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   4665篇
  免费   192篇
  2023年   34篇
  2020年   100篇
  2019年   88篇
  2018年   171篇
  2017年   171篇
  2016年   193篇
  2015年   121篇
  2014年   106篇
  2013年   1376篇
  2012年   134篇
  2011年   148篇
  2010年   106篇
  2009年   101篇
  2008年   104篇
  2007年   69篇
  2006年   82篇
  2005年   114篇
  2004年   67篇
  2003年   48篇
  2002年   63篇
  2001年   64篇
  2000年   40篇
  1999年   50篇
  1998年   37篇
  1997年   40篇
  1996年   35篇
  1995年   30篇
  1994年   47篇
  1993年   45篇
  1992年   41篇
  1991年   29篇
  1990年   42篇
  1989年   34篇
  1988年   38篇
  1987年   38篇
  1986年   44篇
  1985年   36篇
  1984年   52篇
  1983年   54篇
  1982年   52篇
  1981年   41篇
  1980年   35篇
  1979年   42篇
  1978年   42篇
  1977年   31篇
  1976年   32篇
  1975年   35篇
  1973年   28篇
  1972年   31篇
  1970年   32篇
排序方式: 共有4857条查询结果,搜索用时 343 毫秒
101.
In the Andes, there are several pre-Hispanic irrigation networks with structures destined for water storage. However, it has not been widely discussed in archaeological research. This is probably due to their being difficult to identify. The aim of this study is to explore the use of diatom assemblage analysis as a methodological tool suitable to help in the identification and characterization of these ancient hydraulic structures. We analyzed two archaeological structures interpreted as water reservoirs from north-western Argentina (EH1 in Antofagasta de la Sierra and U-88R1 in Yocavil) and compared them to current reservoirs. The diatom species composition and the changes in the dominant ecological groups in the studied structures highlight different periods of hydraulic behavior. EH1 contained and stored water, but there were periods of time in which there was a lack of use or abandonment of the structure. However, the U88-R1 structure does not have diatom evidence of containing standing water for a prolonged time but presence of wet soils. Thus, the structure could have been used for other water management strategies. The results show that diatom analysis is a methodological tool with a high potential to study ancestral hydrotechnologies.  相似文献   
102.
103.
104.
105.
"The spread of HIV-1 in the United Kingdom is simulated by a model which integrates behavioural and epidemiological processes within a multi-regional population projection framework and represents the spatial heterogeneities in the distribution of HIV which have significant effects on transmission patterns. Analyses determine the significance of different parameters in contributing to prediction uncertainty and highlight the importance of behavioural change and international population movements."  相似文献   
106.
Current federal hazardous and low-level radioactive waste management policies (under conjoint federalism) fail to balance national concerns for consistency with state concerns for equity, discretion, and adequate resources. Congress should expand conjoint federalism to permit states to charge differential fees on imported hazardous waste as it does for low-level radioactive waste. For low-level radioactive waste, clarification of the "take title" issue makes the present framework for state discretion implementable, given sufficient time.  相似文献   
107.
108.
109.
The paper examines the ancestry of Europeans in Sydney and that of the two largest non European groups. Spatial divergence occurs between the English, Scottish and Irish, and divergence from those of Australian ancestry. Residential persistence across generations occurs with persons of Greek, Italian, Maltese and Dutch origins, but not spatial segmentation. While there is greater language persistence in Greek and Italian second and third settlement concentrations, few third generation persons speak their ancestral language at home. The Chinese and Lebanese are compared with Greek and Italian ancestry in their areas of strongest representation. First generation Chinese are evident in areas of both low and high socioeconomic status, but without third generation language persistence. An evolving ethnic mix in Sydney is indicated.  相似文献   
110.
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