全文获取类型
收费全文 | 6683篇 |
免费 | 168篇 |
专业分类
6851篇 |
出版年
2020年 | 63篇 |
2019年 | 75篇 |
2018年 | 406篇 |
2017年 | 316篇 |
2016年 | 362篇 |
2015年 | 116篇 |
2014年 | 104篇 |
2013年 | 1591篇 |
2012年 | 150篇 |
2011年 | 307篇 |
2010年 | 303篇 |
2009年 | 146篇 |
2008年 | 197篇 |
2007年 | 210篇 |
2006年 | 87篇 |
2005年 | 116篇 |
2004年 | 90篇 |
2003年 | 45篇 |
2002年 | 62篇 |
2001年 | 81篇 |
2000年 | 69篇 |
1999年 | 70篇 |
1998年 | 58篇 |
1997年 | 59篇 |
1996年 | 53篇 |
1995年 | 46篇 |
1994年 | 55篇 |
1993年 | 60篇 |
1992年 | 62篇 |
1991年 | 45篇 |
1990年 | 42篇 |
1989年 | 47篇 |
1988年 | 53篇 |
1987年 | 58篇 |
1986年 | 45篇 |
1985年 | 76篇 |
1984年 | 62篇 |
1983年 | 86篇 |
1982年 | 76篇 |
1981年 | 70篇 |
1980年 | 75篇 |
1979年 | 62篇 |
1978年 | 59篇 |
1977年 | 84篇 |
1976年 | 50篇 |
1975年 | 66篇 |
1974年 | 51篇 |
1973年 | 40篇 |
1971年 | 38篇 |
1969年 | 36篇 |
排序方式: 共有6851条查询结果,搜索用时 15 毫秒
91.
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
92.
G.J.R. LINGE 《Geographical Research》1995,33(1):116-132
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
93.
94.
95.
96.
97.
Richard S. Davis 《Journal of Archaeological Research》1998,6(2):169-194
Recent Paleolithic work along the middle Enisei River of central Siberia has revealed a long history of occupation that almost certainly begins in the Middle Pleistocene. Although the evidence for the Lower Paleolithic is somewhat tentative, there is good reason to believe that hunter-gatherers had periodically occupied the middle Enisei before the last interglacial. The steppe environment of the region during the Upper Pleistocene was relatively bountiful; more than 200 Upper Paleolithic sites, both before and after the Last Glacial Maximum, have been located. The region appears to have been abandoned during the Last Glacial Maximum. Most of Soviet and Russian archaeological work has been guided by a cultural–historical orientation, but recently there has been increased interest in developing adaptationist and ecological research strategies. The middle Enisei and the wider central Siberian region are key to understanding early adaptations to the north and the dimensions of Paleolithic population movements. 相似文献
98.
Richard Walker 《对极》1996,28(4):329-337
99.
G.A Loud 《Journal of Medieval History》1996,22(4):313-343
The Campania was a fertile area, with a growing population during the eleventh and twelfth centuries, and was economically more advanced than most of the rest of southern Italy. This essay examines the impact of the Norman conquest of the south upon this region, with special reference to the settlement pattern and the aristocracy. It concludes that the role of incastellamento in changing the pattern of settlement was relatively limited, and the extensive incastellamento of the Montecassino lands (a product of Norman pressure upon the abbey) cannot be taken as typical. Furthermore, while the Norman conquest led to colonisation by French aristocrats, this did not entirely displace existing Lombard families, and widespread intermarriage led to a blurring of the distinction between Lombards and Normans. The impact of political crises during the twelfth century was also more limited than might be supposed, and continuity rather than change characterised the nobility of the Norman period. 相似文献
100.