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   508篇
  免费   39篇
  2023年   8篇
  2022年   21篇
  2021年   32篇
  2020年   28篇
  2019年   52篇
  2018年   33篇
  2017年   23篇
  2016年   36篇
  2015年   34篇
  2014年   36篇
  2013年   49篇
  2012年   41篇
  2011年   36篇
  2010年   24篇
  2009年   21篇
  2008年   8篇
  2007年   15篇
  2006年   14篇
  2005年   8篇
  2004年   12篇
  2003年   5篇
  2002年   3篇
  2001年   1篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1991年   1篇
  1981年   1篇
  1980年   1篇
  1977年   1篇
排序方式: 共有547条查询结果,搜索用时 31 毫秒
121.
Sodium benzoate (SB) is a widely used preservative and antimicrobial substance in many foods and soft drinks. However, this compound is generally recognized as safe food additives, but evidence has suggested that a high intake of SB may link to attention deficit‐hyperactivity disorder in children. Present study investigate the effects of oral administration of different concentrations of SB (0.56, 1.125, and 2.25 mg/mL) for 4 weeks, on the learning and memory performance tests, and also the levels of malondialdehyde (MDA), reduced glutathione (GSH), and acetylcholinesterase activity (AChE) in the mouse brain. The results showed that SB significantly impaired memory and motor coordination. Moreover, SB decreased reduced GSH and increased the MDA level in the brain significantly (P < 0.001). However, nonsignificant alteration was observed in the AChE activity. These findings suggest that short‐term consumption of SB can impair memory performance and increased brain oxidative stress in mice.  相似文献   
122.
Strong 14-3-3 zeta protein expression plays an important role in tumorigenesis, including in the maintenance of cell growth, resistance increase, and the prevention of apoptosis. In this study, we focus on two targets: (1) the expression of 14-3-3 zeta in the different grades of human astrocytoma (II–IV), (2) suppression of 14-3-3 zeta protein expression in glioblastoma derived astrocytes by 14-3-3 zeta shRNA lentiviral particles. The tissues of human astrocytoma were provided from 30 patients (ten of each grade of astrocytoma). Control tissues were obtained from the peritumoral brain zone of those patients with glioblastoma. The protein and mRNA expression levels of each astrocytoma grade were assessed via western blotting and RT-PCR, respectively. Results indicated that 14-3-3 zeta was significantly expressed in glioblastoma multiforme (grade IV) and 14-3-3 zeta expression levels enhanced according to the increase of astrocytoma malignancy. In the cellular study for knock down of the 14-3-3 zeta protein, surgical biopsy of glioblastoma was used to isolate primary astrocyte. Astrocytes were transduced with 14-3-3 zeta shRNA or non-targeted shRNA lentiviral particles. Furthermore, reduction of the 14-3-3 zeta protein expression in the astrocytes evaluated through qRT-PCR and western blot after transduction of 14-3-3 zeta shRNA lentiviral particles. Moreover, apoptosis properties, including DNA fragmentation and ratio increase of Bax/Bcl-2 were observed in astrocytes following reduction of 14-3-3 zeta protein expression. Further observation indicated that the mitochondrial pathway through release of cytochorome c and caspase-3 activity was involved in the apoptosis induction. Hence, this study demonstrates a key role of the 14-3-3 zeta protein in tumorigenesis but also indicates that 14-3-3 zeta can be considered as a target for the astrocytoma treatment specially glioblastoma.  相似文献   
123.
In this study, application of response surface methodology for enzymic pretreatment optimization of Gelidiella acerosa was investigated in order to improve the extraction of algal proteins using Viscozyme L and Celluclast 1.5L. The total protein, soluble proteins and reducing sugar recovery in the water‐soluble fraction were studied in relation to the hydrolysis time, type and concentration of the enzymes. Enzymatic digestion appeared to be an effective treatment for protein extraction. While enzyme hydrolysis by Celluclast 1.5L was able to facilitate the protein extraction, it was a relatively inefficient way to improve protein extraction yield, in comparison with Viscozyme L. The optimum conditions for protein extraction was found to be hydrolysis by 2.8 μL mL?1 of Viscozyme L for 12 h.  相似文献   
124.
Recently, bacterial cellulose (BC) based wound dressing have raised significant interests in medical fields. However, to our best knowledge, it is apparent that the BC itself has no antibacterial activity. In this study, we optimized graphene oxide‐silver (GO‐Ag) nanohybrid synthesis using Response Surface Methodology and impregnate it to BC and carefully investigate their antibacterial activities against both the Gram‐negative bacteria Escherichia coli and the Gram‐positive bacteria Staphylococcus aureus. We discover that, compared to silver nanoparticles, GO‐Ag nanohybrid with an optimal GO suspension's pH and ratio is much more effective and shows synergistically enhanced, strong antibacterial activities at rather low dose. The GO‐Ag nanohybrid is more toxic to E. coli than that to S. aureus. The antibacterial and mechanical properties of BC/GO‐Ag composite are further investigated.  相似文献   
125.
126.
127.
Stem cells (SCs) are classes of undifferentiated biological cells existing only at the embryonic, fetal, and adult stages that can divide to produce specialized cell types during fetal development and remain in our bodies throughout life. The progression of regenerative and reproductive medicine owes the advancement of respective in vitro and in vivo biological science on the stem cell nature under appropriate conditions. The SCs are promising therapeutic tools to treat currently of infertility because of wide sources and high potency to differentiate. Nevertheless, no effective remedies are available to deal with severe infertility due to congenital or gonadotoxic stem cell deficiency in prepubertal childhood. Some recent solutions have been developed to address the severe fertility problems, including in vitro formation of germ cells from stem cells, induction of pluripotency from somatic cells, and production of patient‐specific pluripotent stem cells. There is a possibility of fertility restoration using the in vitro formation of germ cells from somatic cells. Accordingly, the present review aimed at studying the literature published on the medical application of stem cells in reproductive concerns.  相似文献   
128.
Type and concentration of edible components, are two main factors which can be affected the chemical, microbial, quality, sensory properties and storage life of coated cheese. In this work, to optimize the concentrations of chitosan and Natamycin for coating Iranian white UF cheese response surface methodology was used. The effects of main edible coating components, chitosan (0.5–2.5%, w/w) and Natamycin (5–20 ppm) on pH, TSS, bacterial total count, yeast and mould population and starter of coated cheese were studied up to 3 weeks after storage at 4?±?2 °C. The obtained results indicated that the second-order polynomial models could be successfully generated with high coefficient of determination (R2?≥?0.9153) using experimental data for all the studied response variables. The optimum concentrations of chitosan and Natamycin were obtained at 1.6% w/w and 18.5 ppm, respectively which the predicted values for pH, TSS, bacterial total count, yeast and mould population and starter were 4.5, 37%, 12 cfu, 14 cfu and 346 cfu, respectively. The verification test was done at obtained optimum concentrations of the main edible components and the statistical analysis indicated insignificant (p?>?0.05) differences between the predicted and experimental values of the response variables.  相似文献   
129.
A localized surface plasmon resonance immunoassay has been developed to determine prolactin hormone in human serum samples. Gold nanoparticles were synthesized, and the probe was prepared by electrostatic adsorption of antibody on the surfaces of gold nanoparticles. The pH and the antibody-to-gold nanoparticle ratio, as the factors affecting the probe functions, were optimized. The constructed nanobiosensor was characterized by dynamic light scattering. The sensor was applied for the determination of prolactin antigen concentration based on the amount of localized surface plasmon resonance peak shift. A linear dynamic range of 1–40 ng ml−1, a detection limit of 0.8 ng ml−1, and sensitivity of 10 pg ml−1 were obtained. Finally, the nanobiosensor was applied for the determination of prolactin in human control serum sample.  相似文献   
130.
Gold and silver nanoparticles (NPs) are shown to exert a positive effect on the chemiluminescence (CL) reaction of permanganate aldehydes. Interestingly, between various shapes examined, Au nanoprisms have the highest beneficial effect. This effect is even more notable in the presence of sodium dodecyl sulfate (SDS) surfactant. UV‐vis spectra and transmission electron microscopy were used to characterize the NP shapes and sizes. Furthermore, it was observed that iron(III) ions can slightly increase CL emission of this system. This intensification is very effective in the presence of fluoride ions (F). These observations form the basis of the method for the high sensitive determination of F in the 6–1200 nmol L–1 concentration range, with a detection limit of 2.1 nmol L–1. The proposed method has good precision and was satisfactorily used in the selective determination of low concentrations of fluoride ion in real samples. Copyright © 2015 John Wiley & Sons, Ltd.  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