全文获取类型
收费全文 | 1461篇 |
免费 | 124篇 |
国内免费 | 94篇 |
专业分类
测绘学 | 184篇 |
大气科学 | 72篇 |
地球物理 | 237篇 |
地质学 | 414篇 |
海洋学 | 74篇 |
天文学 | 402篇 |
综合类 | 94篇 |
自然地理 | 202篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 26篇 |
2019年 | 34篇 |
2018年 | 22篇 |
2017年 | 23篇 |
2016年 | 26篇 |
2015年 | 31篇 |
2014年 | 40篇 |
2013年 | 56篇 |
2012年 | 53篇 |
2011年 | 54篇 |
2010年 | 47篇 |
2009年 | 60篇 |
2008年 | 72篇 |
2007年 | 97篇 |
2006年 | 108篇 |
2005年 | 88篇 |
2004年 | 106篇 |
2003年 | 93篇 |
2002年 | 82篇 |
2001年 | 68篇 |
2000年 | 65篇 |
1999年 | 62篇 |
1998年 | 49篇 |
1997年 | 41篇 |
1996年 | 40篇 |
1995年 | 35篇 |
1994年 | 37篇 |
1993年 | 32篇 |
1992年 | 23篇 |
1991年 | 27篇 |
1990年 | 27篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1679条查询结果,搜索用时 15 毫秒
21.
通过引入带有二阶正则算子的正则化项,建立了一种双参数混合正则化方法.为确定最佳正则化参数,这里主要应用L-曲线法、偏差原理和广义交叉校验准则的优化组合来确定.首先对理论模型进行了数值模拟,通过与截断奇异值分解法、共轭梯度法及标准Tikhonov正则化法的结果比较,表明该方法不仅精度高,而且对于数据的随机扰动具有稳定性.... 相似文献
22.
23.
We develop a new Proper Orthogonal Decomposition (POD) reduced order model for saturated groundwater flow, and apply that model to an inverse problem for the hydraulic conductivity field. We use sensitivities as the POD basis. We compare the output when the optimizer uses the reduced order model against results obtained with a full PDE based model. The solutions generated using the POD reduced model are comparable in residual norm to the solutions formed using only the full-scale model. The material parameters are similarly comparable. The time to solution when using the reduced model is reduced by at least an order of magnitude, as are the number of calls to the full model. 相似文献
24.
25.
26.
The finite element (FE) simulation of large‐scale soil–structure interaction problems (e.g. piled‐raft, tunnelling, and excavation) typically involves structural and geomaterials with significant differences in stiffness and permeability. The symmetric quasi‐minimal residual solver coupled with recently developed generalized Jacobi, modified symmetric successive over‐relaxation (MSSOR), or standard incomplete LU factorization (ILU) preconditioners can be ineffective for this class of problems. Inexact block diagonal preconditioners that are inexpensive approximations of the theoretical form are systematically evaluated for mitigating the coupled adverse effects because of such heterogeneous material properties (stiffness and permeability) and because of the percentage of the structural component in the system in piled‐raft foundations. Such mitigation led the proposed preconditioners to offer a significant saving in runtime (up to more than 10 times faster) in comparison with generalized Jacobi, modified symmetric successive over‐relaxation, and ILU preconditioners in simulating piled‐raft foundations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
27.
A. P. S. Selvadurai 《国际地质力学数值与分析法杂志》2011,35(6):639-651
In this paper, we develop an exact closed form solution for a circular entry point located at the interface between an impermeable material and a stratified porous medium, where the principal plane of hydraulic isotropy is inclined to the interface. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
28.
During the process of one‐dimensional consolidation with a threshold gradient, the seepage front moves downward gradually, and the problem is indicated as a Stefan problem. The novel feature in this Stefan problem is a latent heat that varies inversely with the rate of the moving boundary. An exact solution for the external load that increases in proportion to the square root of time is constructed using the similarity transformation technique. Computational examples concerning the effect of different parameters on the motion of the seepage front are presented. The exact solution provides a worthwhile benchmark for verifying the accuracy of numerical and approximate methods. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
29.
30.
主体功能区建设面临的问题及调整思路 总被引:6,自引:0,他引:6
主体功能区建设是推进我国区域协调发展的重大战略举措,但要从构想走向实际操作却面临一系列问题:一是自身需要完善和发展,在划分标准、划分层次、划分的基本单元等方面需要进一步探讨;二是面临行政区利益的冲突;三是面临与各种空间规划或区划的衔接和协调;四是在实施保障方面,面临差别化区域政策的制定、实施主体的明确和生态补偿机制的完善等问题.因此,主体功能区需要从以下5个方面进行建设:①选择合理的行政区单元;②逐步推进主体功能区规划的编制;③平衡主体功能区与行政区的关系;④建立主体功能区规划的核心地位;⑤完善主体功能区划的生态补偿机制. 相似文献