全文获取类型
收费全文 | 91886篇 |
免费 | 1090篇 |
国内免费 | 1569篇 |
专业分类
测绘学 | 2913篇 |
大气科学 | 6338篇 |
地球物理 | 17812篇 |
地质学 | 35730篇 |
海洋学 | 7250篇 |
天文学 | 17685篇 |
综合类 | 2341篇 |
自然地理 | 4476篇 |
出版年
2022年 | 497篇 |
2021年 | 786篇 |
2020年 | 913篇 |
2019年 | 935篇 |
2018年 | 6459篇 |
2017年 | 5655篇 |
2016年 | 4621篇 |
2015年 | 1395篇 |
2014年 | 2173篇 |
2013年 | 3705篇 |
2012年 | 3218篇 |
2011年 | 5471篇 |
2010年 | 4551篇 |
2009年 | 5570篇 |
2008年 | 4681篇 |
2007年 | 5171篇 |
2006年 | 2802篇 |
2005年 | 2092篇 |
2004年 | 2229篇 |
2003年 | 2105篇 |
2002年 | 1918篇 |
2001年 | 1575篇 |
2000年 | 1490篇 |
1999年 | 1217篇 |
1998年 | 1263篇 |
1997年 | 1189篇 |
1996年 | 1033篇 |
1995年 | 998篇 |
1994年 | 949篇 |
1993年 | 804篇 |
1992年 | 766篇 |
1991年 | 758篇 |
1990年 | 849篇 |
1989年 | 686篇 |
1988年 | 659篇 |
1987年 | 820篇 |
1986年 | 675篇 |
1985年 | 888篇 |
1984年 | 932篇 |
1983年 | 877篇 |
1982年 | 827篇 |
1981年 | 792篇 |
1980年 | 721篇 |
1979年 | 653篇 |
1978年 | 661篇 |
1977年 | 571篇 |
1976年 | 577篇 |
1975年 | 569篇 |
1974年 | 540篇 |
1973年 | 567篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Carlsberg Ridge, northern Indian Ocean: gravity and isostasy 总被引:1,自引:0,他引:1
995.
996.
An assessment was made of the mean levels of major and trace elements and of biogenic and organic matter in glacial and river waters within the Aktru river basin (Gornyi Altai, Russia). The analysis showed a general tendency for an increase in mineralization along the direction from the region of alimentation of glaciers to the mouth of the river. A relatively abrupt increase was revealed in Al, Zn, Cu, Pb, Si, NO2 ? and NH4 + concentrations in the source of the Aktru river and its glacial tributaries, with their subsequent decrease downstream. The mechanism for such changes is governed by the conditions of interaction of rocks with meltwaters and river waters. 相似文献
997.
The Haji-Gak iron deposit of eastern Bamyan Province, eastern Afghanistan, was studied extensively and resource calculations
were made in the 1960s by Afghan and Russian geologists. Recalculation of the resource estimates verifies the original estimates
for categories A (in-place resources known in detail), B (in-place resources known in moderate detail), and C1 (in-place resources estimated on sparse data), totaling 110.8 Mt, or about 6% of the resources as being supportable for the
methods used in the 1960s. C2 (based on a loose exploration grid with little data) resources are based on one ore grade from one drill hole, and P2 (prognosis) resources are based on field observations, field measurements, and an ore grade derived from averaging grades
from three better sampled ore bodies. C2 and P2 resources are 1,659.1 Mt or about 94% of the total resources in the deposit. The vast P2 resources have not been drilled or sampled to confirm their extent or quality. The purpose of this article is to independently
evaluate the resources of the Haji-Gak iron deposit by using the available geologic and mineral resource information including
geologic maps and cross sections, sampling data, and the analog-estimating techniques of the 1960s to determine the size and
tenor of the deposit. 相似文献
998.
999.
G. Wilson D. Damaske H.-D. Möller K. Tinto T. Jordan 《Geophysical Journal International》2007,170(1):93-100
Magnetic anomaly data are presented from a new helicopter-borne high-resolution aeromagnetic survey in southern McMurdo Sound. Anomaly data have been acquired at a common 305 m elevation above the McMurdo and southern McMurdo ice shelves and draped over the volcanic islands that pin them. The resulting anomaly patterns provide a significant advance in the understanding of the rift related geology beneath the floating ice shelves. More extensive Erebus Volcanic Province (McMurdo Volcanic Group) rocks are indicated along with a significant blanket of glaci-volcaniclastic sediment on the seafloor between the volcanic islands in southern McMurdo Sound. These glaci-volcaniclastic sediments are inferred to originate from former grounding of the southern McMurdo Ice Shelf as a marine ice sheet. A strong N–S fabric is also observed in the anomaly data suggesting that the rift structure observed in the Victoria Land basin persists to the south beneath the McMurdo and southern McMurdo ice shelves. W–N–W transfer faults identified within the Transantarctic Mountain rift flank to the west are not obvious in the aeromagnetic data set, implying that the 'Discovery Accommodation Zone' may be restricted to the region between a southward extension of the range bounding fault that marks the limit of the Victoria Land Basin and the right lateral offset in the Transantarctic Mountain front in southern Victoria Land. 相似文献
1000.
This study of fossils (pollen, plant macrofossils, stomata and fish) and sediments (lithostratigraphy and geochemistry) from
the Wendel site in North Dakota, USA, emphasizes the importance of considering ground-water hydrology when deciphering paleoclimate
signals from lakes in postglacial landscapes. The Wendel site was a paleolake from about 11,500 14C yr BP to 11,100 14C yr BP. Afterwards, the lake-level lowered until it became a prairie marsh by 9,300 14C yr BP and finally, at 8,500 14C yr BP, an ephemeral wetland as it is today. Meanwhile, the vegetation changed from a white spruce parkland (11,500 to 10,500
14C yr BP) to deciduous parkland, followed by grassland at 9,300 14C yr BP. The pattern and timing of these aquatic and terrestrial changes are similar to coeval kettle lake records from adjacent
uplands, providing a regional aridity signal. However, two local sources of ground water were identified from the fossil and
geochemical data, which mediated atmospheric inputs to the Wendel basin. First, the paleolake received water from the melting
of stagnant ice buried under local till for about 900 years after glacier recession. Later, Holocene droughts probably caused
the lower-elevation Wendel site to capture the ground water of up-gradient lakes. 相似文献