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   150篇
  免费   13篇
  2024年   2篇
  2023年   3篇
  2021年   3篇
  2020年   4篇
  2019年   7篇
  2018年   21篇
  2017年   18篇
  2016年   14篇
  2015年   11篇
  2014年   4篇
  2013年   27篇
  2012年   4篇
  2011年   5篇
  2010年   5篇
  2009年   3篇
  2008年   3篇
  2007年   3篇
  2005年   1篇
  2004年   1篇
  2003年   2篇
  2002年   3篇
  2001年   1篇
  2000年   3篇
  1999年   2篇
  1997年   2篇
  1995年   1篇
  1993年   2篇
  1991年   1篇
  1989年   2篇
  1984年   1篇
  1983年   2篇
  1972年   2篇
排序方式: 共有163条查询结果,搜索用时 15 毫秒
21.
Spatial clusters contain biases and artifacts, whether they are defined via statistical algorithms or via expert judgment. Graph-based partitioning of spatial data and associated heuristics gained popularity due to their scalability but can define suboptimal regions due to algorithmic biases such as chaining. Despite the broad literature on deterministic regionalization methods, approaches that quantify regionalization probability are sparse. In this article, we propose a local method to quantify regionalization probabilities for regions defined via graph-based cuts and expert-defined regions. We conceptualize spatial regions as consisting of two types of spatial elements: core and swing. We define three distinct types of regionalization biases that occur in graph-based methods and showcase the use of the proposed method to capture these types of biases. Additionally, we propose an efficient solution to the probabilistic graph-based regionalization problem via performing optimal tree cuts along random spanning trees within an evidence accumulation framework. We perform statistical tests on synthetic data to assess resulting probability maps for varying distinctness of underlying regions and regionalization parameters. Lastly, we showcase the application of our method to define probabilistic ecoregions using climatic and remotely sensed vegetation indicators and apply our method to assign probabilities to the expert-defined Bailey's ecoregions.  相似文献   
22.
In this paper, the characterization of Roman amphorae from the Porto dos Cacos (PC) and Quinta do Rouxinol (QR) workshops, in the Tagus estuary, dating to a period between the 1st and 5th century AD was carried out on the basis of instrumental neutron activation analysis data on 260 amphorae fragments, together with mineralogical compositional studies obtained by X-ray diffraction.  相似文献   
23.
ABSTRACT This paper considers a location model to illustrate the effect of zoning on competition. A planner is in charge of designing a city in a circular space where firms and consumers are located on different sides. With this type of market configuration, equilibrium in location under concave transport costs is proved. Then, a welfare function with different weights attached to consumer and firm surpluses is introduced to highlight zoning regulation as an influential competition policy tool. Depending on the regulator's political profiles and the demand, it is shown that zoning can lead to strong, weak, or moderate competition.  相似文献   
24.
This article provides a comprehensive assessment of the effects of social protection interventions on material and subjective elements of well‐being. Drawing on a longitudinal survey located in two relatively deprived parts of Brazil, it assesses the effects of pensions and other cash transfers on the well‐being of older people and their households. This analysis is located within a dynamic economic and public policy context. The article finds that pension benefits significantly increase per capita income and that this is strongly associated with overall levels of satisfaction with household well‐being. Levels of reported subjective well‐being do not fall as respondents age, and the survey finds high levels of optimism about future well‐being. The positive effects of pension benefits were supported by upgraded health services and by more specific policies such as access to credit on favourable terms. Overall, the authors conclude that a combination of economic growth and effective public policies significantly boosted the well‐being of most households in their survey, and that Brazil can be taken as a model of good practice for other middle‐income countries.  相似文献   
25.
SUMMARY: In 2014, during construction work at the ex-Civil Hospital in Gibraltar, excavations led by the Gibraltar Museum revealed a major, previously unknown burial ground containing more than 200 skeletons. We present the historical, archaeological and radiometric dating evidence from the site alongside the results of initial osteological analyses. The data indicate that the burials pertain to an earlier 16th-century Spanish hospice, and therefore stand to offer new insights into the functioning of this early modern hospital and the health and movements of people at a time of incipient globalization.  相似文献   
26.
A review of archaeobotanical data, together with new, still unpublished data, from Roman sites in conventus Bracaraugustanus suggests the Romanization of the northwest Iberia brought little changes to the agricultural strategies of local communities in indigenous-type settlements. The main crops remain the same as in the Iron Age: Triticum aestivum/durum, Panicum miliaceum, Hordeum vulgare subsp. vulgare, Triticum turgidum subsp. dicoccum and T. aestivum subsp. spelta, Avena and Vicia faba. The first secure reference for the cultivation of Secale cereale in the region comes from a Roman context, suggesting that it was introduced in this period, although it probably remained a minor crop.  相似文献   
27.
The rock art in Altamira Cave was the first ensemble of Palaeolithic parietal art to be identified scientifically (Sautuola, 1880). Due to the great thematic, technical and stylistic variety of the art in the cave, which constitutes one of the most complete Palaeolithic art ensembles, Altamira was listed as World Heritage by UNESCO in 1985. Uranium-series dating has recently been applied to figures on the decorated ceiling in the cave. Several motifs are partly covered by thin layers of calcite precipitates, whose formation process is datable by this method. The results provide the date when the calcite formed, which gives a minimum age for the underlying depictions. These results confirm that the parietal art at Altamira was produced during a prolonged period of time, at least 20,000 years (between 35,000 and 15,200 years ago), and that part of the ensemble corresponds to the Aurignacian period.  相似文献   
28.
Marsola, J.C.A., Grellet-Tinner, G., Montefeltro, F.C., Sayão, J.M., Hsiou, A.S. & Langer, M.C., 2014. The first fossil avian egg from Brazil. Alcheringa 38, 563–567. ISSN 0311-5518.

In contrast to the rich record of eggs from non-avian dinosaurs, complete eggs attributable to Mesozoic birds are relatively scarce. Nevertheless, several well-preserved specimens have been discovered over the last three decades revealing functional and phylogenetic characters that shed light on the breeding strategies of extinct birds. Here we report the first fossil avian egg from Brazil, which was discovered in Upper Cretaceous strata of São Paulo in the southeastern part of the country. The taxonomic identity and structural features of the biomineralized tissues were determined using a combination of Scanning Electron Microscopy, Wave Dispersion Energy analyses and Computed Tomography. These show that the 125.5-μm-thick shell of the 31.4?×?19.5?mm egg incorporates three structural layers of similar thickness with both prismatic and aprismatic boundaries. Close similarity between the Brazilian bird egg and those of enantiornithines from the Upper Cretaceous Bajo de la Carpa Formation (Río Colorado Subgroup) of Argentina advocates affinity with basal Ornithothoraces. Furthermore, coherency of their depositional contexts might imply a compatible preference for breeding and nesting environments.

Júlio Cesar de A. Marsola [], Annie Schmaltz Hsiou [] and Max C. Langer [], Laboratório de Paleontologia de Ribeirão Preto, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto, São Paulo state, 14040-901, Brazil. Gerald Grellet-Tinner [], Centro Regional de Investigaciones La Rioja—Consejo Nacional de Investigaciones Científicas y Técnicas, Entre Ríos y Mendoza s/n, 5301 Anillaco, Argentina; Orcas Island Museum, PO Box 134, 181 North Beach Road, Eastsound, WA 98245. Felipe C. Montefeltro [], Departamento de Zoologia, Universidade Estadual Paulista, Avenida 24A 1515, Rio Claro, São Paulo State, 13506-900, Brazil. Juliana M. Sayão [], Laboratório de Diversidade do Nordeste, Núcleo de Biologia, Centro Acadêmico de Vitória, Universidade Federal de Pernambuco, Rua do Alto do Reservatório s/n, Bela Vista, Vitória de Santo Antão, Pernambuco state, 52050-480, Brazil. Received 18.12.2013; revised 30.4.2014; accepted 18.5.2014.  相似文献   
29.
30.
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