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   376篇
  免费   21篇
  国内免费   2篇
  2023年   6篇
  2022年   22篇
  2021年   30篇
  2020年   30篇
  2019年   52篇
  2018年   25篇
  2017年   17篇
  2016年   20篇
  2015年   22篇
  2014年   30篇
  2013年   36篇
  2012年   25篇
  2011年   27篇
  2010年   10篇
  2009年   8篇
  2008年   8篇
  2007年   11篇
  2006年   5篇
  2005年   5篇
  2004年   5篇
  2002年   2篇
  1999年   1篇
  1993年   1篇
  1988年   1篇
排序方式: 共有399条查询结果,搜索用时 31 毫秒
351.
The species of Adialytus Förster in Iran are taxonomically studied and new data on distribution and host associations are presented. The existence of a species complex, in the case of Adialytus ambiguus (Haliday), and the morphological variability in commonly used taxonomic characters has been discussed. In total, four valid species belonging to the genus Adialytus including Adialytus ambiguus (Haliday), Adialytus salicaphis (Fitch), Adialytus thelaxis (Starý) and Adialytus veronicaecola (Starý) have been identified and recorded from Iran. Also, we recognized two additional phenotypes: “Adialytus arvicola” (Starý) and “Adialytus cf. ambiguus” (Haliday). These phenotypes and Adialytus veronicaecola are newly recorded from Iran in association with Sipha and Aphis species, respectively. An illustrated key for identification of the species and two variable phenotypes is presented.  相似文献   
352.
Several techniques have been devised for the dissociation of tissues for primary culture. These techniques can affect the quantity and quality of the isolated cells. The aim of our study was to develop the most appropriate method for the isolation of human umbilical cord-derived mesenchymal (hUCM) cells. In the present study, we compared four methods for the isolation of hUCM cells: three enzymatic methods; collagenase/hyaluronidase/trypsin (CHT), collagenase/trypsin (CT) and trypsin (Trp), and an explant culture (Exp) method. The trypan blue dye exclusion test, the water-soluble tetrazolium salt-1 (WST-1) assay, flow cytometry, alkaline phosphatase activity and histochemical staining were used to evaluate the results of the different methods. The hUCM cells were successfully isolated by all methods but the isolation method used profoundly altered the cell number and proliferation capacity of the isolated cells. The cells were successfully differentiated into adipogenic and osteogenic lineages and alkaline phosphatase activity was detected in the hUCM cell colonies of all groups. Flow cytometry analysis revealed that CD44, CD73, CD90 and CD105 were expressed in all groups, while CD34 and CD45 were not expressed. The expression of C-kit in the enzymatic groups was higher than in the explant group, while the expression of Oct-4 was higher in the CT group compared to the other groups. We concluded that the collagenase/trypsin method of cell isolation yields a higher cell density than the others. These cells expressed a higher rate of pluripotent cell markers such as C-kit and Oct-4, while the explant method of cell isolation resulted in a higher cell proliferation rate and activity compared to the other methods.  相似文献   
353.
In a mechanical component, stress-concentration is one of the factors contributing to reduce fatigue life. This paper presents a design methodology based on shape optimization to improve the fatigue safety factor and increase the radial stiffness of Nitinol self-expandable stent-grafts. A planar lattice free of stress concentrators is proposed for the synthesis of a stent with smooth cell shapes. Design optimization is systematically applied to minimize the curvature and reduce the bending strain of the elements defining the lattice cells. A novel cell geometry with improved fatigue life and radial supportive force is introduced for Nitinol self-expandable stent-grafts used for treating abdominal aortic aneurism. A parametric study comparing the optimized stent-graft to recent stent designs demonstrates that the former exhibits a superior anchoring performance and a reduction of the risk of fatigue failure.  相似文献   
354.

Phytase is an important enzyme poses great nutritional significance in humans and monogastric animals diets. The phytase production yield using wild sources, including micro-organisms, plants, and animals is sorely low. Thus, recombinant expression of phytase has received increasing interest for achieving production rate. Escherichia coli is the most preferred host for expression of heterologous proteins but overexpression of recombinant phytase in E. coli, met with limited success due to the sequestration of the enzyme into inclusion bodies. In the present study, artificial phytases gene with excellent thermostability and activity were designed by detecting the enzymatic region of the E. coli phytase gene by employing bioinformatics tools. Then, the PCR amplified recombinant gene was expressed in E. coli and the active enzyme was recovered from inclusion bodies. Employing cysteine amino acid in the dialysis buffer succeed to the superior activity of the enzyme with a specific activity of 73.8 U/mg. The optimum temperature and pH for enzyme activity were determined at 60 °C and 4, respectively. The novel recombinant enzyme illustrated perfect thermostability up to 70 °C with maintenance 75% of its activity. The enzyme was stable at pH range of 2–10. Moreover, the effects of ions and chemical compounds on enzyme stability and activity were assessed.

  相似文献   
355.
In vivo tracking and monitoring of adoptive cell transfer has a distinct importance in cell‐based therapy. There are many imaging modalities for in vivo monitoring of biodistribution, viability and effectiveness of transferred cells. Some of these procedures are not applicable in the human body because of low sensitivity and high possibility of tissue damages. Shortwave infrared region (SWIR) imaging is a relatively new technique by which deep biological tissues can be potentially visualized with high resolution at cellular level. Indeed, scanning of the electromagnetic spectrum (beyond 1000 nm) of SWIR has a great potential to increase sensitivity and resolution of in vivo imaging for various human tissues. In this review, molecular imaging modalities used for monitoring of biodistribution and fate of administered cells with focusing on the application of non‐invasive optical imaging at shortwave infrared region are discussed in detail.  相似文献   
356.
Molecular Biology Reports - Inflammatory bowel disease (IBD) is considered a chronic inflammatory gastrointestinal disease with treatment options which exhibit low efficacies and lead to...  相似文献   
357.
Molecular Biology Reports - Flavonoids have been demonstrated to have the ability of sensitizing cancer cells to chemotherapy and inverse multidrug resistance via various mechanisms, such as...  相似文献   
358.

The changes in lipid peroxidation, H2O2, proline, protein, involvement of different antioxidant systems (catalase, guaiacol peroxidase, ascorbate peroxidase) and callus-related traits were investigated under salt stress in the callus of two different ploidy levels of Brassica including B. juncea and B. oleracea. The calluses of B. juncea genotypes were less sensitive to NaCl stress in comparison with those of B. oleracea while increasing the concentrations of NaCl from 0 to 200 mM. Tetraploid genotype (B. juncea cr3356) showed a significant increase in the contents of protein and proline, and guaiacol peroxidase activity and catalase enzymes at higher salinity levels. In addition, a significant decrease occurred in the amount of H2O2 and malondialdehyde along with increasing the salinity intensity. Diploid cultivar (B. oleracea bra 2828) had the lowest enzymatic activities and the highest content of H2O2 and malondialdehyde along with an increase in the salinity level. Therefore, this genotype was identified as the most sensitive cultivar under the salinity stress. The salinity resistance difference between diploid and amphidiploid species could be attributed to the differences in the ploidy level of these species. This result underlines the fact that the tetraploid genome of B. oleracea could be considered as a suitable candidate for production under salinity conditions through maintaining higher activities of antioxidant enzymes.

  相似文献   
359.
Angiogenesis, inflammation and endothelial cells’ migration and proliferation exert fundamental roles in different diseases. However, more studies are needed to identify key proteins and pathways involved in these processes. Aflibercept has received the approval of the US Food and Drug Administration (FDA) for the treatment of wet AMD and colorectal cancer. Moreover, the effect of Aflibercept on VEGFR2 downstream signalling pathways has not been investigated yet. Here, we integrated text mining data, protein-protein interaction networks and multi-experiment microarray data to specify candidate genes that are involved in VEGFA/VEGFR2 signalling pathways. Network analysis of candidate genes determined the importance of the nominated genes via different centrality parameters. Thereupon, several genes—with the highest centrality indexes—were recruited to investigate the impact of Aflibercept on their expression pattern in HUVEC cells. Real-time PCR was performed, and relative expression of the specific genes revealed that Aflibercept modulated angiogenic process by VEGF/PI3KA/AKT/mTOR axis, invasion by MMP14/MMP9 axis and inflammation-related angiogenesis by IL-6-STAT3 axis. Data showed Aflibercept simultaneously affected these processes and determined the nominated axes that had been affected by the drug. Furthermore, integrating the results of Aflibercept on expression of candidate genes with the current network analysis suggested that resistance against the Aflibercept effect is a plausible process in HUVEC cells.  相似文献   
360.
The combination of bioceramics and stem cells has attracted the interest of research community for bone tissue engineering applications. In the present study, a combination of Bio-Oss® and type 1 collagen gel as scaffold were loaded with human adipose-tissue derived mesenchymal stem cells (AT-MSCs) after isolation and characterization, and the capacity of them for bone regeneration was investigated in rat critical size defects using digital mammography, multi-slice spiral computed tomography imaging and histological analysis. 8 weeks after implantation, no mortality or sign of inflammation was observed in the site of defect. According to the results of imaging analysis, a higher level of bone regeneration was observed in the rats receiving Bio-Oss®-Gel compared to untreated group. In addition, MSC-seeded Bio-Oss-Gel induced the highest bone reconstruction among all groups. Histological staining confirmed these findings and impressive osseointegration was observed in MSC-seeded Bio-Oss-Gel compared with Bio-Oss-Gel. On the whole, it was demonstrated that combination of AT-MSCs, Bio-Oss and Gel synergistically enhanced bone regeneration and reconstruction and also could serve as an appropriate structure to bone regenerative medicine and tissue engineering application.  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