全文获取类型
收费全文 | 334篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 11篇 |
地球物理 | 111篇 |
地质学 | 141篇 |
海洋学 | 37篇 |
天文学 | 30篇 |
综合类 | 1篇 |
自然地理 | 17篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 17篇 |
2017年 | 20篇 |
2016年 | 17篇 |
2015年 | 23篇 |
2014年 | 20篇 |
2013年 | 19篇 |
2012年 | 22篇 |
2011年 | 22篇 |
2010年 | 26篇 |
2009年 | 18篇 |
2008年 | 31篇 |
2007年 | 20篇 |
2006年 | 4篇 |
2005年 | 15篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有352条查询结果,搜索用时 31 毫秒
251.
Abstract. A three-year set of data from six stations is analysed in order to monitor the environmental quality by use of macrobenthos in addition to chemical data. The communities differ along the depth gradient and no seasonal cycle is evident. Stronger temporal differences in community composition are evident when examining a four-year cycle at one of the stations in connection with an improvement of environmental parameters. 相似文献
252.
Mauro Sclavo Luigi Cavaleri Stephen F. Barstow Gerassimos A. Athanassoulis 《Marine Ecology》2002,23(S1):361-369
Abstract. We describe a software system that allows even an inexperienced user to estimate the wave statistics at any location along the European coastal zone. The system is composed of a solid, well verified data set, a geographical tool, a modelling section and a statistical package. Their use is fully transparent to the user. 相似文献
253.
Abstract. This paper briefly summarises research carried out in 1982–1990 in the coastal area off Monte Conero, SW northern Adriatic Sea. Oceanographic data on temperature, salinity, oxygen saturation, nutrients (nitrates, silicates and orthophosphates), and chlorophylls were collected to characterise this coastal ecosystem in view of the setting up of the "Costa del Monte Conero" protected marine area.
Towards the coast the physical and chemical parameters exhibited a seasonal periodicity.
Temperature showed a clear annual periodicity with a certain interannual variability; this also holds true for oxygen saturation, with peaks in March and minima in September, though without hypoxic events.
Nutrient concentrations peaked at the surface layer at the coastal station from December to March (nitrates: 35–50 μmol 1−1 ; silicates: 22–70 μmol 1−1 ; orthophosphates: 0.37–0.54 μmol 1−1 ) and minima in summer (Jul-Aug) on surface and bottom (0–12μmol 1−1 , 0–18.5 μmol 1−1 , and 0–0.15 μmol 1−1 , respectively). From 1988 to 1990 nutrient peaks were lower and coastal salinity exceed 33, with nitrates below 16 μmol 1−1 , silicates below 8 μmol 1−1 , and orthophosphates less than 0.2 μmol 1−1 .
In the coastal area of Senigallia, 40 km to the north, where the influence of the coastal current that carries the river inflows to the south is stronger, the seasonal cycle was similar, albeit with higher values for nutrients and chlorophylls. 相似文献
Towards the coast the physical and chemical parameters exhibited a seasonal periodicity.
Temperature showed a clear annual periodicity with a certain interannual variability; this also holds true for oxygen saturation, with peaks in March and minima in September, though without hypoxic events.
Nutrient concentrations peaked at the surface layer at the coastal station from December to March (nitrates: 35–50 μmol 1
In the coastal area of Senigallia, 40 km to the north, where the influence of the coastal current that carries the river inflows to the south is stronger, the seasonal cycle was similar, albeit with higher values for nutrients and chlorophylls. 相似文献
254.
Marcos A. E. Chaparro Ana M. Sinito V. Ramasamy Claudia Marinelli Mauro A. E. Chaparro S. Mullainathan S. Murugesan 《Environmental Geology》2008,56(2):425-437
Rock-magnetic techniques have become a useful tool in environmental issues; in particular, magnetic studies constitute an
alternative way to study pollution in different media. The present contribution focuses on magnetic parameters as pollution
indicators, especially from their relationship with contents of heavy metals. The work was carried out in two Indian rivers
located in Tamil Nadu, southern India. Several sediment samples were collected and studied in the laboratory using magnetic
techniques, magnetic susceptibility, anhysteric remanent magnetization, isothermal remanent magnetization, and chemical techniques
to determine contents of heavy metals. Magnetic mineralogy indicates the predominance of ferrimagnetic minerals; although
magnetite-like minerals are the main magnetic carriers, antiferromagnetic minerals can be present as subordinate carriers.
Concentration-dependent magnetic parameters revealed noticeable differences between both rivers, e.g. magnetic susceptibility
is four times higher in Cauvery than in Palaru River. Moreover, such increase can be interpreted as “magnetic enhancement”
and therefore related to the pollution status. This magnetic enhancement indicated a different pollutant contribution in both
rivers, and also, a different spatial distribution along these rivers, where critical (or more polluted) sites were identified.
On the other hand, univariate and multivariate statistical analyses—e.g. PCoordA, Multifactorial Analysis of distance, PCA
and RDA—were examined, revealing a link between magnetic and chemical variables. Among magnetic parameters, the concentration-dependent
magnetic parameters (e.g. magnetic susceptibility) seem to be the most relevant for this study. 相似文献
255.
Rossano Piazza Ana Carolina Ruiz-Fernández Mauro Frignani Roberta Zangrando Luca Giorgio Bellucci Ivo Moret Federico Páez-Osuna 《Environmental Geology》2008,54(7):1537-1545
Concentrations of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were measured in 13 surficial
sediment samples collected at three lacustrine locations in the surroundings of Mexico City and four coastal areas of the
States of Sinaloa, Sonora, Oaxaca and Veracruz. Total PCB concentrations span the interval 3.18–621 ng g−1. The highest values (63.7–621 ng g−1) were found in Mexico City, which is a highly anthropogenically impacted area, whereas low concentrations (3.18–12.9 ng g−1) were characteristic of seven places, some of them subject to intense hydrodynamics. In these latter cases, values increase
by 18–73 times if normalised against the fine fraction (silt plus clay) content in sediment. Two samples from Mexico City
exceed the ERM (Effect Range Median) guidelines and are likely to cause adverse effects. Samples contain only lower chlorinated
PCBs (mainly 2-, 3- and 4-CB), thus suggesting that the most used PCB commercial mixture was Aroclor 1242. The homologue composition
of the sample taken close to the nuclear power plant of Laguna Verde is identical to this commercial mixture. PAHs in the
same samples have relatively low concentrations (14.9–287 ng g−1), well below ERL (Effect Range Low) guidelines. The composition of PAH mixtures accounts for the influence of both petrogenic
and pyrolitic sources, with these latter prevailing at some places in Mexico City. 相似文献
256.
In this work, we present a novel methodology to integrate one of the most advanced technique for modeling fractured media for underground systems with a semantics-based genetic programming technique. The objective of the study is to develop a global framework to forecast the temperature of fractured reservoirs. The numerical method used to solve the physical equations is able to handle different fracture distributions without changing the background computational grid, i.e. the mesh of the rock matrix, as well as letting geometrically uncoupled the one co-dimensional fracture meshes. In the context of temperature forecasting, the use of a recently defined variant of genetic programming is taken into account for finding (quasi-)perfect solutions with high probability and for generating models able to produce near optimal predictions also on unseen data. The proposed computational intelligence technique integrates, in a recently developed version of genetic programming that uses semantic genetic operators, a “greedy” crossover and a self tuning algorithm. Experimental results confirm the suitability of the proposed method in predicting the correct temperature distribution in probes inside the domain. 相似文献
257.
Kiyoto Shibasaki Franca Chiuderi-Drago Mauro Melozzi Cornelis Slottje Ester Antonucci 《Solar physics》1983,89(2):307-321
Hale region 16898 was observed by the Westerbork Synthesis Radio Telescope at 6 cm and by the Ultraviolet Spectrometer and Polarimeter and the X-Ray Spectrometer on the Solar Maximum Mission satellite. Optical pictures of the same active region were taken at Sacramento Peak, Big Bear, and Meudon Observatories. The radio emission mechanisms are identified by comparing radio data with ultraviolet and soft X-ray data. The height of the radio sources and the magnetic field strength at that height are deduced. A radio source above a large sunspot shows a crescent shaped depression of circular polarization and a high brightness temperature. The emission mechanism is identified as gyroresonance at the second and the third harmonic layers and it is found that the second harmonic layer, where the magnetic field strength is 900 G, must be in the corona. An extended loop-like source connecting the leading and the following part of the active region as well as the sources associated with small spots are mainly due to thermal free-free emission by hot and dense plasma which is also observed in ultraviolet and soft X-ray radiation. The calculated radio brightness temperature, using the physical parameters deduced from the ultraviolet and soft X-ray line intensities, agrees with the observed brightness temperature. The height of the low brightness temperature sources above the small spots is 6000 ± 3000 km and that above the large spot is less than 3000 km: the source above the large spot does not show any shift relative to the sunspot due to the projection effect. Very strong radio emission was found which was associated with the merging of a group of small spots into the large sunspot. In the same day, warm ( 106 K) and dense matter was present above the large spot. Evidence for nonthermal emission is presented. 相似文献
258.
Debris-flow phenomena in the Central Apennines of Italy 总被引:1,自引:0,他引:1
The results of a research project on the extent of debris-flow processes in the Monti Sibillini area (Central Italy) are presented. Debris flows have greatly contributed in shaping the landscape of the Monti Sibillini territory. Based on the dominant active process they can be subdivided into three sections: a source area, a transport area and a depositional area. Four environments can be identified as source areas: landslide deposits, highly fractured rocks, scree or talus deposits, and glacial deposits. The evolution of some of the largest features present in the area is examined. These may have developed from an initial stage of mostly gully erosion and minor landsliding, through an intermediate stage characterized by extensive mass-movement, to a final stage dominated by fluvial processes. Lastly, generalizations on the debris-flow hazard in the study area are made. 相似文献
259.
260.
Adriano Ribolini Alessandro Chelli Mauro Guglielmin Marta Pappalardo 《Quaternary Research》2007,68(3):353-363
In the Schiantala Valley of the Maritime Alps, the relationship between a till-like body and a contiguous rock glacier has been analyzed using geomorphologic, geoelectric and ice-petrographic methodologies. DC resistivity tomographies undertaken in the till and in the rock glacier show the presence of buried massive ice and ice-rich sediments, respectively. Ice samples from a massive ice outcrop show spherical gas inclusions and equidimensional ice crystals that are randomly orientated, confirming the typical petrographic characteristics of sedimentary ice. The rock glacier formation began after a phase of glacier expansion about 2550 ± 50 14C yr BP. Further ice advance during the Little Ice Age (LIA) overrode the rock glacier root and caused partial shrinkage of the pre-existing permafrost. Finally, during the 19th and 20th centuries, the glacial surface became totally debris covered. Geomorphological and geophysical methods combined with analyses of ice structure and fabric can effectively interpret the genesis of landforms in an environment where glaciers and permafrost interact. Ice petrography proved especially useful for differentiating ice of past glaciers versus ice formed under permafrost conditions. These two mechanisms of ice formation are common in the Maritime Alps where many sites of modern rock glaciers were formerly occupied by LIA glaciers. 相似文献