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   23篇
  免费   10篇
  国内免费   1篇
系统科学   5篇
现状及发展   4篇
研究方法   1篇
综合类   23篇
自然研究   1篇
  2021年   1篇
  2020年   2篇
  2019年   5篇
  2018年   1篇
  2014年   5篇
  2013年   4篇
  2012年   3篇
  2011年   4篇
  2010年   1篇
  2009年   2篇
  2008年   1篇
  2006年   2篇
  2005年   1篇
  2004年   1篇
  1974年   1篇
排序方式: 共有34条查询结果,搜索用时 15 毫秒
1.
Blood pressure is a heritable trait influenced by several biological pathways and responsive to environmental stimuli. Over one billion people worldwide have hypertension (≥140?mm?Hg systolic blood pressure or ≥90?mm?Hg diastolic blood pressure). Even small increments in blood pressure are associated with an increased risk of cardiovascular events. This genome-wide association study of systolic and diastolic blood pressure, which used a multi-stage design in 200,000 individuals of European descent, identified sixteen novel loci: six of these loci contain genes previously known or suspected to regulate blood pressure (GUCY1A3-GUCY1B3, NPR3-C5orf23, ADM, FURIN-FES, GOSR2, GNAS-EDN3); the other ten provide new clues to blood pressure physiology. A genetic risk score based on 29 genome-wide significant variants was associated with hypertension, left ventricular wall thickness, stroke and coronary artery disease, but not kidney disease or kidney function. We also observed associations with blood pressure in East Asian, South Asian and African ancestry individuals. Our findings provide new insights into the genetics and biology of blood pressure, and suggest potential novel therapeutic pathways for cardiovascular disease prevention.  相似文献   
2.
Mercury(II) is an important factor in hepatotoxicity that can enter the body through marine diets and amalgams.In the present study,the protective effect of the Eriobotrya japonica flower extract(EJFE) on HgCl 2-induced hepatotoxicity was investigated.Five mg/kg of mercuric chloride in drinking water was given to rats either with saline or EJFE(100 and 200 mg/kg as intraperitoneal(IP)) for 30 d.The mercury levels in different groups of liver tissues of the rats were measured with flameless atomic absorption spectroscopy(F-AAS).Also,mercury accumulation in the liver of the rats was modeled by using a parallel chemical kinetic model.The results showed that HgCl 2-induced oxidative damage led to a significant decrease in glutathione(GSH) and the total antioxidant capacity(TAC) levels,and to a significant increase in lipid peroxidation level.Accumulated mercury was 14.47% more in the livers of the stress groups than in those of the control groups(P<0.001),whereas the amount of Hg was adjusted to 13.49% and 13.93% in groups treated with 100 and 200 mg/kg of EJFE respectively,as compared with stress groups(P<0.001).HPLC analysis of EJFE revealed that hesperetin and gallic acid are the major antioxidants in EJFE.Results demonstrate that flowers of the Eriobotrya japonica cause a significant protection against HgCl 2 induced hepatotoxicity in all diagnostic parameters by strengthening the antioxidant defense mechanisms and they may have a therapeutic function in free radical mediated diseases.  相似文献   
3.
Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels were studied. To investigate the microstructure and mechanical properties, optical microscopy, scanning electron microscopy, X-ray diffraction, tensile test, and hardness test were used. The results show that the solution-annealing treatment in the cold-rolled steel redounds to the formation of submicrocrystalline Fe2(Mo, Ti) Laves phase particles, which are stable at high temperatures. These secondary Laves phase particles prevent from recrystallization at high temperatures and correspond to semi-brittle fracture in the subsequent aging treatment.  相似文献   
4.
Measurement of optical properties of skin is an expanding and growing field of research. Recent studies have shown that the biological tissue, especially skin, changes the polarization state of the incident light. Using this property will enable the study of abnormalities and diseases that alter not only the light intensity but also its polarization state. In this paper we report an experimental study for measuring changes of polarization state of the light scattered from a phantom similar to a sample model of scattering skin. Using the notation of Stokes vector for the polarized light and Mueller matrix for the sample with its polarization properties, we have shown that some elements of the matrix were particularly sensitive to the changes of the polarization-altering physical properties of the scatterers within the phantom.  相似文献   
5.
In this paper, an optimized multivariate singular spectrum analysis (MSSA) approach is proposed to find leading indicators of cross‐industry relations between 24 monthly, seasonally unadjusted industrial production (IP) series for German, French, and UK economies. Both recurrent and vector forecasting algorithms of horizontal MSSA (HMSSA) are considered. The results from the proposed multivariate approach are compared with those obtained via the optimized univariate singular spectrum analysis (SSA) forecasting algorithm to determine the statistical significance of each outcome. The data are rigorously tested for normality, seasonal unit root hypothesis, and structural breaks. The results are presented such that users can not only identify the most appropriate model based on the aim of the analysis, but also easily identify the leading indicators for each IP variable in each country. Our findings show that, for all three countries, forecasts from the proposed MSSA algorithm outperform the optimized SSA algorithm in over 70% of cases. Accordingly, this new approach succeeds in identifying leading indicators and is a viable option for selecting the SSA choices L and r, which minimizes a loss function.  相似文献   
6.
Singular spectrum analysis: methodology and application to economics data   总被引:2,自引:0,他引:2  
This paper describes the methodology of singular spectrum analysis (SSA) and demonstrate that it is a powerful method of time series analysis and forecasting, particulary for economic time series. The authors consider the application of SSA to the analysis and forecasting of the Iranian national accounts data as provided by the Central Bank of the Islamic Republic of Iran. This research was in part supported by a grant (No. 88/121230) from Institute for Trade Studies and Research (ITSR), Tehran, Iran.  相似文献   
7.
The subventricular zone (SVZ) is a principal source of adult neural stem cells in the rodent brain, generating thousands of olfactory bulb neurons every day. If the adult human brain contains a comparable germinal region, this could have considerable implications for future neuroregenerative therapy. Stem cells have been isolated from the human brain, but the identity, organization and function of adult neural stem cells in the human SVZ are unknown. Here we describe a ribbon of SVZ astrocytes lining the lateral ventricles of the adult human brain that proliferate in vivo and behave as multipotent progenitor cells in vitro. This astrocytic ribbon has not been observed in other vertebrates studied. Unexpectedly, we find no evidence of chains of migrating neuroblasts in the SVZ or in the pathway to the olfactory bulb. Our work identifies SVZ astrocytes as neural stem cells in a niche of unique organization in the adult human brain.  相似文献   
8.
9.
The fabrication of copper (Cu) and copper matrix silicon carbide (Cu/SiCp) particulate composites via the sinter-forging process was investigated. Sintering and sinter-forging processes were performed under an inert Ar atmosphere. The influence of sinter-forging time, temperature, and compressive stress on the relative density and hardness of the prepared samples was systematically investigated and subsequently compared with that of the samples prepared by the conventional sintering process. The relative density and hardness of the composites were enhanced when they were prepared by the sinter-forging process. The relative density values of all Cu/SiCp composite samples were observed to decrease with the increase in SiC content.  相似文献   
10.
This paper proposes a selfsimilar local neurofuzzy (SSLNF) model with mutual informati onbased input selection algorithm for the shortterm electricity demand forecasting. The proposed self similar model is composed of a number of local models, each being a local linear neurofuzzy (LLNF) model, and their associated validity functions and can be interpreted itself as an LLNF model. The proposed model is trained by a nested local liner model tree (NLOLIMOT) learning algorithm which partitions the input space into axisorthogonal subdomains and then fits an LLNF model and its associated validity function on each subdomain. Furthermore, the proposed approach allows different input spaces for rule premises (validity functions) and consequents (local models). This appealing property is employed to assign the candidate input variables (i.e., previous load and temperature) which influence shortterm electricity demand in linear and nonlinear ways to local models and validity functions, respectively. Numerical results from shortterm load forecasting in the New England in 2002 demonstrated the accuracy of the SSLNF model for the STLF applications.  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