全文获取类型
收费全文 | 686篇 |
免费 | 254篇 |
国内免费 | 284篇 |
专业分类
测绘学 | 93篇 |
大气科学 | 12篇 |
地球物理 | 72篇 |
地质学 | 921篇 |
海洋学 | 64篇 |
天文学 | 10篇 |
综合类 | 32篇 |
自然地理 | 20篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 28篇 |
2020年 | 38篇 |
2019年 | 37篇 |
2018年 | 37篇 |
2017年 | 32篇 |
2016年 | 53篇 |
2015年 | 45篇 |
2014年 | 74篇 |
2013年 | 68篇 |
2012年 | 75篇 |
2011年 | 79篇 |
2010年 | 58篇 |
2009年 | 74篇 |
2008年 | 65篇 |
2007年 | 65篇 |
2006年 | 69篇 |
2005年 | 47篇 |
2004年 | 37篇 |
2003年 | 27篇 |
2002年 | 32篇 |
2001年 | 29篇 |
2000年 | 27篇 |
1999年 | 28篇 |
1998年 | 21篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1224条查询结果,搜索用时 281 毫秒
1.
Effects of the geometry of two‐dimensional fractures on their hydraulic aperture and on the validity of the local cubic law
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Flow through rough fractures is investigated numerically in order to assess the validity of the local cubic law for different fracture geometries. Two‐dimensional channels with sinusoidal walls having different geometrical properties defined by the aperture, the amplitude, and the wavelength of the walls' corrugations, the corrugations asymmetry, and the phase shift between the two walls are considered to represent different fracture geometries. First, it is analytically shown that the hydraulic aperture clearly deviates from the mean aperture when the walls' roughness, the phase shift, and/or the asymmetry between the fracture walls are relatively high. The continuity and the Navier–Stokes equations are then solved by means of the finite element method and the numerical solutions compared to the theoretical predictions of the local cubic law. Reynolds numbers ranging from 0.066 to 66.66 are investigated so as to focus more particularly on the effect of flow inertial effects on the validity of the local cubic law. For low Reynolds number, typically less than 15, the local cubic law properly describes the fracture flow, especially when the fracture walls have small corrugation amplitudes. For Reynolds numbers higher than 15, the local cubic law is valid under the conditions that the fracture presents a low aspect ratio, small corrugation amplitudes, and a moderate phase lag between its walls. 相似文献
2.
介绍了广州地区基坑支护近年来的主要类型及其适用范围,并在分析选型各影响因素的基础上,总结出设计选型的要点。 相似文献
3.
Based on the Nansha Islands' closed atoll conception-remote sensing system in Part Ⅰ,through the solution of the information function value and isostatic value of closed and quasi-closed atoll, and by using topological analysis on growth form and the composite remote sensing quantization date as the calculating coefficients, the feature vector system and its mathematical model of two kinds of atoll are built, and the multivariate analysis is made with some examples. 相似文献
4.
5.
Formation Dynamics and Quantitative Prediction of Hydrocarbons of the Superpressure System in the Dongying Sag 总被引:1,自引:0,他引:1
Based on the theory of formation dynamics of oil/gas pools, the Dongying sag can be divided into three dynamic systems regarding the accumulation of oil and gas: the superpressure closed system, the semi-closed system and the normal pressure open system. Based on the analysis of genesis of superpressure in the superpressure closed system and the rule of hydrocarbon expulsion, it is found that hydrocarbon generation is related to superpressure, which is the main driving factor of hydrocarbon migration. Micro fractures formed by superpressure are the main channels for hydrocarbon migration. There are three dynamic patterns for hydrocarbon expulsion: free water drainage, hydrocarbon accumulation and drainage through micro fissures. In the superpressure closed system, the oil-driving-water process and oil/gas accumulation were completed in lithologic traps by way of such two dynamic patterns as episodic evolution of superpressure systems and episodic pressure release of faults. The oil-bearing capacity of lithologic traps is intimately related to reservoir-forming dynamic force. Quantitative evaluation of dynamic conditions for pool formation can effectively predict the oil-bearing capability of traps. 相似文献
6.
7.
以流线、流面、汇点的概念为基础,对稳定流双井干扰和直线隔水边界附近涌水量理论公式进行对比分析,提出了二个虚拟界面,其中虚拟界面Ⅰ,运用流线、流面的性质,流线方程等给出证明;虚拟界面Ⅱ则通过半无限条形降落漏斗的分析,应用元流和总流的能量方程得到流量为零,流线为零的平面。在同样条件下,条形无限涌水量是半无限潜含水层涌水量的二倍。应用总流能量方程对三种情况水头损失的分析,解释了这种关系存在的合理性,得出虚拟界面Ⅱ,并以此得出该界面内的最大残余水头计算公式。将基坑降水运用虚拟界面简化为扇形,条形半无限含水层,从而实现单井预测,该方法应用到昊华水泥厂基坑降水中,预测效果理想。 相似文献
8.
9.
10.
北京市深基坑工程中土钉墙支护技术应用比较广泛,对于边坡变形要求严格的基坑,采用土钉墙与预应力锚杆联合支护技术可有效控制变形,结合工程实例,介绍了该技术的设计思路及应用过程,说明了该技术的适用性,并就施工中遇到的问题进行分析,给出相应的处理措施。 相似文献