全文获取类型
收费全文 | 899篇 |
免费 | 37篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 65篇 |
地球物理 | 190篇 |
地质学 | 270篇 |
海洋学 | 87篇 |
天文学 | 176篇 |
综合类 | 8篇 |
自然地理 | 112篇 |
出版年
2024年 | 9篇 |
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 21篇 |
2018年 | 17篇 |
2017年 | 27篇 |
2016年 | 20篇 |
2015年 | 18篇 |
2014年 | 29篇 |
2013年 | 21篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 36篇 |
2009年 | 54篇 |
2008年 | 47篇 |
2007年 | 44篇 |
2006年 | 37篇 |
2005年 | 31篇 |
2004年 | 39篇 |
2003年 | 43篇 |
2002年 | 31篇 |
2001年 | 17篇 |
2000年 | 20篇 |
1999年 | 18篇 |
1998年 | 23篇 |
1997年 | 9篇 |
1996年 | 17篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 15篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有938条查询结果,搜索用时 0 毫秒
51.
52.
The mechanisms of finite brittle strain 总被引:1,自引:0,他引:1
53.
54.
Electron microprobe analyses and petrographic observations demonstrate that Almelo Township (L6), Beeler (LL6), Kalvesta (H4), Phillips County (L6), and Yocemento (L5) are typical ordinary chondrites. Selden has abnormally iron-rich silicates and nickel-rich metal, and it may have been a lower petrologic type that has been shocked to an LL5. Shielding corrected exposure ages range from 0.80 m.y. (Kalvesta) to 47.0 m.y. (Yocemento). 相似文献
55.
"This paper investigates the life, migration and retirement experiences of elderly British residents of Tuscany and its adjacent districts.... Many pathways have led the elderly British to Tuscany; only a minority have simply migrated from the UK on retirement.... Key themes explored include class background, reasons for migration to Tuscany, previous connections to Italy, post-retirement behaviour, integration and future plans. The findings challenge some commonly-held ?expectations' about the nature of retirement migration." 相似文献
56.
Differences in trace metal concentrations among fluvial morphologic units and implications for sampling 总被引:2,自引:0,他引:2
This study examines the segregation of trace metals within and between fluvial morphologic units in sand-sized and finer
bed sediments in a cobble bed stream. The types of fluvial morphologic units sampled are low gradient riffles, high gradient
riffles, glides, eddy drop zones, lateral scour pools, attached bars, and detached bars. Three to nine samples were collected
from ten of each type of morphologic unit. All 12 metals show significantly different concentrations between some morphologic
units in sediments smaller than 2 mm. Eddy drop zones and attached bars consistently have the highest metal concentrations,
while low gradient riffles, high gradient riffles, and glides typically have the lowest concentrations. Metals showing the
greatest between-unit variability are Al, Cr, Fe, Cu, and Ti, followed by Co, Mn, and Pb, while Mg, Mn, V, and Zn display
relatively few differences between units. Lateral and longitudinal variations of metals within units are not significant,
and there was no consistent, predictable variation in metal concentrations with distance downstream. Results indicate that
metal studies in other gravel- and cobble-bed streams should include a reconnaissance survey to determine variations between
morphologic units, stratify sampling by morphologic unit, and analyze spatial autocorrelation to determine sample spacing.
Received: October 1997 · Accepted: 23 March 1998 相似文献
57.
L.J. King N. Jackson R.D. Blandford M.N. Bremer I.W.A. Browne A.G. de Bruyn C. Fassnacht L. Koopmans D. Marlow P.N. Wilkinson 《Monthly notices of the Royal Astronomical Society》1998,295(2):L41-L44
We report the discovery, using NICMOS on the Hubble Space Telescope , of an arcsec-diameter Einstein ring in the gravitational lens system B1938+666. The lensing galaxy is also detected, and is most likely an early-type galaxy. Modelling of the ring is presented and compared with the radio structure from MERLIN maps. We show that the Einstein ring is consistent with the gravitational lensing of an extended infrared component, centred between the two radio components. 相似文献
58.
59.
60.
Split Butte is a volcanic crater of Quaternary age consisting of a tephra ring which at one time retained a lava lake. The tephra is thinly bedded and is composed of partially palagonitized sideromelane clasts and subordinate lithic fragments. The beds typically dip radially away from the center of the crater, but locally dip toward the crater center. The tephra ring resulted from phreatomagmatic eruptions as a result of interaction of groundwater with rising basaltic magma, evidenced by glassy and granulated pyroclastic debris, the presence of abundant palagonite and other secondary minerals, numerous armored lapilli, and plastically deformed ash layers below ejecta blocks. Statistical analysis of the grain size distribution of the ash also indicates a phreatomagmatic origin of Split Butte tephra. In addition, the analysis reveals that the stratigraphically lowest tephra was deposited primarily by pyroclastic flow mechanisms while the upper tephra layers, comprising the bulk of the deposits, were deposited dominantly by airfall and pyroclastic surge. The lava lake and four en echelon basalt dikes were emplaced when phreatomagmatic activity at the vent ceased. Subsequent collapse caused a broad, shallow pit crater to form in the laval lake, and minor spattering occurred at one point along the pit crater scarp. Partial erosion of the tephra, deposition of aeolian sediments and encroachment of the Butte by later lava flows completed the development of Split Butte. 相似文献