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   417篇
  免费   24篇
  2023年   6篇
  2022年   12篇
  2021年   32篇
  2020年   33篇
  2019年   60篇
  2018年   27篇
  2017年   20篇
  2016年   27篇
  2015年   31篇
  2014年   25篇
  2013年   42篇
  2012年   34篇
  2011年   34篇
  2010年   9篇
  2009年   10篇
  2008年   10篇
  2007年   3篇
  2006年   8篇
  2005年   2篇
  2004年   6篇
  2003年   1篇
  2002年   3篇
  2001年   1篇
  2000年   1篇
  1998年   1篇
  1996年   2篇
  1994年   1篇
排序方式: 共有441条查询结果,搜索用时 890 毫秒
81.
The biological evaluation of a new synthesized Pt(II)-complex, 2,2'-bipyridin Butylglycinato Pt(II) nitrate, an anti-tumor component, was studied at different temperatures by fluorescence and far UV circular dichroism (CD) spectroscopic methods. Human serum albumin (HSA) and human tumor cell line K562 were as targets. The Pt(II)-complex has a strong ability to quench the intrinsic fluorescence of HSA. Binding and thermodynamic parameters of the interaction were calculated by fluorescence quenching method. Far-UV-CD results showed that Pt(II)-complex induced increasing in content of α helical structure of the protein and stabilized it. The 50% cytotoxic concentration (Cc(50)) of complex was determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay at different incubation times. Also, fluorescence staining with DAPI (4,6-diamidino-2-phenylindole) revealed some typical nuclear changes, which are characteristic of apoptosis. Above results suggest that Pt (II) complex is a promising anti-proliferative agent and should execute its biological effects by inducing apoptosis.  相似文献   
82.
A series of novel copper(II) complexes, L2Cu with newly synthesized 3,5--salicylaldimine (or 5--salicylaldimine) ligands derived from 2,4-di-tert-butyl phenol (or 4-tert-butyl phenol) and alkyl (aryl) amines have been prepared and their spectroscopic (IR, UV-Vis, ESI-MS), X-ray, magnetic and redox properties have been investigated. The X-ray crystallography analysis shows that all complexes are monomeric and their copper(II) centers are surrounded by phenolate oxygens and imine nitrogen atoms. Therefore, the coordination sphere around the copper atoms is N2O2 as seen in galactose oxidase active site. In addition, the geometric configurations of all complexes are square planar or slightly distorted square planar. The crystal system for all complexes is monoclinic, except for which is orthorhombic. The temperature dependence of magnetic susceptibility of complexes confirms the mononuclear structure of complexes. Oxidation of the Cu(II) complexes yielded the corresponding Cu(II)-phenoxyl radical species during the cyclic voltammetry experiments.  相似文献   
83.
Olfactory learning may allow insects to forage optimally by more efficiently finding and using favourable food sources. Although olfactory learning has been shown in bees, insect herbivores and parasitoids, there are fewer examples from polyphagous predators. In this study, olfactory learning by a predatory coccinellid beetle is reported for the first time. In laboratory trials, adults of the aphidophagous ladybird Coccinella septempunctata did not prefer the odour of one aphid-infested barley cultivar over another. However, after feeding on aphids for 24 h on a cultivar, they preferred the odour of that particular cultivar. The mechanism appeared to be associative learning rather than sensitisation. Although inexperienced ladybirds preferred the odour of an aphid-infested barley cultivar over uninfested plants of the same cultivar, after feeding experience on a different cultivar this preference disappeared. This may indicate the acquisition and replacement of olfactory templates. The odour blends of the different aphid-infested barley cultivars varied qualitatively and quantitatively, providing a potential basis for olfactory discrimination by the ladybird. The results show that predatory coccinellids can learn to associate the odour of aphid-infested plants with the presence of prey, and that this olfactory learning ability is sensitive enough to discriminate variability between different genotypes of the same plant.  相似文献   
84.
Forty heifers at the late stage of gestation were randomly assigned into five groups. Heifers were balanced for age, weight, and time of calving in each group. Four and 2?weeks before expected time of calving, the heifers were injected with 0?ml (C), 10?ml (T1), 20?ml (T2), 30?ml (T3), and 40?ml (T4) Se and VE supplements, respectively. Each milliliter of the supplement contained of 0.5?mg Se as sodium selenite and 50?IU of dl-alpha-tocopheryl acetate. Blood samples were collected from the heifers 4?weeks before expected calving and at calving day and from the calves at birth and 7?days of age. The serum Se and immunoglobulin G (IgG) concentrations, white blood cell and differential leukocyte counts were measured. The Se concentrations in the sera of the heifers before the injections of Se and VE supplements were the same among the groups (P?>?0.05), but after calving were significantly increased in the treated heifers (P??0.05). The white blood cell counts were higher in calves of heifers in groups T3 and T4 compared with the control group at 7?days of age (P?相似文献   
85.
The aim of this study was to confirm if there is a link between the alteration in blood levels of trace elements (chromium, copper, lead, cadmium, and zinc) and dehydroepiandrosterone sulfate (DHEAS) in healthy and diabetic states. This study is the first study to test these parameters in Egyptians. The study included 150 subjects divided into the following four groups: healthy middle-aged, healthy elderly, middle-aged diabetics, and elderly diabetics. Our results revealed a statistically significant decrease in the level of DHEAS in the elderly compared to middle-aged healthy and diabetic groups (p < 0.05). There was a significant difference between the middle-aged groups with respect to zinc, copper, chromium, and cadmium levels. Zinc and copper were lower in the diabetic subjects while chromium and cadmium were higher in the same group in comparison to healthy subjects. In the elderly groups, there were significant increases in chromium and cadmium levels in diabetic subjects rather than healthy ones. There was a significant increase in the thiobarbituric acid reactive substance level in the elderly healthy and diabetic groups and a significant decrease in the glutathione level in the elderly groups. There was no correlation between the levels of trace elements and DHEAS or between the levels of DHEAS, oxidants, and antioxidants in all of the tested groups. In conclusion, only the DHEAS level was correlated with age. There was no difference between the diabetic and healthy groups with respect to the levels of trace elements, with the exception of chromium and cadmium, which suggests the effect of pollution on the pathogenesis of diabetes in Egyptians. No correlation existed between the levels of DHEAS and trace elements, oxidants, and antioxidants. Finally, we believe that there is a large regional variation in the levels of trace elements due to different environmental exposure and nutritional factors which are responsible for contradictory results regarding the pathogenesis of diseases related to alterations in the levels of trace elements.  相似文献   
86.
Rapid growth in the biotechnological industry and production has put tremendous pressure on the biological methods that may be used according to the guidelines of green chemistry. However, despite continuing dramatic increases in published research on organic biotransformation by microorganisms, more research exists with microalgae. Our efforts in transforming chemicals such as organic compounds for the production of functionalized products help to lessen the environmental effects of organic synthesis. These biotransformations convert organic contaminants to obtain carbon or energy for growth or as cosubstrates. This review aims to focus on the potential of microalgae in transformation, conversion, remediation, accumulation, degradation, and synthesis of various organic compounds. However, these technologies have the ability to provide the most efficient and environmentally safe approach for inexpensive biotransforming of a variety of organic contaminants, which are most industrial residues. In addition, the recent advances in microalgal bioactivity were discussed.  相似文献   
87.
88.
Pompe disease or glycogen storage disease type II is a glycogen storage disorder associated with malfunction of the acid α-glucosidase enzyme (GAA; EC.3.2.1.3) leading to intracellular aggregations of glycogenin muscles. The infantile-onset type is the most life-threatening form of this disease, in which most of patients suffer from cardiomyopathy and hypotonia in early infancy. In this study, a typical case of Pompe disease was reported in an Iranian patient using molecular analysis of the GAA gene. Our results revealed a new c.1824_1828dupATACG mutation in exon 13 of the GAA gene. In conclusion, with the finding of this novel mutation, the genotypic spectrum of Iranian patients with Pompe disease has been extended, facilitating the definition of disease-related mutations.  相似文献   
89.
90.
Arthrobacter sp. strains D2 and D3 and Labrys sp. strain D1 capable of degrading 20 mM monochloroacetic acid (MCA) were isolated from soil contaminated with herbicides and pesticides. All three isolates were able to grow on MCA as the sole source of carbon and energy with concomitant chloride ion release in the growth medium (19 mM). Strains D2 and D3 (cells doubling time 7 ± 0.3 h) grew four times faster than D1 (26 ± 0.1 h). Strain D2 was then further investigated and could also grow in 10 mM of monobromoacetic acid (MBA), 2,2-dichloropropionic acid (2,2DCP), d,l-2-chloropropionic acid (D,L2CP), l-2-chloropropionic acid (L-2CP), d-2-chloropropionic acid (D-2CP), and glycolate as the sole sources of carbon and energy. Dehalogenase gene amplification using group I primers revealed a 410-bp polymerase chain reaction (PCR) product, but there was none using group II primers. The partial amino acid sequence analysis of group I DehD2 dehalogenase showed at least 32% identity to the corresponding regions of DehE, DhlIV, DehI, and D,L-DEX, with key amino acid residues Ser188, Ala187, and Asp189. These amino acid residues were involved in substrate binding and catalysis and were conserved in the partial amino acid sequence.  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