全文获取类型
收费全文 | 231篇 |
免费 | 21篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 8篇 |
地球物理 | 87篇 |
地质学 | 106篇 |
海洋学 | 13篇 |
天文学 | 36篇 |
综合类 | 2篇 |
自然地理 | 2篇 |
出版年
2024年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 19篇 |
2016年 | 13篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 14篇 |
2012年 | 11篇 |
2011年 | 19篇 |
2010年 | 17篇 |
2009年 | 17篇 |
2008年 | 12篇 |
2007年 | 13篇 |
2006年 | 3篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 5篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有255条查询结果,搜索用时 15 毫秒
251.
Antonella Baiocchi Francesca Lotti Simone M. Piacentini Vincenzo Piscopo 《Environmental Earth Sciences》2014,72(4):989-996
Determining the yield of a production well remains one of the main problems in hydrogeological studies. Starting from the results of a 3-year-long monitoring of a continuously exploited well functioning at constant head (i.e., at a variable discharge rate), a new pumping style has been examined using numerical models. The objective is to control the impact of pumping on the aquifer in accordance with the principle of sustainability. Different models were developed in a transient state and were calibrated using discharge data of the well during the recession periods. Successively, the trends of the residual outflow from the aquifer system with the well operating at variable discharge and at constant discharge were simulated. The results indicate that the ratio of the volume of water pumped from the well to the volume of residual outflow is a significant indicator of the sustainability of groundwater withdrawals. Modeling confirms that a constant discharge rate can be derived from the information gained through a preliminary production phase of a well at constant head. This approach appears to be particularly useful when the problem is determining the sustainable yield of a single well from aquifers with low hydraulic diffusivity. 相似文献
252.
The progressive bond breakage of artificially cemented sands induced by shear straining was investigated through conventional isotropically consolidated drained triaxial compression tests. Sand specimens were prepared with a low degree of cementation by adopting a chemical grout. Test results were interpreted in terms of two stress–dilatancy theories for cohesive-frictional materials proposed in literature. The influence of debonding on the stress–dilatancy behaviour of cemented sands was analysed with particular emphasis on the ‘delayed dilatancy’ phenomenon. A bonding degradation curve was determined for each test relating the interparticle cohesion (c) to the magnitude of the total plastic strain vector (εd) and a bond degradation rate factor (Dc) was assessed from each curve. The maximum value of interparticle cohesion (c0) before the onset of bond degradation under shearing was found to correspond with a sharp decrease in the soil stiffness of the specimens. The influence of the effective confining stress (p′c) on both c0 and Dc parameters gathered from each test was also ascertained. 相似文献
253.
Vincenzo Costanzo-Álvarez Rosa Devesa-Rey Milagrosa Aldana María Teresa Barral Diego López-Rodríguez Belkys Andrade 《Environmental Earth Sciences》2017,76(13):454
A study of surface sediments from the Anllóns riverbed (northwestern Spain) was conducted to assess the use of their magnetic properties as proxies of recent trace element contamination (i.e., As, Zn, Pb, Cr, Ni and Cu). Thermomagnetic curves, hysteresis parameters, specific magnetic susceptibility χ, frequency-dependent magnetic susceptibility κ FD%, magnetic remanence and saturation isothermal remanent magnetization ratios (i.e., S and SIRM/χ) reveal the presence of mostly fine-grained magnetite and maghemite in these samples. The Tomlinson Pollution Load Index (PLI), as well as the magnetic parameters χ, κ FD%, SIRM/χ and S-ratios, vary more or less in agreement to each other when they are sequentially arranged throughout a 30-km-long transect that goes from the town of Carballo to the river mouth in Ponteceso. From that profile, it is possible to identify an anomaly of χ that lies between two small peaks of the PLI and seems to define a contaminated area probably linked to a diffuse low-impact source of pollution. There is also a conspicuous peak of the PLI that is likely associated to a nearby gold mine. The variations of the κ FD%’s along the transect are the ones that best reflect the changes in the PLI values, regardless of the level of contamination. This result suggests that adsorption is the main mechanism of trace elements removal by Fe oxides in these samples. Direct signal analyses, used to decompose the isothermal remanent magnetization curves, reveal the presence of four magnetic fractions, with varying relative concentrations all over the profile, namely single-domain magnetite, close to the superparamagnetic threshold (SD/SP) and/or maghemite (\(\log B_{1/2}\) ca 1.2), single-domain magnetite (\(\log B_{1/2}\) ca 2), hematite (\(\log B_{1/2}\) ca 2.5) and goethite (\(\log B_{1/2}\) ca 3.5). Integrating all the available information, it was sketched out a likely sequence of events that included magnetic minerals neoformation in parent soils, their subsequent chemical transformations and the contamination episodes that affected the region. 相似文献
254.
Michele Punzo Giuseppe Cavuoto Daniela Tarallo Vincenzo Di Fiore 《Marine Geophysical Researches》2017,38(3):313-323
We present high-resolution Vp models of the Capo Granitola harbor, Sicily (Italy) obtained by first arrival traveltime tomography. Seismic data were collected along four hydrophone arrays on the sea-bottom and via a Watergun as seismic source, in order to plan dredging operations in the harbor. Using a hydrophone spacing of 2.5 m and shot spacing of 5 m, very high resolution quality data were recorded. Seismic tomography expands existing knowledge of the harbour subsoil with a penetration of about 20 m, illuminating the Lower Pleistocene bedrock (Marsala calcarenites) that corresponds to high-Vp regions (Vp?>?4.5 km/s). Low Vp (1.8–4.5 km/s) deposits belonging to terraced calcarenites (Upper Pleistocene in age) are also well imaged; they are about 8 m thick and lie below loose sand deposits (Vp?=?1.5 km/s). The substratum has an articulated morphology; Vp images unravel small steps in the basement probably related to structural discontinuities (e.g., faults). Processing data with 3D techniques enables images of the structure and the thickness of the lithotypes to be reconstructed, thus leading to large-scale, realistic estimates of the total quantity of material to be excavated or dredged. Tomographic profiles permit clear discrimination of the soft sediment above the basement and thus allow the determination of the total volume of sediment above the seismic bedrock, estimated at about 265,000 m3. 相似文献
255.