全文获取类型
收费全文 | 1677篇 |
免费 | 119篇 |
国内免费 | 80篇 |
专业分类
测绘学 | 90篇 |
大气科学 | 99篇 |
地球物理 | 451篇 |
地质学 | 879篇 |
海洋学 | 80篇 |
天文学 | 123篇 |
综合类 | 27篇 |
自然地理 | 127篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 56篇 |
2021年 | 56篇 |
2020年 | 67篇 |
2019年 | 75篇 |
2018年 | 150篇 |
2017年 | 130篇 |
2016年 | 176篇 |
2015年 | 81篇 |
2014年 | 182篇 |
2013年 | 172篇 |
2012年 | 92篇 |
2011年 | 104篇 |
2010年 | 61篇 |
2009年 | 73篇 |
2008年 | 57篇 |
2007年 | 39篇 |
2006年 | 54篇 |
2005年 | 30篇 |
2004年 | 23篇 |
2003年 | 25篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 13篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有1876条查询结果,搜索用时 31 毫秒
51.
52.
53.
54.
55.
56.
The present work aimed to determine the mineralogical composition of Ypresian series and to clarify the influence of the dissolution of siliceous frustules on the genesis of fibrous clay minerals. The specimens sampled from CPG trench are mainly constituted of silica-rich rocks at Mides area located at the western part of Gafsa-Metlaoui basin. The samples were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to determine texture of constituents. The data obtained indicate that the bulk rock samples are mainly made up of opal CT and clay minerals. The latter consists of palygorskite-sepiolite minerals associated with smectite and few amount of illite. The trend of mineralogical composition indicates that fibrous clay minerals are more concentrated at the upper part. SEM observations indicated that palygorskite mineral appears as thread-like facies, which surround foliated texture of smectite in the lower part of the Mides section, although with the low Mg activity confirmed by the absence of dolomite. But, at the upper part of the Mides section, SEM observations revealed the occurrence of siliceous frustules, which have numerous dissolved areas and replacement of carbonate tests by silica. The dissolution saturated the depositional environment with silica which is required for the formation of palygorskite and sepiolite minerals, in addition to high Mg activity confirmed by the presence of dolomite in the bulk rock, which is required basically for the formation of sepiolite. Although the genesis mode of palygorskite and sepiolite is similar with very little difference, the genesis of sepiolite needs a high alkalinity than the formation of palygorskite. 相似文献
57.
Shahid Manzoor Michael G. Edwards Ali H. Dogru Tareq M. Al-Shaalan 《Computational Geosciences》2018,22(1):195-230
Grid generation for reservoir simulation must honor classical key constraints and be boundary aligned such that control-volume boundaries are aligned with geological features such as layers, shale barriers, fractures, faults, pinch-outs, and multilateral wells. An unstructured grid generation procedure is proposed that automates control-volume and/or control point boundary alignment and yields a PEBI-mesh both with respect to primal and dual (essentially PEBI) cells. In order to honor geological features in the primal configuration, we introduce the idea of protection circles, and to generate a dual-cell feature based grid, we construct halos around key geological features. The grids generated are employed to study comparative performance of cell-centred versus cell-vertex control-volume distributed multi-point flux approximation (CVD-MPFA) finite-volume formulations using equivalent degrees of freedom. The formulation of CVD-MPFA schemes in cell-centred and cell-vertex modes is analogous and requires switching control volume from primal to dual or vice versa together with appropriate data structures and boundary conditions. The relative benefits of both types of approximation, i.e., cell-centred versus vertex-centred, are made clear in terms of flow resolution and degrees of freedom required. 相似文献
58.
Katerina Georgiou John Harte Ali Mesbah William J. Riley 《Computational Geosciences》2018,22(3):851-865
We present a numerical method for solving a class of systems of partial differential equations (PDEs) that arises in modeling environmental processes undergoing advection and biogeochemical reactions. The salient feature of these PDEs is that all partial derivatives appear in linear expressions. As a result, the system can be viewed as a set of ordinary differential equations (ODEs), albeit each one along a different characteristic. The method then consists of alternating between equations and integrating each one step-wise along its own characteristic, thus creating a customized grid on which solutions are computed. Since the solutions of such PDEs are generally smoother along their characteristics, the method offers the potential of using larger time steps while maintaining accuracy and reducing numerical dispersion. The advantages in efficiency and accuracy of the proposed method are demonstrated in two illustrative examples that simulate depth-resolved reactive transport and soil carbon cycling. 相似文献
59.
Farid Asam Khalid Perveiz Ali Muhammad Y. Iqbal Muhammad Asim Jadoon Khan Zaib 《International Journal of Earth Sciences》2018,107(5):1557-1578
International Journal of Earth Sciences - Regional seismic reflection profiles, deep exploratory wells, and outcrop data have been used to study the structure and stratigraphic architecture of the... 相似文献
60.
H. Hajinezhad Ali R. Soheili Mohammad R. Rasaei F. Toutounian 《Computational Geosciences》2018,22(6):1433-1444
In this paper, the numerical methods for solving the problem of steam injection in the heavy oil reservoirs are presented. We consider a 3-dimensional model of 3-phase flow, oil, water, and steam, with the effect of 3-phase relative permeability. Interphase mass transfer of water and steam is considered; oil is assumed nonvolatile. We apply the simultaneous solution approach to solve the corresponding nonlinear discretized partial differential equation in the fully implicit form. The convergence of finite difference scheme is proved by the Rosinger theorem. The heuristic Jacobian-Free-Newton-Krylov (HJFNK) method is proposed for solving the system of algebraic equations. The result of this proposed numerical method is well compared with some experimental results. Our numerical results show that the first iteration of the full approximation scheme (FAS) provides a good initial guess for the Newton method. Therefore, we propose a new hybrid-FAS-HJFNK method while there is no steam in the reservoir. The numerical results show that the hybrid-FAS-HJFNK method converges faster than the HJFNK method. 相似文献