全文获取类型
收费全文 | 779篇 |
免费 | 80篇 |
国内免费 | 268篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 10篇 |
地球物理 | 208篇 |
地质学 | 743篇 |
海洋学 | 51篇 |
综合类 | 10篇 |
自然地理 | 95篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 24篇 |
2019年 | 28篇 |
2018年 | 35篇 |
2017年 | 32篇 |
2016年 | 42篇 |
2015年 | 45篇 |
2014年 | 32篇 |
2013年 | 101篇 |
2012年 | 40篇 |
2011年 | 56篇 |
2010年 | 50篇 |
2009年 | 65篇 |
2008年 | 67篇 |
2007年 | 58篇 |
2006年 | 57篇 |
2005年 | 57篇 |
2004年 | 66篇 |
2003年 | 41篇 |
2002年 | 30篇 |
2001年 | 29篇 |
2000年 | 18篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1127条查询结果,搜索用时 15 毫秒
61.
62.
长三角经济高速发展地区土壤pH时空变化及其影响因素 总被引:13,自引:0,他引:13
通过调查和分析长三角地区张家港市2004年和第二次土壤普查时(1980)的土壤pH,探讨了该市近20年来基于经济高速发展影响下的土壤pH变化及影响因素。结果表明,自第二次土壤普查以来,该市土壤pH变化明显。南部人为土地区绝大部分土壤pH值都下降了一个单位,平均值由7.39降至6.33;北部雏形土区,两个时期的土壤pH值分别为7.92和7.98。土壤pH的降低可能同该地区长期施用化学肥料、酸雨及工业酸性“三废”排放的增加有关。此外,土地利用和田间管理也对土壤pH变化起着较为重要的作用,而土壤地球化学性质差异则是导致南北地区土壤pH变化不同的内在因素。 相似文献
63.
本文采用Novak薄层法推导粘弹性地基的扭转动力阻抗,并将其用于考虑桩土相互作用的单桩扭转动力阻抗,又通过传递矩阵法将此公式推广到求取层状地基单桩扭转动力阻抗。而且本文以工程中常用的端承桩为例,推导了层状地基中端承桩扭转动力阻抗的简化计算公式。根据此公式,分析了频率、上覆软土层厚度、上覆软土层刚度等因素对单桩扭转动力阻抗的影响,分析结果表明,随着振动频率提高,层状地基中端承单桩的扭转动力阻抗的实部有缓慢下降的趋势,而虚部则增大;随着上覆土层厚度的增加,层状地基中端承单桩的扭转动力阻抗的实部和虚部均减小;随着上覆土层刚度的减小,层状地基中端承单桩的扭转动力阻抗的实部减小,虚部在低频段减小,而在较高频率段则增大。 相似文献
64.
The method of smoothed particle hydrodynamics (SPH) has recently been applied to computational geomechanics and has been shown to be a powerful alternative to the standard numerical method, that is, the finite element method, for handling large deformation and post‐failure of geomaterials. However, very few studies apply the SPH method to model saturated or submerged soil problems. Our recent studies of this matter revealed that significant errors may be made if the gradient of the pore‐water pressure is handled using the standard SPH formulation. To overcome this problem and to enhance the SPH applications to computational geomechanics, this article proposes a general SPH formulation, which can be applied straightforwardly to dry and saturated soils. For simplicity, the current work assumes hydrostatic pore‐water pressure. It is shown that the proposed formulation can remove the numerical error mentioned earlier. Moreover, this formulation automatically satisfies the dynamic boundary conditions at a submerged ground surface, thereby saving computational cost. Discussions on the applications of the standard and new SPH formulations are also given through some numerical tests. Furthermore, techniques to obtain the correct SPH solution are also proposed and discussed throughout. As an application of the proposed method, the effect of the dilatancy angle on the failure mechanism of a two‐sided embankment subjected to a high groundwater table is presented and compared with that of other solutions. Finally, the proposed formulation can be considered a basic formulation for further developments of SPH for saturated soils. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
65.
S. Sadiku 《国际地质力学数值与分析法杂志》2013,37(16):2789-2800
One‐dimensional consolidation analysis of layered soils conventionally entails solving a system of differential equations subject to the flow conditions at the bounding upper and lower surfaces, as well as the continuity conditions at the interface of every pair of contiguous layers. Formidable computational efforts are required to solve the ensuing transcendental equations expressing the matching conditions at the interfaces, using this method. In this paper, the jump discontinuities in the flow parameters upon crossing from one layer to the other have been systematically built into a single partial differential equation governing the space–time variation of the excess pore pressure in the entire composite medium, by the use of the Heaviside distribution. Despite the presence of the discontinuities in the coefficients of the differential equation, a closed‐form solution in the sense of an infinite generalized Fourier series is obtained, in addition to which is the development of a Green's function for the differential problem. The eigenfunctions of the composite medium are the coordinate functions of the series, obtained computationally through the application of the extended equations of Galerkin. The analysis has been illustrated by solving the consolidation problem of a four‐layer composite, and the results obtained agree very well with the results obtained by previous researchers. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
66.
A numerically efficient and stable method is developed to analyze Biot's consolidation of multilayered soils subjected to non‐axisymmetric loading in arbitrary depth. By the application of a Laplace–Hankel transform and a Fourier expansion, the governing equations are solved analytically. Then, the analytical layer‐element (i.e. a symmetric stiffness matrix) describing the relationship between generalized displacements and stresses of a layer is exactly derived in the transformed domain. Considering the continuity conditions between adjacent layers, the global stiffness matrix of multilayered soils is obtained by assembling the inter‐related layer‐elements. Once the solution in the Laplace–Hankel transformed domain that satisfies the boundary conditions has been obtained, the actual solution can be derived by the inversion of the Laplace–Hankel transform. Finally, numerical examples are presented to verify the theory and to study the influence of the layered soil properties and time history on the consolidation behavior. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
67.
在大连新港油罐区的建设中,发现了一种具有高孔隙性、高含水量、高塑性、中低压缩性的特殊土。作者对这种土及其母岩的矿物学、岩石学、地球化学、物理化学和工程特性进行了系统研究,揭示了该区红粘土及其工程特性的形成机理,该区红粘土乃是蒙脱石化的粗玄岩,在中温带气候区红土花作用的产物。 相似文献
68.
D. M. Orazulike 《Natural Hazards》1993,7(2):109-119
Field and chemical data show that soils in some parts of Bauchi State, Nigeria, are rich in illite (20–35%), montmorillonite (60–75%), and kaolinite (45–73%). These expansive clays cause the soils to shrink and swell alternatively in response to the seasonal supply of moisture; resulting in observed damaging cracks. Plasticity index (PI) determinations on these soils are high (7–13.4%) suggesting that they are potentially hazardous. The attendant hazards and huge losses to the State are blamed on the expansive nature of these soils. The hazardous conditions can be mitigated by adopting proper construction precautions as well as by using chemical additives such as lime and phosphates, to lower the PI and help to increase the strength of the soils. 相似文献
69.
70.