part of their amino acid
sequences (e.g. domain C succeeding the catalytic TIM-barrel), also the representatives of bacterial liquefying (Bacillus licheniformis) and saccharifying (Bacillus subtilis) α-amylases as well as the one from Thermotoga maritima should be included into the relatedness with the archaeal and plant α-amylases. Based on the bioinformatics analysis of the α-amylase from T. hydrothermalis, the position of tyrosine 39 (Y16 if the putative 23-residue long signal peptide is considered) was mutated to isoleucine
(present in the α-amylase from T. maritima) by the in vitro mutagenesis. The biochemical characterization of the wild-type α-amylase and its Y39I mutant revealed that: (i) the specific activity of both enzymes was approximately equivalent (0.55 ±
0.13 U/mg for the wild-type and 0.52 ± 0.15 U/mg for the Y39I); (ii) the mutant exhibited decreased temperature optimum (from
85°C for the wild-type to 80°C for the Y39I); and (iii) the pH optimum remained the same (pH 5.5 for both enzymes). The remaining
activity of the α-amylases was also tested by one-hour incubation at 80°C, 85°C, 90°C and 100°C. Since the wild-type α-amylase lost only 13% of its activity after one-hour incubation at the highest tested temperature (100°C), whereas 27% decrease
was seen for the mutant Y39I under the same conditions, it is possible to conclude that the position of tyrosine 39 could
contribute to the thermostability of the α-amylase from T. hydrothermalis. 相似文献
193.
Trávnícek P Kubátová B Curn V Rauchová J Krajníková E Jersáková J Suda J 《Annals of botany》2011,107(1):77-87
Background and Aims
One of the prerequisites for polyploid research in natural systems is knowledge of the geographical distribution of cytotypes. Here inter- and intrapopulational ploidy diversity was examined in the Gymnadenia conopsea aggregate in central Europe and potential explanations and evolutionary consequences of the observed spatial patterns investigated.Methods
DAPI flow cytometry supplemented by confirmatory chromosome counts was used to determine ploidy in 3581 samples of the G. conopsea aggregate from 43 populations. The fine-scale spatial pattern of cytotype distribution (intra- and interploidy associations) was analysed with univariate and bivariate K-functions.Key Results
Gymnadenia tissues undergo a progressively partial endoreplication, which accounts for about 60 % and 75 % of the total genome in G. conopsea and G. densiflora, respectively. Flow cytometric profiles are therefore species-specific and can be used as a marker for rapid and reliable species recognition. Two majority (4x, 8x) and three minority (6x, 10x, 12x) cytotypes were found, often in mixed-ploidy populations (harbouring up to all five different ploidy levels). The scarcity of the minority cytotypes (about 2·7 %) suggests the existence of strong pre- or postzygotic mating barriers. Spatial structure was observed in plots of populations with the highest cytotype variation, including clumping of individuals of the same ploidy and negative association between tetra- and octoploids.Conclusions
The remarkable ploidy coexistence in the G. conopsea aggregate has reshaped our perception of intrapopulational ploidy diversity under natural conditions. This system offers unique opportunities for studying processes governing the formation and establishment of polyploids and assessing the evolutionary significance of the various pre- and postzygotic mating barriers that maintain this ploidy mixture. 相似文献194.
195.
Background
The highly prevalent parasite Toxoplasma gondii reportedly manipulates rodent behavior to enhance the likelihood of transmission to its definitive cat host. The proximate mechanisms underlying this adaptive manipulation remain largely unclear, though a growing body of evidence suggests that the parasite-entrained dysregulation of dopamine metabolism plays a central role. Paradoxically, the distribution of the parasite in the brain has received only scant attention.Methodology/Principal Findings
The distributions of T. gondii cysts and histopathological lesions in the brains of CD1 mice with latent toxoplasmosis were analyzed using standard histological techniques. Mice were infected per orally with 10 tissue cysts of the avirulent HIF strain of T. gondii at six months of age and examined 18 weeks later. The cysts were distributed throughout the brain and selective tropism of the parasite toward a particular functional system was not observed. Importantly, the cysts were not preferentially associated with the dopaminergic system and absent from the hypothalamic defensive system. The striking interindividual differences in the total parasite load and cyst distribution indicate a probabilistic nature of brain infestation. Still, some brain regions were consistently more infected than others. These included the olfactory bulb, the entorhinal, somatosensory, motor and orbital, frontal association and visual cortices, and, importantly, the hippocampus and the amygdala. By contrast, a consistently low incidence of tissue cysts was recorded in the cerebellum, the pontine nuclei, the caudate putamen and virtually all compact masses of myelinated axons. Numerous perivascular and leptomeningeal infiltrations of inflammatory cells were observed, but they were not associated with intracellular cysts.Conclusion/Significance
The observed pattern of T. gondii distribution stems from uneven brain colonization during acute infection and explains numerous behavioral abnormalities observed in the chronically infected rodents. Thus, the parasite can effectively change behavioral phenotype of infected hosts despite the absence of well targeted tropism. 相似文献196.
Martina Bla?ková Barbora Jav?rková Ji?í Vlach Sandra G?selová Ludmila Karamonová Pauline Ogrodzki Stephen Forsythe Ladislav Fukal 《Applied and environmental microbiology》2015,81(16):5574-5582
Cronobacter species are Gram-negative opportunistic pathogens that can cause serious infections in neonates. The lipopolysaccharides (LPSs) that form part of the outer membrane of such bacteria are possibly related to the virulence of particular bacterial strains. However, currently there is no clear overview of O-antigen diversity within the various Cronobacter strains and links with virulence. In this study, we tested a total of 82 strains, covering each of the Cronobacter species. The nucleotide variability of the O-antigen gene cluster was determined by restriction fragment length polymorphism (RFLP) analysis. As a result, the 82 strains were distributed into 11 previously published serotypes and 6 new serotypes, each defined by its characteristic restriction profile. These new serotypes were confirmed using genomic analysis of strains available in public databases: GenBank and PubMLST Cronobacter. Laboratory strains were then tested using the current serotype-specific PCR probes. The results show that the current PCR probes did not always correspond to genomic O-antigen gene cluster variation. In addition, we analyzed the LPS phenotype of the reference strains of all distinguishable serotypes. The identified serotypes were compared with data from the literature and the MLST database (www.pubmlst.org/cronobacter/). Based on the findings, we systematically classified a total of 24 serotypes for the Cronobacter genus. Moreover, we evaluated the clinical history of these strains and show that Cronobacter sakazakii O2, O1, and O4, C. turicensis O1, and C. malonaticus O2 serotypes are particularly predominant in clinical cases. 相似文献
197.
Plzák J Holíková Z Dvoránková B Smetana K Betka J Hercogová J Saeland S Bovin NV Gabius HJ 《The Histochemical journal》2002,34(5):247-253
Tandem-repeat C-type lectins (pattern-recognition receptors) with specificity for mannosides are intimately involved in antigen recognition, uptake, routing and presentation in macrophages and dendritic cells. In Langerhans cells, Langerin (CD207), a type-II transmembrane protein with a single C-type carbohydrate recognition domain attached to a heptad repeat in the neck region, which is likely to establish oligomers with an -coiled-coil stalk, has been implicated in endocytosis and the formation of Birbeck granules. The structure of Langerin harbours essential motifs for Ca2+-binding and sugar accommodation. Lectin activity has previously been inferred by diminished antibody binding to cells in the presence of the glycan ligand mannan. In view of the complexity of the C-type lectin/lectin-like network, it is unclear what role Langerin plays for Langerhans cells in binding mannosides. In order to reveal in frozen tissue sections to what extent mannose-binding activity co-localizes with Langerin, we have used a synthetic marker, i.e. a neoglycoprotein carrying mannose maxiclusters, as a histochemical ligand, and computer-assisted fluorescence monitoring in a double-labelling procedure. Mannoside-binding capacity was detected in normal epithelial cells. Double labelling ensured the unambiguous assessment of the binding of the neoglycoprotein in Langerhans cells. Light-microscopically, its localization profile resembled the pattern of immunohistochemical detection of Langerin. This result has implications for suggesting rigorous controls in histochemical analysis of this cell type, because binding of kit reagents, i.e. mannose-rich glycoproteins horseradish peroxidase or avidin, to Langerin (or a spatially closely associated lectin) could yield false-positive signals. To show that recognition of carbohydrate ligands in dendritic cells is not restricted to mannose clusters, we have also documented binding of carrier-immobilized histo-blood group A trisaccharide, a ligand of galectin-3, which was not affected by the presence of a blocking antibody to Langerin. Remarkably, access to the carbohydrate recognition domain of Langerin appeared to be impaired in proliferatively active environments (malignancies, hair follicles), indicating presence of an endogenous ligand with high affinity to saturate the C-type lectin under these conditions. 相似文献
198.
Palaearctic species of the Rhamphomyia (Pararhamphomyia) anfractuosa group are revised. Rhamphomyia (Pararhamphomyia) biflexata
sp. n., Rhamphomyia (Pararhamphomyia) lineodorsata
sp. n., Rhamphomyia (Pararhamphomyia) nudiscutellata
sp. n., and Rhamphomyia (Pararhamphomyia) shatalkini
sp. n. (all from Russian Far East) are described and illustrated. A key to Palaearctic species of the Rhamphomyia (Pararhamphomyia) anfractuosa group is provided. 相似文献
199.
B Tencerová A Zahradníková J Gaburjáková M Gaburjáková 《The Journal of general physiology》2012,140(2):93-108
The synergic effect of luminal Ca(2+), cytosolic Ca(2+), and cytosolic adenosine triphosphate (ATP) on activation of cardiac ryanodine receptor (RYR2) channels was examined in planar lipid bilayers. The dose-response of RYR2 gating activity to ATP was characterized at a diastolic cytosolic Ca(2+) concentration of 100 nM over a range of luminal Ca(2+) concentrations and, vice versa, at a diastolic luminal Ca(2+) concentration of 1 mM over a range of cytosolic Ca(2+) concentrations. Low level of luminal Ca(2+) (1 mM) significantly increased the affinity of the RYR2 channel for ATP but without substantial activation of the channel. Higher levels of luminal Ca(2+) (8-53 mM) markedly amplified the effects of ATP on the RYR2 activity by selectively increasing the maximal RYR2 activation by ATP, without affecting the affinity of the channel to ATP. Near-diastolic cytosolic Ca(2+) levels (<500 nM) greatly amplified the effects of luminal Ca(2+). Fractional inhibition by cytosolic Mg(2+) was not affected by luminal Ca(2+). In models, the effects of luminal and cytosolic Ca(2+) could be explained by modulation of the allosteric effect of ATP on the RYR2 channel. Our results suggest that luminal Ca(2+) ions potentiate the RYR2 gating activity in the presence of ATP predominantly by binding to a luminal site with an apparent affinity in the millimolar range, over which local luminal Ca(2+) likely varies in cardiac myocytes. 相似文献
200.
Pavel Trávní?ek Jana Jersáková Barbora Kubátová Jana Krej?íková Richard M. Bateman Magdalena Lu?anová Eva Krajníková Tamara Tě?itelová Zuzana ?típková Jean-Pierre Amardeilh Emilia Brzosko Edyta Jermakowicz Olivier Cabanne Walter Durka Peter Efimov Mikael Hedrén Carlos E. Hermosilla Karel Kreutz Tiiu Kull Kadri Tali Olivier Marchand Manel Rey Florian P. Schiestl Vladislav ?urn Jan Suda 《Annals of botany》2012,110(5):977-986