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   5104篇
  免费   172篇
  2020年   57篇
  2019年   80篇
  2018年   128篇
  2017年   128篇
  2016年   150篇
  2015年   110篇
  2014年   102篇
  2013年   1524篇
  2012年   121篇
  2011年   165篇
  2010年   139篇
  2009年   104篇
  2008年   108篇
  2007年   92篇
  2006年   77篇
  2005年   82篇
  2004年   78篇
  2003年   51篇
  2002年   51篇
  2001年   76篇
  2000年   69篇
  1999年   68篇
  1998年   55篇
  1997年   59篇
  1996年   47篇
  1995年   47篇
  1994年   51篇
  1993年   51篇
  1992年   59篇
  1991年   44篇
  1990年   34篇
  1989年   44篇
  1988年   44篇
  1987年   54篇
  1986年   38篇
  1985年   60篇
  1984年   42篇
  1983年   75篇
  1982年   64篇
  1981年   65篇
  1980年   69篇
  1979年   53篇
  1978年   58篇
  1977年   71篇
  1976年   56篇
  1975年   61篇
  1974年   46篇
  1973年   41篇
  1972年   41篇
  1971年   38篇
排序方式: 共有5276条查询结果,搜索用时 31 毫秒
121.
122.
The fossil record suggests that modern human morphology evolved in Africa between 150,000 and 50,000 years ago, when the sole inhabitants of Eurasia were the Neanderthals and other equally nonmodern people. However, the earliest modern or near-modern Africans were behaviorally (archaeologically) indistinguishable from their nonmodern, Eurasian contemporaries, and it was only around 50,000-40,000 years ago that a major behavioral difference developed. Archaeological indications of this difference include the oldest indisputable ornaments (or art broadly understood); the oldest evidence for routine use of bone, ivory, and shell to produce formal (standardized) artifacts; greatly accelerated variation in stone artifact assemblages through time and space; and hunting-gathering innovations that promoted significantly larger populations. As a complex, the novel traits imply fully modern cognitive and communicative abilities, or more succinctly, the fully modern capacity for Culture. The competitive advantage of this capacity is obvious, and preliminary dates suggest that it appeared in Africa about 50,000 years ago and then successively in western Asia, eastern Europe, and western Europe, in keeping with an African origin. Arguably, the development of modern behavior depended on a neural change broadly like those that accompanied yet earlier archaeologically detectable behavioral advances. This explanation is problematic, however, because the putative change was in brain organization, not size, and fossil skulls provide little or no secure evidence for brain structure. Other potential objections to a neural advance in Africa 50,000-40,000 years ago or to the wider Out-of-Africa hypothesis, include archaeological evidence (1) that some Neanderthals were actually capable of fully modern behavior and (2) that some Africans were behaviorally modern more than 90,000 years ago.  相似文献   
123.
124.
Acid sulphate soils form when iron pyrite oxidises to sulphuric acid on atmospheric exposure, lowering soil pH below 4. In the Richmond River estuary, northern New South Wales, flood mitigation, drainage works and floodplain excavations have augmented acid sulphate soil formation by increasing pyrite availability for oxidation. These engineering works have facilitated the transport of acidified water and have impeded recovery from tributary acidification. The increased frequency and duration of acidification are associated with elevated concentrations of inorganic monomeric aluminium and dissolved iron, and major iron hydroxide precipitation, with deleterious effects on exposed aquatic biota and habitat. Fish kills and an outbreak of epizootic ulcerative syndrome (EUS) have been recorded from acidified sites in the estuary.  相似文献   
125.
The sovereignty of the bleak Kurile islands, off northern Japan, has long been the subject of a bitter stand-off between Russia and Japan. This has not only prevented their signing a post-1945 Peace Treaty but has retarded the flow of official financial assistance and corporate investment funds across the few hundred kilometre-wide Sea of Japan. As a result the reconstruction of the Russian Far East has been made more difficult, thus exacerbating the economic and social hardship there. Examples like this should cause us to reflect on the dangers of making simplistic explanations about the spatial organisation of economic activity as well as the need to rediscover political geography.  相似文献   
126.
127.
128.
129.
130.
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