全文获取类型
收费全文 | 321篇 |
免费 | 8篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 48篇 |
地球物理 | 59篇 |
地质学 | 114篇 |
海洋学 | 32篇 |
天文学 | 37篇 |
综合类 | 2篇 |
自然地理 | 29篇 |
出版年
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 17篇 |
2013年 | 29篇 |
2012年 | 14篇 |
2011年 | 12篇 |
2010年 | 6篇 |
2009年 | 27篇 |
2008年 | 13篇 |
2007年 | 18篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有333条查询结果,搜索用时 15 毫秒
141.
Bryan A. P. Kent Shahin E. Dashtgard Chuqiao Huang James A. MacEachern H. Dan Gibson Gwyneth Cathyl-Huhn 《Basin Research》2020,32(1):163-185
The lower Nanaimo Group was deposited in the (forearc) Georgia Basin, Canada and records the basin's initiation and early depositional evolution. Nanaimo Group strata are subdivided into 11 lithostratigraphic units, which are identified based on lithology, paleontology, texture and position relative to both the basal nonconformity and to each other. Significant topography on the basal nonconformity, however, has resulted in assignment of lithostratigraphic units that are not time correlative, and hence, cannot reliably be used to accurately reconstruct basin evolution. Herein, we present a sequence stratigraphic framework for lower Nanaimo Group strata in the Comox Sub-Basin (northern Georgia Basin) that integrates both facies analysis and maximum depositional ages (MDAs) derived from detrital zircon. This stratigraphic framework is used to define significant sub-basin-wide surfaces that bound depositional units and record the evolution of the basin during its early stages of development. Seven distinct depositional phases are identified in the lower 700 m of the lower Nanaimo Group. Depositional phases are separated by marine flooding surfaces, regressive surfaces, or disconformities. The overall stratigraphy reflects net transgression manifested as an upwards transition from braided fluvial conglomerates to marine mudstones. Transgression was interrupted by periods of shoreline progradation, and both facies analysis and MDAs reveal a disconformity in the lowermost part of the Nanaimo Group in the Comox Sub-Basin. Stratigraphic reconstruction of the Comox Sub-Basin reveals two dominant depocenters (along depositional strike) for coarse clastics (sandstones and conglomerates) during early development of the Georgia Basin. The development and position of these depocenters is attributed to subduction/tectonism driving both subsidence in the north-northwest and uplift in the central Comox Sub-Basin. Our work confirms that in its earliest stages of development, the Georgia Basin evolved from an underfilled, ridged forearc basin that experienced slow and stepwise drowning to a shoal-water ridged forearc basin that experienced rapid subsidence. We also propose that the Georgia Basin is a reasonable analogue for ridged forearc basins globally, as many ridged forearcs record similar depositional histories during their early evolution. 相似文献
142.
Accuracy of the Copernicus snow water equivalent (SWE) product and the impact of SWE calibration and assimilation on modelled SWE and streamflow was evaluated. Daily snowpack measurements were made at 12 locations from 2016 to 2019 across a 4104 km2 mixed-forest basin in the Great Lakes region of central Ontario, Canada. Sub-basin daily SWE calculated from these sites, observed discharge, and lake levels were used to calibrate a hydrologic model developed using the Raven modelling framework. Copernicus SWE was bias corrected during the melt period using mean bias subtraction and was compared to daily basin average SWE calculated from the measured data. Bias corrected Copernicus SWE was assimilated into the models using a range of parameters and the parameterizations from the model calibration. The bias corrected Copernicus product agreed well with measured data and provided a good estimate of mean basin SWE demonstrating that the product shows promise for hydrology applications within the study region. Calibration to spatially distributed SWE substantially improved the basin scale SWE estimate while only slightly degrading the flow simulation demonstrating the value of including SWE in a multi-objective calibration formulation. The particle filter experiments yielded the best SWE estimation but moderately degraded the flow simulation. The particle filter experiments constrained by the calibrated snow parameters produced similar results to the experiments using the upper and lower bounds indicating that, in this study, model calibration prior to assimilation was not valuable. The calibrated models exhibited varying levels of skill in estimating SWE but demonstrated similar streamflow performance. This indicates that basin outlet streamflow can be accurately estimated using a model with a poor representation of distributed SWE. This may be sufficient for applications where estimating flow is the primary water management objective. However, in applications where understanding the physical processes of snow accumulation, melt and streamflow generation are important, such as assessing the impact of climate change on water resources, accurate representations of SWE are required and can be improved via multi-objective calibration or data assimilation, as demonstrated in this study. 相似文献
143.
Bryan K Mignone Matthew D Hurteau Yihsu Chen Brent Sohngen 《Carbon balance and management》2009,4(1):3-6
Background
One controversial issue in the larger cap-and-trade debate is the proper use and certification of carbon offsets related to changes in land management. Advocates of an expanded offset supply claim that inclusion of such activities would expand the scope of the program and lower overall compliance costs, while opponents claim that it would weaken the environmental integrity of the program by crediting activities that yield either nonexistent or merely temporary carbon sequestration benefits. Our study starts from the premise that offsets are neither perfect mitigation instruments nor useless "hot air." 相似文献144.
Late Holocene chronology,origin, and evolution of the St. Bernard Shoals,Northern Gulf of Mexico,USA
Several shore-parallel marine sand bodies lie on the Louisiana continental shelf. They are Trinity Shoal, Ship Shoal, Outer
Shoal, and the St. Bernard Shoals. These shoals mark the submerged positions of ancient shorelines associated with abandoned
deltas. Three of these shoals are single elongate deposits. The fourth shoal, the St. Bernard Shoals, consists of a group
of discrete sand bodies ranging in size from 44 to 0.05 km2, 25 km southeast of the Chandeleur Islands in 15–18 m of water. The St. Bernard Shoals are stratigraphically above the St.
Bernard delta complex, which was active 2,500–1,800 years b.p. Understanding the evolution of the St. Bernard Shoals is necessary to reconstruct the Holocene chronology of the St. Bernard
delta complex and the eastern Louisiana continental shelf. For this study, 47 vibracores and 400 km of shallow seismic reflection
data collected in 1987 across the Louisiana shelf were analyzed. In June 2008, 384 km of higher-resolution seismic reflection
data were acquired across the study area and appended to the preexisting datasets. Vibracores were integrated with seismic
profiles to identify facies and their regional distribution. Our results demonstrate that the deltaic package stratigraphically
below the St. Bernard Shoals is chronologically younger than the northern distributaries, but derived from the same trunk
distributary channel (Bayou la Loutre). The river eventually bypassed the northern distributaries, and began to deposit sediment
further onto the continental shelf. After abandonment, the overextended delta lobe was rapidly transgressed, creating a transgressive
shoreline that eventually coalesced with earlier shorelines in the region to form the Chandeleur Islands. The St. Bernard
Shoals formed by the reworking of the relict distributary deposits exposed on the inner to mid shelf during and subsequent
to shoreface ravinement. 相似文献
145.
146.
Abstract The characteristics of microseisms measured in four vaults of the Southern Ontario Seismic Network within 30 km of the shore of Lake Ontario are analysed. It is shown that the rms values in the 1–3 Hz band are coherent between the stations, indicating a common generative mechanism. A distinct onshore intermittent flux of Rayleigh‐like wave energy was detected at a site near the shore. Microseismic energy in this band is distinctly correlated with the wind speed. The incremental microseismic energy above an absolute minimum activity as a function of wind direction, for a given fixed wind speed, correlates with the average fetch of the wind over the lake, indicating that the source of microseisms is the lake itself. The sensitivity to fetch effects is similar for both onshore and offshore stations indicating that shoaling is probably not a source. Niagara Falls, which also can have a wind‐dependent flow from Lake Erie, causes a measurable effect to at least 25 km but does not significantly affect stations at a distance of 150 km. 相似文献
147.
Bryan Lintott 《New Zealand geographer》2008,64(2):172-173
148.
The vertebrate fossil record of Cement Creek Cave, Colorado, spans from > 45,000 yr ago to the present and represents the richest stratified series of high-elevation (> 2900 m) mammal remains known from the late Quaternary of North America. Stable carbon and oxygen isotope analyses of tooth enamel were used to assess potential ecological responses of two species found commonly throughout the cave, Yellow-bellied marmots (Marmota flaviventris) and Bushy-tailed woodrats (Neotoma cinerea), to late Quaternary climate and environmental changes of the Southern Rocky Mountains. Results indicate that despite such perturbations, the dietary ecologies of both species were maintained across this period. Neither taxon shifted to consuming C4 taxa or different C3 functional groups; similarly, no significant shifts in surface water use were detected. Variations in enamel δ13C were observed, however, that represent the physiological responses of high-elevation plants to changing levels of late Quaternary atmospheric CO2. While our findings extend both the geographic and elevational record of this plant CO2 response, they simultaneously highlight the ecological stability of high-elevation M. flaviventris and N. cinerea during climate changes of late Quaternary magnitude. 相似文献
149.
Sustainable management of groundwater resources is vital for development of areas at risk from water-resource over-exploitation. In northeast Thailand, the Phu Thok aquifer is an important water source, particularly in the Thaphra area, where increased groundwater withdrawals may result in water-level decline and saline-water upconing. Three-dimensional finite-difference flow models were developed with MODFLOW to predict the impacts of future pumping on hydraulic heads. Four scenarios of pumping and recharge were defined to evaluate the system response to future usage and climate conditions. Primary model simulations show that groundwater heads will continue to decrease by 4–12?m by the year 2040 at the center of the highly exploited area, under conditions of both increasing pumping and drought. To quantify predictive uncertainty in these estimates, in addition to the primary conceptual model, three alternative conceptual models were used in the simulation of sustainable yields. These alternative models show that, for this case study, a reasonable degree of uncertainty in hydrostratigraphic interpretation is more impactful than uncertainty in recharge distribution or boundary conditions. The uncertainty-analysis results strongly support addressing conceptual-model uncertainty in the practice of groundwater-management modeling. Doing so will better assist decision makers in selecting and implementing robust sustainable strategies. 相似文献
150.
Local groundwater governance in Yemen: building on traditions and enabling communities to craft new rules 总被引:1,自引:1,他引:0
Taha Taher Bryan Bruns Omar Bamaga Adel Al-Weshali Frank van Steenbergen 《Hydrogeology Journal》2012,20(6):1177-1188
Local groundwater management in Yemen and the means by which stakeholders can work together to improve water governance are discussed. In the last few decades the discourse on groundwater management in Yemen has increasingly been cast in terms of crisis, triggered by rapidly declining water tables around cities and in the main agricultural areas. However, in some places in Yemen, communities have responded by implementing local rules that have reduced conflict and provided more reliable and equitable access to water. This trend towards development of local groundwater governance is described, and could make a major contribution in realizing the goals of national water-sector policies and strategies. Twenty-four cases have been identified from different parts of the country and five cases are presented in detail. The article discusses how the process of local management could be nurtured and how it could contribute to rebalancing water use in several parts of Yemen. 相似文献