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283.
Implemented on behalf of the Federal Ministry for Research and Technology (BMFT), a model is developed to trace the nutrient flow of nitrate in the soil and the groundwater on a supraregional scale. Research work is intended to indicate regionally differentiated hazardous potentials and thereby provide a basis for recommending comprehensive measures to protect groundwater in Germany. The adaption of the model to the hydrogeological and agricultural conditions of other states is possible in principle. This article focuses on the hydrogeological model parts. A high nitrate pollution of groundwater can be expected in all regions with intensive agricultural use of the topsoil. In particular, groundwater in solid rock areas is susceptible to nitrate pollution. There a rapid groundwater turnover and thus a short residence time for the groundwater in the aquifer is typical. Oxidizing aquifer conditions usually prevail in solid rock aquifers, preventing nitrate degradation. In many loose rock areas, in contrast, the groundwater has a low flow velocity and a long residence time in the aquifer. Because of a lack of free oxygen, a complete degradation of nitrate can occur, as long as iron sulfide compounds and/or organic carbon are available in the aquifer. A more detailed presentation of the whole research work is given in Wendland et al. (1993). 相似文献
284.
研究环流和沉积物输运对北部湾的环境保护和资源开发十分重要。本文使用区域海洋模型(ROMS),研究了北部湾海域的季节环流、沉积物输运以及长期的地形演变过程。展示了湾内冬季和夏季都存在逆时针环流,冬季的风生环流比夏季强的特征。悬沙浓度较大值主要分布在琼州海峡、海南岛西侧海域,以及越南沿岸、雷州半岛沿岸等近岸地区。沉积物在琼州海峡附近表现为在冬季由东向西输运,夏季则相反;在琼州海峡西口处,沉积物全年以西向输运为主。结果显示,北部湾内沉积物输运主要由潮流引起的再悬浮控制。侵蚀和淤积的分布模式为:(1)湾内大部分区域侵蚀淤积不明显,(2)琼州海峡两侧口门附近淤积比较明显,(3)琼州海峡内深槽侵蚀严重,(4)海南岛西侧海域存在侵蚀和淤积交替发生区域。 相似文献
285.
基于小波变换的SA误差建模与预报 总被引:2,自引:0,他引:2
运用小波分析方法对GPS单点动态定位误差进行分解,提出了基于小波变换的信号去噪与粗差的定位和剔除方法。将时间序列分析方法用于SA误差建模,提出了基于小波变换的SA误差建模及预报方法,并通过实例验证了方法的正确性 相似文献
286.
Estimating depths of buried lava tubes is important for determining the thermal budgets and effusion rates of basaltic volcanic
systems. This research used a laboratory experiment scaled to a lava tube system to measure the 3D temperature field surrounding
a hot viscous fluid flowing through a buried glass tube while varying conditions such as flow rate and temperature. The depth
of the glass tube was changed for different experimental runs. Numerical techniques were applied to model the laboratory experiment.
The surface thermal distributions from 166 thermal traverses, constrained to a depth to width ratio of 0.6 to 1.6, were analyzed
to empirically derive a depth estimation function using regression techniques. This “Linear Anomaly Surface Transect (LAST)”
depth function is a scaleable depth estimation technique which can be solved with thermal imaging data alone. The minimum
temperature, maximum temperature and width of a Lorentzian distribution fit to a surface thermal transect, are the only inputs
required for the LAST function to estimate the depths of the hot source. The input parameters were then applied to non-laboratory
situations including the Kuhio lava tube system in Hawai’i. The LAST function produced depth estimates of ∼ 0.3 m for the
Kuhio lava tube in Hawai’i, which did not agree with observations on the ground. This is the result of the complex composition
and geometry of an actual lava tube where heat transfer is controlled by more than a simple fluid filling a tube, but also
by convection of gasses and fluids in a partially filled passage. Though not effective for lava tubes at this time, the model
provides promising results for simple cases applied to engineering and underground coal fires. 相似文献
287.
J.M. Lenes B.A. Darrow J.J. Walsh J.M. Prospero R. He R.H. Weisberg G.A. Vargo C.A. Heil 《Continental Shelf Research》2008
The availability of iron within the surface waters of the broad, oligotrophic West Florida Shelf (WFS) controls periodic blooms of the pelagic marine cyanobacterium Trichodesmium. Summer delivery of Saharan dust provided adequate iron (Fe) to shift limitation of growth to the availability of phosphorus (P). Florida's rivers drain Miocene phosphorus deposits to provide the WFS with freshwater nutrient supplies at molar dissolved inorganic nitrogen/phosphate (DIN/PO4) ratios of <6. These diazotrophs draw upon ubiquitous stocks of dissolved nitrogen gas, once stimulated by Fe-deposition within P-replete waters of the WFS. 相似文献
288.
Time series of fractional snow covered area (SCA) estimates from Landsat Enhanced Thematic Mapper (ETM+), Moderate Resolution Imaging Spectroradiometer (MODIS), and Advanced Very High Resolution Radiometer (AVHRR) data were combined with a spatially distributed snowmelt model to reconstruct snow water equivalent (SWE) in the Rio Grande headwaters (3419 km2). In this reconstruction approach, modeled snowmelt over each pixel is integrated during the period of satellite-observed snow cover to estimate SWE. Due to underestimates in snow cover detection, maximum basin-wide mean SWE using MODIS and AVHRR were, respectively, 45% and 68% lower than SWE estimates obtained using ETM+ data. The mean absolute error (MAE) of SWE estimated at 100-m resolution using ETM+ data was 23% relative to observed SWE from intensive field campaigns. Model performance deteriorated when MODIS (MAE = 50%) and AVHRR (MAE = 89%) SCA data were used. Relative to differences in the SCA products, model output was less sensitive to spatial resolution (MAE = 39% and 73% for ETM+ and MODIS simulations run at 1 km resolution, respectively), indicating that SWE reconstructions at the scale of MODIS acquisitions may be tractable provided the SCA product is improved. When considering tradeoffs between spatial and temporal resolution of different sensors, our results indicate that higher spatial resolution products such as ETM+ remain more accurate despite the lower frequency of acquisition. This motivates continued efforts to improve MODIS snow cover products. 相似文献
289.
This study aims at modeling the transport of a conservative tracer in two dimensions, as experimentally observed in a strongly heterogeneous medium under conditions of variable water saturation during drainage and imbibition. Solute transport experiments were conducted in a sand tank containing an artificial packing of three quartz sands of different particle sizes. The packing was characterized by the presence of numerous homogeneous layers (0.5 × 5 × 5 cm) inclined at 45° and randomly distributed in a tank. Six different stationary flow conditions were sequentially established during imbibition and drainage. When a stationary flow regime was reached, several solute pulses were applied at different positions at the upper surface of the sand structure. The transport regime was studied by monitoring the tracer plumes injected as point-like pulses at the surface, as they travelled through the sand bedding. 相似文献
290.
WenJun Zhang GuangHua Liu HongQing Dai 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(1):123-133
Neural networks are universal approximators for nonlinear functions. This study aimed to develop an algorithm for functional
link artificial neural network (FLANN), and to simulate insect’s food intake dynamics using the algorithm. Complete Matlab
codes for FLANN algorithm were given in the paper. Conventional models and FLANN were used to modeling accumulated food intake
of the larva of a holometabolous insect, Spodoptera litura. Simulation performance of FLANN was compared against conventional models and sensitivity analysis was conducted on FLANN.
The results showed that the FLANN algorithm performed better than conventional models in the simulation of dynamics and temperature–time
dependent relationship of larva’s food intake. The conventional models like fractional function, polynomial function, and
exponential function were indicated to simulate the food intake dynamics at a higher accuracy but their performances were
worse than FLANN. Both multivariate linear regression and trend surface model were used to describe temperature–time dependent
relationship of food intake. The overall trend for this relationship could be simulated using these models, however, the simulation
accuracy of these models was lower than FLANN. Sensitivity analysis showed that Legendre functions, Chebyshov functions, and
trigonometric functions, used as the basis functions in FLANN, yielded better fitness than Laguerre functions and Hermite
functions. The mean squared error of simulation using Legendre functions, Chebyshov functions, and trigonometric functions
decreased as the increase of the number of these basis functions. Simulation performance also varied with the change of type
of nonlinear functions and parameter values in the function. Linear function, negative exponential function and power function
were the best nonlinear functions, which yielded more stable outputs as the change of parameter values. 相似文献