全文获取类型
收费全文 | 3475篇 |
免费 | 591篇 |
国内免费 | 620篇 |
专业分类
测绘学 | 636篇 |
大气科学 | 202篇 |
地球物理 | 865篇 |
地质学 | 1863篇 |
海洋学 | 293篇 |
天文学 | 22篇 |
综合类 | 279篇 |
自然地理 | 526篇 |
出版年
2024年 | 5篇 |
2023年 | 26篇 |
2022年 | 91篇 |
2021年 | 121篇 |
2020年 | 122篇 |
2019年 | 121篇 |
2018年 | 96篇 |
2017年 | 133篇 |
2016年 | 149篇 |
2015年 | 162篇 |
2014年 | 230篇 |
2013年 | 224篇 |
2012年 | 237篇 |
2011年 | 305篇 |
2010年 | 244篇 |
2009年 | 268篇 |
2008年 | 210篇 |
2007年 | 236篇 |
2006年 | 253篇 |
2005年 | 186篇 |
2004年 | 205篇 |
2003年 | 159篇 |
2002年 | 131篇 |
2001年 | 124篇 |
2000年 | 122篇 |
1999年 | 99篇 |
1998年 | 86篇 |
1997年 | 54篇 |
1996年 | 62篇 |
1995年 | 46篇 |
1994年 | 52篇 |
1993年 | 25篇 |
1992年 | 24篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有4686条查询结果,搜索用时 281 毫秒
141.
142.
143.
郯庐断裂带晚中生代演化历史及其对华北克拉通破坏过程的指示 总被引:13,自引:8,他引:5
郯庐断裂带晚中生代的演化历史是华北克拉通破坏过程的重要记录。中侏罗世末(燕山运动A幕),郯庐断裂带局部发生左行平移活动,而华北克拉通上出现了一系列北北东走向的缩短构造,指示了西太平洋伊泽奈崎板块俯冲的开始。晚侏罗世期间,郯庐断裂带没有发生活动,而华北克拉通出现局部伸展与岩浆活动及区域性隆升,应为弧后弱拉张背景。早白垩世初(燕山运动B幕),郯庐断裂带再次发生强烈的左行平移活动,华北克拉通北部与东部出现了一系列近南北向挤压产生的构造,应是鄂霍茨克洋最终关闭与伊泽奈崎板块高速俯冲双重作用的结果。随后的早白垩世期间,华北克拉通在弧后拉张背景下发生峰期破坏,郯庐断裂带呈现为强烈的伸展活动。早白垩世末的区域性挤压作用,结束了华北克拉通的峰期破坏,并使郯庐断裂带再次发生了一期左行平移活动。这期挤压作用出现在太平洋板块接替伊泽奈崎板块这一重大板块调整的背景之中。 相似文献
144.
145.
Based on the dynamic analysis and research of pollution risk of groundwater sources, this paper creates the dynamic assessment method of pollution risk of groundwater source area under the theory of “source-pathway-receptor”, and applies this method to one typical fissure karst groundwater source area in northern China. Following the 30-year petroleum pollutant migration simulation and pollution risk assessment of groundwater source area, this study finds that the very high risk zone is mainly located in Q Petrochemical Company and the surrounding area and the area adjacent to River Z. Within this period of thirty years, the pollution risk of groundwater source area has showed a dynamic trend that features an inverted “V” shape. The ratio of very high risk zone to the total area will be 18.1%, 17.47% and 16.62% during the tenth year, the twentieth year and the thirtieth year separately, and will reach the highest level of 19.45% during the fifteenth year. Meanwhile, the vertical migration distance of pollutant centre concentration changed from the surface soil at the outset to the deepest point of about 250 meters underground during the tenth year. The results of this risk assessment indicate the dynamic feature of pollution risk. The dilution, degradation and migration of petroleum pollutants in groundwater system contribute to an ultimate decline in pollution risk. 相似文献
146.
The demise of the high-relief, steep-slope, prograding Ladinian-Early Carnian carbonate platforms of the Esino Limestone (Central Southern Alps of Italy) is marked by subaerial exposure of the platform top associated with different erosional (mainly karst-related), depositional and diagenetic processes (Calcare Rosso). The exposure-related deposits consist of three major facies associations: 1) residual soils with thin lenses of conglomerates with black pebbles, and, locally, weathered vulcanites; 2) chaotic breccia lenses irregularly distributed in the uppermost part of the Esino Limestone carbonate platform, interpreted as collapse breccias in karstic setting: 3) inter-supratidal carbonate cycles with dissolution and development of paleosols and tepee structures.Facies distribution follows the sub-environments of the underlying Esino Limestone. Facies 1 and 2 typically characterize the core of the platform, covering the underlying inner platform facies. Facies 3 instead develops toward the edge of the platform, above reef-upper slope facies of the prograding facies of the Esino Limestone. The thickness of facies 3 decreases toward the core of the platform. Facies distribution reflects differences in the accommodation space and sedimentary processes from the rim (highest accommodation, favouring the deposition of peritidal-supratidal carbonates) to the core (reduced accommodation, causing pedogenesis and karstification) of the carbonate system.The observed thickness changes may be controlled by different factors: 1) syndepositional tectonics, 2) subsidence induced by magmatic activity or 3) differential subsidence controlled by the stratigraphic architecture of the Esino Limestone platform and adjoining basins. As evidence of tectonics was not observed and the presence of volcanic bodies is only documented tens of km away from the study area, the scenario involving the creation of accommodation space by compaction of the basinal sediments (resedimented, fine-grained calciturbidites) during the progradation of the carbonate platform is here investigated. Numerical modelling was performed to verify the compatibility of compaction-induced subsidence with the observed depositional architecture. The models were built to simulate the architectural evolution of the platform by progressively adding layers from deepest to shallowest, while compacting the underlying sediments, in order to evaluate compaction-induced subsidence (and accommodation space for the Calcare Rosso) after the deposition of the youngest platform strata. Modelling results allow us to conclude that the wedge geometry of the Calcare Rosso, deposited on top of the extinct Esino carbonate platform, can be explained by subsidence controlled by compaction of the basinal sediments present below the early-cemented, fast prograding platform slope deposits. 相似文献
147.
148.
随着国家地下水监测工程的启动,国土资源部提出了国家、省、市新的三级地下水监测站网建设要求。该文介绍了各级地下水监测站网的基本概念、主要建设内容,各级地下水监测站网建设服务对象、基本要求,细化了各级地下水监测站网建设要求,规范了建设行动。 相似文献
149.
Abhishek Kumar Singh Anirban Lakshman Amares Chattopadhyay 《Geomechanics and Geoengineering》2016,11(3):201-218
Heterogeneity, being a trivial feature inside the earth or in a geostructure, makes a strong basis for its consideration in the study of geomechanics. Inclusion of the concept of heterogeneity along with irregularity in the medium brings a novelty to the existing literature related to the study of the moving load. The present study investigates the effects of linear and exponential heterogeneity on the dynamic response due to a normal load moving with constant velocity on a rough irregular heterogeneous isotropic half-space in a comparative approach. Expressions for both normal and shear stresses for either case of heterogeneity have been established in closed form. Substantial effects of the affecting parameters such as depth, irregularity factor, maximum depth of irregularity, frictional coefficient, linear heterogeneity parameter and exponential heterogeneity parameter on normal and shear stresses for both the cases of heterogeneity have been observed. Numerical computation has been carried out and the effects of said parameters have been meticulously examined by means of graphs. Moreover, different cases of heterogeneity and homogeneity along with various types of irregularity namely rectangular, parabolic and no irregularity are compared which serve as a focal theme of the study. 相似文献
150.
Jun Chen Zhen-Yu Yin Ye-Shuang Xu Suksun Horpibulsuk 《Marine Georesources & Geotechnology》2016,34(5):420-430
This article presents a case history of determination of effective depth of prefabricated vertical drains (PVDs) under embankment loading on a very soft clay deposit in central China, near Jiujiang, Jiangxi Province. The height of the embankment was 5.3 m and construction time was about one year. The PVDs were installed to a depth of 8.5 m at a spacing of 1.5 m in a triangular pattern. Field observations and the finite element method (FEM) were employed to analyze the performance of the soft deposit during embankment construction. The influential depth of the embankment loading was evaluated based on settlement, excess pore pressure, and stress increase in subsoil, both from the observed data and FEM analysis. The effective PVD depth was determined in the following ways: (1) the depth of 5% subsoil settlement of surface settlement; (2) vertical stress increase in subsoil of 25% in-situ stress; and (3) consolidation time/PVD depth relation by FEM. Based on the analysis, the effective depth of PVDs was determined to be between 10 and 12.8 m for this field case. 相似文献