全文获取类型
收费全文 | 1459篇 |
免费 | 83篇 |
国内免费 | 48篇 |
专业分类
测绘学 | 86篇 |
大气科学 | 77篇 |
地球物理 | 429篇 |
地质学 | 767篇 |
海洋学 | 62篇 |
天文学 | 81篇 |
综合类 | 13篇 |
自然地理 | 75篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 53篇 |
2021年 | 80篇 |
2020年 | 75篇 |
2019年 | 61篇 |
2018年 | 147篇 |
2017年 | 127篇 |
2016年 | 164篇 |
2015年 | 90篇 |
2014年 | 129篇 |
2013年 | 159篇 |
2012年 | 95篇 |
2011年 | 94篇 |
2010年 | 64篇 |
2009年 | 52篇 |
2008年 | 33篇 |
2007年 | 21篇 |
2006年 | 24篇 |
2005年 | 5篇 |
2004年 | 16篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1969年 | 1篇 |
排序方式: 共有1590条查询结果,搜索用时 62 毫秒
951.
Mohammad M. Sohrabi Daniele Tonina Rohan Benjankar Mukesh Kumar Patrick Kormos Danny Marks Charlie Luce 《水文研究》2019,33(8):1260-1275
Hydrological processes in mountainous settings depend on snow distribution, whose prediction accuracy is a function of model spatial scale. Although model accuracy is expected to improve with finer spatial resolution, an increase in resolution comes with modelling costs related to increased computational time and greater input data and parameter information. This computational and data collection expense is still a limiting factor for many large watersheds. Thus, this work's main objective is to question which physical processes lead to loss in model accuracy with regard to input spatial resolution under different climatic conditions and elevation ranges. To address this objective, a spatially distributed snow model, iSnobal, was run with inputs distributed at 50‐m—our benchmark for comparison—and 100‐m resolutions and with aggregated (averaged from the fine to the large resolution) inputs from the 50‐m model to 100‐, 250‐, 500‐, and 750‐m resolution for wet, average, and dry years over the Upper Boise River Basin (6,963 km2), which spans four elevation bands: rain dominated, rain–snow transition, and snow dominated below treeline and above treeline. Residuals, defined as differences between values quantified with high resolution (>50 m) models minus the benchmark model (50 m), of simulated snow‐covered area (SCA) and snow water equivalent (SWE) were generally slight in the aggregated scenarios. This was due to transferring the effects of topography on meteorological variables from the 50‐m model to the coarser scales through aggregation. Residuals in SCA and SWE in the distributed 100‐m simulation were greater than those of the aggregated 750 m. Topographic features such as slope and aspect were simplified, and their gradient was reduced due to coarsening the topography from the 50‐ to 100‐m resolution. Therefore, solar radiation was overestimated, and snow drifting was modified and caused substantial SCA and SWE underestimation in the distributed 100‐m model relative to the 50‐m model. Large residuals were observed in the wet year and at the highest elevation band when and where snow mass was large. These results support that model accuracy is substantially reduced with model scales coarser than 50 m. 相似文献
952.
Mohammad Nuruzzama Waliur Rahaman Gyana R. Tripathy Rahul Mohan Shramik Patil 《水文研究》2020,34(11):2351-2364
Dissolved major ions, Sr concentrations and 87Sr/86Sr ratios of 10 coastal lakes from the Larsemann Hills, East Antarctica have been studied to constrain their solute sources, transport and glacial weathering patterns in their catchments. In absence of perennial river/streams, lakes serve as only reliable archive to study land surface processes in these low-temperature regions. The lake water chemistry is mostly Na-Cl type and it does not show any significant depth variations. Sr isotope compositions of these lakes vary from 0.7110 to 0.7211 with an average value of 0.7145, which is higher than modern seawater value. In addition to oceanic sources, major ions and Sr isotopic data show appreciable amount of solute supply from chemical weathering of silicate rocks in lake catchments and dissolution of Ca-Mg rich salts produced during the freezing of seawaters. The role of sulphide oxidation and carbonate weathering are found to be minimal on lake hydro-chemistry in this part of Antarctica. Inverse model calculations using this chemical dataset provide first-order estimates of dissolved cations and Sr; they are mostly derived from oceanic (seawater + snow) sources (cations approximately 76%) and (Sr approximately 92%) with minimal supplies from weathering of silicates (cations approximately 15%); (Sr approximately 2%) and Ca-rich minerals (cations approximately 9%); (Sr approximately 7%). The silicate weathering rate and its corresponding atmospheric CO2 consumption rate estimates for Scandrett lake catchment (3.6 ± 0.3 tons/km2/year and 0.5 × 105 moles/km2/year), are lower than that of reported values for the average global river basins (5.4 tons/km2/year and 0.9 × 105 tons/km2/year) respectively. The present study provides a comprehensive report of chemical weathering intensity and its role in atmospheric CO2 consumption in low-temperature pristine environment of Antarctica. These estimates underscore the importance of Antarctica weathering on atmospheric CO2 budget, particularly during the past warmer periods when the large area was exposed and available for intense chemical weathering. 相似文献
953.
Naira Chaouch Marouane Temimi Scott Hagen John Weishampel Stephen Medeiros Reza Khanbilvardi 《水文研究》2012,26(11):1617-1628
This work proposes a method for detecting inundation between semi‐diurnal low and high water conditions in the northern Gulf of Mexico using high‐resolution satellite imagery. Radarsat 1, Landsat imagery and aerial photography from the Apalachicola region in Florida were used to demonstrate and validate the algorithm. A change detection approach was implemented through the analysis of red, green and blue (RGB) false colour composites image to emphasise differences in high and low tide inundation patterns. To alleviate the effect of inherent speckle in the SAR images, we also applied ancillary optical data. The flood‐prone area for the site was delineated a priori through the determination of lower and higher water contour lines with Landsat images combined with a high‐resolution digital elevation model. This masking technique improved the performance of the proposed algorithm with respect to detection techniques using the entire Radarsat scene. The resulting inundation maps agreed well with historical aerial photography as the probability of detection reached 83%. The combination of SAR data and optical images, when coupled with a high‐resolution digital elevation model, was shown to be useful for inundation mapping and have a great potential for evaluating wetting/drying algorithms of inland and coastal hydrodynamic models. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
954.
Salam Roquia Ghose Bonosri Shill Badhon Kumar Islam Md. Aminul Islam Abu Reza Md. Towfiqul Sattar Md. Abdus Alam G. M. Monirul Ahmed Bayes 《Natural Hazards》2021,108(3):2589-2589
Natural Hazards - A correction to this paper has been published: https://doi.org/10.1007/s11069-021-04825-3 相似文献
955.
Density currents are caused by a difference in density,though low,of an entering fluid with the ambient fluid.This type of current is two-phased and found on riverbeds or in reservoirs behind dams,and is nonlinear in nature,complex,and sensitive to initial conditions.Fractal geometry is used as a powerful tool for studying complex natural phenomena.Using experimental studies and changes in inlet current conditions,the fractal and multi-fractal analyses of the interface between the density current and the ambient fluid were done.In addition,a search was made to find a possible connection between the nonlinear patterns.According to the results,with an increase in the inlet discharge and inlet density of the current the fractal dimension decreased.Further,the smaller the range of the singularity spectrum diagram was,i.e.,the more it was less than 0.34,the lower the system's tendency was to be multi-fractal,and the system sensitive to large local changes.In the interface between the density current and the ambient fluid,using the fractal dimension-based Richardson number could improve experimental data by 12.4%.Moreover,with an increase in the Richardson number,the Reynolds number of the current decreased.Further,upon considering the fractal dimension,the Reynolds number improved by 23%and a good correlation with a coefficient of determination of 0.76. 相似文献
956.
Reza Sadeghi Hamid Reza Esmaeili Fatah Zarei Bettina Reichenbacher 《Marine Ecology》2021,42(1):e12629
The Persian Gulf and Oman Sea are characterized by an interesting paleoclimatic history and different ecological settings, and offer a unique study area to investigate the genetic structure of marine organisms including fishes. The Ornate goby Istigobius ornatus is widely distributed throughout the tropical Indo‐West Pacific including the Persian Gulf and Oman Sea. Here, we present the population structure, genetic diversity, and demographic history of four populations of I. ornatus from the latter two regions using the D‐loop marker of mitochondrial DNA. The results reveal a shallow genealogy, a star‐like haplotype network, significance of neutrality tests, and unimodal mismatch distribution. This is concordant with a recent demographic expansion of I. ornatus in the Persian Gulf and Oman Sea at about 63,000–14,000 years ago, which appears to be related to Late Pleistocene sea level fall and rise. The results of the pairwise Fst estimates imply high gene flow along the coast of the Persian Gulf, which is probably due to larval dispersion, whereas the Oman Sea population clearly differs from all Persian Gulf populations. The AMOVA result indicates that 7.74% of the variation is related to differences among ecoregions, while inter‐ and intra‐population differences explained ?3.20% and 95.47% of the variation, respectively. The haplotype network depicts two groups of haplotypes, most of them were specific to the Persian Gulf. No further evidence for geographic lineage substructuring was evident. The Mantel test result indicates that isolation by distance is not the main mechanism that promoted the genetic differentiation among the studied populations of I. ornatus. We suggest that cumulative effects of ecological and geographic barriers such as salinity, oceanographic conditions, and the presence of the Strait of Hormuz have shaped the genetic structure of I. ornatus in the Persian Gulf and Oman Sea. 相似文献
957.
Al-Najjar Tariq Wahsha Mohammad Al-Khushman Mwaffaq Khalaf Maroof Hardage Kyle Hayek Wissam Khadra Khalid Abu Paytan Adina 《Ocean Science Journal》2021,56(4):364-377
Ocean Science Journal - To assess the utility of the seagrass (Halophila stipulacea) for biomonitoring of metal pollution, seagrass samples were collected from four sites along the Jordanian coast... 相似文献
958.
Ali Akbar Shahsavari Kamal Khodaei Farhad Asadian Farhad Ahmadi Seyed Mohammad Zamanzadeh 《Environmental Earth Sciences》2012,65(1):231-239
Study area with an area of about 415 km2 is located from 31°40′ to 32°05′ northern latitudes and 48°45′ to 49°00′ eastern longitudes 85 km to the north-east of Ahwaz
city, in the north of Khuzestan province, and south west of Iran. The purpose of this study is: (1) the determination of the
pesticides concentration in the groundwater of the Shushtar plain (Mian-Ab) and (2) the assessment of geology, hydrogeology
and anthropogenic activities impacts the groundwater quality. Thirty-seven groundwater samples were taken from product wells
based on the standard methods. A simple and efficient automated method for extraction and preconcentration was used. In this
method, a pyrrole-based polymer was synthesized and applied as an efficient sorbent for micro-solid-phase extraction. After
extraction, analytes were desorbed in ethyl acetate and analyzed using gas chromatography–flame. The study area is surrounded
by Aghajari Formation dominated by silt and clay sediments and the Bakhtiari Formation dominated by sand and gravel. Existence
of these formations affects the aquifer sediments and the hydrogeological properties. In the study area, the sediments grade
from gravel and sand in the north and east into silt and clay to the south and west, respectively. The topsoil in the south
of the study area contains more clay sediments. In this study, the concentration of two common herbicides, i.e., 2,4-D and
clodinafop propargyl and two pesticides, i.e., permethrin and diazinon, in the groundwater of Mian-Ab aquifer was assessed.
Chemical analysis results showed that the 2,4-D residue in the groundwater has the highest concentration (15 ppm). About 50%
of the samples have concentration values more than the maximum contamination level based on EPA drinking standard. The pesticides
concentrations decrease from the north to the south of the study area. Pesticides influx to the groundwater in the south of
the area is prevented or diminished due to the specific geological situation and soil type. Distribution pattern of population
centers, which increase to the north of the study area, and the role of groundwater as the main source of drinking water are
two important issues that must be considered in management of pesticides use in the area. 相似文献
959.
Hossein Mirmehrabi Mohammad Ghafoori Gholamreza Lashkaripour Sadegh Tarigh Azali Jafar Hassanpour 《Environmental Earth Sciences》2012,66(2):529-535
Occurrence of hydrogen sulfide gas (H2S) is one of the most important engineering geological hazards during tunneling. Its hazards and consequent challenges are
very difficult and costly to solve. During site investigation, one of the tasks for engineering geologists is prediction and
evaluation of the risk of H2S gas in the underground spaces. In this study, water conveyance tunnel of Aspar, which was excavated in H2S-bearing environments, is discussed. The tunnel is excavated in the hydrocarbon formations. Applied experiments suggest that
geological formations pertaining to hydrocarbon resources are crucial in formation and reservation of H2S gas. This paper briefly discusses hazards and geological sources of H2S, as well as remedial measures for decreasing the risks and problems in excavation of the tunnel. To predict the risk of
H2S gas in the underground spaces, it is possible to use some precursors such as: sulfur springs, organic traces, organic argillaceous
rocks, exposure of H2S odor from fresh surface of rock and smell of H2S during boreholes drilling. Controlling the inflow of groundwater into the excavation, diluting the concentration of H2S, training the personnel and utilization of some proper safety equipment have been used to mitigate risks and problems in
tunnel excavation. 相似文献
960.
Basin analysis study of block 10 in the Say'un-Masilah Basin, Yemen, using a 1D backstripping method
Geohistory analysis was carried out on block 10 in the Say??un-Masilah Basin. The present study is based on the analysis of the well logs of six exploration wells. In the Middle Jurassic to the Middle Eocene, Say??un-Masilah Basin exhibited a complex subsidence history over a period of about 155?Ma. Backstripped subsidence curves are constructed by removing the effects of decompaction to the water column and sediment loads. In the Middle Jurassic, slow subsidence was driven under the effect of sediment load as Kuhlan and Shuqra Formations were deposited as pre-rift deposits. The average total subsidence value of the basement during the deposition of Shuqra Formation was 276?m. The highest subsidence rates during this time are observed northeast of the study area. Rapid subsidence initiated in the Upper Jurassic driven by mechanical extension of the rift, resulting in the deposition of Madbi and Safer Formations, or the so-called Syn-rift deposits. The average tectonic subsidence value of the basements during the deposition of Madbi Formation was 368?m. The highest subsidence rates during this time are observed southwest of the study area. Mechanical extension ceased at about 145?Ma, being replaced by a phase of post-rift subsidence, resulting in more widespread uniform sedimentation, with reduced tectonic subsidence rates forming post-rift deposits represented by Nayfa Formation, Sa??ar Formation, Biyad Formation, and Mahra Group. The total subsidence value of the basement during the deposition of the post-rift sediments increases gradually due to the increase of the sediment load as the rate of deposition was high especially northeast of the area. 相似文献