全文获取类型
收费全文 | 1718篇 |
免费 | 102篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 46篇 |
大气科学 | 121篇 |
地球物理 | 453篇 |
地质学 | 700篇 |
海洋学 | 226篇 |
天文学 | 157篇 |
综合类 | 12篇 |
自然地理 | 115篇 |
出版年
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 38篇 |
2020年 | 35篇 |
2019年 | 40篇 |
2018年 | 67篇 |
2017年 | 80篇 |
2016年 | 96篇 |
2015年 | 83篇 |
2014年 | 88篇 |
2013年 | 104篇 |
2012年 | 93篇 |
2011年 | 129篇 |
2010年 | 98篇 |
2009年 | 125篇 |
2008年 | 107篇 |
2007年 | 87篇 |
2006年 | 73篇 |
2005年 | 57篇 |
2004年 | 69篇 |
2003年 | 48篇 |
2002年 | 32篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 12篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1962年 | 2篇 |
排序方式: 共有1830条查询结果,搜索用时 15 毫秒
861.
862.
Mauricio da Rocha Fragoso Gabriel Vieira de Carvalho Felipe Lobo Mendes Soares Daiane Gracieli Faller Luiz Paulo de Freitas Assad Raquel Toste Lívia Maria Barbosa Sancho Elisa Nóbrega Passos Carina Stefoni Böck Bruna Reis Luiz Landau Hernan G. Arango Andrew M. Moore 《Ocean Dynamics》2016,66(3):419-434
863.
864.
Xavier Comas Nicholas Kettridge Andrew Binley Lee Slater Andrew Parsekian Andy J. Baird Maria Strack James M. Waddington 《水文研究》2014,28(22):5483-5494
Northern peatlands are a large source of atmospheric methane (CH4) and both a source and a sink of atmospheric carbon dioxide (CO2). The rate and temporal variability in gas exchanges with peat soils is directly related to the spatial distribution of these free‐phase gases within the peat column. In this paper, we present results from surface and borehole ground‐penetrating radar surveys – constrained with direct soil and gas sampling – that compare the spatial distribution of gas accumulations in two raised bogs: one in Wales (UK), the other in Maine (USA). Although the two peatlands have similar average thickness, physical properties of the peat matrix differ, particularly in terms of peat type and degree of humification. We hypothesize that these variations in physical properties are responsible for the differences in gas distribution between the two peatlands characterized by (1) gas content up to 10.8% associated with woody peat and presence of wood layers in Caribou Bog (Maine) and (2) a more homogenous distribution with gas content up to 5.7% at the surface (i.e. <0.5 m deep) in Cors Fochno (Wales). Our results highlight the variability in biogenic gas accumulation and distribution across peatlands and suggest that the nature of the peat matrix has a key role in defining how biogenic gas accumulates within and is released to the atmosphere from peat soils. © 2015 The Authors. Hydrological Processes published by John Wiley & Sons Ltd. 相似文献
865.
The combination of magnetic and geochemical methods was used to determine the mineralogy, grain size and domain structure of magnetic particles in indoor dust collected in 195 sites in Warsaw, Poland. Data show an asymmetric distribution of magnetic susceptibility (χ) in the wide range of 20–1514 × 10?8 m3 kg?1. Comparison of magnetic parameters shows that the internal dust contains outside pollution characteristic for air and soil. More than 90% of indoor dust samples were characterized by roughly uniform magnetic mineralogy, typical for fine grained magnetite (diameter of 0.2–5 μm), and grain size between pseudo-single-domain and small multi-domain with small contribution of superpara-magnetic particles (~10%). Samples with χ larger than 220 × 10?8 m3 kg?1 contain mainly magnetite and an anthropogenic metallic Fe with T C > 700°C. The indoor dust contains, characteristic for the urban areas, spherical magnetic particles originated from fossil fuel combustion processes and mixture of irregular angular iron-oxides grains containing other elements, including Na, Ca, Al, Si, K, S, Mn, Cl, and Mg. 相似文献
866.
867.
对青海共和盆地内的达连海湖泊流域54个样点进行植被调查及表土花粉分析,研究了植被与表土花粉之间的关系. 结果显示: 表土花粉组合可反映出该区植被的总体特征;达连海湖泊流域花粉沉积来源于整个流域植被,花粉与主要植被类型之间相关性良好,但不能完全反映出群落的建群种、优势种和盖度等. 蒿属和藜科花粉具有超代表性,禾本科表现为低代表性,蒿/藜比具有区域植被生态特点与气候指示意义,在不同的植被区域A/C变化明显;影响达连海湖泊流域表土花粉组合的主要控制因素是风力作用. 相似文献
868.
Assessing reparability: simple tools for estimation of costs and performance loss of earthquake damaged reinforced concrete buildings 下载免费PDF全文
Maria Polese Marco Di Ludovico Marco Marcolini Andrea Prota Gaetano Manfredi 《地震工程与结构动力学》2015,44(10):1539-1557
Tools for assessing building reparability via the estimation of expected performance loss (PL) and associated costs for repair of existing RC building classes damaged by an earthquake are presented. The assessment approach relies on the availability of a number of suitably developed: (i) capacity curves for representative building classes; (ii) curves relating global ductility demand μ to the expected PL for the same classes; and (iii) PL–cost for repair relationship calibrated on database collecting cost data of more than 2300 buildings damaged after 2009 L'Aquila earthquake. The tools are developed applying a simplified procedure involving the simulated design of existing building classes, the assumption of predefined collapse mechanism types and the analyses of the seismic behavior of equivalent SDOF systems representative of ‘intact’ and ‘damaged’ structures after an earthquake. The use of these tools may give useful preliminary indications to decision makers for establishing reparability priorities in the aftermath of damaging earthquakes or to insurance companies to value sound insurance premium for existing building classes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
869.
Hermann A. Buness Hartwig von Hartmann Hanna‐Maria Rumpel Charlotte M. Krawczyk Rüdiger Schulz 《Geophysical Prospecting》2014,62(3):443-452
Cost reduction in seismic reconnaissance is an issue in geothermal exploration and can principally be achieved by sparse acquisition. To address the adherent decrease in signal/noise ratio, the common‐reflection‐surface method has been proposed. We reduced the data density of an existing 3D dataset and evaluated the results of common‐reflection‐surface processing using seismic attributes. The application of the common‐reflection‐surface method leads in all cases to an improvement of the signal/noise ratio. The most distinct improvement can be seen in the low fold regions. The improvement depends strongly on the midpoint aperture, and there is a tradeoff between reflector continuity and horizontal resolution. If small scale targets are to be imaged, a small aperture size is necessary, which may be far below the Fresnel zone for a specific reflector. The substantial reduction of the data density leads in our case to an irrecoverable information loss. 相似文献
870.
Aurélie Guilbert Alvaro Alvarez-Candal Maria Antonietta Barucci Catherine de Bergh 《Icarus》2009,201(1):272-283
We present in this work the observations performed with SINFONI in the framework of a new ESO-Large Program (2006-2008) on Trans-Neptunian Objects (TNOs) and Centaurs. We obtained 21 near-infrared (1.49 to 2.4 microns) spectra of high quality, including 4 spectra of objects never observed before. We search for the presence of features due to ices, particularly water ice. Eris is the only object showing deep methane ice absorption bands. The spectra of 4 objects are featureless, and 6 others show clearly the presence of water ice. For 7 objects, the detections are more ambiguous, but absorption bands could be embedded in the noise. The 3 remaining spectra are too noisy to draw any reliable conclusion. The possible amount of water ice on each object's surface has been computed. The analysis shows that some objects present strong compositional heterogeneities over the surface (e.g. Chariklo), while some others are completely homogeneous (e.g. Quaoar). 相似文献