全文获取类型
收费全文 | 37072篇 |
免费 | 594篇 |
国内免费 | 579篇 |
专业分类
测绘学 | 934篇 |
大气科学 | 3079篇 |
地球物理 | 7399篇 |
地质学 | 12246篇 |
海洋学 | 3366篇 |
天文学 | 8694篇 |
综合类 | 120篇 |
自然地理 | 2407篇 |
出版年
2021年 | 198篇 |
2020年 | 258篇 |
2019年 | 255篇 |
2018年 | 611篇 |
2017年 | 563篇 |
2016年 | 878篇 |
2015年 | 619篇 |
2014年 | 848篇 |
2013年 | 1889篇 |
2012年 | 1035篇 |
2011年 | 1449篇 |
2010年 | 1197篇 |
2009年 | 1772篇 |
2008年 | 1569篇 |
2007年 | 1494篇 |
2006年 | 1406篇 |
2005年 | 1287篇 |
2004年 | 1211篇 |
2003年 | 1166篇 |
2002年 | 1093篇 |
2001年 | 977篇 |
2000年 | 984篇 |
1999年 | 925篇 |
1998年 | 836篇 |
1997年 | 846篇 |
1996年 | 723篇 |
1995年 | 652篇 |
1994年 | 565篇 |
1993年 | 517篇 |
1992年 | 513篇 |
1991年 | 484篇 |
1990年 | 482篇 |
1989年 | 420篇 |
1988年 | 403篇 |
1987年 | 449篇 |
1986年 | 435篇 |
1985年 | 523篇 |
1984年 | 583篇 |
1983年 | 559篇 |
1982年 | 519篇 |
1981年 | 463篇 |
1980年 | 435篇 |
1979年 | 397篇 |
1978年 | 412篇 |
1977年 | 358篇 |
1976年 | 323篇 |
1975年 | 336篇 |
1974年 | 336篇 |
1973年 | 338篇 |
1972年 | 201篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
J. C. Gutmanis 《Geological Journal》1989,24(3):183-192
A tectonic study of the Newberry Crater region of central Oregon has been based on the interpretation of Landsat Thematic Mapper imagery. Two major faults, the Brothers-Tumalo and Eugene-Denio Faults, pass NW-SE through the region and step to the right at the eastern margin of the Cascades Range. Dextral wrench faulting on these structures during the Tertiary controlled the formation of the La Pine Basin, a pull-apart structure containing Tertiary and Quaternary sediments and volcanics. Tertiary wrench faulting appears to have been associated with rotations of crustal blocks at a plate margin, but was superseded in the Quaternary by extensional faulting of the Basin and Range province. Newberry Crater and other major bimodal volcanic centres in the NW Cordillera (Crater Lake, Medicine Lake, Mt. St. Helens) seem to have a similar tectonic setting in crustal pull-aparts. A relationship between magma type and fault trend at Newberry and Medicine Lake is suggested. 相似文献
155.
156.
Summary Future research directions for agricultural geography were the subject of debate in Area in the late 1980s, and the subsequent application of political economy ideas undoubtedly revived interest in agricultural research. This paper argues that agricultural geography contains greater diversity than the dominant political economy discourse would suggest. It reviews 'other' areas of agricultural research such as policy, post- productivism, people, culture and animals, presenting future suggestions which should ensure that agricultural research continues revitalized rather than redundant into the next millennium. 相似文献
157.
158.
159.
K.D. Wake-Dyster M.J. Sexton D.W. Johnstone C. Wright D.M. Finlayson 《Geophysical Journal International》1987,89(1):423-430
Summary. In 1984, the Australian Bureau of Mineral Resources and the Geological Survey of Queensland recorded a regional seismic reflection profile of over 800 km length from the eastern part of the Eromanga Basin to the Beenleigh Block east of the Clarence Moreton Basin. A relatively transparent upper crustal basement with an underlying, more reflective lower crust is characteristic of much of the region. Prominent westerly dipping reflectors occur well below the sediments of the eastern margin of the Clarence Moreton Basin and the adjacent Beenleigh Block, and provide some of the most interesting features of the entire survey. A wide angle reflection/refraction survey of 192 km length and an expanding reflection spread of 25 km length were recorded across the Nebine Ridge. The only clear deep reflectors are interpreted as P-to-SV or SV-to-P converted reflections from a mid-crustal boundary at a depth of about 17 km. The combined Nebine Ridge data provide well-constrained P and S wave velocity models of the upper crust, and suggest a crustal structure quite different from that beneath the adjacent Mesozoic basins. 相似文献
160.
This paper investigates the impact of a 1000‐year flood in August 2002 on floodplains and valley morphology of an Austrian mixed alluvial bed rock river. Discharges with a recurrence interval between 500 and 2000 years caused distinctive overbank scouring and material deposition in the floodplains. After the 1000‐year flood, those morphologically affected areas were at random intervals documented over the whole longitudinal profile. In addition to overbank erosion in curved sections (cut‐offs), the river bed locally widened, floodplain stripping occurred and local overbank scours were documented along straight parts of the river. A hydrodynamic‐numerical model, combined with field measurements, was used to analyse the cause of these erosional landforms. Based on the modelled hydraulic conditions for a one‐year flood (30–78 m3 s–1) and the catastrophic 2002 event (700–800 m3 s–1), the numerical results allowed a cause‐effect study with 19 parameters. Deterministic and statistical analysis (ANOVA, discriminant analysis) showed that the morphodynamic effects of the 2002 flood were influenced by the variability of valley morphology of the Kamp River, which led partially to supercritical flow during flood constriction. These processes were in some cases also anthropogenically influenced. Lateral constriction and expansion of the valley geometry over short distances led to scouring and aggradation within the inundated areas during the event. These morphological features were therefore responsible for the elongated scour holes in the floodplains. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献