全文获取类型
收费全文 | 201篇 |
免费 | 21篇 |
专业分类
222篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 10篇 |
2012年 | 26篇 |
2011年 | 13篇 |
2010年 | 14篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 10篇 |
2006年 | 7篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 15 毫秒
1.
A brief pulse of red light (R) given to darkgrown seedlings ofArabidopsis thaliana (L.) Heyn. potentiates rapid synthesis of chlorophyll upon transfer to continuous white light. The time course for potentiation
of rapid greening shows that a R pulse in the LF (low fluence) range has maximal effect within a few hours, and that there
is a small VLF (very low fluence) component as well. Partial reversal of the effect of R by far-red light (FR) indicates that
the pulse acts through phytochrome. As it does in the wild-type (WT), a pulse of R accelerates greening of long-hypocotyl
(hy) mutants. The extent of induction by the R pulse was about the same in the WT and in allhy mutants studied. Reversibility by FR was greatly decreased in thehy-1 andhy-2 strains. It is possible that these mutants contain a species of phytochrome with defective phototransformation kinetics.
If there is such a defective phytochrome species, it nevertheless appears to be active in the potentiation of rapid greening.
Dedicated to Professor Hans Mohr on the occasion of his 60th birthday 相似文献
2.
Characterization of DNA topoisomerase activity in two strains of Mycoplasma fermentans and in Mycoplasma pirum. 下载免费PDF全文
DNA topoisomerases (topos) are essential enzymes that participate in many cellular processes involving DNA. The presence of the DNA-gyrase genes in various mycoplasmas has been reported elsewhere. However, the characterization of DNA topo activity in mycoplasmas has not been previously undertaken. In this study, we characterized the topo activity in extracts of Mycoplasma fermentans K7 and incognitus and in Mycoplasma pirum, as well as in partially purified extract of M. fermentans K7. The topo activity in these microorganisms had the following properties. (i) The relaxation of supercoiled DNA was ATP dependent. (ii) ATP independent relaxation activity was not detected. (iii) Supercoiling of relaxed topoisomers was not observed. (iv) The relaxation activity was inhibited by DNA gyrase and topo IV antagonists (novobiocin and oxolinic acid) and by eukaryotic topo II (m-AMSA [4'-(9-acridylamino)methanesulfon-m-anisidide]) and topo I antagonists (camptothecin). Other eukaryotic topo II antagonists (teniposide and etoposide) did not affect the topo relaxation activity. (v) Two polypeptides of 66 and 180 kDa were found to be associated with the mycoplasma topo activity. These results suggest that the properties of the topo enzyme in these mycoplasma species resemble those of the bacterial topo IV and the eukaryotic and the bacteriophage T4 topo II. The findings that mycoplasma topo is inhibited by both eukaryotic topo II and topo I antagonists and that m-AMSA and camptothecin inhibited the growth of M. fermentans K7 in culture support our conclusion that these mycoplasma species have topo with unique properties. 相似文献
3.
Bovine ephemeral fever (BEF) is an economically important viral vector-borne cattle disease. Several live-attenuated, inactivated and recombinant vaccines have been tested, demonstrating varying efficacy. However, to the best of our knowledge, duration of immunity conferred by an inactivated vaccine has never been reported. In the last decade, Israel has faced an increasing number of BEF outbreaks. The need for an effective vaccine compatible with strains circulating in the Middle East region led to the development of a MONTANIDE™ ISA 206 VG (water-in-oil-in-water), inactivated vaccine based on a local strain. We tested the safety, immunogenicity and duration of immunity conferred by this vaccine. The induced neutralizing antibody (NA) response was followed for 493 days in 40 cows vaccinated by different protocols. The vaccine did not cause adverse reactions or a decrease in milk production. All cows [except 2 (6.7%) which did not respond to vaccination] showed a significant rise in NA titer of up to 1:256 following the second, third or fourth booster vaccination. Neutralizing antibody levels declined gradually to 1:16 up to 120 days post vaccination. This decline continued in cows vaccinated only twice, whereas cows vaccinated 3 or 4 times showed stable titers of approximately 1:16 for up to 267 days post vaccination. At least three vaccinations with the inactivated BEF vaccine were needed to confer long-lasting immunity. These results may have significant implications for the choice of vaccination protocol with inactivated BEF vaccines. Complementary challenge data should however be added to the above results in order to determine what is the minimal NA response conferring protection from clinical disease. 相似文献
4.
Lina Abu-Tair Sarit Doron Mahmud Mahamid Johnny Amer Rifaat Safadi 《Mitochondrion》2013,13(5):473-480
We investigated leptin effects on lymphocyte interactions with hepatic-stellate-cells (HSCs). Leptin showed pro-fibrotic effects on HSCs with oxidative status imbalance.In co-cultures, leptin activates HSCs and consequently adhered HCV-lymphocytes more than healthy ones. Leptin also increased healthy and HCV lymphocyte proliferations; increased their reactive-oxygen-species; decreased antioxidants (reduced-glutathione) levels while inhibited apoptosis only of HCV-lymphocytes. The leptin-treated HCV-lymphocytes activated HSCs, increase interleukin-4 while decreased their apoptosis.Leptin-receptor-deficient (db–db)-HSCs did not adhere lymphocytes. db/db-lymphocytes however showed fewer adherences to HSCs when compared to WT-counterparts.This study presents immune and oxidative modulatory effects of leptin on lymphocytes and their consequent interaction with HSCs. 相似文献
5.
Rob J. Van Geest Ingeborg Klaassen Sarit Y. Lesnik-Oberstein H. Stevie Tan Marco Mura Roel Goldschmeding Cornelis J. F. Van Noorden Reinier O. Schlingemann 《Journal of cell communication and signaling》2013,7(1):1-9
In proliferative diabetic retinopathy (PDR), vascular endothelial growth factor (VEGF) and CCN2 (connective tissue growth factor; CTGF) cause blindness by neovascularization and subsequent fibrosis. This angio-fibrotic switch is associated with a shift in the balance between vitreous levels of CCN2 and VEGF in the eye. Here, we investigated the possible involvement of other important mediators of fibrosis, tissue inhibitor of metalloproteinases (TIMP)-1 and transforming growth factor (TGF)-β2, and of the matrix metalloproteinases (MMP)-2 and MMP-9, in the natural course of PDR. TIMP-1, activated TGF-β2, CCN2 and VEGF levels were measured by ELISA in 78 vitreous samples of patients with PDR (n = 28), diabetic patients without PDR (n = 24), and patients with the diabetes-unrelated retinal conditions macular hole (n = 10) or macular pucker (n = 16), and were related to MMP-2 and MMP-9 activity on zymograms and to clinical data, including degree of intra-ocular neovascularization and fibrosis. TIMP-1, CCN2 and VEGF levels, but not activated TGF-β2 levels, were significantly increased in the vitreous of diabetic patients, with the highest levels in PDR patients. CCN2 and the CCN2/VEGF ratio were the strongest predictors of degree of fibrosis. In diabetic patients with or without PDR, activated TGF-β2 levels correlated with TIMP-1 levels, whereas in PDR patients, TIMP-1 levels, MMP-2 and proMMP-9 were associated with degree of neovascularization, like VEGF levels, but not with fibrosis. We confirm here our previous findings that retinal fibrosis in PDR patients is significantly correlated with vitreous CCN2 levels and the CCN2/VEGF ratio. In contrast, TIMP-1, MMP-2 and MMP-9 appear to have a role in the angiogenic phase rather than in the fibrotic phase of PDR. 相似文献
6.
Prasanna M. Chandramouleeswaran Dawen Shen Anna J. Lee Alain Benitez Kara Dods Fiona Gambanga Benjamin J. Wilkins Jamie Merves Yuliana Noah Sarit Toltzis Jennifer H. Yearley Jonathan M. Spergel Hiroshi Nakagawa Rene deWaal Malefyt Amanda B. Muir Mei-Lun Wang 《PloS one》2016,11(3)
Eosinophilic esophagitis (EoE) is a chronic Th2 and food antigen-mediated disease characterized by esophageal eosinophilic infiltration. Thymic stromal lymphopoetin (TSLP), an epithelial derived cytokine which bridges innate and Th2-type adaptive immune responses in other allergic conditions, is overexpressed in esophageal biopsies of EoE subjects. However, the triggers of TSLP expression in the esophageal epithelium are unknown. The objective of the current study was to characterize TSLP expression in human esophageal epithelium in EoE in vivo and to determine the role of food antigens upon epithelial TSLP expression in vitro. Using immunohistochemistry (IHC), we localized TSLP in esophageal biopsies of active EoE (≥15 eos/hpf), inactive EoE (<15 eos/hpf) and non-EoE control subjects, and found that TSLP expression was restricted to the differentiated suprabasal layer of the epithelium in actively inflamed EoE biopsies. Consistent with these results in vivo, inducible TSLP protein secretion was higher in CaCl2 differentiated telomerase-immortalized esophageal epithelial cells (EPC2-hTERT) compared to undifferentiated cells of the basal phenotype, following stimulation with the TLR3 ligand poly(I:C). To determine whether food antigens could directly induce epithelial TSLP secretion, differentiated and undifferentiated primary esophageal epithelial cells from EoE and non-EoE subjects were challenged with food antigens clinically relevant to EoE: Chicken egg ovalbumin (OVA), wheat, and milk proteins beta-lactoglobulin (blg) and beta-casein. Food antigens failed to induce TSLP secretion by undifferentiated cells; in contrast, only OVA induced TSLP secretion in differentiated epithelial cells from both EoE and control cell lines, an effect abolished by budesonide and NF-κb inhibition. Together, our study shows that specific food antigens can trigger innate immune mediated esophageal TSLP secretion, suggesting that esophageal epithelial cells at the barrier surface may play a significant role in the pathogenesis of EoE by regulating TSLP expression. 相似文献
7.
The C7-cyclitol 2-epi-5-epi-valiolone is the first precursor of the cyclitol moiety of the -glucosidase inhibitor acarbose in Actinoplanes sp. SE50. The 2-epi-5-epi-valiolone becomes phosphorylated at C7 by the ATP dependent kinase AcbM prior to the next modifications. Preliminary data gave evidences that the AcbO protein could catalyse the first modification step of 2-epi-5-epi-valiolone-7-phosphate. Therefore, the AcbO protein, the encoding gene of which is also part of the acbKMLNOC operon, was overproduced and purified. Indeed the purified protein catalysed the 2-epimerisation of 2-epi-5-epi-valiolone-7-phosphate. The chemical structure of the purified reaction product was proven by nuclear magnetic resonance spectroscopy to be 5-epi-valiolone-7-phosphate. 相似文献
8.
The mechanisms that regulate neuronal function are a sum of genetically determined programs and experience. The effect of
experience on neuronal function is particularly important during development, because early-life positive and adverse experience
(stress) may influence the still “plastic” nervous system long-term. Specifically, for hippocampal-mediated learning and memory
processes, acute stress may enhance synaptic efficacy and overall learning ability, and conversely, chronic or severe stress
has been shown to be detrimental. The mechanisms that enable stress to act as this “double-edged sword” are unclear. Here,
we discuss the molecular mediators of the stress response in the hippocampus with an emphasis on novel findings regarding
the role of the neuropeptide known as corticotropin-releasing hormone (CRH). We highlight the physiological and pathological
roles of this peptide in the developing hippocampus, and their relevance to the long-term effects of early-life experience
on cognitive function during adulthood. 相似文献
9.
Effect of Cetylpyridinium Chloride on Microbial Adhesion to Hexadecane and Polystyrene 总被引:1,自引:1,他引:1 下载免费PDF全文
Microbial adhesion at the oil-water interface is a subject of both basic interest (e.g., as a technique for the measurement of hydrophobicity) and applied interest (e.g., for use in two-phase oil-water mouthwashes for the desorption of oral microorganisms). In general, surfactants inhibit microbial adhesion to oils and other hydrophobic surfaces. In the present study, we demonstrated that the cationic surfactant cetylpyridinium chloride (CPC) significantly enhanced microbial adhesion to hexadecane and various oils, as well as to the solid hydrophobic surface polystyrene. CPC increased adhesion to hexadecane of Escherichia coli, Candida albicans and Acinetobacter calcoaceticus MR-481 and of expectorated oral bacteria from near 0% to over 90%. The CPC concentration required for optimal enhancement of adhesion was a function of the initial cell density. This phenomenon was inhibited by high salt concentrations and, in the case of E. coli, by a low pH. CPC-pretreated cells were able to bind to hexadecane, but CPC-pretreated hexadecane was unable to bind untreated cells. Another cationic, surface-active antimicrobial agent, chlorhexidine gluconate, was similarly able to promote microbial adhesion to hexadecane. The results suggest that (i) CPC enhances microbial adhesion to hexadecane by binding via electrostatic interactions at the cell surface, thus diminishing surface charge and increasing cell surface hydrophobicity, and (ii) this phenomenon may have applications in oral formulations and in the use of hydrocarbon droplets as a support for cell immobilization. 相似文献
10.
Eliahu Heldman Ayala Balan Ora Horowitz Sarit Ben-Zion Michael Torten 《FEBS letters》1985,180(2):243-248
Antiparaoxon immune sera were employed in a new immunoassay based on competition between acetylcholinesterase and antibodies for the binding ofparaoxon. Unlike radioimmunoassay, the new assay described herein can be extended to predict the feasibility of antibodies to confer in vivo protection of acetylcholinesterase against organophosphate poisoning. The toxicity of paraoxon was reduced in mice which were pre-injected with the immune sera. 相似文献