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   281篇
  免费   15篇
  2023年   3篇
  2021年   6篇
  2020年   5篇
  2019年   7篇
  2018年   14篇
  2017年   13篇
  2016年   10篇
  2015年   9篇
  2014年   5篇
  2013年   85篇
  2012年   3篇
  2011年   13篇
  2010年   9篇
  2009年   12篇
  2008年   9篇
  2007年   7篇
  2006年   9篇
  2005年   4篇
  2004年   3篇
  2003年   4篇
  2002年   5篇
  2001年   8篇
  2000年   5篇
  1998年   5篇
  1997年   3篇
  1995年   5篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   5篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1979年   1篇
  1978年   2篇
  1976年   2篇
  1975年   1篇
  1974年   1篇
  1972年   2篇
  1971年   1篇
  1970年   1篇
  1969年   1篇
  1968年   1篇
  1967年   1篇
  1965年   1篇
  1954年   1篇
排序方式: 共有296条查询结果,搜索用时 15 毫秒
131.
132.
We have amplified Mycobacterium leprae DNA from the skeleton of an adult human female exhibiting signs of lepromatous leprosy (LL). The remains were excavated from the site of Devkesken 6 on the Ustyurt plateau of Uzbekistan and date to between the 1st and 4th centuries AD. Recovered DNA was fragmented but of sufficient quality and quantity to allow a series of biomolecular genotyping methods to be applied. These methods included variable nucleotide tandem repeat (VNTR) typing of two microsatellite and one minisatellite regions and also single-nucleotide polymorphism (SNP) typing for nine informative loci.Genotyping showed that the causative strain of M. leprae exhibited a SNP-type 3 profile, characteristic of cases associated geographically with Europe and North Africa. Further SNP sub-typing was performed and the data obtained from the Uzbek leper was compared with the same loci amplified from a case of LL recovered from Blackfriars, Ipswich, UK dating to between the 13th and 16th centuries AD. Unique group 3 subtypes were found in both the Uzbek case and Ipswich 1914. These appear to be ancestral to recent type 3 strains. Mycolic acid analysis confirmed the presence of M. leprae in the Uzbek samples. Phylogenetically informative SNPs and other polymorphic loci will contribute to the study of human migrations, as well as the origin and spread of leprosy.  相似文献   
133.
The study focuses on the evidence for tuberculosis apparent in an Iron Age population recovered from the cemetery of Aymyrlyg, Tyva (Tuva), South Siberia. A recent wholly molecular study of five of the cases confirmed the presence of Mycobacterium tuberculosis (MTB) complex DNA in four of the individuals. In all cases the disease was caused by strains of Mycobacterium bovis rather than Mycobacterium tuberculosis and represents the first positive identification of the bovine form of the disease in archaeological human remains. Details of the palaeopathological characteristics of the cases are provided in the current paper, while the molecular observations are extended to include a quantitative evaluation of the surviving mycobacterial DNA using real-time PCR. The observation that bovine tuberculosis was the pathogen responsible is discussed in terms of current understanding of the evolution of the MTB complex as well as the implications for future ancient DNA studies in this area.  相似文献   
134.
DNA appears to decay by random chain scission resulting in a predictable range of fragment lengths. Collagen decay has also been modelled in this same way, although it has become increasingly evident that collagen decay does not follow this same pattern. Radiocarbon and stable isotope analysis now use ultra-filtration to isolate large fragments (>30% of original polymer length) even in Pleistocene bone. How then does collagen decay? This study contrasts experimentally degraded samples with collagen extracted from forensic, archaeological and fossil bone. In experimentally degraded bone, values for amino acid and elemental (C:N) composition, bulk δ 13C, δ 15N, and aspartic acid racemisation (AAR) changed very little until 99% of the collagen was lost, suggesting that the collagen triple helix and polypeptide chains remained remarkably intact. This suggestion was demonstrated directly by examining the integrity of individual polypeptide chains using cyanogen bromide (CNBr) cleavage followed by SDS-PAGE electrophoresis. In ancient samples, AAR values remain remarkably stable and the pattern of CNBr-cleavage was only replaced with a smear of smaller polypeptides in the oldest (Pleistocene) bones investigated. Smearing may reflect both modification of the methionine resides (the sites of CNBr-cleavage) and/or partial hydrolysis of the collagen molecule. The findings reveal why it is not usually necessary to worry about collagen diagenesis; it is mostly intact. However, evidence of partial deterioration of the oldest bone samples suggests that alternative purification strategies may increase yields in some samples.  相似文献   
135.
Phil Taylor  Peter Bain 《对极》2008,40(1):131-154
Abstract: The offshoring of business processes from the global North to low‐cost countries of the global South has grown spectacularly in the current decade. Self‐evidently, transnational relocation presents considerable challenges for organised labour since it suggests both a ‘race to the bottom’ in respect of pay, conditions and workers' rights and wholesale redundancies in the developed economies. This paper examines the specific case of the migration of call centres from the UK to India and trade union responses in both geographies. Informed by theoretical developments, insights and evidence from diverse disciplines and literatures, the authors concur particularly with Herod's conviction that union strategies to counter TNCs should not be counterposed between ‘organising globally’ and ‘organising locally’and that ‘organising at both scales simultaneously may best serve their goals’. Following reflection upon the nature of the call centre and consideration of important contradictions in the offshoring process, we present evidence of UK union responses ranging from the nationalistic, even xenophobic, to the internationalsist, and conclude that membership mobilisation on a principled basis has been key to the limited successes unions have achieved. The paper also evaluates developments in India and the emergence of an embryonic organisation UNITES which is attempting to organise its call centre and business process outsourcing (BPO) workforce. We conclude by considering the gap between the potential and the reality of effective internationally co‐ordinated union activity.  相似文献   
136.
High mobility among Scythian populations is often cited as the driving force behind pan‐regional interactions and the spread of new material culture c.700–200 bce , when burgeoning socioeconomic interactions between the Greeks, Scythian steppe pastoralists and the agro‐pastoral tribes of the forest‐steppe played out across the region. While interregional mobility central to warrior lifestyles is assumed to have been a defining feature of Scythian populations, strikingly few studies have investigated human mobility among communities located along the steppe and forest‐steppe boundary zone. Here, we document movement and dietary intake of individuals interred at Bel'sk, a large urban settlement in Ukraine, through strontium, oxygen and carbon isotope analyses of human tooth enamel. The results provide direct evidence for limited mobility among populations from Bel'sk, demonstrating the movement into, and out of, urban complexes. Strontium and oxygen isotope analyses reveal that groups at Bel'sk remained local to the urban complex. Dietary intake, reflected in carbon isotopes, was based on domesticated crops and livestock herding. The combination of low mobility alongside dietary evidence suggests local groups engaged in sedentary agro‐pastoral subsistence strategies that contrast sharply with the picture of highly mobile Scythian herders dependent on livestock portrayed in historical sources.  相似文献   
137.
Inference regarding the impact of urban areas on health is limited by cross‐sectional studies assessing few dimensions and ignoring area‐level socio‐economic status. This study simultaneously assessed several dimensions of the built environment against incident cardiometabolic risk (CMR) arising over 10 years. It tested the hypothesis that, accounting for local area relative wealth, features of the built environment would not predict incident CMR. Initially, disease‐free adults in a biomedical cohort in Adelaide, Australia, provided address and clinical data over three waves of follow‐up. CMR was defined as the count of five clinical CMR factors. Built environment measures were derived for urban form, and natural, and food environments. Local area wealth was expressed using the relative location factor index. Poisson growth models accounting for within‐suburb clustering, age, sex, and education were used to estimate associations between built environment measures and increasing CMR. Fitted linear trajectories had statistically significant mean values of intercepts and slopes. CMR trajectories were associated with age, male sex, and low education. In models including measures of the food, natural, and urban form environments, per standard deviation increase, only POS count predicted incident CMR, which was more strongly predicted by relative location factor. Not accounting for local area socio‐economic status may overestimate the strength of relationships between health and the built environment. Inequity in accessible POS is robustly related to incident CMR.  相似文献   
138.
139.
R. Williams  G. Taylor  C. Orr 《Archaeometry》2020,62(6):1145-1163
Portable X-ray fluorescence (pXRF) is now widely used for detecting the elemental composition of a material. Elemental analysis can enhance archaeological interpretations, such as mapping, preservation analysis and identifying anthropogenic activities. However, validated and reproducible protocols for analysing archaeological soil are still required. The elemental concentrations detected with three sets of preparation methods were compared: in-situ (no preparation), in-field (analysing through plastic bags) and ex-situ analysis (laboratory-based preparation). Influential factors were also investigated: calibration parameter, moisture, homogeneity, sieve size and soil type. In-field analysis attempted to improve reliability without offsite processing, but instead substantially reduced elemental concentrations and skewed the proportional distributions. Ex-situ analysis significantly increased elemental concentrations and reduced variation. Proportional distribution was different between the three methods, but unchanged following homogenizing and sieving. These comparisons demonstrated that ex-situ analysis maximizes detection and ensures consistent samples.  相似文献   
140.
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