全文获取类型
收费全文 | 178篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 13篇 |
地球物理 | 46篇 |
地质学 | 91篇 |
海洋学 | 9篇 |
天文学 | 17篇 |
综合类 | 1篇 |
自然地理 | 6篇 |
出版年
2022年 | 1篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 2篇 |
2014年 | 9篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 11篇 |
2008年 | 9篇 |
2007年 | 4篇 |
2006年 | 11篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 6篇 |
1994年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1972年 | 2篇 |
1944年 | 1篇 |
排序方式: 共有185条查询结果,搜索用时 0 毫秒
61.
Observed irregular oscillations of the ion tail axis in comets have by some authors been brought in connection with changes in the flow conditions in the solar wind. We are defending in this paper — by arguments resting on well known observations — the conception that these oscillations are caused by slight variations in the emission conditions for the ions at their source which has always its place close to the cometary nucleus. A complete renovation of the innermost tail part up to a length of a few million km (called by Hoffmeister the primary tail) and defining the tail axis can take place within a few to several hours. Shifts of this axis are becoming visible when the new tail rays finish their closure along another direction than the earlier ones.The not so rarely observed jumps in the direction of the primary tail lead in connection with the large time scale — of about 24h — for a complete closure of a ray system from an individual ion out-break to the conclusion that we should expect occasionally the existence of two (or even more) different axis to which tail rays make their closure. Some photographs of Comet Bennett 1969i seem to show such double axis. 相似文献
62.
AbstractNew wavelet and artificial neural network (WA) hybrid models are proposed for daily streamflow forecasting at 1, 3, 5 and 7 days ahead, based on the low-frequency components of the original signal (approximations). The results show that the proposed hybrid models give significantly better results than the classical artificial neural network (ANN) model for all tested situations. For short-term (1-day ahead) forecasts, information on higher-frequency signal components was essential to ensure good model performance. However, for forecasting more days ahead, lower-frequency components are needed as input to the proposed hybrid models. The WA models also proved to be effective for eliminating the lags often seen in daily streamflow forecasts obtained by classical ANN models. Editor D. Koutsoyiannis; Associate editor L. SeeCitation Santos, C.A.G. and Silva, G.B.L., 2013. Daily streamflow forecasting using a wavelet transform and artificial neural network hybrid models. Hydrological Sciences Journal, 59 (2), 312–324. 相似文献
63.
Consequences on water retention properties of double-porosity features in a compacted silt 总被引:2,自引:1,他引:1
The paper deals with an experimental investigation aimed at studying microstructural features and their consequences on water
retention properties of statically compacted unsaturated silt. The evolution of the microstructure of the aggregate fabric
induced by compaction is investigated by studying the pore size distribution changes under different initial conditions (void
ratio and water content). The material used is low plasticity silt from Jossigny near Paris, France. A series of mercury intrusion
porosimetry tests (MIP) were performed at different void ratios and water contents to provide microstructural information.
The arrangement of aggregation/particles and pore network was also investigated with environmental scanning electron microscopy
(ESEM). The MIP data were used to determine the water retention curve on drying for the specific pore network configuration
induced on compaction. The MIP data were used to formulate and calibrate a multimodal water retention model for a specific
pore network configuration, which is obtained by linear superposition of subcurves of a modified van Genuchten type. The study
is then complemented with controlled suction oedometer tests on compacted samples to obtain the water retention properties
of the material at two different void ratios. Finally, we compare the water retention properties obtained by the simulated
progression of the different pore network configurations induced on the hydraulic path with the water retention properties
under suction-controlled conditions. Good agreement between the two methods for the drying path is reached. 相似文献
64.
Josefa V. Guerra Marcelo M. Azevedo Luciana S. Esteves Susana B. Vinzon Nelson Violante-Carvalho Carlos Augusto F. Schettini Roberto F. Oliveira Aleksandro R. Zaleski 《Continental Shelf Research》2009
Water column profiles and near-bed time series of pressure, current velocity, suspended-particulate matter (SPM) concentration and seawater temperature and salinity were collected during three short cruises carried out in May 2005 in the shoreface and inner shelf area adjacent to Cassino Beach, southern Brazil. The measurements were part of the Cassino Experiment, a project conducted at an open, sandy coastal area known for the occurrence of patches of fairly large amounts of muddy sediments that are sporadically fluidized, transported onshore and eventually stranded on the beach. The study area is close to the Patos Lagoon mouth, being influenced by its water and suspended-sediment discharge. The presence of the Patos Lagoon outflow on the inner shelf was detected in one of the cruises (May 13) through measurements of near-surface salinity: while close to shore salinity was 29.4, a minimum value of 13.8 was measured at ∼10 km from the coast. Four days later, no trace of the plume was detected in the area. Regarding seawater temperature, no large temporal or spatial variability was documented with measured values ranging from 19.3 to 20 °C. Water column currents were prominently to N and NE, except at the outermost station, located ∼42 km from the coast, where NW-directed flows were observed at surface and mid-depth. Maximum near-bed current velocity oscillated between 18 and 42 cm s−1 in the east–west direction and between 14 and 42 cm s−1 in the north–south direction. Near-surface concentration of SPM oscillated between 11 and 99 mg L−1, in general one order of magnitude lower than near-bed values. However, near-bed concentration of SPM showed large spatial variability: the highest value (2200 mg L−1) was yielded by a water sample collected at ∼8 m water depth, at a station located ∼2 km away from the shoreline; two water samples collected 500 m, apart from this station, yielded SPM concentrations of 148 and 205 mg L−1, one order of magnitude lower. Spectral analyses of near-bed current speed and SPM concentration indicate the relevance of oscillations in the low-frequency (<0.05 Hz) range. Detailed sampling of bottom sediment indicated that in May 2005 the mud patch was centered at ∼8.5 m water depth. 相似文献
65.
Joaquim C.B. Queiroz José R. Sturaro Augusto C.F. Saraiva Paulo M.B. Landim 《Journal of Geochemical Exploration》2009
This paper presents a methodology based on geostatistical theory for quantifying the risks associated with heavy-metal contamination in the harbor area of Santana, Amapá State, Northern Brazil. In this area there were activities related to the commercialization of manganese ore from Serra do Navio. Manganese and arsenic concentrations at unsampled sites were estimated by postprocessing results from stochastic annealing simulations; the simulations were used to test different criteria for optimization, including average, median, and quantiles. For classifying areas as contaminated or uncontaminated, estimated quantiles based on functions of asymmetric loss showed better results than did estimates based on symmetric loss, such as the average or the median. The use of specific loss functions in the decision-making process can reduce the costs of remediation and health maintenance. The highest global health costs were observed for manganese. 相似文献
66.
Denis Scholz Christian Mühlinghaus Augusto Mangini 《Geochimica et cosmochimica acta》2009,73(9):2592-695
We derive equations describing the evolution of the carbon and oxygen isotope composition of the bicarbonate in a calcite precipitating solution on the surface of a stalagmite using a classical Rayleigh approach. The combined effects of calcite precipitation, degassing of CO2 and the buffering effect of the water reservoir are taken into account. Whereas δ13C shows a progressive increase to a final constant value, δ18O shows an initial isotopic enrichment, which exponentially decays due to the buffering effect of the water reservoir. The calculated evolution is significantly different for both carbon and oxygen isotopes than derived in a recent paper [Dreybrodt W. (2008) Evolution of the isotopic composition of carbon and oxygen in a calcite precipitating H2O-CO2-CaCO3 solution and the related isotopic composition of calcite in stalagmites. Geochim. Cosmochim. Acta72, 4712-4724.].Furthermore, we discuss the isotopic evolution of the bicarbonate in the solution for long residence times on the stalagmite surface, i.e., for t→∞. The equilibrium isotope ratio of the bicarbonate is then determined by isotopic exchange between the cave atmosphere and the bicarbonate in the solution and can be calculated by equilibrium isotope fractionation. For strongly ventilated caves exchange with the cave atmosphere will result in higher δ13C and δ18O values than those observed in a pure Rayleigh distillation scenario, for sparsely ventilated caves it will result in lower δ13C and δ18O values. 相似文献
67.
Carlos Augusto Ramos e Silva Pablo Bezerra Dávalos Leonel da Silveira Lobo Sternberg Flavo Elano Soares de Souza Maria Helena Constantino Spyrides Paulo Sérgio Lucio 《Estuarine, Coastal and Shelf Science》2010
We evaluated the physical–chemical properties and nutrient concentrations in two shrimp ponds under conventional management, intensive (I-P) and semi-intensive (SI-P), and one under organic management (O-P), three days after loading and before stoking. The mean’s total alkalinity concentrations were 2.26 ± 0.04 mM, 2.28 ± 0.01 mM and 2.59 ± 0.01 mM, respectively for I-P, SI-P and O-P. Bicarbonate and carbonate accounted for 62% and 37% in I-P, 64% and 36% in SI-P and 83–17% in O-P, respectively. Aragonite and calcite were oversaturated around Ω = 5. Mean total phosphate (TP) concentrations were 441.37 ± 92.06 μg/L, 449 ± 48 μg/L and 473.64 ± 84.17 μg/L, under I-P SI-P and O-P management respectively. Following this sequence, NO3− concentration was 2.98 ± 0.7 μg/L, 1.16 ± 0.16 μg/L and 0.32 ± 0.12 μg/L, under I-P, SI-P and O-P management respectively. Thus, the data suggest that different management of farm organic waste leads to different chemical water quality. 相似文献
68.
Geochemical characterization of heavy metal contaminated area using multivariate factorial kriging 总被引:1,自引:0,他引:1
Joaquim C. B. Queiroz José R. Sturaro Augusto C. F. Saraiva Paulo M. Barbosa Landim 《Environmental Geology》2008,55(1):95-105
This paper describes a geostatistical method, known as factorial kriging analysis, which is well suited for analyzing multivariate
spatial information. The method involves multivariate variogram modeling, principal component analysis, and cokriging. It
uses several separate correlation structures, each corresponding to a specific spatial scale, and yields a set of regionalized
factors summarizing the main features of the data for each spatial scale. This method is applied to an area of high manganese-ore
mining activity in Amapá State, North Brazil. Two scales of spatial variation (0.33 and 2.0 km) are identified and interpreted.
The results indicate that, for the short-range structure, manganese, arsenic, iron, and cadmium are associated with human
activities due to the mining work, while for the long-range structure, the high aluminum, selenium, copper, and lead concentrations,
seem to be related to the natural environment. At each scale, the correlation structure is analyzed, and regionalized factors
are estimated by cokriging and then mapped. 相似文献
69.
Dominik Fleitmann Stephen J BurnsUlrich Neff Augusto ManginiAlbert Matter 《Quaternary Research》2003,60(2):223-232
Speleothems from Hoti Cave in northern Oman provide a record of continental pluvial periods over the last 330,000 yr. Periods of rapid speleothem deposition occurred from 6000 to 10,500, 78,000 to 82,000, 120,000 to 135,000, 180,000 to 200,000, and 300,000 to 330,000 yr ago, with little or no growth during the intervening periods. During each of these five pluvial periods, δD values of water extracted from speleothem fluid inclusions (δDFI) are between −60 and −20‰ (VSMOW) and δ18O values of speleothem calcite (δ18OC) are between −12 and −4‰ to (VPDB). These values are much more negative than modern rainfall (for δD) or modern stalagmites (for δ18O). Previous work on the isotopic composition of rainfall in Oman has shown that northern and southern moisture sources are isotopically distinct. Combined measurements of the δD values of fluid-inclusion water with calculated δ18O values from peak interglacial speleothems indicate that groundwater was predominantly recharged by the southern (Indian Ocean) moisture source, when the monsoon rainfall belt moved northward and reached Northern Oman during each of these periods. 相似文献
70.
Fazzito Sabrina Y. Rapalini Augusto E. Cortés José M. Terrizzano Carla M. 《International Journal of Earth Sciences》2017,106(2):631-657
International Journal of Earth Sciences - Palaeomagnetic data from poorly consolidated to non-consolidated late Cenozoic sediments along the central segment of the active El Tigre Fault... 相似文献