全文获取类型
收费全文 | 6168篇 |
免费 | 1420篇 |
国内免费 | 1691篇 |
专业分类
测绘学 | 381篇 |
大气科学 | 1714篇 |
地球物理 | 2470篇 |
地质学 | 3139篇 |
海洋学 | 733篇 |
天文学 | 61篇 |
综合类 | 352篇 |
自然地理 | 429篇 |
出版年
2024年 | 31篇 |
2023年 | 65篇 |
2022年 | 193篇 |
2021年 | 235篇 |
2020年 | 220篇 |
2019年 | 316篇 |
2018年 | 240篇 |
2017年 | 229篇 |
2016年 | 257篇 |
2015年 | 332篇 |
2014年 | 408篇 |
2013年 | 371篇 |
2012年 | 384篇 |
2011年 | 398篇 |
2010年 | 364篇 |
2009年 | 470篇 |
2008年 | 444篇 |
2007年 | 543篇 |
2006年 | 450篇 |
2005年 | 429篇 |
2004年 | 402篇 |
2003年 | 327篇 |
2002年 | 312篇 |
2001年 | 236篇 |
2000年 | 229篇 |
1999年 | 217篇 |
1998年 | 195篇 |
1997年 | 190篇 |
1996年 | 159篇 |
1995年 | 104篇 |
1994年 | 101篇 |
1993年 | 87篇 |
1992年 | 72篇 |
1991年 | 73篇 |
1990年 | 49篇 |
1989年 | 41篇 |
1988年 | 47篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有9279条查询结果,搜索用时 46 毫秒
1.
2.
Analytical study of ground motion caused by seismic wave propagation across faulted rock masses
下载免费PDF全文
![点击此处可从《国际地质力学数值与分析法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Qp and Qs. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions. 相似文献
3.
本文以丰富的实际资料,论证了地下水的卤素元素(F、Cl、Br、I)的形成、含量及其分布规律与含水介质成分、上覆岩土性质、地下水退流条件、氧化还原环境、地下水矿化度之间的关系。根据江汉平原东部区和鄱阳湖区地下水中Br、I元素的调查研究结果及它们形成的控制因素与分布规律,结合长江三角洲南部区水文地球化学环境条件分析对比,指出该区是一个形成Br、I矿泉水的有利地区。 相似文献
4.
介绍了自动高精度测距系统。该系统能以5×10-7的测距精度测定多个观测点的形变,可作为跨断层动态连续观测的新仪器。 相似文献
5.
Ren Tinawi Marc Sarrazin Andr Filiatrault 《Soil Dynamics and Earthquake Engineering》1993,12(8):469-477
The 1990 edition of the National Building Code of Canada (Associate Committee of the National Building Code, National Research Council, Ottawa, 1990) makes a clear distinction between eastern and western Canada in terms of seismic acceleration and velocity zones. While it is well established that ground motions can be amplified significantly through loose clay deposits, no results are available that take into consideration the typical high frequency content of ground motions in eastern Canada. This paper develops ground amplification curves for clays having depths between 10 and 70 m excited by typical eastern Canadian ground motions scaled to two different values of peak horizontal accelerations. Simplified free-field spectral design curves, which could be used by structural designers, are proposed. The curves show that maximum spectral accelerations occur for structural periods between 0.2 and 0.5 s. In addition, soil depth does not appear to be an important parameter controlling the response of typical clay deposits in eastern Canada. 相似文献
6.
Based on the Intensive Field Campaign(IFC-1)data of Boreal Ecosystem-Atmosphere Study(BOREAS).a three-dimensional meso-β scale model is used to simulate the effect of boreal forests onthe lower atmosphere.A fine horizontal resolution of 2 km×2 km is used in order to distinguish thevegetative heterogeneity in the boreal region.A total of 20×25 grid points cover the entire sub-modeling area in BOREAS' South Study Area(SSA).The ecosystem types and their coverage ineach grid square are extracted from the North American Land Cover Characteristics Data Base(NALCCD)generated by the U.S.Geographical Survey(USGS)and the University of Nebraska-Lincoln(UNL).The topography of the study area is taken from the Digital Elevation Map(DEM)of USGS.The model outputs include the components of the energy balance budget within the canopyand at the ground.the turbulence parameters in the atmospheric boundary layer and the wind.temperature and humidity profiles extending up to a height of 1500 m.In addition to the fine timeand spatial step,the unique feature of the present model is the incorporation of both dynamic andbiological effects of the Boreal forest into the model parameterization scheme.The model resultscompare favorably with BOREAS' IFC-1 data in 1994 when the forest was in the luxuriant growingperiod. 相似文献
7.
8.
9.
1IntroductionOne of the key factors related to basin geody-namics is deep process controlling formation and evolution of sedimentary basin. Depth and tempera-ture of asthenosphere,existence of mantle plume,occurrence of mantle melting,and amounts of melts under depressurization during thinning of lithosphere are controlling factors influenced formation and characteristics of extensional basin directly (Li,1994). Rifting is probably governed by frictional forces exerted on the base of litho… 相似文献
10.
Results of a single group participating in an international experiment are analyzed. The experiment served to verify computational predictions of the ground-motion variations due to near-surface geological effects at a site established for that purpose by the California Department of Conservation. Based on an acceleration record at a rock location, and geotechnical model of medium, records at the other locations of a nearby sedimentary deposit were predicted. A 2-D finite-difference sensitivity analysis suggested that the lateral wave-propagation effects are negligibly small, and locally 1-D computations are sufficient for the present site. Those computations are compared with observations not available to the authors during the blind prediction. Peak accelerations, peak velocities and RMS accelerations were predicted with errors less than 159%, 114% and 62%, respectively. Maxima of the response spectra were fitted within a factor of 2. The predicted and observed Husid's plots (i.e., the normalized cumulative plots of the acceleration squared) have the correlation coefficients 0.98. The detected misfits do not show any simple relation to the instrument location, component, frequency, or time. 相似文献