全文获取类型
收费全文 | 1385篇 |
免费 | 159篇 |
国内免费 | 247篇 |
专业分类
测绘学 | 201篇 |
大气科学 | 240篇 |
地球物理 | 285篇 |
地质学 | 425篇 |
海洋学 | 173篇 |
天文学 | 20篇 |
综合类 | 106篇 |
自然地理 | 341篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 44篇 |
2021年 | 56篇 |
2020年 | 59篇 |
2019年 | 83篇 |
2018年 | 61篇 |
2017年 | 65篇 |
2016年 | 49篇 |
2015年 | 63篇 |
2014年 | 89篇 |
2013年 | 121篇 |
2012年 | 87篇 |
2011年 | 65篇 |
2010年 | 52篇 |
2009年 | 90篇 |
2008年 | 59篇 |
2007年 | 81篇 |
2006年 | 94篇 |
2005年 | 78篇 |
2004年 | 77篇 |
2003年 | 41篇 |
2002年 | 48篇 |
2001年 | 51篇 |
2000年 | 53篇 |
1999年 | 27篇 |
1998年 | 24篇 |
1997年 | 21篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
排序方式: 共有1791条查询结果,搜索用时 31 毫秒
21.
The evaluation of seismic site response in the urban area of Catania was tackled by selecting test areas having peculiar lithological
and structural features, potentially favourable to large local amplifications of ground motion. The two selected areas are
located in the historical downtown and in the northern part of Catania where the presence of a fault is evident. Site response
was evaluated using spectral ratio technique taking the horizontal- to-vertical component ratio of ambient noise. Inferences
from microtremor measurements are compared with results from synthetic accelerograms and response spectra computed at all
drillings available for this area. Such method is particularly suitable in urban areas where the nature of the outcropping
geological units is masked by city growth and anthropic intervention on the surface geology. The microtremor H/V spectral
ratios evaluated at soft sites located within the downtown profile tend to be smaller than that usually reported in the literature
for such soils. A tendency for amplifications to peaks near 2 Hz is observed only in some sites located on recent alluvial
deposits. Evidences for amplifications of site effects (frequency range 4–8 Hz) were observed in the sampling sites located
on the fault, with a rapid decrease of spectral amplitude just a few tenths of metres away from the discontinuity. Numerical
simulations evidenced the importance of geolithological features at depth levels even greater than 20–30 m. Besides this,
the results strongly confirm the importance of the subsurface geological conditions, in the estimate of seismic hazard at
urban scale. 相似文献
22.
Dire financial constraints and the threats of forced structural reform have had the unforeseen effect of forcing municipal councils across Australia to reconsider their operational activities and organisational arrangements. With considerable ingenuity, numerous municipalities have proposed and sometimes adopted new structural formations that embody various forms of co-operative service provision. This remarkable development has unfortunately been largely ignored in the scholarly literature on Australian local government. In a modest effort aimed at remedying this neglect, the present paper seeks to outline the small, rural New South Wales Gilgandra Shire Council's (2004) ‘Co-operative/Local Government Service Company’ model, place it in the broader context of alternative models of local governance suitable for Australian conditions, and evaluate its characteristics. 相似文献
23.
Yahia E.-A. Mohamedzein Mohammed H. Aboud 《Geotechnical and Geological Engineering》2006,24(5):1385-1401
A detailed study was performed to investigate the compressibility and the shear strength of a residual soil in Omdurman, Sudan.
The soil resulted from weathering of sandstone and mudstone. The soil is classified as sandy clayey silt (MH-CH) and is generally
partially saturated. Consolidation tests were performed to study the compressibility of the soil and UU, CIU and insitu tests
(CPT and SPT) were performed to study the shear strength characteristics of the soil. The characteristics of this residual
soil can generally be predicted using correlations proposed in the literature for transported soils. The soil is of low to
medium compressibility and exhibits slight apparent overconsolidation behavior. The soil dilates during shear and shows no
long term effective cohesion. Problems associated with open cuts in this soil are attributed to loss of strength upon saturation. 相似文献
24.
新疆冰雹天气过程的基本特征 总被引:5,自引:0,他引:5
通过对新疆39a冰雹天气资料的普查,得到76次系统性冰雹天气过程和1279次局地冰雹天气过程,局地冰雹天气的发生远远多于系统性雹天气。冰雹天气过程与地形密切相关,主要发生在山区,冰雹天气以1天为主,多发生于夏季,系统性冰雹天气均由中尺度高压造成。 相似文献
25.
Introduction The azimuth and slowness are two major features of seismic signals. The accurate estimation of them is quite important for both phase identification and event location. Generally, there are two types of seismic stations, i.e. 3-component stations (3C) and arrays. To estimate the two direc-tional parameters, the polarization analysis (Jurkevics, 1988) is commonly used for 3C stations and the frequency-wavenumber spectrum analysis ( f-k) (Capon, 1969; Kvaerna, Doornbos, 1986) is … 相似文献
26.
27.
This is the second part of a contribution to the debate on the possibilities of leveraging economic globalisation — through incorporation in international production networks and global commodity chains (GCCs) — as a strategy for developing countries to industrialise and advance their position in the world economy. In the first part, we analysed the experience of the East Asian apparel industry and addressed the issues of sustaining positions, upgrading to more rewarding roles, and advancing to less dependent positions within production networks and GCCs. We developed an analytical framework at both the firm and industry levels, and subsequently identified alternative firm- and industry-level strategies and trajectories. The present paper deals with these issues in the context of the Singapore apparel industry. Based on extensive empirical research, we demonstrate that although the East Asian experience of upgrading and repositioning within the GCC is to some extent emulated in the case of the Singapore apparel industry, the outcomes have been less favourable in terms of the depth, extent and strength of these trajectories. The differing outcomes can be explained in terms of different (systemic) conditions in the Singapore business environment, including the agency of local players, the geography of sourcing networks, and the role of the state and prevailing business attitudes. Our conclusions merit continued attention in both research and policy circles on the development of capabilities at the firm level, and the role of local business and institutional environments in local industry development processes under globalisation. 相似文献
28.
29.
30.
公婆泉盆地局部排泄源氧化还原属性与铀矿化关系探讨 总被引:1,自引:0,他引:1
在系统分析公婆泉盆地地质背景、水文地质条件的基础上,对该区局部排泄源氧化还原属性与铀矿化的关系进行了探讨。研究结果表明,局部排泄源的存在对铀矿化具有重要作用,当局部排泄源属于还原性质时,铀矿体常常分布于该排泄源上游;若属氧化性质,排泄源铀矿体通常位于其下游或附近。公婆泉盆地存在相对氧化和相对还原的二种局部排泄源,北骆驼泉区的沙泉沟与平沙地、麻黄沟、北骆驼泉沟排泄源之间应为有利的铀矿化地段。 相似文献