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   7568篇
  免费   291篇
  2020年   98篇
  2019年   148篇
  2018年   169篇
  2017年   193篇
  2016年   240篇
  2015年   165篇
  2014年   157篇
  2013年   2185篇
  2012年   214篇
  2011年   223篇
  2010年   258篇
  2009年   228篇
  2008年   204篇
  2007年   208篇
  2006年   200篇
  2005年   105篇
  2004年   97篇
  2003年   95篇
  2002年   103篇
  2001年   113篇
  2000年   78篇
  1999年   100篇
  1998年   69篇
  1997年   61篇
  1996年   75篇
  1995年   74篇
  1994年   75篇
  1993年   88篇
  1992年   75篇
  1991年   62篇
  1990年   53篇
  1989年   68篇
  1988年   59篇
  1987年   66篇
  1986年   66篇
  1985年   76篇
  1984年   67篇
  1983年   97篇
  1982年   75篇
  1981年   76篇
  1980年   71篇
  1979年   75篇
  1978年   75篇
  1977年   66篇
  1976年   73篇
  1975年   69篇
  1974年   56篇
  1973年   56篇
  1972年   59篇
  1970年   50篇
排序方式: 共有7859条查询结果,搜索用时 0 毫秒
971.
This paper explains, with the example of a Roman object (the ‘Mars from Oberweningen’, Switzerland), why neutrons can be used preferentially for the non‐destructive analysis of metallic objects of relatively large size. This method is superior to the conventional X‐ray tomography method due to the higher penetration ability in metals such as copper, tin and even lead. With this method, differing materials can also easily be differentiated. In this way, the inner and outer structures of objects can be observed with the help of tools based on mathematical algorithms. Slices at arbitrary positions and segmentation of different material clusters aid the understanding of manufacturing processes and can describe the present preservation status. This helps in selecting optimal and additional conservation measures in museums for further preservation. Beside the qualitative overview on structure and inner properties of the objects, quantitative information can be derived about material content and composition. This method and the subsequently needed facilities for this method are available at PSI for similar studies on demand.  相似文献   
972.
In 2005–2006 we initiated a major archaeological survey and chemical characterization study to investigate the long-term use of obsidian along the eastern shores of Lake Urmia, northwestern Iran. Previous research in the area suggested that almost all archaeological obsidian found in this area originated from the Nemrut Daĝ source located in the Lake Van region of Anatolia (Turkey). More recent research on obsidian artefacts from the Lake Urmia region has identified a significant number of obsidian artefacts with compositions different from the sources near Lake Van. This suggests that the obsidian artefacts are from a yet to be identified geological source, but possibly one that was not too distant. In order to advance our knowledge of Iranian obsidians and eventually refine provenance criteria we analysed obsidian from 22 Chalcolithic sites and some source areas. The compositions of both obsidian source samples and artefacts were determined using wave length dispersive X-ray fluorescence spectrometry (WDXRF). This paper presents results from the trace elemental analysis of both geological and archaeological obsidians, providing important new data concerning the diachronic relationship between lithic technology and raw material in the north-west of Iran.  相似文献   
973.
974.
975.
976.
977.
978.
Examination of the histological structure of bone not only helps investigators to estimate age at death but can also aid in the diagnosis of palaeopathological lesions. The purpose of this paper is to assess whether histological features as described in the literature can confirm the macroscopic diagnoses of ossified subperiosteal haematomas associated with healed scurvy and syphilitic bone changes observed on the anterior tibiae of individuals from a 19th century mining community from Kimberley South Africa. The frequent occurrence of these two diseases amongst the deceased was well established in related hospital documents and governmental documents. A section of bone was removed from lesions on the tibiae of 14 individuals. These bone changes were macroscopically diagnosed as being indicative of either treponematosis ossified subperiosteal haematomas or non‐specific periostitis. Cross‐sections were prepared for microscopic investigation using a manual ground section technique. Ossified haematomas were histologically identified in seven individuals. These sections were characterised by normal cortical bone an intact original periosteal surface and newly formed radiating trabecular bone apposing it. Three phases of ossified subperiosteal haematoma formation and remodelling could be distinguished. Infectious bone changes most likely associated with treponematosis were observed in one individual. These were characterised by lysis and numerous resorption holes/channels. No clear distinction could be made between the internal spongy cortical or newly formed bone. Histological features described by some authors as characteristic of this condition could not be identified. In addition three individuals presented with microscopic features indicative of both the aforementioned bone affections and three did not show any pathological changes on microscopic level. It was concluded that although specific pathological conditions can most likely not be diagnosed purely on the basis of histomorphological observations broad distinctions could be made between lesions caused by the ossification of subperiosteal haematomas and bone changes due to infectious diseases. Copyright © 2009 John Wiley & Sons Ltd.  相似文献   
979.
Civil law rules were adopted in Florida that granted married women property rights long before legal reforms occurred in northern states. This article analyzes white wives' property and law in Florida between 1820 and 1860. Initially, married women's property rights were inadvertently protected by treaty law and limited to women who married before 1818. Wives' right to own separate property in Florida was subsequently reconfirmed in statute and extended to include later marriages. In contrast, nonwhites generally lost the rights and property they had enjoyed under Spain's civil law in the same period. This contrast reveals that in Florida (and other southern borderlands) it was not concern for women, or simply legal precedent, but the desire to incorporate new territory and expand slavery that influenced the development of marital property law. This challenges previous histories, which have excluded the earlier acts in the Southern borderlands and emphasized those passed in the Northeast beginning in the late 1840s. While those later acts were influenced by the early woman's rights movement and by concern for families reduced to poverty during the rise of market capitalism, this case study indicates that expansion of United States territory and slavery were responsible for the earlier married women's property rights in southern borderland territories such as Florida.  相似文献   
980.
Cranioplasty is a well‐known procedure in modern neurosurgery. Although some authors have claimed it was also performed by prehistoric trepanners in various parts of the world, there is little hard evidence to support this. Here we review various claims of cranioplasty in Peru, where trepanation was widely practised in Prehispanic times. We find little support for assertions that cranioplasty was common. One recently discovered burial from the Cuzco region, however, provides the first documented case of the reinsertion of a bone plug into a trepanation opening. Copyright © 2008 John Wiley & Sons, Ltd.  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