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   1927篇
  免费   16篇
  1943篇
  2024年   17篇
  2023年   38篇
  2022年   21篇
  2021年   43篇
  2020年   37篇
  2019年   31篇
  2018年   79篇
  2017年   73篇
  2016年   92篇
  2015年   49篇
  2014年   65篇
  2013年   124篇
  2012年   141篇
  2011年   143篇
  2010年   89篇
  2009年   56篇
  2008年   96篇
  2007年   120篇
  2006年   99篇
  2005年   93篇
  2004年   87篇
  2003年   95篇
  2002年   86篇
  2001年   30篇
  2000年   45篇
  1999年   18篇
  1998年   8篇
  1997年   5篇
  1996年   3篇
  1995年   2篇
  1994年   4篇
  1992年   2篇
  1991年   2篇
  1984年   2篇
  1983年   2篇
  1982年   2篇
  1978年   2篇
  1975年   7篇
  1974年   3篇
  1973年   4篇
  1972年   2篇
  1971年   3篇
  1969年   2篇
  1968年   1篇
  1967年   2篇
  1966年   2篇
  1965年   1篇
  1964年   2篇
  1959年   1篇
  1933年   1篇
排序方式: 共有1943条查询结果,搜索用时 0 毫秒
1.
Plantago is the most important genus of Plantaginaceae family and is used in traditional medicine around the world for different purposes. Plantago coronopus L., Plantago major L., Plantago media L. and Plantago lanceolata L. are most commonly used species of Plantago in traditional medicine in Turkey. The main goal of this study was to investigate the eventual anti-mitotic and anti-genotoxic effects of P. lanceolata L. leaf aqueous extracts (15 g/L and 30 g/L) on Allium cepa L. root tip meristem cells which were treated with 0.7% hydrogen peroxide. For this purpose, two different experiments were performed under the same conditions. In the first experiment, Allium cepa onion bulbs were treated with 0.7% H2O2 for 1 h. After the H2O2 treatment, the onion bulbs were treated with two different concentrations (15 g/L and 30 g/L) of P. lanceolata extracts for 24 h. In the second experiment, A. cepa onion bulbs were treated with two different extract concentrations (15 g/L and 30 g/L) for 24 h and then with 0.7% H2O2 for 1 h. The test concentrations were determined according to doses which are recommended in alternative medicinal usage by people. As positive and negative control 0.7% H2O2 and tap water was used, respectively. As a result, it was determined that aqueous extracts reduced mitotic index and chromosome aberrations in treatment groups in comparison with controls. These results showed that P. lanceolata aqueous extracts have anti-mitotic and anti-genotoxic effects.  相似文献   
2.
Hyperhydricity can cause significant loss in the in vitro propagated plantlets. In order to predict and control its occurrence, a better understanding of the structural aspects and physiological features of hyperhydric plantlets is required. In this study, the ultrastructural and physiological changes associated with hyperhydric red beet plantlets were investigated. Our objective was to establish a correlation between the ultrastructural aspects of Beta vulgaris var. Conditiva leaflets and hypocotyls and the content of chlorophyll pigments extracted in N,N-dimethylformamide (DMF) of two type of plantlets: hyperhydric from a basal culture medium Murashige and Skoog (JAMA 15:473–497, 1962) prepared with distilled water (DW—155 ppm Deuterium) and non-hyperhydric, cultivated on identical medium where distilled water was replaced with deuterium depleted water (DDW- 25 ppm Deuterium) as a method of preventing hyperhydricity. Cell ultrastructure in hyperhydricity, both from the leaves, but especially from hypocotyls, showed denatured chloroplasts in a myxoplasm mass formed by the damage of the tonoplast and the mixing of the cytoplasm with the vacuolar juice. The nuclei were picnotic, presenting paranucleolar corpuscles. The amount of assimilating pigments was significantly reduced in the plantlets grown on medium prepared with DW as compared to the normal, non-hyperhydric ones from medium prepared with DDW. Both evaluations showed that, in red beet, DDW also prevents the appearance of hyperhydricity.  相似文献   
3.
4.
A new enzymatic method has been developed to determine trace amounts of Zn2+ in vegetables. The basis of the method is that apocarbonic anhydrase regains its activity in proportion to the concentration of Zn2+ present in solution. Bovine carbonic anhydrase was purified from erythrocyte haemolysate by affinity chromatography and the bound Zn2+ removed by dialysis of purified enzyme against a solution of pyridine-2, 6-dicarboxylic acid. Pure (100%) apoenzyme was obtained. The concentration of Zn2+ in vegetable samples was determined using the enzymatic method and by atomic absorption spectroscopy. Determinations made using the two methods were not significantly different one from another.  相似文献   
5.
The aim of this study is to develop magnetically loaded nanosorbents carrying specific monoclonal antibodies (namely CD105 and CD73) for separation of mesenchymal stem cells from cell suspensions. Super-paramagnetic magnetite (Fe3O4) nanoparticles were produced and then coated with a polymer layer containing carboxylic acid functional groups (average diameter: 153 nm and polydispersity index: 0.229). In order to obtain the nanosorbents, the monoclonal antibodies were immobilized via these functional groups with quite high coupling efficiencies up to 80%. These nanosorbents and also a commercially available one (i.e., microbeads carrying CD105 antibodies from Miltenyi Biotec., Germany) were used for separation of CD105+ and CD73+ mesenchymal stem cells from model cell suspension composed of peripheral blood (97.6%), human bone marrow cells (1.2%) and fibroblastic cells (1.2%). The initial concentrations of the CD105+ and CD73+ cells in this suspension were measured as 5.86% and 6.56%, respectively. A flow-through separation system and a very simple homemade batch separator unit were used. We were able to increase the concentration of CD105+ cells up to about 86% in the flow-through separation system with the nanosorbents produced in this study, which was even significantly better than the commercial one. The separation efficiencies were also very high, especially for the CD73+ cells (reached to about 64%) with the very simple and inexpensive homemade batch unit.  相似文献   
6.
    
Interferons are important proteins for the immune system because of their antiviral, anti‐proliferating and immunomodulatory activities. Therapeutic value of these proteins against certain types of tumors caused interest and investigations aimed to obtain highly purified interferons. Molecular imprinting is an efficient method for purification with high selectivity, specificity and good reproducibility. In this study, we utilized advantages of molecular imprinting technique for the purification of interferon from human gingival fibroblast culture. For this purpose, interferon α‐2b imprinted poly(hydroxyethyl methacrylate) cryogel (hIFN‐α‐MIP) was prepared. Optimum adsorption conditions were determined, and maximum adsorption capacity of hIFN‐α‐MIP cryogel was found as 254.8 × 104 IU/g from aqueous solution. All interferon measurements are expressed as International Unit (IU), which is a unit measurement used to quantify biologically active substances like interferon based on their biological activity or effect. Selectivity experiments were performed using competitive proteins and repeated adsorption–desorption studies showed that the adsorption capacity maintained almost at a constant value after ten cycles. For the purification of interferon from human gingival fibroblast culture, fast protein liquid chromatography was used and the specific activity of the purified interferon α‐2b on HeLa cell line was found between the values 3.45 × 108 IU/mg and 3.75 × 108 IU/mg. The results are promising, and the molecular imprinting technique is effective for the purification of interferon α‐2b. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
7.
    
Abstract

Purpose/Aim: There have been conflicting results regarding which muscle contribute most to the elbow spastic flexion deformity. This study aimed to investigate whether flexor spasticity of the elbow changed according to the position of the forearm, and to determine the muscle or muscles that contributed most to the elbow spastic flexion deformity by clinical examination.

Methods: This study is a single group, observational and cross-sectional study. Sixty patients were assessed for elbow flexor spasticity in different forearm positions (pronation, neutral and supination) with Modified Tardieu Scale. The primary outcome measure was a domain of the Modified Tardieu Scale, the dynamic component of spasticity (spasticity angle).

Results: In general, there was a significant difference between forearm positions regarding spasticity angle (p?<?.001). In pairwise comparisons, median spasticity angles in pronation (70 degrees) and neutral position (60 degrees) were significantly higher than those in supination (57.5 degrees) (adjusted p?<?.001 and adjusted p?=?.003, respectively). However, median spasticity angle in pronation did not differ significantly from those in neutral position in favour of pronation (adjusted p?=?.274).

Conclusions: The severity of spasticity changes according to the elbow position which suggests that the magnitude of contribution of each elbow flexor muscle to spastic elbow deformity is different. Reduction of spasticity from pronation to supination leads us to consider brachialis as the most spastic muscle. Since biceps was suggested to be the least spastic muscle in this study, and also to avoid spastic pronation deformity of the forearm, it should be rethought before performing chemodenervation into biceps muscle.  相似文献   
8.
9.
10.
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