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   42027篇
  免费   1631篇
  2020年   537篇
  2019年   827篇
  2018年   933篇
  2017年   1134篇
  2016年   1226篇
  2015年   935篇
  2014年   912篇
  2013年   14107篇
  2012年   1054篇
  2011年   1089篇
  2010年   1090篇
  2009年   1073篇
  2008年   1014篇
  2007年   923篇
  2006年   823篇
  2005年   582篇
  2004年   575篇
  2003年   540篇
  2002年   515篇
  2001年   533篇
  2000年   471篇
  1999年   543篇
  1998年   468篇
  1997年   420篇
  1996年   409篇
  1995年   421篇
  1994年   366篇
  1993年   418篇
  1992年   395篇
  1991年   297篇
  1990年   293篇
  1989年   315篇
  1988年   311篇
  1987年   335篇
  1986年   312篇
  1985年   428篇
  1984年   458篇
  1983年   465篇
  1982年   400篇
  1981年   394篇
  1980年   431篇
  1979年   425篇
  1978年   411篇
  1977年   432篇
  1976年   380篇
  1975年   384篇
  1974年   295篇
  1973年   269篇
  1972年   250篇
  1970年   226篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Abstract. This article considers the debate that has recently developed in studies of nationalism between those scholars who see the nation as a modern and constantly changing construction ex nihilo and those who see it as an immemorial, unchanging communal essence. It outlines the so-called ‘gastronomical’ and ‘geological’ metaphors of nation formation and suggests a synthetic model which balances the influence of the ethnic past and the impact of nationalist activity. It shows that the central question which has divided theorists of nationalism is the place of the past in the life of modern nations. The author recognises the role of nationalists in national mobilisation but stresses that nationalists are not social engineers or mere image makers as modernist and post-modernist accounts would have it, but rather social and political archaeologists whose activities consist in the rediscovery and reinterpretation of the ethnic past and through it the regeneration of their national community.  相似文献   
922.
923.
924.
925.
926.
927.
Random Time Sampling is an innovative data collection method which has potential for adaptation and use by geographers. Individual pocket-sized programmable beepers were used in a pilot study of the uses of time by older households and older people's attitudes to different activities. Random beeps were used to prompt individuals living in eleven Melbourne suburbs to record time use data in diaries over a period of a week. The method proved extremely effective and reliable, and many participants reporting that they enjoyed the exercise.  相似文献   
928.
The Lane Cove River drains an established urbanised catchment and is impacted by urban runoff, point sources of pollution from sewer overflows and leachate from a refuse tip. The Sydney Water Board conducted a three year water quality monitoring programme assessing the impacts of pollution. The findings are presented and the impact of urbanisation evaluated by comparing water quality in urban and non-urban catchments. Water quality in a near-pristine control creek was consistently better than the urban catchment in all weather conditions. During wet weather, water quality in urban creeks deteriorated significantly, although the control creek generally remained in a near-pristine condition. Poor water quality in urbanised reaches of the catchment has degraded the aquatic ecosystem, encouraged and sustained weed infestation of the riparian environment and restricted recreational use of the river.  相似文献   
929.
A trial, monitored release on the Wingecarribee River over 27 days had a peak discharge below the Wingecarribee Dam of 1090 ML/d, which had a flow duration of 0.95 per cent. Morphological impacts on 29 km of channel below the dam included bank erosion, concentrated neck overflow, bed degradation and channel widening at recent cutoffs, sedimentation in weir pools and overbank flow, particularly at discharges greater than 800 ML/d. Prolonged operational releases at bankfull discharge (400–800 ML/d) will have the greatest morphologic impacts and should be avoided. Pulses which dissipate stream power over a broad, well-vegetated floodplain should be incorporated in the operational release policy, provided such pulses are phased to facilitate channel and vegetation recovery.  相似文献   
930.
There is increasing concern about environmental impacts of acidic drainage from acid sulphate soils on Holocene estuarine flood plains. Acidity derives from oxidation of iron pyrite in the sediments. Natural factors determine concentrations and distributions of pyrite accumulations, but human activities have reduced pyrite accumulation in the Pearl River Delta with land use practices increasing terrestrial sediment discharge. Large freshwater discharges and management techniques have enabled sustainable use of these soils. High concentrations of pyrite occur in many estuarine flood plains of Australia because of relatively greater marine inputs. Drainage of these soils enhances pyrite oxidation and estuarine acidification, which is associated with fish-kills. For sustainable development, the problems of acid sulphate soil drainage must be recognised and overcome.  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