全文获取类型
收费全文 | 126篇 |
免费 | 8篇 |
出版年
2022年 | 1篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 31篇 |
2012年 | 5篇 |
2011年 | 8篇 |
2008年 | 4篇 |
2007年 | 2篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有134条查询结果,搜索用时 15 毫秒
51.
52.
A technological crossroads: Exploring diversity in the pressure blade technology of Mesolithic Latvia 下载免费PDF全文
Hege Damlien Inger Marie Berg‐Hansen Ilga Zagorska Mārcis Kalniņš Svein V. Nielsen Lucia U. Koxvold Valdis Bērziņš Almut Schülke 《Oxford Journal of Archaeology》2018,37(3):229-246
A long‐standing debate in archaeology concerns the sources of technological diversification among prehistoric hunter‐gatherers. This includes the study of the emergence and spread of pressure blade technology in Northern Europe during the Early Holocene. Until now, there has been little technological study of lithic collections from the East Baltic region, and our knowledge of the development and spread of this technology in the area is inadequate. This article presents for the first time a technological analysis of lithic assemblages from seven Early and Middle Mesolithic sites in the territory of present‐day Latvia, offering new possibilities for discussing pressure blade technology and research objectives connected with it. Furthermore, variation in elements of this technology is explored in relation to raw‐material characteristics through experimental flint knapping. Finally, the factors influencing diversity in craft traditions, as well as large‐scale communication and shifting spheres of interaction within Northern Europe during the Mesolithic, are discussed. 相似文献
53.
54.
The classical traveling-salesman problem involves the establishment of a tour around a set of points in a plane such that each point is intersected only once and the circuit is of minimal total length. When the length of a salesman's tour cannot exceed a specified constant, the problem becomes that of finding the fewest number of salesmen such that every city is visited by a salesman and the length of each salesman's tour does not exceed a specified constant. This is the chromatic traveling-salesmen problem. An algorithm for this problem is developed and is used to create periodic markets in parts of Sierra Leone. Fifteen rural areas were examined from Sierra Leone, and weekly market places were identified in each area. Salesmen were to be assigned to an area so that each market place was visited and each tour (or periodic ring) did not exceed forty hours. The chromatic traveling-salesmen algorithm was used to minimize the number of periodic rings needed for each area and provide the specific tour for each ring. 相似文献
55.
56.
Recent analyses and theories of public choice suggest faster public sector expansion in states with highly elastic revenue structures. This paper estimates the contribution of elasticity of tax revenues to the growth of expenditures in the 50 American states since 1960, based on elasticity measures for state revenue sources compiled by the Advisory Commission on Intergovernmental Relations, an index of state tax structural change, and controls for federal aid to states, population increase, and per capita growth in real income. Results for 1960-1970 show a small positive relationship between revenue elasticity and expenditure growth, but this becomes weak and negative for 1970-1976. Spending has increased most in states with the least elastic revenue sources; these states have made considerable changes in tax laws, while states with elastic revenue sources have been more likely to cut taxes than to increase spending. Federal aid, rather than tax elasticity, is the best predictor of state expenditure growth, while legislative changes in tax structure have enabled states to keep pace with rising demand for revenue due to growth in population and real income. 相似文献
57.
Randall W. Jackson 《Journal of regional science》1986,26(3):515-531
ABSTRACT. This paper presents a probabilistic specification of coefficients in the input- output modeling framework. Although previous works on probabilistic input-output models attribute uncertainty to measurement and sampling errors, this specification derives from systematic variation directly attributable to industrial, institutional, and location factors. Experiments with national input-output data support the existence of such variation. Employing the specification not only yields a more flexible aggregate modeling framework capable of producing interval impact estimates, but also an alternative perspective on such issues as interregional differentiation and structural comparison, the identification of key industrial sectors, aggregation, and spatial variation in production. 相似文献
58.
59.
M. T. P. Gilbert A. J. Hansen E. Willerslev G. Turner‐Walker M. Collins 《International Journal of Osteoarchaeology》2006,16(2):156-164
A principal problem facing human DNA studies that use old and degraded remains is contamination from other sources of human DNA. In this study we have attempted to contaminate deliberately bones and teeth sampled from a medieval collection excavated in Trondheim, Norway, in order to investigate this poorly understood phenomenon. Five pairs of teeth and bone samples were bathed in water containing various concentrations (from 10−9 and 10−21 g/l) of purified ΦX174 DNA. Subsequently the samples were subjected to a routine decontamination protocol involving a bleach bath followed by exposure to λ=254 nm ultraviolet light, prior to DNA extraction and analysis for evidence of the persistence of the contaminant. The results support previous speculation that bone is more susceptible to water‐borne sources of contaminant DNA, although both bone and teeth are readily contaminated and are difficult to decontaminate using the tested protocol. We believe that this is largely due to the porous nature of bone and teeth facilitating the deep penetration of the contaminant DNA. To simulate a more realistic handling situation, 27 further teeth were directly handled and washed, then decontaminated, prior to assaying for the residual presence of the handler's DNA. Surprisingly, although our results suggest that a large proportion of the teeth were contaminated with multiple sources of human DNA prior to our investigation, we were unable to contaminate the samples with further human DNA. One potential explanation may be the deposition of sediment or other structural changes that occur within the samples as they desiccate post‐excavation, which may protect samples from subsequent contamination, but also prevent the efficacy of bleach baths in decontaminating specimens. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
60.