全文获取类型
收费全文 | 603篇 |
免费 | 22篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 35篇 |
地球物理 | 153篇 |
地质学 | 217篇 |
海洋学 | 103篇 |
天文学 | 59篇 |
综合类 | 6篇 |
自然地理 | 40篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 15篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 22篇 |
2017年 | 28篇 |
2016年 | 40篇 |
2015年 | 21篇 |
2014年 | 31篇 |
2013年 | 41篇 |
2012年 | 29篇 |
2011年 | 54篇 |
2010年 | 33篇 |
2009年 | 50篇 |
2008年 | 45篇 |
2007年 | 27篇 |
2006年 | 28篇 |
2005年 | 19篇 |
2004年 | 26篇 |
2003年 | 15篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1960年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有629条查询结果,搜索用时 15 毫秒
601.
Teresa Salvatici Stefano Morelli Veronica Pazzi William Frodella Riccardo Fanti 《山地科学学报》2017,14(4):636-648
On 4th November 2010, a debris flow detached from a large debris cover accumulated above the lowermost portion of the Rotolon landslide (Vicentine Pre-Alps, NE Italy) and channelized in the valley below within the Rotolon Creek riverbed. Such event evolved into a highly mobile and sudden debris flow, damaging some hydraulic works and putting at high risk four villages located along the creek banks. A monitoring campaign was carried out by means of a ground based radar interferometer (GB-InSAR) to evaluate any residual displacement risk in the affected area and in the undisturbed neighbouring materials. Moreover, starting from the current slope condition, a landslide runout numerical modelling was performed by means of DAN-3D code to assess the impacted areas, flow velocity, and deposit distribution of the simulated events. The rheological parameters necessary for an accurate modelling were obtained through the back analysis of the 2010 debris flow event. Back analysis was calibrated with all of the available terrain data coming from field surveys and ancillary documents, such as topographic, geomorphological and geological maps, with pre- and post-event LiDAR derived DTMs, and with orthophotos. Finally, to identify new possible future debris flow source areas as input data for the new modelling, all the obtained terrain data were reanalysed and integrated with the GB-InSAR displacement maps; consequently, new simulations were made to forecast future events. The results show that the integration of the selected modelling technique with ancillary data and radar displacement maps can be a very useful tool for managing problems related to debris flow events in the examined area. 相似文献
602.
Arthur Ayres Neto Vanessa Alves da Costa Clara Pinto Ferreira Maia Porto Thais Cristina Vargas Garrido Jean-Pierre Hermand 《Marine Georesources & Geotechnology》2020,38(4):437-449
AbstractMarine mining is the ocean’s new exploration frontier, and polymetallic crusts (PMCs) and ferromanganese nodules are considered a strategic resource for the future. Acoustic geophysical methods are a valuable tool for oceanic research and have been employed for several decades in the exploration of marine resources and environmental evaluations. The main objective of this work was to investigate the correlation between the chemical composition of PMCs from three different areas along the Brazilian continental margin and their physico-acoustic attributes (P-wave velocity, density and acoustic impedance). The results show that the geoacoustic properties of PMCs are correlated to their chemical composition. Measurements showed positive and negative trends between acoustic impedance and studied elements (Fe, Mn, Co, Cu, Zn, W and Ni) according to the direction of measurement, indicting high anisotropy levels. Our study sheds initial light on the correlation between acoustic properties and metal content of PMCs. The study facilitates assessments of the acoustic responses of PMCs allowing more efficient prospection and exploitation compared to ship-board geophysical techniques that are too qualitative to identify PMCs. The results can contribute to determining the best procedures and techniques for more efficient future exploration of this resource. 相似文献
603.
Teresa M. Konlechner 《New Zealand geographer》2008,64(2):154-156
Abstract: Marine dispersal provides a mechanism for introduced plants to invade coastal systems. Regular surveillance is essential for management of marine dispersed weeds. This paper outlines the biological, physical and management dimensions of this coastal issue in New Zealand. 相似文献
604.
This study compares the marker pigment composition in three different lake compartments: the water column; the surface sediment
biofilm (0–0.5 cm), where production and main degradation processes take place; and the deep sediment (15–17 cm), where the
signal is finally stored and marker pigments are used as a proxy in paleolimnological studies. The aim was to evaluate which
marker pigments better record in the sediment the relative contributions of planktonic and benthic production in high mountain
lakes, taking into account the differential preservation existing among pigments. A survey of 82 high mountain lakes distributed
along the major environmental gradients was carried out in the Pyrenees. Comparison of pigments between the three compartments
revealed that both water column and sediment biofilm signals could be distinguished in old sediment layers, despite the observation
that some of the most characteristic carotenoids that appeared frequently and in high concentrations in the water column were
already less common or even absent from the sediment biofilm. In the shallowest lakes, pigment composition in the sediment
biofilm was typical of photosynthetically active communities and their deep sediment samples were characterised by a substitution
of fucoxanthin by diatoxanthin as the dominant diatom marker pigment. However, in the deepest lakes the pigment composition
of the sediment biofilm and deep sediment was similar, characterised by marker pigments of mainly planktonic algal groups
and pheophytins, which are typical pigments of decaying communities. Results are discussed in terms of how pigment source
(planktonic or benthic) and pigment type (lability of molecule) interact to shape pigment composition in the sediment record
of high mountain lakes. 相似文献
605.
Ferreira Doneivan F. Suslick Saul B. Moura Paula C. S. S. 《Natural Resources Research》2003,12(4):273-290
This paper is concerned with potential financial impacts of different bonding instruments on oil and gas projects. An algorithm was prepared in order to assist decision makers, both regulators and industry, evaluate potential Net Present Value (NPV) impacts of financial instruments used to satisfy bonding requirements. Instrument option is the main variable for the proposed model. The user will be able to select between four instruments (Letters of Credit, Prepaid Collateral Closure Accounts, Leasing Specific Closure Accounts, and Ex-post Insurance Policies). This study includes simulations for three producing fields of different economically recoverable reserves (9 MMbbl, 53 MMbbl, and 148 MMbbl5), where four financial instruments, in addition to a no instrument scenario, are tested under a proposed bonding regime. Sensitivity analysis of NPV and Government Take (GT) value indicate ex-post insurance policies and letters of credit cause fewer impacts yielding significantly better payoffs. Preliminary simulations also confirm that small projects, around 9 MMbbl, can be severely affected when collateral account instruments are used. 相似文献
606.
Mangroves commonly found along tropical and subtropical coastlines are susceptible to oil pollution. In December 2000, around 500 1 m tall Kandelia candel saplings at the age of 3–5 years old located at the foreshore region of Sheung Pak Nai swamp, Hong Kong SAR, were found to be damaged by oil pollution. More than 80% of the saplings were either dead or washed away and leaving less than 5% healthy saplings with dense green leaves. Elevated concentrations of light n-alkanes (ranging from n-C14 to n-C20), pristane and phytane were recorded in surface sediments collected in December 2000. The ratio between light and total n-alkanes was 0.4. The total petroleum hydrocarbons (60–80 μg g−1 TPH) and unresolved complex mixtures (60–70 μg g−1 UCM) were higher than the background values of other mangrove sediments in Hong Kong, which were 40 and 20 μg g−1, respectively. In certain root zone sediments, TPH concentrations were above 1000 μg g−1. These results suggest that surface sediments in Sheung Pak Nai were contaminated by petroleum oil, most likely by illegal discharge of fuel oil which occurred between 1998 and 2002. One year later, in December 2001, unhealthy saplings had recovered and re-grown. The concentrations of TPH and UCM in sediments declined to around 40 μg g−1, pristane and phytane dropped by 80%, and the ratio of light to total n-alkanes was 0.15, suggesting that residual oil in sediments was weathered leading to a remarkable recovery of the unhealthy saplings. 相似文献
607.
Clia Ferreira Pernille Jensen Lisbeth Ottosen Alexandra Ribeiro 《Engineering Geology》2005,77(3-4):339-347
This paper aims to assess the applicability of the electrodialytic remediation technique for the removal of zinc, lead, copper and cadmium from municipal solid waste (MSW) incinerator fly ash. A broad range of experimental conditions were studied including current densities, remediation times, use of assisting agents and cell design.
Several operational problems were identified during the electrodialytic experiments, among which are formation of precipitates, dryness of sample and partial dissolution of sample creating preferential pathways for the electric current. These problems may explain the low remediation efficiencies obtained.
Comparison between experiments showed that generally the use of Na-gluconate as assisting agent leads to better results than distilled water. Increasing the concentration of the assisting agent also results in higher removals. 相似文献
608.
Drying of masonry specimens was monitored by means of a two-dimensional (2D) magnetic resonance imaging (MRI) technique. The
external surfaces stayed wet for longer if NaCl was present instead of pure water only. This corroborates many practical observations
that salts aggravate dampness in masonry. A slower evaporation process and not hygroscopicity was the cause. That suggests
that salt-induced dampness may, in general, arise simply from changes in the drying process of masonry materials. That also
implies that the height and depth at which crystallization occurs in walls may depend on the relative equilibrium humidity
(RHeq) and other properties of salts that influence drying of porous materials. Evaporation rates of free surfaces of pure
water and saturated NaCl solution were measured by a gravimetric technique. The results indicate that slow drying of salt-contaminated
materials is not due only to the lower RHeq of salt solutions. The effective surface of evaporation is likely to be reduced
perhaps due to blocking of pores by salt crystals. Final salt-distribution maps of the specimens show that: (a) salts may
affect the inner materials of the masonry, even in evaporation-induced processes that lead crystallization to occur predominantly
on the external surface; (b) distinct internal distribution patterns occur if masonry composition varies.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
609.
A. Viana Da Fonseca J. Carvalho C. Ferreira J. A. Santos F. Almeida E. Pereira J. Feliciano J. Grade A. Oliveira 《Geotechnical and Geological Engineering》2006,24(5):1307-1348
This paper summarizes the results of an experimental site investigation and characterization survey, on a residual (saprolitic)
soil from granite, in the framework of a research project led by the Faculty of Engineering of the University of Porto (FEUP).
This project aims at characterizing these unusual soils in the context of the development of an International Prediction Event
(Class A) on the behaviour of different types of piles. A very extensive site characterization campaign, including a large
variety of in-situ tests and field methods, has been held. These investigations comprised the application of several geophysical
borehole and surface methods, namely P- and S-wave seismic refraction, reflection, cross-hole (CH), down-hole (DH), electrical
resistivity imaging and ground probing radar (GPR), as well as mechanical tests, namely SPT, CPT and DMT, among others. The
site is geologically formed by an upper layer of heterogeneous residual granitic soil, overlaying rather weathered granite
contacting a gneissic migmatite. Direct and indirect results from some of the referred surveys were compared between them
and with some of the available geological and geotechnical information, namely those obtained from seismic, electrical and
GPR profiles, conducted adjacent to three boreholes in which undisturbed soil samples were collected previously to geophysical
data acquisition. In addition, a comprehensive laboratory testing program was carried out using the collected undisturbed
samples. A discussion of the obtained results is hereby presented, giving emphasis to the correlations encountered between
the different tests, specific of saprolitic soils with weak relic structures. 相似文献
610.
We investigate the effect of laterally varying earth structure on centroid moment tensor inversions using fundamental mode mantle waves. Theoretical seismograms are calculated using a full formulation of surface wave ray theory. Calculations are made using a variety of global tomographic earth models. Results are compared with those obtained using the so-called great-circle approximation, which assumes that phase corrections are given in terms of mean phase slowness along the great circle, and which neglects amplitude effects of heterogeneity. Synthetic tests suggest that even source parameters which fit the data very well may have large errors due to incomplete knowledge of lateral heterogeneity. The method is applied to 31 shallow, large earthquakes. For a given earthquake, the focal mechanisms calculated using different earth models and different forward modelling techniques can significantly vary. We provide a range of selected solutions based on the fit to the data, rather than one single solution. Difficulties in constraining the dip-slip components of the seismic moment tensor often produce overestimates of seismic moment, leading to near vertical dip-slip mechanisms. This happens more commonly for earth models not fitting the data well, confirming that more accurate modelling of lateral heterogeneity can help to constrain the dip-slip components of the seismic moment tensor. 相似文献