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   10145篇
  免费   183篇
  10328篇
  2023年   58篇
  2020年   175篇
  2019年   244篇
  2018年   297篇
  2017年   288篇
  2016年   370篇
  2015年   254篇
  2014年   237篇
  2013年   2528篇
  2012年   289篇
  2011年   345篇
  2010年   320篇
  2009年   304篇
  2008年   264篇
  2007年   264篇
  2006年   232篇
  2005年   140篇
  2004年   139篇
  2003年   125篇
  2002年   154篇
  2001年   196篇
  2000年   128篇
  1999年   149篇
  1998年   121篇
  1997年   106篇
  1996年   102篇
  1995年   91篇
  1994年   81篇
  1993年   97篇
  1992年   97篇
  1991年   77篇
  1990年   82篇
  1989年   68篇
  1988年   81篇
  1987年   91篇
  1986年   89篇
  1985年   94篇
  1984年   120篇
  1983年   108篇
  1982年   98篇
  1981年   97篇
  1980年   98篇
  1979年   81篇
  1978年   90篇
  1977年   85篇
  1976年   87篇
  1975年   82篇
  1974年   61篇
  1973年   61篇
  1972年   66篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The Indigenous people of New England’s middle Connecticut River Valley are often imagined as having been subservient to powerful tribal nations elsewhere. Yet, archaeological and ethnohistorical evidence suggests Pocumtuck independence and autonomy in relations with neighboring Native groups and with Dutch, English, and French colonizers during the seventeenth century. We employ a decolonizing framework, drawing on H.M. Wobst’s critique of the preoccupation with dominance and geopolitical “centers” to analyze this evidence. By framing artifacts, colonial texts, and cultural interactions as both past and present “material interventions,” we can generate better understandings of Pocumtuck political autonomy, agency and identity.  相似文献   
72.
A metallurgically-oriented excavation in Area A at Tell es-Safi/Gath yielded evidence for iron and bronze production dating to the early Iron Age IIA. Two pit-like features, which differed considerably from one another in colour, texture and content, were excavated. Evidence shows that each feature represents a different in situ activity related to iron production, inferred by the presence of hammerscales, slag prills and slag. An upturned crucible was found on top of one of the features. Analysis of the crucible slag showed that it was used for bronze metallurgy. Tuyères, both round and square in cross-section, were found in and around the two features. The presence of the two industries together presents a unique opportunity to explore the relationship between copper and iron working. This is especially important against the background of the scarcity of evidence for iron production in the Levant during the early phases of the Iron Age.  相似文献   
73.
74.
Through isotopic investigations of directly dated human remains recovered from the Eton College Rowing Course, we examine changes in diet from the Neolithic to the Roman period. The human isotope signatures point to a diet based on C3 terrestrial resources. A significant correlation is visible between human ??13C values and time, but no such trend is observed in ??15N. The animal isotope data from Eton are unevenly distributed, making it difficult to determine if the human values mirror the animal values. To assess whether the results from Eton are typical, we compare our results to isotope data from other British sites dating from the Neolithic to the Roman period. Across this time period, we see a strong correlation between the mean ??15N of the humans and that of the main domesticated herbivores, with an offset of ??4.5?? between the two. Thus, the changes in the human isotope values are likely linked to changes in the isotopic signatures of the herbivores rather than changes in the protein composition of human diets. By contrast, no clear temporal relationship is observed between the mean ??13C of the humans and that of the main domesticated herbivores, with an offset of ??1.4?? between the two. There is, however, a weak correlation observed between the mean ??13C of the humans and that of the cattle, which may account for some of the variation in human ??13C values between sites. The absence of a strong correlation between mean human and animal ??13C suggests that the primary factor influencing human ??13C values between sites is dietary composition. The lack of co-variation between ??13C and ??15N is likely to reflect the different representation of dietary macronutrients. Given that the nitrogen results suggest that the animal protein consumption patterns are similar across sites, the human ??13C variation between sites is likely to reflect the plant portion of the diet.  相似文献   
75.
Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is applied to the study of four samples of opaque glass of Late Bronze Age date. The technique is uniquely capable of identifying compositional heterogeneity at a sub-micron resolution within the crystalline opacifiers dispersed through homogeneous glass matrices. It is shown that this provides crucial information on the possible raw ingredients of the opacifying inclusions used, and has the potential for highlighting regional variations in the production technology involved in creating different colours of opaque glass.  相似文献   
76.
X-ray fluorescence analysis of obsidian artifacts from sites located in Chaco Canyon and from three Chaco-era communities in New Mexico permits determination of their geological origin. These source data are used to describe patterning in obsidian procurement in sites located in Chaco Canyon dating from A.D. 500–1150, and in a three non-Canyon communities occupied during the period of Chaco Canyon's regional prominence (ca. A.D. 875–1150). These data demonstrate that the most proximate sources generally dominate the sourced obsidian assemblages from sites of all periods, but also suggest differences in procurement patterning both over time and across space. Within Chaco Canyon, there is a notable shift from Mount Taylor obsidian to use of Jemez Mountains sources over time. These data also suggest that earlier analyses of obsidian from sites in Chaco Canyon misidentified some obsidian artifact sources; these new data indicate the central areas of disagreement and provide a revision of procurement patterning. In the Chaco-era communities located outside Chaco Canyon, procurement patterning diverges. The Blue J community shows an increase in use of the nearby Mount Taylor source over time. Two communities located toward the southern extent of the Chaco great house distribution reveal a markedly distinct procurement pattern, obtaining nearly all of their obsidian from southern sources largely unrepresented at Chaco Canyon. Combined, these data provide new insights into raw material procurement and artifact production at sites in Chaco Canyon, and in communities occupied during the Chaco Phenomenon, the period of the Canyon's greatest regional influence.  相似文献   
77.
Many chronological and cultural facets of Early and Middle Holocene Prehistoric Oman are still unclear. Archaeological excavations of settlements and cemeteries are adding new data to the reconstruction of a chronological and cultural framework. Wadi Shab-GAS1 is a Middle Holocene site found at the beginning of the 1980s and later destroyed by urbanisation. It is located in a rich environmental niche, on a cliff facing the sea and near a permanent freshwater source. Three years of fieldwork at this site brought to light structural remains, a cemetery and interesting material culture.  相似文献   
78.

The ocean's profound inaccessibility makes it impossible to comprehend except through the mediation of technology. The first investigators to explore the great depths were hydrographers whose work was animated by mid‐nineteenth century growth of political, economic, and cultural interest in the oceans. While submarine telegraphy certainly boosted ocean science, interest in this field derived first from commercial concerns related to whaling and shipping as well as the intellectual pursuits of physical geography and questions about the existence of life at great depths. Hydrographers’ developing conception of the oceanic environment never represented a clear translation from technology. Dramatic changes in the understanding of the shape of the deep‐sea floor testified to the complexity of interaction between sounding machines, methods, and interpretations of depth. The shifting image of the sea floor not only reflected increasingly accurate measurements, but also mirrored shifting human motivations for studying this unexplored territory.  相似文献   
79.
Benson, R.B.J., Fitzgerald, E.M.G., Rich, T.H. & Vickers-Rich, P., 2013. Large freshwater plesiosaurian from the Cretaceous (Aptian) of Australia. Alcheringa 37, 1–6. ISSN 0311-5518

We report a large plesiosaurian tooth from the freshwater early–middle Aptian (Early Cretaceous) Eumeralla Formation of Victoria, Australia. This, combined with records of smaller plesiosaurian teeth with an alternative morphology, provides evidence for a multitaxic freshwater plesiosaurian assemblage. Dental and body size differences suggest ecological partitioning of sympatric freshwater plesiosaurians analogous to that in modern freshwater odontocete cetaceans. The evolutionarily plastic body plan of Plesiosauria may have facilitated niche differentiation and helped them to exclude ichthyosaurs from freshwater environments during the Mesozoic. However, confirmation of this hypothesis requires the discovery of more complete remains.

Roger B.J. Benson [roger.benson@earth.ox.ac.uk], Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK; Erich M.G. Fitzgerald [efitzgerald@museum.vic.gov.au], Thomas H. Rich [trich@museum.vic.gov.au], Museum Victoria, GPO Box 666, Melbourne, Victoria 3001, Australia; Thomas H. Rich and Patricia Vickers-Rich [pat.rich@monash.edu], School of Geosciences, Monash University, Clayton, Victoria 3800, Australia. Received 30.10.2012; revised 27.1.2013; accepted 31.1.2013.  相似文献   
80.
Disc-like galls are reported on the Triassic corystosperm leaf Dicroidium hughesii (Feistmantel) Lele from the Parsora Formation of South Rewa Gondwana Basin, central India. Although there have been numerous reports of arthropod–plant interactions from Permian and Lower Cretaceous successions, this is the first unequivocal report of arthropod–plant interactions from the Triassic succession of Peninsular India. The new record adds to global evidence that arthropod herbivory and gall formation, in particular, had rediversified by the Late Triassic in the wake of the end-Permian mass extinction.  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