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   5488篇
  免费   193篇
  2020年   66篇
  2019年   85篇
  2018年   394篇
  2017年   294篇
  2016年   353篇
  2015年   99篇
  2014年   97篇
  2013年   1176篇
  2012年   146篇
  2011年   283篇
  2010年   294篇
  2009年   149篇
  2008年   194篇
  2007年   228篇
  2006年   86篇
  2005年   95篇
  2004年   54篇
  2003年   61篇
  2002年   50篇
  2001年   74篇
  2000年   57篇
  1999年   61篇
  1998年   53篇
  1997年   37篇
  1996年   39篇
  1995年   48篇
  1994年   45篇
  1993年   37篇
  1992年   42篇
  1991年   35篇
  1990年   35篇
  1989年   31篇
  1988年   38篇
  1987年   47篇
  1986年   36篇
  1985年   48篇
  1984年   48篇
  1983年   50篇
  1982年   51篇
  1981年   46篇
  1980年   39篇
  1979年   33篇
  1978年   37篇
  1977年   41篇
  1976年   32篇
  1974年   37篇
  1973年   21篇
  1971年   22篇
  1970年   24篇
  1969年   20篇
排序方式: 共有5681条查询结果,搜索用时 15 毫秒
61.
This paper describes a system of versatile software packages that has been developed by the author for population analysis on IBM-compatible microcomputers using PC or MS DOS. The series includes programs for the production of life tables, the analysis of spatial patterns and temporal trends in mortality, population projections, stationary-state population simulations and demographic planning, cohort survival estimates of net migration, and the analysis of migration matrices. Each of the programs in the series is discussed in terms of its principal analytical features, associated conceptual and methodological issues, and potential applications. The programs are intended for use both as basic research and planning tools and as instructional aids in university-level courses. The programs and related documentation are available on a set of four 360K diskettes.  相似文献   
62.
63.
Mormons and Jews established agricultural settlements in western Canada around the turn of the century. Mormon colonization was generally successful, characterized by its great stability. Abandonment of the land by Mormon communities was rare. In contrast, almost all the Jewish settlements failed. Settlers abandoned their land and retreated to the urban centres of the West. A comparative analysis of the two groups suggests that this difference in agricultural stability may not have been a reflection of prior experience, nor was it necessarily attributable to vagaries of the physical environment. Social structures, religious demands, and institutional backing, along with the geographical concentration and inter connectivity of settlements were critical elements in determining success or failure in agriculture colonization.
C'est au début du siècle que les Mormons et les juifs etablirent dans l'Ouest canadien leurs colonies agricoles. La colonisation des Mormons, caractérisée par sa grande stabilite, réussit dans l'ensemble; rares furent les colonies qu'ils abandonnèrent. Par contre, presque toutes les colonies juives echouerent; abandonnant leurs terres, les colons se retirerent dans les centres urbains de l'Ouest. Une analyse comparative des deux groupes permet de conchre que leur stabilite agricole relative ne fut pas necessairement fonction de leur experience prealable en agriculture; elle ne fut pas non plus attribuable aux seules contraintes géographiques et clirnatiques.
Les structures sociales, les exigences religieuses, l'appui de leurs établissements en plus de la proximité d'autres colonies et leurs interrelations, tous ces facteurs s'avérèrent cruciaux pour déterminer la reussite ou l'échec de la colonisation agricole.  相似文献   
64.
65.
66.
67.
68.
69.
The chemical and mineralogical characterization of seven ceramic fragments produced within Tiwanaku state (c.500–1000 ce ) is reported. The instrumental techniques used included X‐ray elemental and mineralogical chemical analysis, Raman spectroscopy, and scanning and light microscopy. The results indicate there are several clay types, although they show similarities, such as the use of a plant‐based temper. The red colour of the decoration is hematite, and manganese oxides such as jacobsite are present in the black. The white colour is a mixture of gypsum and clay, and the orange is a mixture of hematite and clay. The use of colours, the quality of the clays and the temperatures reached during pottery firing point to expertise in ceramic production and to complex decision‐making processes. The multi‐elemental archaeometric approach documented here could become an important tool to shed a light on ancient ceramic technology and the internal variance of Tiwanaku pottery.  相似文献   
70.
In order to carry out strontium (Sr) isotope analysis, glass artefacts from South Asia were sampled with portable laser ablation (pLA), a relatively novel sampling technique that leaves damage invisible to the naked eye. Subsequently, thermal ionization mass spectrometry (TIMS) was used to obtain Sr isotope ratios after sample dissolution and separation. In this study, the goal was twofold: to determine whether the measurements of Sr isotope ratios were impacted by using a portable laser as a sample tool; and to assess the pertinence of using Sr isotope ratios to provenance Indian glass. Despite a deterioration in the precision of the measurement of the Sr isotope ratios for artefacts sampled with pLA compared with the traditional sampling method, the Sr isotope ratios of certain Indian glass are so different that this does not affect their separation but a comparison of data sets obtained using standard methods and pLA might be challenging.  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