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   1352篇
  免费   104篇
  1456篇
  2024年   3篇
  2023年   38篇
  2022年   6篇
  2021年   12篇
  2020年   65篇
  2019年   70篇
  2018年   170篇
  2017年   143篇
  2016年   134篇
  2015年   89篇
  2014年   90篇
  2013年   283篇
  2012年   56篇
  2011年   53篇
  2010年   47篇
  2009年   30篇
  2008年   33篇
  2007年   19篇
  2006年   9篇
  2005年   15篇
  2004年   11篇
  2003年   4篇
  2002年   9篇
  2001年   16篇
  2000年   7篇
  1999年   5篇
  1998年   4篇
  1997年   6篇
  1996年   4篇
  1995年   11篇
  1994年   2篇
  1993年   2篇
  1992年   3篇
  1989年   1篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1982年   2篇
  1979年   1篇
排序方式: 共有1456条查询结果,搜索用时 15 毫秒
991.
In this paper we present a virtual reconstruction of prehistoric funerary practices in Pastora Cave, a collective burial site in Eastern Spain that dates from the Late Neolithic, Chalcolithic and Bronze Age. Modern data of the cave was captured by 3D laser scanning techniques and added to recorded archaeological data and 3D graphic information. The combination of these data sets allowed us to create a hypothetical reconstruction to analyze the material excavated in the 1940s and 50s in greater spatial context. A 3D model of the current cave was created in order to serve as a basis for modeling the relative stratigraphic information available. We present the methodology employed and the results and implications of the analysis for Pastora Cave with particular emphasis on the spatial and chronological data.  相似文献   
992.
993.
Cenizo, M.M., Tambussi, C.P. & Montalvo, C.I., iFirst Article. Late Miocene continental birds from the Cerro Azul Formation in the Pampean region (central-southern Argentina). Alcheringa, 1–22. ISSN 0311-5518.

The oldest known birds from the Cerro Azul Formation are described, including the oldest records for the genera Eudromia and Nothura (Tinamidae), Milvago (Falconidae), Pterocnemia (Rheidae) and an undetermined Tyrannidae. The first remains of Phorusrhacidae for this formation are reported and a specimen previously referred to the giant teratorn Argentavis magnificens is reassigned to this family. We outline and update the current knowledge of the groups studied herein. The palaeornithological record from the Cerro Azul Formation is congruent with palaeoenvironmental inferences previously drawn from mammalian assemblages recovered from this unit, which point to the existence of open environments, possibly xerophyllous shrubby steppes, perhaps with some trees. These records are the first indications of a typically Pampean bird fauna at the end of the late Miocene in central-southern Argentina.  相似文献   
994.
Artabe, A.E. & Zamuner, A.B., March 2007. Elchaxylon, a new corystosperm based on permineralized stems from the Late Triassic of Argentina. Alcheringa 31, 85‐96. ISSN 0311-5518.

Anatomically preserved stems of Late Triassic corystosperms from the Río Blanco Formation of Argentina are described and assigned to Elchaxylon zavattieriae gen. et sp. nov. The polyxylic gymnospermous axes have two discontinuous cambial rings, which develop centrifugal secondary xylem and centripetal secondary xylem around the mesarch primary xylem bundles. The centrifugal undivided pycnoxylic secondary xylem incorporates uniseriate rays, uni- to biseriate radial pitting either alternate or opposite, and one or two simple pits in each cross-field. Atypical secondary growth is restricted to localized development of centripetal secondary xylem (inverted xylem). Elchaxylon could represent a basal member of the rhexoxyloid lineage. This basal clade is characterized by limited centripetal secondary xylem, lack of perimedullar bundles, and modest development of centrifugal xylem.

Analia E. Artabe [aeartabe@museo.fcnym.unlp.edu.ar] and Alba B. Zamuner [azamuer@museo.fcnym.unlp.edu.ar]. División Paleobotánica, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque SN, 1900 La Plata, Argentina and Consejo Nacional de Investigaciones Científicas y Técnicas; received 20.5.2005, revised and accepted 14.9.2005.  相似文献   
995.
Konservat-Lagerstätten are a source of insurmountable information on the diversity of fossil assemblages during the lower Palaeozoic. Soft-bodied fossils are especially rare in South America, but a new locality has been discovered from the Middle Ordovician of Peru that has produced the fairly well-preserved possible palaeoscolecidan Juninscolex ingemmetianum gen. et sp. nov. The distinctive characteristics of this worm make it similar to European taxa within the group.  相似文献   
996.
Palynofloras from an outlier of Tertiary sediments in the One Tree Hill area north of Adelaide are nonmarine and correlate with similar assemblages from Middle Eocene North Maslin Sands from Maslin Bay and Golden Grove. Although there are similarities with time-equivalent Lower Nothofagidites asperus Zone palynofloras in the Gippsland Basin, a number of species in the South Australian palynofloras do not extend below the Late Eocene in the Gippsland sequences. This indicates earlier appearances for these species in southcentral Australia. The sediments overlie a highly weathered bedrock palaeosurface, indicating that a phase of significant weathering occurred prior to the Middle Eocene. A number of selected taxa are illustrated and their distribution in the palynofloras is discussed. Two new species, Proteacidites mildenhallii and Proteacidites parrawirrensis, are described and one species, Rhoipites byfieldensis, is emended.  相似文献   
997.
Sánchez Botero, C.A., Oboh-Ikuenobe, F.E. & Macphail, M.K., 2013. First fossil pollen record of the Northern Hemisphere species Aglaoreidia cyclops Erdtman, 1960 in Australia. Alcheringa 37, 1–5. ISSN 0311-5518.

Aglaoreidia cyclops Erdtman, 1960 is a fossil pollen species associated with upper Eocene to lower Oligocene freshwater deposits in Europe and North America. Specimens preserved in upper Eocene lignites near Norseman, Western Australia, are the first record of this Northern Hemisphere species both in Australia and the Southern Hemisphere. This new report widens the biogeographic distribution originally considered for this species. The stratigraphical and environmental characteristics of A. cyclops also make it an excellent stratigraphic indicator of upper Eocene freshwater deposits in Western Australia.

Carlos A. Sánchez Botero [casmwc@mail.mst.edu], Francisca E. Oboh-Ikuenobe [ikuenobe@mst.edu] Department of Geological Sciences and Engineering, Missouri University of Science and Technology, 129 McNutt Hall, Rolla, MO 65409, USA; Mike Macphail [mike.macphail@anu.edu.au] Department of Archaeology and Natural History, College of Asia and the Pacific, Australian National University Canberra, ACT 0200, Australia. Received 12.10.2012; revised 6.3.2013; accepted 7.3.2013.  相似文献   
998.
999.
In nineteenth-century Europe, the foundling hospital grew beyond its traditional purpose of mitigating the shame of unwed mothers by also permitting widows, widowers, and poor married couples to abandon their children there temporarily. In the Foundling Hospital of Madrid (FHM), this new short-term abandonment could be completely anonymous due to the implementation of a wheel—a device on the outside wall of the institution that could be turned to place a child inside—which remained open until 1929. The use of survival-analysis techniques to disentangle the determinants of retrieval in a discrete framework reveals important differences in the situations of the women who abandoned their children at the FHM, partly depending on whether they accessed it through the Maternity Hospital after giving birth or they accessed it directly. The evidence suggests that those who abandoned their children through the Maternity Hospital retrieved them only when they had attained a certain degree of economic stability, whereas those who abandoned otherwise did so just as soon as the immediate condition prompting the abandonment had improved.  相似文献   
1000.
Stone weapon points constitute a major innovation appearing at the end of the Middle Pleistocene in Europe, Africa and the Near East; that is, among both sapiens and Neanderthal populations. The microscopic analysis of the stone weapons used by Neanderthal groups in Atlantic southern Europe suggests that this technology was widespread and became a recurrent behaviour within organised strategies developed by these societies. In this southern region of Europe, stone weapon hunting technology appears at an early time (about 150 ka, OIS 6) and is associated with the hunting of large mammals. This behaviour can be recognised in a geomorphologically complex region and at a time of great environmental change (OIS 6–5–4). The fact that these innovations were used by European Neanderthals long before the spread of anatomically modern humans in the area is of great evolutionary significance.  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