全文获取类型
收费全文 | 282篇 |
免费 | 14篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 29篇 |
地球物理 | 101篇 |
地质学 | 95篇 |
海洋学 | 23篇 |
天文学 | 23篇 |
综合类 | 2篇 |
自然地理 | 23篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 31篇 |
2012年 | 16篇 |
2011年 | 18篇 |
2010年 | 18篇 |
2009年 | 12篇 |
2008年 | 13篇 |
2007年 | 8篇 |
2006年 | 18篇 |
2005年 | 14篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有304条查询结果,搜索用时 265 毫秒
241.
Generalized linear models may be used as a systematic and flexible alternative to existing practices in fitting sediment or solute concentration and load rating curves. Through widely available statistical software they offer a one‐step solution to the common and awkward problem that a bias correction is needed when estimating total loads. In particular, using a logarithmic link function has an advantage over logarithmic transformation of concentration or load, as generalized linear models return predictions directly on the original measured scale; there is thus no need for back‐transformation or subsequent correction factors. Example analyses are given for suspended sediment concentration for an upland stream in the Northern Pennines and for phosphorus load for the Illinois River. General criteria for choosing models and good practice in the use of figures of model merit and of residual plots are also discussed in detail. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
242.
Kathryn J. Amos Jeff Peakall P. William Bradbury Mat Roberts Gareth Keevil Sanjeev Gupta 《Marine and Petroleum Geology》2010
We present a series of experiments that investigate the morphology of sediment deposits within sinuous submarine channels of different sinuosity (S = 1.14–1.94) and planform (symmetric and asymmetric bends), generated by bedload-dominated turbidity current flows. Flows were generated by releasing dense saline gravity currents over a mobile sediment bed through pre-formed sinuous channels. Flows had a basal-outwards helicity and produced a characteristic bed morphology with point bars downstream of the bend apex at the inside of bends and scour at the outside of bends. An increasing loss of fluid through overspill with increasing channel sinuosity results in a decreasing magnitude of cross-stream velocity downstream, a decreasing amount of erosion and deposition, and decreasing transverse slopes of in-channel deposits. Basal fluid from within the channel is transported over the outer-levee at bends, implying that proximal outer-bend levee deposits will have similar sediment composition to that within the channel. More deposition of coarse material might be expected on levees and in overbank regions close to higher amplitude bends. No simple relationship was observed between superelevation and sinuosity, probably due to changes in the relative influences of downstream velocity and bend curvature on centrifugal force and inertial run-up. In the channel with the tightest initial bend curvature, overspill fluid from Bend 1 re-entered the channel at Bend 2, dominating flow characteristics and disrupting the basal-outwards helicity observed in the other channels. Higher sinuosity channels and those with shallow regional and levee slopes are thus more likely to have a higher proportion of anomalous flow and sedimentation patterns due to the influence of overspill fluid re-entry into the channel. The results of this investigation are combined with published observations to enable the synthesis of a new model for sedimentation in sinuous submarine channels. 相似文献
243.
Steady convective exchange flows down slopes 总被引:2,自引:0,他引:2
Jeff J. Sturman Carolyn E. Oldham Greg N. Ivey 《Aquatic Sciences - Research Across Boundaries》1999,61(3):260-278
244.
Carrier phase multipath error characterization and reduction in single aircraft relative positioning
This paper describes GPS carrier phase (CP) multipath characterization and error reduction techniques and their application
in single aircraft relative positioning. In particular, the single aircraft relative positioning scenario has applications
for high-accuracy multi-sensor stabilization where CP multipath is a major error source that limits system performance. We
will briefly review the requisite multipath theory and discuss models for quantifying the error characteristics. Field-test
data will be used to validate the multipath models considering the underlying assumptions. A basic geometric reflection point
theory will be presented to demonstrate the physical environmental sensitivity of CP multipath to parameters such as surface
flatness and antenna height. Several different quantities will be described as multipath indicators for time-domain detection
and will be compared with a frequency-domain technique. A new multipath detection approach will be introduced that is suitable
to track multipath from time-varying reflection/diffraction points. Finally, the narrow-lane antenna baseline processing technique
will be presented as a real-time approach to mitigate CP noise and multipath errors that is well suited for a very short baseline
single aircraft high accuracy relative positioning system. Field-test results and analysis will be used to illustrate the
key concepts in this paper and to help characterize the total navigation system performance. 相似文献
245.
246.
Andrs E. Tejada-Martnez Chester E. Grosch Ann E. Gargett Jeff A. Polton Jerome A. Smith J.A. MacKinnon 《Ocean Modelling》2009,30(2-3):115-142
A three-dimensional numerical model for large-eddy simulation (LES) of oceanic turbulent processes is described. The numerical formulation comprises a spectral discretization in the horizontal directions and a high-order compact finite-difference discretization in the vertical direction. Time-stepping is accomplished via a second-order accurate fractional-step scheme. LES subgrid-scale (SGS) closure is given by a traditional Smagorinsky eddy-viscosity parametrization for which the model coefficient is derived following similarity theory in the near-surface region. Alternatively, LES closure is given by the dynamic Smagorinsky parametrization for which the model coefficient is computed dynamically as a function of the flow. Validation studies are presented demonstrating the temporal and spatial accuracy of the formulation for laminar flows with analytical solutions. Further validation studies are described involving direct numerical simulation (DNS) and LES of turbulent channel flow and LES of decaying isotropic turbulence. Sample flow problems include surface Ekman layers and wind-driven shallow water flows both with and without Langmuir circulation (LC), generated by wave effects parameterized via the well-known Craik–Leibovich (C–L) vortex force. In the case of the surface Ekman layers, the inner layer (where viscous effects are important) is not resolved and instead is parameterized with the Smagorinsky models previously described. The validity of the dynamic Smagorinsky model (DSM) for parameterizing the surface inner layer is assessed and a modification to the surface stress boundary condition based on log-layer behavior is introduced improving the performance of the DSM. Furthermore, in Ekman layers with wave effects, the implicit LES grid filter leads to LC subgrid-scales requiring ad hoc modeling via an explicit spatial filtering of the C–L force in place of a suitable SGS parameterization. 相似文献
247.
Male and female hornyhead turbot (Pleuronichthys verticalis) were exposed to four concentrations (0, 0.75, 14.7 and 46.5 ng/g dry weight) of E2-amended sediment for 7 days. Sediment-derived E2 was bioavailable to the flatfish, though the route of uptake was unclear. A concentration of 46.5 ng/g E2 in sediment led to a significant increase in vitellogenin concentrations in the plasma in both sexes after 7 days of exposure. Though plasma E2 concentrations increased significantly in males at sediment E2 concentrations of 0.75 ng/g dry weight and above, a dose-dependent increase was not observed. There was also no correlation between sediment E2 concentrations, plasma E2 concentrations, and oxidative DNA damage in male gonads. The results suggest that the DNA damage previously seen in the gonads of feral hornyhead turbot at a sewage outfall is likely not caused by acute exposure to exogenous E2 from sediments. 相似文献
248.
Although high seas resources are being exploited, reciprocal legal obligations to protect its environment have not been met. Marine spatial planning (MSP) is clearly a practical way forward, particularly for the high seas, where non-spatial monitoring is difficult, and where data gaps obstruct conventional management approaches. To ensure the effective application of MSP in the high seas, however, some institutional reforms are necessary. This paper outlines the main hurdles, summarizes existing high seas spatial protections, presents an example of a high seas marine protected area that resulted through MSP, identifies three institutional priorities, and suggests three immediate steps. 相似文献
249.
Masek J.G. Vermote E.F. Saleous N.E. Wolfe R. Hall F.G. Huemmrich K.F. Feng Gao Kutler J. Teng-Kui Lim 《Geoscience and Remote Sensing Letters, IEEE》2006,3(1):68-72
The Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center has processed and released 2100 Landsat Thematic Mapper and Enhanced Thematic Mapper Plus surface reflectance scenes, providing 30-m resolution wall-to-wall reflectance coverage for North America for epochs centered on 1990 and 2000. This dataset can support decadal assessments of environmental and land-cover change, production of reflectance-based biophysical products, and applications that merge reflectance data from multiple sensors [e.g., the Advanced Spaceborne Thermal Emission and Reflection Radiometer, Multiangle Imaging Spectroradiometer, Moderate Resolution Imaging Spectroradiometer (MODIS)]. The raw imagery was obtained from the orthorectified Landsat GeoCover dataset, purchased by NASA from the Earth Satellite Corporation. Through the LEDAPS project, these data were calibrated, converted to top-of-atmosphere reflectance, and then atmospherically corrected using the MODIS/6S methodology. Initial comparisons with ground-based optical thickness measurements and simultaneously acquired MODIS imagery indicate comparable uncertainty in Landsat surface reflectance compared to the standard MODIS reflectance product (the greater of 0.5% absolute reflectance or 5% of the recorded reflectance value). The rapid automated nature of the processing stream also paves the way for routine high-level products from future Landsat sensors. 相似文献
250.
Martin Austin Tim Scott Jeff Brown Jenna Brown Jamie MacMahan Gerd Masselink Paul Russell 《Continental Shelf Research》2010
A field experiment was conducted on a high energy macro-tidal beach (Perranporth, UK) to examine rip current dynamics over a low-tide transverse bar/rip system in response to changing tide and wave conditions. Hydrodynamic data were collected using an array of in situ acoustic doppler current meters and pressure transducers, as well as 12 GPS-tracked Lagrangian surf zone drifters. Inter-tidal and sub-tidal morphology were measured through RTK-GPS and echo-sounder surveys. Data were collected for eight consecutive days (15 tides) over a spring-neap tidal cycle with tidal ranges of 4–6.5 m and offshore significant wave heights of 1–2 m and peak periods of 5–12 s. 相似文献