全文获取类型
收费全文 | 395篇 |
免费 | 51篇 |
国内免费 | 63篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 56篇 |
地球物理 | 111篇 |
地质学 | 206篇 |
海洋学 | 51篇 |
天文学 | 4篇 |
综合类 | 11篇 |
自然地理 | 52篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 17篇 |
2016年 | 14篇 |
2015年 | 24篇 |
2014年 | 20篇 |
2013年 | 25篇 |
2012年 | 14篇 |
2011年 | 13篇 |
2010年 | 16篇 |
2009年 | 28篇 |
2008年 | 20篇 |
2007年 | 28篇 |
2006年 | 40篇 |
2005年 | 26篇 |
2004年 | 23篇 |
2003年 | 23篇 |
2002年 | 27篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有509条查询结果,搜索用时 31 毫秒
91.
Anne-Marie Lézine Augustin F.-C. Holl Judicaël Lebamba Annie Vincens Chimène Assi-Khaudjis Louis Février Émmanuelle Sultan 《Comptes Rendus Geoscience》2013,345(7-8):327-335
This paper discusses the relationship between patterns of human settlements and environmental change during the Holocene along the northwestern margins of the equatorial rain forest of central Africa. Palaeoenvironmental data from high-resolution sediment cores from lacustrine deposits, plant macro-remains from forest soils, and archaeological data are harnessed to discuss the differential impact of climate and/or humans on the central African rain forest. It is shown that climate change impacted the rain forest well before the widespread expansion of human settlements all over the study area. 相似文献
92.
The in‐plane cyclic behaviour of three types of unreinforced clay masonry was characterized by means of laboratory tests on full‐scale specimens. The masonry walls were assembled with various bonding arrangements (head joints made with mortar pockets, dry head joints with mechanical interlocking, thin‐layer mortar bed joints), which are not yet inserted in seismic codes. Experimental behaviour was modelled with an analytical hysteretic model able to predict lateral load–displacement curves in case of shear failure of the unreinforced walls. According to the experimental results and those of the selected analytical model, parametric study to evaluate the reduction in lateral strength demand produced by non‐linear behaviour in masonry walls, i.e. the load reduction factor was carried out by non‐linear dynamic analyses. The calculated values of the load reduction factor were modest. The differences in values found for the three masonry types, although consistent with them, were not great. This may indicate that, in the ultimate limit state, the type of masonry cannot significantly affect the behaviour of an entire building. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
93.
利用测井声波时差、自然电位和伽玛重构声波时差,分析了以上3种曲线结果对地质体响应方面的机制差异,给出了这些曲线的深度相对移动校正的方法。研究了多条测井曲线去噪的协方差矩阵特征向量滤波方法。在此基础上,利用小波多尺度分解技术进行声波时差曲线重构。在分析这3种测井曲线不同尺度小波分解结果的信号和噪音特点后,利用相邻分解尺度相关滤波技术,对各种曲线的小尺度(高频)分解结果进行滤波处理。为保证重构声波曲线的真实性,深入分析了多曲线、多尺度分解结果的冗余性(相关性)问题;利用特征值技术,对高频多尺度分解分量进行了非相关(正交)分析,最后实现了声波时差曲线的重构,并对重构结果与钻井岩心录井资料进行了对比验证,重构后的声波曲线在区分砂、泥岩性分辨率方面具有明显的提高 相似文献
94.
In this paper, a soil–pile–structure model is tested on a shaking table subject to both a sinusoidal wave and the acceleration time history of the scaled 1940 El Centro earthquake. A medium-size river sand is compacted into a 1.7-m-high laminar rectangular tank to form a loose fill with a relative density of 15%. A single-storey steel structure of 2.54 ton is placed on a concrete pile cap, which is connected to the four end-bearing piles. A very distinct pounding phenomenon between soil and pile is observed; and, the acceleration response of the pile cap can be three times larger than that of the structural response. The pounding is due to the development of a gap separation between soil and pile, and the extraordinary large inertia force suffered at the top of the pile also induces cracking in the pile. To explain this observed phenomenon, nonlinear finite element method (FEM) analyses with a nonlinear gap element have been carried out. The spikes in the acceleration response of the pile cap caused by pounding can be modeled adequately by the FEM analyses. The present results suggest that one of the probable causes of pile damages is due to seismic pounding between the laterally compressed soil and the pile near the pile cap level. 相似文献
95.
96.
公路桥涵台背回填稳定性极限分析上限解 总被引:3,自引:0,他引:3
运用塑性力学极限分析的上限定理,分析公路桥涵台背回填的稳定性问题。首先,由模型试验和数值分析结果确定回填区和地基的滑动模式;其次,根据位移协调条件建立滑动体的速度场,并计算各滑动楔块的位移速度;最后,运用虚功原理和优化算法寻找最不利滑动面位置,计算不同回填材料的土压力或临界填筑高度。研究发现:地基与回填材料的强度、性能以及加筋条件对台背回填稳定性的影响都非常显著。结果表明:增加地基与回填材料的强度,采用轻质回填材料,减小加筋间距和增加筋材强度,都有利于提高台背回填材料的稳定性。 相似文献
97.
98.
本文利用太平洋海温距平场资料,对1986年以来发生的厄尔尼诺过程的开始时间、发展过程及强度等方面进行了分析。并与历史上的厄尔尼诺过程进行比较,结果表明,90年代是厄尔尼诺事件的多发期,在1991 ̄98年的8年中,间连续发生四次厄经诺事件,其中1997 ̄98年的厄尔尼诺,成为有历史记录以来最强的一次过程。 相似文献
99.
A synthesis of pollen evidence from Etang du Pourra, a small pond in Rhodanian Provence, France, complemented by new sedimentological, mineralogical and palynological data allow a reassessment of the Lateglacial-Holocene vegetation and climatic history of the area. The Etang du Pourra succession is shown to consist of two parts; the lower part dates from the Lateglacial and the upper reveals the Holocene pollen-stratigraphic succession typical of the region. In the Lateglacial, a humid and cooler phase is recorded before the Younger Dryas conditions progressively set in. In the Holocene succession, the consequences of human modifications on the environment are clearly visible in changes in mineralogy and pollen stratigraphy. 相似文献
100.
罗甸南部位于右江造山带北缘,褶皱断层较为复杂,穹状构造发育,有利于多金属矿床形成。本文简要叙述该区多金属矿产特征,并对其成矿条件进行初步分析。 相似文献