全文获取类型
收费全文 | 682篇 |
免费 | 105篇 |
国内免费 | 99篇 |
专业分类
测绘学 | 78篇 |
大气科学 | 50篇 |
地球物理 | 121篇 |
地质学 | 418篇 |
海洋学 | 72篇 |
天文学 | 41篇 |
综合类 | 48篇 |
自然地理 | 58篇 |
出版年
2023年 | 5篇 |
2022年 | 35篇 |
2021年 | 49篇 |
2020年 | 22篇 |
2019年 | 44篇 |
2018年 | 33篇 |
2017年 | 27篇 |
2016年 | 42篇 |
2015年 | 45篇 |
2014年 | 35篇 |
2013年 | 42篇 |
2012年 | 33篇 |
2011年 | 31篇 |
2010年 | 28篇 |
2009年 | 22篇 |
2008年 | 24篇 |
2007年 | 23篇 |
2006年 | 29篇 |
2005年 | 18篇 |
2004年 | 37篇 |
2003年 | 32篇 |
2002年 | 65篇 |
2001年 | 49篇 |
2000年 | 33篇 |
1999年 | 24篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有886条查询结果,搜索用时 31 毫秒
51.
52.
工作状态下桥梁结构的模态参数识别是桥梁损伤识别的重要环节,考虑桥梁检测的实用性,桥梁检测一般应建立在环境激励的基础上,已有的环境激励下模态参数识别的方法对模态频率的识别的精度较高,而对位移模态的识别则误差较大。提出了一种利用移动质量块在不同位置时对桥梁的模态频率进行多次测量,用各次测得的频率值确定位移模态的新方法,使得位移模态识别的精度接近频率识别的精度,建立了该方法的初步模型,推导了频率与位移模态关系的理论公式,并通过数值模拟对该方法的有效性进行了说明。 相似文献
53.
介绍了分布式GIS和分布式计算模式的概念,探讨了基于分布式计算模式的地理信息系统的体系结构、运作机制、关键技术和实现方法,最后对未来的分布式地理信息系统发展进行了展望。 相似文献
54.
55.
56.
Liliane Janikian Renato Paes De Almeida Ricardo Ivan Ferreira Da Trindade Antonio Romalino Santos Fragoso‐Cesar Manoel Souza D′Agrella‐Filho Elton Luis Dantas Eric Tohver 《地学学报》2008,20(4):259-266
The Ediacaran is one of the most important periods on Earth evolution, including the first appearance of soft‐bodied macrofossils, major climatic changes and a supposed rise in free oxygen. In southernmost Brazil, this period is represented by Camaquã Supergroup, including the Bom Jardim Group and the Acampamento Velho Formation, both of which record continental palaeoenvironmental changes in a more than 5000 m thick stratigraphic succession. Age constraints are given by seven Ar‐Ar and U‐Pb determinations on volcanic rocks, which bracket these units between c. 605 and 574 Ma, revealing the best dated and most continuous documented Ediacaran continental succession to date. Depositional systems evolution supports a Phanerozoic‐type glacial context during the last Neoproterozoic glacial event and presents the Picada das Graças Formation (580 ± 3.6 Ma) as the first dated non‐glacial unit coeval to the Gaskiers Formation. 相似文献
57.
Shell‐shape and morphometric variability in Mytilus galloprovincialis from micro‐tidal environments: responses to different hydrodynamic drivers
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tidal conditions differently influence inter‐tidal organisms in terms of general physiological and metabolic responses. In this study we investigated the morphological response in shells of Mytilus galloprovincialis native to different micro‐tidal coastal environments in the Northern Adriatic Sea. Our purpose was to highlight the ecophenotypic variability across tidal levels and to elucidate how tidal currents and waves produced by anthropogenic activities may play a part in modulating shell morphology. Three sampling sites were selected: an open‐sea area 15 km off‐shore and two sites within the lagoon of Venice, the first near one of its three inlets, and the other one in the proximity of Venice city centre. At each sampling site, organisms were seasonally collected at different depths within their vertical zonation, either in the inter‐tidal zone – i.e. at both the highest and lowest tide zonation limits, and subtidally. The mussel shells were analysed by investigation of their morphometric relationships (height/length and width/length ratios) and by elliptic Fourier analysis of the shell contours. Shell thickness and condition index were also evaluated for a better comprehension of energy allocation/partitioning. Estimates based on long‐term measurements, visual observation, wind statistics and wave growth laws allowed an evaluation of the forces acting on shells. At the open‐sea site, the observed phenotypic variability of both shell shape and thickness was clearly related to the tidal vertical zonation. At the two lagoon sites, the currents generated by tidal flow through the inlet and the waves caused by the frequent passage of boats influenced both shell shape and thickness. A trade‐off between protection and growth was apparent along the tide gradient, as emphasized by the differences in the partitioning and allocation of energy between shell and flesh production. 相似文献
58.
59.
???????????????????о??м????????????ε??????????????????????????????????????????????????????Э??????????????????????????б????????С??????????????????????????????????????????????о??????????????????????????????????????Σ?????б????????????? 相似文献
60.