首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   372篇
  免费   8篇
  国内免费   1篇
  2023年   2篇
  2022年   3篇
  2021年   10篇
  2020年   5篇
  2019年   9篇
  2018年   10篇
  2017年   11篇
  2016年   11篇
  2015年   11篇
  2014年   23篇
  2013年   27篇
  2012年   33篇
  2011年   28篇
  2010年   20篇
  2009年   12篇
  2008年   21篇
  2007年   21篇
  2006年   20篇
  2005年   25篇
  2004年   17篇
  2003年   36篇
  2002年   12篇
  2001年   3篇
  2000年   1篇
  1998年   3篇
  1997年   1篇
  1996年   3篇
  1990年   1篇
  1977年   1篇
  1976年   1篇
排序方式: 共有381条查询结果,搜索用时 78 毫秒
81.
Parkinson's disease (PD) is a neurodegenerative disease caused by the loss of dopaminergic neurons in the substantia nigra. Cell‐replacement therapies have emerged as a promising strategy to slow down or replace neuronal loss. Compared to other stem cell types, endometrium‐derived stem cells (EDSCs) are an attractive source of stem cells for cellular therapies because of their ease of collection and vast differentiation potential. Here we demonstrate that endometrium‐derived stem cells may be transplanted into an MPTP exposed monkey model of PD. After injection into the striatum, endometrium‐derived stem cells engrafted, exhibited neuron‐like morphology, expressed tyrosine hydroxylase (TH) and increased the numbers of TH positive cells on the transplanted side and dopamine metabolite concentrations in vivo. Our results suggest that endometrium‐derived stem cells may provide a therapeutic benefit in the primate model of PD and may be used in stem cell based therapies.  相似文献   
82.
83.
FGFs 19, 21, and 23 are hormones that regulate in a Klotho co-receptor-dependent fashion major metabolic processes such as glucose and lipid metabolism (FGF21) and phosphate and vitamin D homeostasis (FGF23). The role of heparan sulfate glycosaminoglycan in the formation of the cell surface signaling complex of endocrine FGFs has remained unclear. Here we show that heparan sulfate is not a component of the signal transduction unit of FGF19 and FGF23. In support of our model, we convert a paracrine FGF into an endocrine ligand by diminishing heparan sulfate-binding affinity of the paracrine FGF and substituting its C-terminal tail for that of an endocrine FGF containing the Klotho co-receptor-binding site to home the ligand into the target tissue. In addition to serving as a proof of concept, the ligand conversion provides a novel strategy for engineering endocrine FGF-like molecules for the treatment of metabolic disorders, including global epidemics such as type 2 diabetes and obesity.  相似文献   
84.
85.
Caulerpa racemosa (Forsskål) is a green marine alga which spreads from tropical to warm-water regions. Due to having invasive capacity C. racemosa var. cylindracea is a well-known biological pollution in Mediterranean Sea. One of the most important secondary metabolites of C. racemosa is Caulerpenyne (CPN). In the present study, antiproliferative and apoptotic effects of C. racemosa var. cylindracea extract and purified CPN on two well-known neuroblastoma cell lines, SHSY5Y and Kelly, are investigated. The antiproliferative and, additionally, newly attributed apoptotic effects of both C. racemosa var. cylindracea extract and purified CPN on SHSY5Y and Kelly cell lines have been shown in the present study. IC50 values are 0.59 ± 0.06; 1.06 ± 0.23 g wet alga/methanol and 5.64 ± 0.09; 6.02 ± 0.09 μM CPN for C. racemosa var. cylindracea extract and purified CPN on SHSY5Y and Kelly cell lines, respectively. Percentages of apoptotic cells of SHSY5Y and Kelly in 0, 0.1 and 1 μM CPN conditions were 1.00 ± 0.71, 3.00 ± 0.71 and 49.40 ± 3.78, 39.60 ± 6.19 and 78.00 ± 2.74, 69.40 ± 3.78, respectively. In conclusion, the present study shows the antiproliferative effect of C. racemosa var. cylindracea extract and newly attributed apoptotic effects of C. racemosa var. cylindracea this extract. Compared to other alkylating anticancer drugs, CPN and also C. racemosa var. cylindracea extract might be considered as an alternative native source of antitumor drugs. Inasmuch as both C. racemosa extract and CPN have shown both antiproliferative and apoptotic effects on SHSY5Y and Kelly cell lines, the CPN and CPN derivatives might be considered as multifunctional agents in cell metabolism.  相似文献   
86.
Methotrexate (MTX), a folic acid antagonist, is widely used as a cytotoxic chemotherapeutic agent. MTX-associated neurotoxicity is an important clinical problem. The aim of this study was to investigate the role of caffeic acid phenethyl ester (CAPE) on cerebellar oxidative stress induced by MTX in rats. A total of 19 adult male rats were divided into three experimental groups as follows: MTX group (MTX treated), MTX+CAPE group (MTX+CAPE treated), and control group. MTX was administered intraperitoneally (i.p.) with a single dose of 20 mg kg−1 on the second day of experiment. CAPE was administered i.p. with a dose of 10 μmol kg−1 day−1 for 7 days. Malondialdehyde (MDA) levels and activities of superoxide dismutase (SOD) and catalase (CAT) were determined in cerebellar tissue of rats. MTX caused to significant increase in MDA levels (an important marker of lipid peroxidation) in the MTX group compared with the controls (p = 0.006). CAPE significantly reduced the MTX induced lipid peroxidation in the MTX+CAPE group compared to the MTX (p = 0.007). The activities of SOD and CAT were significantly increased in the MTX group when compared with the control group (p = 0.0001, p = 0.004, respectively). The increased activities of these enzymes were significantly reduced by CAPE treatment (p = 0.004, p = 0.034, respectively). As a result, CAPE may protect from oxidative damage caused by MTX treatment in rat cerebellum.  相似文献   
87.
The objective of this study was to prepare new calix[n]arene-based silica polymers for immobilization of Candida rugosa lipase. The amino functionalized calix[4]arene (C4P), calix[6]arene (C6P) and calix[8]arene (C8P)-based silica polymers were used for the covalent attachment of C. rugosa lipase using glutaraldehyde as a coupling agent. The characterization of synthesized CnP polymers and immobilized lipases were made by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and scanning electron microscope (SEM) techniques. The hydrolytic activities of immobilized lipases (CnP-L) were evaluated and compared with the free enzyme. The activity recovery of immobilized CRL (C. rugosa lipase) based on the carrier C4P, C6P and C8P reaches 74.6%, 68.5% and 51.4%, respectively. The optimal pH and temperature region of the immobilized lipases for the hydrolysis of p-NPP were 7.0 and 50 °C. Nevertheless, the immobilized lipase has good stability, adaptability and reusability in comparison with the free enzyme.  相似文献   
88.
89.
By design, structural genomics (SG) solves many structures that cannot be assigned function based on homology to known proteins. Alternative function annotation methods are therefore needed and this study focuses on function prediction with three-dimensional (3D) templates: small structural motifs built of just a few functionally critical residues. Although experimentally proven functional residues are scarce, we show here that Evolutionary Trace (ET) rankings of residue importance are sufficient to build 3D templates, match them, and then assign Gene Ontology (GO) functions in enzymes and non-enzymes alike. In a high-specificity mode, this Evolutionary Trace Annotation (ETA) method covered half (53%) of the 2384 annotated SG protein controls. Three-quarters (76%) of predictions were both correct and complete. The positive predictive value for all GO depths (all-depth PPV) was 84%, and it rose to 94% over GO depths 1-3 (depth 3 PPV). In a high-sensitivity mode, coverage rose significantly (84%), while accuracy fell moderately: 68% of predictions were both correct and complete, all-depth PPV was 75%, and depth 3 PPV was 86%. These data concur with prior mutational experiments showing that ET rank information identifies key functional determinants in proteins. In practice, ETA predicted functions in 42% of 3461 unannotated SG proteins. In 529 cases—including 280 non-enzymes and 21 for metal ion ligands—the expected accuracy is 84% at any GO depth and 94% down to GO depth 3, while for the remaining 931 the expected accuracies are 60% and 71%, respectively. Thus, local structural comparisons of evolutionarily important residues can help decipher protein functions to known reliability levels and without prior assumption on functional mechanisms. ETA is available at http://mammoth.bcm.tmc.edu/eta.  相似文献   
90.
The present study was carried out to determine interactive and comparative effects of salinity and water stress on growth, proline accumulation, chlorophyll, carotenoid and macro nutrient content and antioxidative enzymes such as superoxide dismutase (SOD), guaiacol peroxidase (POX), and polyphenol oxidase (PPO) in hydroponically grown maize (Zea mays L.cv DKC647) plants. Plants were treated two salt (NaCl) concentrations and polyethylene glycol 6000 (PEG 6000) to create water stress. The results obtained from this experiment show that high salinity reduced growth through decreasing shoot and root dry and fresh weight, chlorophyll, and carotenoid content, but PEG treatment had no significant effect on this parameters. Under NaCl and PEG 6000 treatment, uptake and translocation of mineral nutrients changed drastically. The high presence of Na+ in nutrient solution affected considerably the plant nutritional requirement, especially influencing the uptake of Ca2+ and K+, which were restricted for competition. Proline accumulation, and SOD, POX and PPO activities were increased with the increasing intensity of NaCl stress, but PEG 6000 treatment in addition to NaCl had more significant effect on this enzyme activities. These results suggest that maize plants may be increased proline content to maintain osmotic adjustment and increased the activity of antioxidant enzymes to have a better protection against active oxygen species (AOS) under salt and water stress.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号