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   7618篇
  免费   273篇
  2020年   96篇
  2019年   121篇
  2018年   173篇
  2017年   174篇
  2016年   236篇
  2015年   150篇
  2014年   151篇
  2013年   2197篇
  2012年   216篇
  2011年   266篇
  2010年   242篇
  2009年   198篇
  2008年   177篇
  2007年   163篇
  2006年   155篇
  2005年   117篇
  2004年   98篇
  2003年   81篇
  2002年   92篇
  2001年   120篇
  2000年   105篇
  1999年   127篇
  1998年   84篇
  1997年   78篇
  1996年   66篇
  1995年   70篇
  1994年   65篇
  1993年   78篇
  1992年   70篇
  1991年   67篇
  1990年   67篇
  1989年   71篇
  1988年   61篇
  1987年   82篇
  1986年   68篇
  1985年   91篇
  1984年   87篇
  1983年   109篇
  1982年   86篇
  1981年   93篇
  1980年   90篇
  1979年   73篇
  1978年   75篇
  1977年   87篇
  1976年   66篇
  1975年   65篇
  1974年   56篇
  1973年   56篇
  1972年   52篇
  1971年   51篇
排序方式: 共有7891条查询结果,搜索用时 78 毫秒
31.
32.
A palaeoecological approach was undertaken to investigate the last 400 years of change in vegetation, fire, nutrient mobility, lake productivity and erosion associated with Aboriginal and European land-use practices in a forested environment in eastern Victoria. Melaleuca ericifolia scrub, although present prior to European settlement, has expanded around Lake Curlip in the last 200 years, primarily due to the action of fire on a forest already weakened by drought. A fern understorey has declined in extent and a more open aspect has developed in the forest. Fire has been a major component of vegetation dynamics in the historical period. Erosion rates were comparatively low and associated with fire during prehistoric times, but after European settlement its increase is more closely related to land clearance and flooding than fire. The response of vegetation to both anthropogenic and natural influences changed during the historical period. Although fire is an integral part of vegetation change, it is not an over-riding effect at Lake Curlip. Drain construction in the swamp has reduced the impact that any accumulation of pasture improvement chemicals may have had on eutrophication of the lake.  相似文献   
33.
ABSTRACT. The dynamic relationship between sectoral value added and regional economic growth is analyzed using a stochastic intersectoral model estimated by ordinary least squares and linear systems techniques. A state-space portion of the model identifies the time element of sedoral value added. Dynamic multipliers, tracing the temporal path of regional growth, are calculated for the state of Georgia over the period 1963–1986. This application shows that the impacts of sectoral shocks can follow cyclical as well as monotonic patterns and that the direction and magnitude of the impact may change over time.  相似文献   
34.
35.
Charcot-Marie-Tooth disease is a hereditary motor and sensory neuropathy first described in 1886. Our increasing knowledge of this disease correlates well with the development of methods used in neurology over the past 100 years. Although its physiopathology and treatment is still not fully understood, current developments in techniques are opening the way to future discoveries. We have divided its history into three theoretical periods: the first from 1886 to 1956, which was devoted to clinical and pathological study of the disease; the second from 1956 to 1982, which saw the development of electromyography in the investigation of neuromuscular diseases; and the last and current period based upon genetic research, using the methods of molecular biology.  相似文献   
36.
Spatial compactness has been proposed as a suitable criterion for assessing whether electoral boundaries reflect partisan interests. Although several different measures of spatial compactness have been developed, only limited efforts have been made to compare and evaluate them in the context of electoral redistricting. This paper assesses alternative spatial compactness measures and applies conceptually appealing measures to the provincial ridings proposed by British Columbia's Royal Commission on Electoral Boundaries (1988).  相似文献   
37.
ABSTRACT. This paper examines the impacts of JRS articles in the areas of theory, methods and empirical analysis, as represented by subsequent citations reported in the Social Sciences Citation Index. A model relating the mix of theoretical, methodological and empirical research published in the JRS to subsequent citations is estimated. The time distribution of theoretical and empirical citations also indicates that the knowledge diffusion process in these two areas may be segmented.  相似文献   
38.
Three rare Himyaritic coins found in the territory of the ancient Hadramawt kingdom are published for the first time. Two of the coins bear the name of the king,'Amdan Bayyin, while the third has the name of Tha'ran Ya'ub.  相似文献   
39.
40.
Summary At the end of the second chapter of the Buddhist Klacakra-Tantra (dated c. 10th century) we find a group of verses in which several doctrines are characterized and criticized: Brahmanism, Vaisnavism, aivism, materialism, Islam and Jainism. Moreover the text refers to Buddhism itself as well as the so-called heterodox Buddhist schools. It is the only old Sanskrit text known until now in which the Islam is mentioned and recognized as a doctrine.  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