全文获取类型
收费全文 | 973篇 |
免费 | 68篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 19篇 |
2020年 | 6篇 |
2019年 | 15篇 |
2018年 | 27篇 |
2017年 | 18篇 |
2016年 | 31篇 |
2015年 | 51篇 |
2014年 | 53篇 |
2013年 | 88篇 |
2012年 | 72篇 |
2011年 | 84篇 |
2010年 | 63篇 |
2009年 | 50篇 |
2008年 | 55篇 |
2007年 | 65篇 |
2006年 | 60篇 |
2005年 | 52篇 |
2004年 | 36篇 |
2003年 | 48篇 |
2002年 | 49篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有1041条查询结果,搜索用时 312 毫秒
61.
62.
Dexamethasone‐loaded biopolymeric nanoparticles promote gingival fibroblasts differentiation
下载免费PDF全文
![点击此处可从《Biotechnology progress》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Laura Chronopoulou Adriana Amalfitano Cleofe Palocci Giuseppina Nocca Cinzia Callà Alessandro Arcovito 《Biotechnology progress》2015,31(5):1381-1387
Polymer‐based nanoparticles (NPs) can be efficiently used for the delivery of bioactive molecules for both in vitro and in vivo applications affording high drug loading and controlled release profiles. Within this framework polylactic‐co‐glycolic acid (PLGA) NPs with a diameter of 290 ± 41 nm have been fabricated and loaded with dexamethasone (DXM) using a patented procedure. The aim of the project was to setup a controlled delivery system to promote the in vitro differentiation of Human Gingival Fibroblasts (HGFs). First the uptake of fluorescent PLGA NPs by HGFs cells was investigated; then experiments were also addressed to analyze the specific cell response to DXM, in order to evaluate its functional efficiency in comparison with its conventional addition to the culture medium. The results showed that cells treated with DXM‐loaded NPs acquired the osteoblast phenotype faster in comparison to those treated with the free drug. The slow and sustained release of DXM from PLGA NPs produced a constant and uniform concentration of drug inside cells with long‐term and enhanced biochemical effects. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:1381–1387, 2015 相似文献
63.
Laura Zuccaro Cinzia Tesauro Barbara Cerroni Alessio Ottaviani Birgitta Ruth Knudsen Kannan Balasubramanian Alessandro Desideri 《Analytical biochemistry》2014
A high-sensitivity assay has been developed for the detection of human topoisomerase I with single molecule resolution. The method uses magnetic sepharose beads to concentrate rolling circle products, produced by the amplification of DNA molecules circularized by topoisomerase I and detectable with a confocal microscope as single and discrete dots, once reacted with fluorescent probes. Each dot, corresponding to a single cleavage–religation event mediated by the enzyme, can be counted due to its high signal/noise ratio, allowing detection of 0.3 pM enzyme and representing a valid method to detect the enzyme activity in highly diluted samples. 相似文献
64.
Piscopo P Rivabene R Adduci A Mallozzi C Malvezzi-Campeggi L Crestini A Confaloni A 《Neurochemistry international》2010,57(8):893-898
Progranulin (PGRN) is a widely expressed multifunctional protein, involved in regulation of cell growth and cell cycle progression with a possible involvement in neurodegeneration. We looked for PGRN regulation in three different human neuroblastoma cell lines, following exposure to two different stimuli commonly associated to neurodegeneration: hypoxia and oxidative stress. For gene and protein expression analysis we carried out a quantitative RT-PCR and western blotting analysis. We show that PGRN is strongly up-regulated by hypoxia, through the mitogen-actived protein kinase (MAPK)/extracellular signal-regulated kinase (MEK) signaling cascade. PGRN is not up-regulated by H(2)O(2)-induced oxidative stress. These results suggest that PGRN in the brain could exert a protective role against hypoxic stress, one of principal risk factors involved in frontotemporal dementia pathogenesis. 相似文献
65.
Cappelli A Valenti S Mancini A Giuliani G Anzini M Altieri S Bortolussi S Ferrari C Clerici AM Zonta C Carraro F Filippi I Giorgi G Donati A Ristori S Vomero S Concas A Biggio G 《Bioconjugate chemistry》2010,21(12):2213-2221
Potential boron neutron capture therapy (BNCT) agents have been designed on the basis of the evidence about translocator protein (TSPO) overexpression on the outer mitochondrial membrane of tumor cells. The structure of the first TSPO ligand bearing a carborane cage (compound 2d) has been modified in order to find a suitable candidate for in vivo studies. The designed compounds were synthesized and evaluated for their potential interaction with TSPO and tumor cells. In vitro biological evaluation showed in the case of fluoromethyl derivative 4b a nanomolar TSPO affinity very similar to that of 2d, a significantly lower cytotoxicity, and a slightly superior performance as boron carrier toward breast cancer cells. Moreover, compound 4b could be used as a 1?F magnetic resonance imaging (MRI) agent as well as labeled with 11C or 1?F to obtain positron emission tomography (PET) radiotracers in order to apply the "see and treat" strategy in BNCT. 相似文献
66.
Starting from (R)‐6,6′‐dimethyldiphenyl‐2,2′‐dicarboxylic acid, a novel class of enantiomerically pure cyclic dialkyl phosphates was synthesized and properly characterized. The absolute configuration was determined by 2D NOESY experiments. The catalytic behavior of the new chiral Bronsted acids was investigated in the stereoselective addition of a silyl keteneacetal to aldimines. The Mannich‐type reaction was promoted in up to 94% yields and enantioselectivities up to 55%. On the basis of preliminary molecular mechanic calculations, a model of stereoselection was also proposed to explain the sense of the enantioselectivity observed in the reaction. Chirality 2010. © 2009 Wiley‐Liss, Inc. 相似文献
67.
Mariapaola Nitti Anna Lisa Furfaro Claudia Cevasco Nicola Traverso Umberto Maria Marinari Maria Adelaide Pronzato Cinzia Domenicotti 《Cellular signalling》2010,22(5):828-835
The role of reactive oxygen species (ROS) in the regulation of signal transduction processes has been well established in many cell types and recently the fine tuning of redox signalling in neurons received increasing attention. With regard to this, the involvement of NADPH oxidase (NOX) in neuronal pathophysiology has been proposed but deserves more investigation. In the present study, we used SH-SY5Y neuroblastoma cells to analyse the role of NADPH oxidase in retinoic acid (RA)-induced differentiation, pointing out the involvement of protein kinase C (PKC) delta in the activation of NOX. Retinoic acid induces neuronal differentiation as revealed by the increased expression of MAP2, the decreased cell doubling rate, and the gain in neuronal morphological features and these events are accompanied by the increased expression level of PKC delta and p67phox, one of the components of NADPH oxidase. Using DPI to inhibit NOX activity we show that retinoic acid acts through this enzyme to induce morphological changes linked to the differentiation. Moreover, using rottlerin to inhibit PKC delta or transfection experiments to overexpress it, we show that retinoic acid acts through this enzyme to induce MAP2 expression and to increase p67phox membrane translocation leading to NADPH oxidase activation. These findings identify the activation of PKC delta and NADPH oxidase as crucial steps in RA-induced neuroblastoma cell differentiation. 相似文献
68.
69.
Rika Ozawa Cinzia M Bertea Maria Foti Ravishankar Narayana Gen-Ichiro Arimura Atsushi Muroi Massimo E Maffei Junji Takabayashi 《Plant signaling & behavior》2010,5(3):308-310
Exogenous polyamines [cadaverine (Cad), putrescine (Put), spermidine (Spd) and spermine (Spm)] elicit the production of volatiles in Lima bean (Phaseolus lunatus). Among the tested PAs, Spm induces the production of some volatile terpenoids that are known to be induced by the spider mite Tetranychus urticae. Spm treatment elicits the biosynthesis of Jasmonic acid (JA), a phytohormone known to regulate the production of the volatile terpenoids. The treatment with JA together with Spm resulted in the increased volatile emission, and predatory mites Phytoseiulus persimilis preferred JA and Spm-treated leaves over those treated with JA alone.5 JA and Spm treatment has no effects on polyamine oxidase (PAO) and Cu-amine oxidase (CuAO) but has a significant induction of calcium influx, ROS production, enzyme activities for NADPH-oxidase complex, superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and glutathione peroxidase, and gene expressions except for NADPH-oxidase complex.5 Here, we report that a plasma membrane potential (Vm) depolarization was observed after polyamine perfusion with an increasing trend: Spm, Cad, Put and Spd. JA perfusion did not alter Vm but the perfusion of JA and the polyamines significantly increased Cad and Put Vm depolarization. When JA was perfused with polyamines, a negative correlation was found between Vm depolarization and the number of amino group of the polyamines tested.Key words: polyamines, lima bean, herbivore-induced volatile organic compounds, calcium and ROS signalling, jasmonic acid, quantitative gene expression, transmembrane potentialPolyamines are involved in plants’ stress responses and growth. By activating biosynthesis of nucleic acids, polyamines concern the plant growth and differentiation.1–3 Furthermore, it has been reported that polyamines are involved in the response against environmental stress and plant disease.1–4 We recently reported that exogenously applied polyamines ∼diamines [cadaverine (Cad), putrescine (Put)], triamine [spermidine (Spd)] and tetraamine ]spermine (Spm)]∽ induce volatile emission in Lima bean leaves.5 Membrane potentials (Vm) and intracellular calcium variations were also studied in Lima bean leaves after perfusion with the polyamines and with these addition of JA and here we report on these additional results.The primary candidate for intercellular signaling in higher plants is the stimulus-induced change in Vm.6 The plasma membrane potential (Vm), which lies in the range of −50 to −200 mV in Lima bean leaves,7 may be shifted either to more negative (hyperpolarization) or to more positive values (depolarization) in response to various biotic or abiotic stresses.Measurement of Vm were performed and data statistically treated as previously described (ANOVA and Tukey-Kramer’s HSD test).7 Perfusion with the polyamines (Fig. 1 single arrow) shows a specific response of the leaf tissues with a different Vm depolarization, depending on the polyamine. In general, a Vm depolarization was observed after polyamine perfusion with an increasing trend: Spm, Cad, Put and Spd (Fig. 1). Spm and Spd Vm depolarization values were significantly different (p < 0.05) from all other polyamines, whereas no significant difference was found between Put and Cad Vm depolarization (p = 0.435). In all cases, Vm depolarization was reversed by washing polyamine-treated leaves with a fresh buffer solution (Fig. 1 double arrow); however, a full recovery of the Vm was observed only for Put (Fig. 1). The linearization of the data from Figure 1 allowed to calculate the rate of Vm depolarization after perfusion of the polyamines which was higher for Spd (6.0 mV min−1; R = 0.96), equal for Put and Cad (4.8 mV min−1; Put R = 0.95; Cad R = 0.97) and lower for Spm (3.0 mV min−1; R = 0.96).Open in a separate windowFigure 1Effect of 1 mM polyamines (arrow) on the Vm of Lima bean palisade cells. Spermine (Spm) caused the lowest Vm depolarization, whereas spermidine (Spd) showed the highest values of Vm depolarization. intermediate values were found when putrescine (Put) and cadaverine (cad) were perfused. after washing the tissues with fresh buffer (double arrow) Vm was always hyperpolarized, however the initial potential was recovered only for Put, while for all other polyamines the Vm never reached the initial values. Metric bars indicate standard deviation.Perfusion with JA caused a slight and not significant (p = 0.332) Vm depolarization (Fig. 2) with respect to control. The addition of JA caused a significant increase (p < 0.01) in Vm depolarization when perfused with Cad, with respect to the sole perfusion with Cad (Fig. 1). The same was observed when JA was perfused with Put, whereas not significant differences were observed when Spm (p = 0.513) and Spd (p = 0.107) were perfused with JA (Fig. 2), with respect to the sole perfusion with Spm and Spd (Fig. 1). The linearization of the data from Figure 2 allowed to calculate the rate of Vm depolarization after perfusion of the polyamines + JA, which was higher for Cad (24.40 mV min−1; R = 0.99), almost equal for Put and Spd (Put: 14.21 mV min−1, R = 0.99; Spd: 13.49 mV min−1, R = 0.99) and lower for Spm (1.34 mV min−1; R = 0.93). For JA the rate of Vm depolarization was 0.19 mV min−1 (R = 0.96). With the addition of JA, a negative correlation was found between Vm depolarization and the number of amino group of the polyamines tested.Open in a separate windowFigure 2Effect of 1 mM polyamines + 0.1 mMJA (arrow) on the Vm of Lima bean palisade cells. the perfusion with Ja did not cause any variation in the Vm. addition of JA to Spm and Spd caused the same Vm depolarization observed in the absence of JA, whereas when JA was added to Put and Cad a stronger and significantly different Vm depolarization was observed. even in this case washing the tissues with fresh buffer (double arrow) caused a Vm hyperpolarized, however in this case Spd reached Vm values significantly more negative that the initial Vm. Metric bars indicate standard deviation. For abbreviations see Figure 1.Since ion fluxes through channels directly influence Vm, it seems reasonable to assume that molecules able to act on channel activity might be considered as important factors inducing electrical signals. Among the various channels, calcium and potassium channels are predominantly involved in cell signaling.8 In the present study, rapid and reversible Vm depolarization observed upon perfusion of Lima bean mesophyll cells with polyamines was found to be significantly increased when JA was added to Cad and Put. The reversibility of the Vm may be linked to the overall physico-chemical amphiphilic properties of polyamines, probably depending on non covalent interaction with plasma membrane molecules, as polyamines occur in plants in free form, bound electrostatically to negatively charged molecules, and conjugated to small molecules and proteins.9 Liu et al.10 showed that Spm, Spd, Cad and Put strongly inhibited opening and closing of stomata in Vicia faba, suggesting that polyamines target inward potassium channels in guard cells and modulate stomatal movements, so providing a link between abiotic stress, polyamine levels and stomatal regulation. Moreover, the transport of polyamines across the plasma membrane of plant cells is energy-dependent and calcium is involved in the uptake mechanism.1,11 Both mechanisms can be correlated to the observed Vm depolarization, and the positive correlation between intracellular Ca2+ concentration5 and Vm depolarizing activity of polyamines confirms the involvement of Ca2+ during polyamine uptake.11 相似文献
70.
Manuela Grimaldi Mario Scrima Cinzia Esposito Anna Ramunno Gerardino D'Errico Anna Maria D'Ursi 《生物化学与生物物理学报:生物膜》2010,1798(3):660-1426
Aβ (16-35) is the hydrophobic central core of β-amyloid peptide, the main component of plaques found in the brain tissue of Alzheimer's disease patients. Depending on the conditions present, β-amyloid peptides undergo a conformational transition from random coil or α-helical monomers, to highly toxic β-sheet oligomers and aggregate fibrils. The behavior of β-amyloid peptide at plasma membrane level has been extensively investigated, and membrane charge has been proved to be a key factor modulating its conformational properties. In the present work we probed the conformational behavior of Aβ (16-35) in response to negative charge modifications of the micelle surface. CD and NMR conformational analyses were performed in negatively charged pure SDS micelles and in zwitterionic DPC micelles “doped” with small amounts of SDS. To analyze the tendency of Aβ (16-35) to interact with these micellar systems, we performed EPR experiments on three spin-labeled analogues of Aβ (16-35), bearing the methyl 3-(2,2,5,5-tetramethyl-1-oxypyrrolinyl) methanethiolsulfonate spin label at the N-terminus, in the middle of the sequence and at the C-terminus, respectively. Our conformational data show that, by varying the negative charge of the membrane, Aβ (16-35) undergoes a conformational transition from a soluble helical-kink-helical structure, to a U-turn shaped conformation that resembles protofibril models. 相似文献