全文获取类型
收费全文 | 8588篇 |
免费 | 1717篇 |
国内免费 | 2927篇 |
专业分类
测绘学 | 780篇 |
大气科学 | 537篇 |
地球物理 | 3726篇 |
地质学 | 5068篇 |
海洋学 | 1364篇 |
天文学 | 34篇 |
综合类 | 671篇 |
自然地理 | 1052篇 |
出版年
2024年 | 25篇 |
2023年 | 98篇 |
2022年 | 268篇 |
2021年 | 310篇 |
2020年 | 411篇 |
2019年 | 485篇 |
2018年 | 411篇 |
2017年 | 402篇 |
2016年 | 479篇 |
2015年 | 511篇 |
2014年 | 557篇 |
2013年 | 599篇 |
2012年 | 593篇 |
2011年 | 667篇 |
2010年 | 576篇 |
2009年 | 665篇 |
2008年 | 576篇 |
2007年 | 620篇 |
2006年 | 648篇 |
2005年 | 546篇 |
2004年 | 560篇 |
2003年 | 451篇 |
2002年 | 360篇 |
2001年 | 296篇 |
2000年 | 308篇 |
1999年 | 292篇 |
1998年 | 250篇 |
1997年 | 221篇 |
1996年 | 208篇 |
1995年 | 161篇 |
1994年 | 139篇 |
1993年 | 125篇 |
1992年 | 112篇 |
1991年 | 64篇 |
1990年 | 58篇 |
1989年 | 47篇 |
1988年 | 29篇 |
1987年 | 26篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 9篇 |
1977年 | 14篇 |
1971年 | 1篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
301.
The spatial calculating analysis model is based on GIS overlay. It will compartmentalize the land in research district into three spatial types: unchanged parts, converted parts and increased parts. By this method we can evaluate the numerical model and dynamic degree model for calculating land-use change rates. Furthermore, the paper raises the possibility of revising the calculating analysis model of spatial information in order to predicate more precisely the dynamic changing level of all types of land uses. In the most concrete terms, the model is used mainly to understand changed area and changed rates (increasing or decreasing) of different land types from microcosmic angle and establish spatial distribution and spatio-temporal principles of the changing urban lands. And we will try to find out why the situation can take place by combining social and economic situations. The result indicates the calculating analysis model of spatial information can derive more accurate procedure of spatial transference and increase of all kinds of land from microcosmic angle. By this model and technology we can conduct the research of land-use spatio-temporal structure evolution more systematically and more deeply, and can obtain a satisfactory result. The result will benefit the rational planning and management of urban land use of developed coastal areas in China in the future. 相似文献
302.
303.
304.
305.
306.
Introduction The Great North China, located at longitude 106E to 124E and latitude 31N to 42N, in-cludes three secondary active tectonic blocks, Ordos, Yanshan and North China plain (Figure 1). The geological tectonics of these three secondary blocks is much different from each other. As a stable block with high rigidity, the Ordos block is mostly surrounded by down-faulted basins with an inactive interior since Cenozoic, although the fault zones along its boundary are strongly active wi… 相似文献
307.
Preliminary study on variation characteristics of ocean tide dynamic stress in crust and its relationship with earthquakes 总被引:1,自引:0,他引:1
~~Preliminary study on variation characteristics of ocean tide dynamic stress in crust and its relationship with earthquakes@陆明勇$China Center for Earthquake Disaster Emergency and SAR,Beijing 100049,China
@郑文衡$Huazhong University of Science and Technology,Wuhan 430074,China①Strong earthquake catalogues in China. Earthquake catalogues reported monthly by Center for Analysis and Prediction, CEA.
①YI Zhi-gang. Institute of Crustal Dynamics, China Earthquake Administrati… 相似文献
308.
Introduction The acceleration response spectrum and peak ground acceleration are the necessary and im-portant parameters in earthquake-resistant design at present. They are still active research field. With the increase of digital high accurate strong motion observation data, especially the earth-quakes of Loma Prieta (M=7.0) in 1989; Landers (M=7.3) in 1992; Big Bear (M=6.4) in 1994 and Northridge (M=6.7) in 1994 in USA; Kozani (M=6.6) earthquake and afteshocks in 1995 in Greece; Dinar… 相似文献
309.
T. Wichtmann A. Niemunis Th. Triantafyllidis 《Soil Dynamics and Earthquake Engineering》2005,25(12):967-979
Our aim is the prediction of the accumulation of strain and/or stress under cyclic loading with many (thousands to millions) cycles and relatively small amplitudes. A high-cycle constitutive model is used for this purpose. Its formulas are based on numerous cyclic tests. This paper describes drained tests with triaxial compression and uniaxial stress cycles. The influence of the strain amplitude, the average stress, the density, the cyclic preloading history and the grain size distribution on the direction and the intensity of strain accumulation is discussed. 相似文献
310.
Caldera formation has been explained by magma withdrawal from a crustal reservoir, but little is known about the conditions that lead to the critical reservoir pressure for collapse. During an eruption, the reservoir pressure is constrained to lie within a finite range: it cannot exceed the threshold value for eruption, and cannot decrease below another threshold value such that feeder dykes get shut by the confining pressure, which stops the eruption. For caldera collapse to occur, the critical reservoir pressure for roof failure must therefore be within this operating range. We use an analytical elastic model to evaluate the changes of reservoir pressure that are required for failure of roof rocks above the reservoir with and without a volcanic edifice at Earth's surface. With no edifice at Earth's surface, faulting in the roof region can only occur in the initial phase of reservoir inflation and affects a very small part of the focal area. Such conditions do not allow caldera collapse. With a volcanic edifice, large tensile stresses develop in the roof region, whose magnitude increase as the reservoir deflates during an eruption. The edifice size must exceed a threshold value for failure of the roof region before the end of eruption. The largest tensile stresses are reached at Earth's surface, indicating that faulting starts there. Failure affects an area whose horizontal dimensions depend on edifice and chamber dimensions. For small and deep reservoirs, failure conditions cannot be achieved even if the edifice is very large. Quantitative predictions are consistent with observations on a number of volcanoes. 相似文献