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   203篇
  免费   15篇
  2023年   1篇
  2022年   1篇
  2021年   1篇
  2020年   3篇
  2019年   6篇
  2018年   17篇
  2017年   16篇
  2016年   11篇
  2015年   12篇
  2014年   12篇
  2013年   34篇
  2012年   8篇
  2011年   11篇
  2010年   8篇
  2009年   12篇
  2008年   6篇
  2007年   7篇
  2006年   4篇
  2005年   8篇
  2004年   2篇
  2003年   2篇
  2002年   4篇
  2001年   4篇
  2000年   5篇
  1999年   3篇
  1998年   3篇
  1997年   2篇
  1996年   1篇
  1994年   2篇
  1993年   2篇
  1990年   1篇
  1987年   1篇
  1986年   3篇
  1982年   2篇
  1975年   1篇
  1969年   2篇
排序方式: 共有218条查询结果,搜索用时 15 毫秒
1.
The diversity and ubiquity measures of archaeological macrobotanical remains can be utilized to help define mobility strategies of hunter–gatherers. Differences in the diversity and ubiquity of plant remains are predicted to occur between different types of sites utilized by hunter–gatherers. Such sites include base camps of residentially and logistically mobile groups, as well as special-purpose sites usually associated with logistically mobile groups. The focus upon the importance of strategies of mobility and plant use instead of the typological determination of plant taxa allows for the use of specimen types in such analyses when scientific identifications are difficult to make. Data from the archaeological site of San Jacinto 1, located in northern Colombia, are utilized to examine this relationship.  相似文献   
2.
3.
4.
A vibrant artisanal fishery of the brackish water marsh clam (Polymesoda acuta) is located in the lower Río Tempisque, Costa Rica. Fishermen harvest clams from shoals according to tidal and lunar cycles. They take most clams directly to riverside processing stations to be cooked and sold as salted meat, although some cooked clams are dried, and others sold live. Processing activities result in the formation of shellmounds that share significant similarities and some differences with ancient marsh clam shellmounds of coastal Chiapas, Mexico. In this study, procurement and processing activities are described and quantified, revealing the substantial amount of labor and skill involved in the modern fishery. Implications for archaeological preservation and predictions from optimal foraging theory are evaluated.  相似文献   
5.
We investigated the contribution of freshwater resources to the diet of seven Late Mesolithic hunter-gatherers (ca. 5300–7000 BC) from Northern France and Luxembourg using stable isotope ratios. In addition to the carbon and nitrogen stable isotope ratios (δ13C, δ15N), we explored the potential of the sulphur isotopic ratios (δ34S) to detect and quantify the proportion of protein derived from aquatic foodstuff. In only two sites, animal remains from an associated settlement were available and subsequently examined to decipher the isotopic differential between terrestrial and freshwater resources. The quantification of their relative contribution was simulated using a Bayesian mixing model. The measurements revealed a significant overlap in δ13C values between freshwater and terrestrial resources and a large range of δ15N values for each food category. The δ34S values of the aquatic and terrestrial animals were clearly distinct at the settlement in the Seine valley, while the results on fish from Belgium demonstrated a possible overlap in δ34S values between freshwater and terrestrial resources. Local freshwater ecosystem likely contributed to ca. 30–40 % of the protein in the diet of the individuals found in the Seine settlement. Out of this context, the isotopic signature and thus contribution of the available aquatic foods was difficult to assess. Another potential source of dietary protein is wild boar. Depending on the local context, collagen δ34S values may contribute to better assessment of the relative contribution of freshwater and terrestrial resources.  相似文献   
6.
Seismic assessment of gravity dams is generally carried out using time history analyses. Scaling of the motions is commonly used; however, in contrast to buildings, the performance of scaling procedures at predicting the mean and reducing the dispersion in engineering demand parameters (EDPs) is not known. The main goal of this study is to assess the performance of different scaling procedures in predicting seismic demands on dams. The performance regarding the prediction of the damage and the required number of motions for effective analysis was investigated. The results show that techniques commonly used for moment frames should not readily be applied to these structures.  相似文献   
7.
The paper investigates the patterns of technology and knowledge of the regions. The first aim of the paper is to determine cluster templates at the national level. The second aim of the paper is to investigate the technology and knowledge composition of the regional highpoint clusters. The paper identifies patterns of industrial linkages to define cluster templates and regional highpoints. The second part uncovers regional distributions of technology and knowledge. The data comes from Turkey’s 2012 input–output table. The location quotients use industrial employment statistics from the Turkish Statistical Institute. The technological and knowledge intensity classification follows Eurostat. The findings reveal 10 cluster templates in Turkey. Spatial distribution of the highpoint clusters reveals that most regions contain highpoint clusters with low technology and low knowledge-intensive sectors. The results reveal that highpoint clusters in Turkey’s regions contain industries whose technologies do not demand high skills, knowledge and sophistication. Limited existence of high-tech industries and low knowledge intensity in Turkey’s industry composition is a limiting factor for transition to high value-added manufacturing. Special emphasis should be directed towards constructing regional advantage, given the current levels of technology and knowledge intensity.  相似文献   
8.
The aim of this paper is to discuss the importance of different types of global services for industrial firms and clusters in terms of their economic competitiveness and innovative performance. The theoretical debates argue that globalization, deregulation and the new production organization make it necessary to use global services that are supplied easily with the help of new telecommunication technologies. The existing empirical studies provide some supporting evidence. However, they also indicate that global service firms can be attained by only smaller numbers of industrial firms and clusters. Still, in-house services besides temporal and informal mechanisms are important to meet the needs of the specialized services, even for the firms that try to become a part of the global production system. The paper focuses on three main questions: “What types of global services are becoming crucial for manufacturing firms and what type of services are still local and national? Is there a significant difference between the characteristics of firms that use the same type of services? To what extent is having access to global services important for the innovativeness of industrial firms and clusters? This paper looks for the answers to these questions based on existing case studies as well as this study of three industrial clusters in Turkey. The findings indicate that there is not a perfect match between theory and empirical evidence and there is a need for more refined theoretical discourses on industry–service relations.  相似文献   
9.
In this study, we relax one of the general assumptions in the hub location literature by allowing routed flows between nonhub nodes. In hub networks, different flows are consolidated and routed via collection, interhub, and distribution arcs. Due to consolidation, some flows travel long paths despite closeness of their origin and destination. In this study, we allow direct flows by penalizing by a scalar factor of original cost of transshipment between these arcs. We present mathematical models for median, center, and set covering versions of the problem for single‐ and multi‐allocation cases. We test the models with the CAB and TR data sets. We discuss the properties of established direct connections for different models by using another mathematical model where the number of direct flows is bounded and interpret the effect of changes in problem parameters.  相似文献   
10.
Can age, period and cohort effects help explain support for Quebec sovereignty? Previous work on this question has focused mostly on the effects of age and cohort. We contribute to this debate by adding a period perspective. As such, our study is the first to investigate the impact of age, cohort and period effects in a single study of opinion towards sovereignty in Quebec. We take advantage of an original dataset that includes survey data collected between 1985 and 2012. We use these data to examine the impact of age, birth year and survey year on support for this constitutional option among francophone Quebeckers. Our results are in line with previous work: we show that younger Quebeckers are more likely to support sovereignty, and that some cohorts – namely, respondents born between 1945 and 1959 – are also more likely to favour this option. Perhaps more surprisingly, we find that specific events are comparatively the most important factor to explain fluctuations in Quebeckers' attitudes towards sovereignty.  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