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   92篇
  免费   7篇
  2023年   1篇
  2022年   2篇
  2021年   1篇
  2020年   2篇
  2019年   4篇
  2018年   5篇
  2017年   3篇
  2016年   2篇
  2015年   4篇
  2014年   8篇
  2013年   9篇
  2012年   5篇
  2011年   7篇
  2010年   5篇
  2009年   5篇
  2008年   2篇
  2007年   5篇
  2006年   4篇
  2005年   3篇
  2004年   2篇
  2003年   3篇
  2002年   4篇
  2001年   2篇
  1999年   2篇
  1996年   1篇
  1992年   3篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
排序方式: 共有99条查询结果,搜索用时 46 毫秒
1.
The molecular phylogeny of the genus Odontobuthus Vachon, 1950 (Scorpiones: Buthidae) in Iran was evaluated using two mitochondrial DNA genes, cytochrome c oxidase, subunit I (COI) and 16S ribosomal RNA (16S rRNA). The molecular phylogenetic analyses were performed using Maximum Parsimony, Maximum Likelihood and Bayesian inference methods. The resulting topologies supported two main clades: the clade comprising Odontobuthus doriae, O. bidentatus, and O. tavighiae, and another one which is the O. tirgari clade. The results clearly presented additional support for the taxonomic validity of the recently described species, O. tirgari and O. tavighiae. In addition, the monophyly of two previously described species O. doriae and O. bidentatus was confirmed. According to the data presented here, three taxonomically valid species belonging to the genus Odontobuthus occur in Iran.  相似文献   
2.
Despite rapid expansion of our knowledge of vascular adaptation, developing patient-specific models of diseased arteries is still an open problem. In this study, we extend existing finite element models of stress-mediated growth and remodelling of arteries to incorporate a medical image-based geometry of a healthy aorta and, then, simulate abdominal aortic aneurysm. Degradation of elastin initiates a local dilatation of the aorta while stress-mediated turnover of collagen and smooth muscle compensates the loss of elastin. Stress distributions and expansion rates during the aneurysm growth are studied for multiple spatial distribution functions of elastin degradation and kinetic parameters. Temporal variations of the degradation function are also investigated with either direct time-dependent degradation or stretch-induced degradation as possible biochemical and biomechanical mechanisms for elastin degradation. The results show that this computational model has the capability to capture the complexities of aneurysm progression due to variations of geometry, extent of damage and stress-mediated turnover as a step towards patient-specific modelling.  相似文献   
3.
We analysed 87 species of Onosma (Boraginaceae) from throughout its distribution range to investigate its evolutionary history. Using nrDNA ITS and two plastid (rpl32‐trnL(UAG) and trnH–psbA) markers, we reconstructed phylogenetic relationships within Onosma by conducting maximum parsimony, maximum likelihood, Bayesian, and BEAST analyses. The analyses revealed that Onosma as currently circumscribed is not monophyletic. However, the vast majority of Onosma species appear to belong to a single clade, the so‐called Onosma s.s. Outside of this core clade is a clade containing O. rostellata, a subclade of Sino‐Indian species and Maharanga emodii. Podonosma orientalis (as O. orientalis) appear only distantly related to Onosma but is more closely related to Alkanna, as also suggested in previous molecular studies. The Onosma s.s. clade includes all representatives of O. sect. Onosma, and encompasses three subsections, i.e. Onosma, Haplotricha and Heterotricha, corresponding to asterotrichous, haplotrichous and heterotrichous groups, respectively, but none of these subsections was retrieved as monophyletic. We observed significant incongruence between nuclear and chloroplast phylogenies regarding the phylogenetic status of the heterotrichous group. A dozen of the Iranian haplotrichous species formed a lineage which may not hybridize with asterotrichous species. Divergence time estimates suggested that the early radiation of Onosma s.l. took place at the Oligocene‐Miocene boundary and the diversification within Onosma s.s. occurred during middle to late Miocene and Pliocene.  相似文献   
4.
In order to evaluate the phylogenetic relationships and taxonomic classification of the Iranian endemic Tanacetum paradoxum Bornm. (Asteraceae, Anthemideae), a molecular analysis based on nrDNA ITS sequences of 16 species of Tanacetum together with representatives of 27 genera of subtribes Artemisiinae and Handeliinae as well as a micromorphological study of achenes and pollen grains was performed. The chromosome number of 2n?=?2x?=?16 and the genome size of T. paradoxum (2C?=?8.81?±?0.19?pg) are reported here for the first time. Due to the well-supported close phylogenetic relationship of T.?paradoxum to the species of the genus Artemisia (Bayesian inference, posterior probability PP?=?1), which is supported by cytological (x?=?8) and micromorphological features concerning the achene shape and pollen type, the combination Artemisia paradoxa (Bornm.) Sonboli is proposed.  相似文献   
5.
Widespread use of mobile phones has increased the human exposure to electromagnetic fields (EMFs). It is required to investigate the effect of EMFs on the biological systems. In this paper the effect of mobile phone RF (910 MHz and 940 MHz) on structure and function of HbA was investigated. Oxygen affinity was measured by sodium dithionite with UV–vis spectrophotometer. Structural changes were studied by circular dichroism and fluorescence spectroscopy. The results indicated that mobile phone EMFs altered oxygen affinity and tertiary structure of HbA. Furthermore, the decrease of oxygen affinity of HbA corresponded to the EMFs intensity and time of exposure.  相似文献   
6.
7.
A neutralizing anti-interleukin-(IL-)8 monoclonal antibody was humanized by grafting the complementary determining regions onto the human IgG framework. Subsequent alanine scanning mutagenesis and phage display enabled the production of an affinity matured antibody with a >100-fold improvement in IL-8 binding. Antibody fragments can be efficiently produced in Escherichia coli but have the limitation of rapid clearance rates in vivo. The Fab' fragment of the antibody was therefore modified with polyethylene glycol (PEG) in order to obtain a more desirable pharmacokinetic profile. PEG (5-40 kDa) was site-specifically conjugated to the Fab' via the single free cysteine residue in the hinge region. In vitro binding and bioassays showed little or no loss of activity. The pharmacokinetic profiles of the 20 kDa, 30 kDa, 40 kDa, and 40 kDa branched PEG-Fab' molecules were evaluated in rabbits. Relative to the native Fab', the clearance rates of the PEGylated molecules were decreased by 44-175-fold. In a rabbit ear model of ischemia/reperfusion injury, all PEGylated Fab' molecules were as efficacious in reducing oedema as the original monoclonal antibody. These studies demonstrate that it is possible to customize the pharmacokinetic properties of a Fab' while retaining its antigen binding activity.  相似文献   
8.
9.
Wide ranging surveys of the ant fauna of Iran have enabled us to add a further 30 named species to the country list. A review of almost all the published literature and of photographs of unidentified specimens within the public domain gives a grand total of 248 species, from seven subfamilies and 37 genera. In the majority of instances, our own specimens were compared with type images available from antweb.com. This has led us to propose new or revised status for Cataglyphis turcomanica Crawley 1920, Lepisiota integrisquama (Kuznetsov-Ugamsky, 1929), Lepisiota surchanica (Kuznetsov-Ugamsky, 1929) and Messor obscurior Crawley 1920. We note that the total includes a number of what may be misidentifications and a small number of named species that seem unlikely to occur in Iran.  相似文献   
10.
? Premise of the study: Phenolic compounds exuded by roots have been implicated in allelopathic interactions among plants. Root enzymes that destroy phenolics may protect plants against allelopathic inhibition and thus may aid in invasiveness. Phenolic-degrading enzymes are chiefly found in aboveground plant parts, but have also been previously reported in root tissues where the enzyme's function is unknown. We explored phenolic oxidase activity in emerging roots of grasses in a survey across different grass genera; in particular, we aimed to test whether grasses of the genus Bromus, known for their large invasion potential, differ in this respect from other grass taxa. ? Methods: We assayed a range of grass genera commonly found in the United States for root enzyme activity with spectrophotometric assays of phenol oxidase activity using l-DOPA as the main substrate. ? Key results: In the survey of a grass genera, we discovered that roots of the genus Bromus contain large amounts of polyphenol oxidase (PPO) activity, while all other tested grass genera, even ones closely related to Bromus, did not. PPO was found to be present at germination and remained active throughout the life of the plant. Compared to other PPOs, the enzyme present in Bromus appears to have a narrow substrate range. ? Conclusions: The specific functions of the root PPO and the ecological ramifications of the special status of Bromus are not yet clear. The possibility that the enzyme plays a role in plant species interaction for bromes, a genus of grasses known to have high invasive potential, is raised.  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