全文获取类型
收费全文 | 2206篇 |
免费 | 146篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 87篇 |
大气科学 | 227篇 |
地球物理 | 646篇 |
地质学 | 846篇 |
海洋学 | 127篇 |
天文学 | 292篇 |
综合类 | 21篇 |
自然地理 | 118篇 |
出版年
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 51篇 |
2020年 | 46篇 |
2019年 | 42篇 |
2018年 | 87篇 |
2017年 | 92篇 |
2016年 | 128篇 |
2015年 | 109篇 |
2014年 | 124篇 |
2013年 | 203篇 |
2012年 | 157篇 |
2011年 | 137篇 |
2010年 | 120篇 |
2009年 | 100篇 |
2008年 | 86篇 |
2007年 | 62篇 |
2006年 | 70篇 |
2005年 | 58篇 |
2004年 | 44篇 |
2003年 | 45篇 |
2002年 | 57篇 |
2001年 | 41篇 |
2000年 | 20篇 |
1999年 | 21篇 |
1998年 | 22篇 |
1997年 | 23篇 |
1996年 | 16篇 |
1995年 | 26篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 22篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 19篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 20篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1973年 | 17篇 |
1969年 | 10篇 |
排序方式: 共有2364条查询结果,搜索用时 221 毫秒
91.
By incorporating the fabric effect and Lode’s angle dependence into the Mohr–Coulomb failure criterion, a strength criterion for cross-anisotropic sand under general stress conditions was proposed. The obtained criterion has only three material parameters which can be specified by conventional triaxial tests. The formula to calculate the friction angle under any loading direction and intermediate principal stress ratio condition was deduced, and the influence of the degree of the cross-anisotropy was quantified. The friction angles of sand in triaxial, true triaxial, and hollow cylinder torsional shear tests were obtained, and a parametric analysis was used to detect the varying characteristics. The friction angle becomes smaller when the major principal stress changes from perpendicular to parallel to the bedding plane. The loading direction and intermediate principal stress ratio are unrelated in true triaxial tests, and their influences on the friction angle can be well captured by the proposed criterion. In hollow cylinder torsional shear tests with the same internal and external pressures, the loading direction and intermediate principal stress ratio are related. This property results in a lower friction angle in the hollow cylinder torsional shear test than that in the true triaxial test under the same intermediate principal stress ratio condition. By comparing the calculated friction angle with the experimental results under various loading conditions (e.g., triaxial, true triaxial, and hollow cylinder torsional shear test), the proposed criterion was verified to be able to characterize the shear strength of cross-anisotropic sand under general stress conditions. 相似文献
92.
93.
94.
95.
Rafael J. de Moraes José R. P. Rodrigues Hadi Hajibeygi Jan Dirk Jansen 《Computational Geosciences》2018,22(6):1527-1541
A generic framework for the computation of derivative information required for gradient-based optimization using sequentially coupled subsurface simulation models is presented. The proposed approach allows for the computation of any derivative information with no modification of the mathematical framework. It only requires the forward model Jacobians and the objective function to be appropriately defined. The flexibility of the framework is demonstrated by its application in different reservoir management studies. The performance of the gradient computation strategy is demonstrated in a synthetic water-flooding model, where the forward model is constructed based on a sequentially coupled flow-transport system. The methodology is illustrated for a synthetic model, with different types of applications of data assimilation and life-cycle optimization. Results are compared with the classical fully coupled (FIM) forward simulation. Based on the presented numerical examples, it is demonstrated how, without any modifications of the basic framework, the solution of gradient-based optimization models can be obtained for any given set of coupled equations. The sequential derivative computation methods deliver similar results compared to FIM methods, while being computationally more efficient. 相似文献
96.
Terrinha Pedro Pueyo Emilio L. Aranguren Aitor Kullberg José Carlos Kullberg Maria Carla Casas-Sainz Antonio Azevedo Maria do Rosário 《International Journal of Earth Sciences》2018,107(5):1807-1833
International Journal of Earth Sciences - The geometry and emplacement of the ~ 96 km2, Late Cretaceous Sintra Igneous complex (SIC, ca. 80 Ma) into the West Iberian passive... 相似文献
97.
Grajales-Nishimura José Manuel Ramos-Arias Mario Alfredo Solari Luigi Murillo-Muñetón Gustavo Centeno-García Elena Schaaf Peter Torres-Vargas Ricardo 《International Journal of Earth Sciences》2018,107(3):1005-1031
International Journal of Earth Sciences - The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated... 相似文献
98.
Hydrogeology and sustainable future groundwater abstraction from the Agua Verde aquifer in the Atacama Desert,northern Chile 总被引:1,自引:0,他引:1
Javier Urrutia Jorge Jódar Agustín Medina Christian Herrera Guillermo Chong Harry Urqueta José A. Luque 《Hydrogeology Journal》2018,26(6):1989-2007
The hyper-arid conditions prevailing in Agua Verde aquifer in northern Chile make this system the most important water source for nearby towns and mining industries. Due to the growing demand for water in this region, recharge is investigated along with the impact of intense pumping activity in this aquifer. A conceptual model of the hydrogeological system is developed and implemented into a two-dimensional groundwater-flow numerical model. To assess the impact of climate change and groundwater extraction, several scenarios are simulated considering variations in both aquifer recharge and withdrawals. The estimated average groundwater lateral recharge from Precordillera (pre-mountain range) is about 4,482 m3/day. The scenarios that consider an increase of water withdrawal show a non-sustainable groundwater consumption leading to an over-exploitation of the resource, because the outflows surpasses inflows, causing storage depletion. The greater the depletion, the larger the impact of recharge reduction caused by the considered future climate change. This result indicates that the combined effects of such factors may have a severe impact on groundwater availability as found in other groundwater-dependent regions located in arid environments. Furthermore, the scenarios that consider a reduction of the extraction flow rate show that it may be possible to partially alleviate the damage already caused to the aquifer by the continuous extractions since 1974, and it can partially counteract climate change impacts on future groundwater availability caused by a decrease in precipitation (and so in recharge), if the desalination plant in Taltal increases its capacity. 相似文献
99.
Rainfall thresholds for the triggering of landslides considering previous soil moisture conditions (Asturias,NW Spain) 总被引:1,自引:0,他引:1
Pablo Valenzuela María José Domínguez-Cuesta Manuel Antonio Mora García Montserrat Jiménez-Sánchez 《Landslides》2018,15(2):273-282
Given its geological and climatic conditions and its rugged orography, Asturias is one of the most landslide prone areas in the North of Spain. Most of the landslides occur during intense rainfall episodes. Thus, precipitation is considered the main triggering factor in the study area, reaching average annual values of 960 mm. Two main precipitation patterns are frequent: (i) long-lasting periods of moderate rainfall during autumn and winter and (ii) heavy short rainfall episodes during spring and early summer. In the present work, soil moisture conditions in the locations of 84 landslides are analysed during two rainfall episodes, which represent the most common precipitation patterns: October–November 2008 and June 2010. Empirical data allowed the definition of available water capacity percentages of 99–100% as critical soil moisture conditions for the landslide triggering. Intensity-duration rainfall thresholds were calculated for each episode, considering the periods with sustained high soil moisture levels before the occurrence of each analysed landslide event. For this purpose, data from daily water balance models and weather stations were used. An inverse relationship between the duration of the precipitation and its intensity, consistent with published intensity-duration thresholds, was observed, showing relevant seasonal differences. 相似文献
100.