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A complexometric titration technique was employed to measure the total capacity of a variety of marine organisms to adsorb Cu2+. Measured adsorption capacities were 0.22 meq g−1 for phytoplankton, 0.3–1.0 meq g−1 for macrophytes, 1.0–2.5 meq g−1 for zooplankton and 0.3 meq g−1 for suspended particulate matter. The capacity of these materials to adsorb Cu2+ was reduced significantly in the presence of Mg2+ at seawater concentrations. Competition between Mgt2+ and Cu2+ for adsorption sites at pH 6 is described by an average conditional equilibrium constant of 103.7. This constant is such that very little Cu2+ may be adsorbed onto particulates and marine phytoplankton in the presence of Mg2+. Further, primary productivity data and estimates of the detrital carbon sedimentation in Long Island Sound suggest that the flux of particulate carbon is insufficient to remove significant amounts of Cu from the water column to sediments by adsorption mechanisms. 相似文献
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We describe finite-difference approximations to the equations of 2-D electromagnetic induction that permit discrete boundaries to have arbitrary geometrical relationships to the nodes. This allows finite-difference modelling with the flexibility normally ascribed to finite-element modelling. Accuracy is demonstrated by comparison with finite-element computations. We also show that related approximations lead to substantially improved accuracy in regions of steep, but not discontinuous, conductivity gradient. 相似文献
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为了研究西藏中、北部壳、幔导电性结构,讨论高原中、北部岩石圈热状态,1998年和1999年(INDEPTH(Ⅲ) MT)在西藏中、北部完成了德庆—龙尾错(500线)和那曲—格尔木(600线)超宽频带大地电磁深探测剖面的研究.研究结果表明,西藏中、北部以昆仑山断裂为界,其南北壳、幔电性结构有很大差异.昆仑山断裂以北地壳和上地幔为高阻区.而昆仑山以南,地壳和上地幔的导电性有明显的分层结构:地壳上部以不连续的高阻体为主,夹有局部低阻异常体,沿南北方向上地壳的电性结构复杂,具有不连续、分块的特点;但中、下地壳为大范围的高导异常区,区内发育有大规模、不相连续、产状各异的高导体,其电阻率均小于4Ωm;在班公—怒江和金沙江缝合带之下,壳内高导体都具有向上地幔延伸的趋势,存在连通壳、幔的低阻通道.根据西藏高原中、北部壳、幔电性结构的研究推断:如同藏南一样,这里也普遍存在部分熔融体和热流体,它们的成因主要与班公—怒江和金沙江缝合带的壳-幔热交换、热活动有关,这是两期形成的壳-幔热交换通道.其中,班公—怒江缝合带的壳-幔热交换通道形成时间比金沙江缝合带早.因此,研究区壳、幔的热活动是从南边和西边开始,向北、向东扩展,导致现今西藏中、北部地壳和上地幔的热流分布由西向东、由南向北增大. 相似文献
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Brian N. Tissot Barbara A. Best Eric H. Borneman Andrew W. Bruckner Cara H. Cooper Heather D’Agnes Timothy P. Fitzgerald Amanda Leland Susan Lieberman Amy Mathews Amos Rashid Sumaila Teresa M. Telecky Frazer McGilvray Brian J. Plankis Andrew L. Rhyne Glynnis G. Roberts Benjamin Starkhouse Todd C. Stevenson 《Marine Policy》2010
As the world’s largest importer of marine ornamental species for the aquaria, curio, home décor, and jewelry industries, the United States has an opportunity to leverage its considerable market power to promote more sustainable trade and reduce the effects of ornamental trade stress on coral reefs worldwide. Evidence indicates that collection of some coral reef animals for these trades has caused virtual elimination of local populations, major changes in age structure, and promotion of collection practices that destroy reef habitats. Management and enforcement of collection activities in major source countries such as Indonesia and the Philippines remain weak. Strengthening US trade laws and enforcement capabilities combined with increasing consumer and industry demand for responsible conservation can create strong incentives for improving management in source countries. This is particularly important in light of the March 2010 failure of the parties to the Convention on International Trade in Endangered Species (CITES) to take action on key groups of corals. 相似文献
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Abstract This paper experimentally investigates the convective planform near critical in a fluid layer whose temperature-dependent viscosity varies from top to bottom by up to a factor of 1500. Convection occurs in three different planforms: rolls, hexagons and squares. The square planform, which appears only for fluids with viscosity variation greater than about 50, replaces the hexagonal convection pattern as the Rayleigh number increases much above critical. The large amplitude of hexagonal convection with strong viscosity variation precludes studying the hexagon-square transition with perturbation methods of the type used to study the hexagon-roll transitions at smaller viscosity variations. 相似文献
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The finite element method has often been used to simulate excavation. When the soil is linearly elastic, the results of excavation should be independent of the number of stages in the excavation process, and lack of such independence indicates an incorrect procedure. The simple direct method described in this paper provides the required independence in the case of linearly elastic materials, and hence can be used for multi-stage excavation in non-linear problems without excessive errors. However methods whose errors increase with the number of stages of excavation are quite unsuitable for non-linear problems. Alternative methods of analysis, errors arising from the inability of the elements to model adequately the stress gradients near the toe of the excavation and excavation adjacent to a diaphragm wall are discussed. 相似文献
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The sources and composition of mercury in Pacific Ocean rain 总被引:1,自引:0,他引:1
Here we report measurements of total Hg (HgT), reactive Hg (HgR), and methylmercury (MMHg) in precipitation from the equatorial Pacific Ocean, collected during a cruise in January and February 1990, and from a mid-continental location in the rural temperate lacustrine northcentral Wisconsin environs. The concentrations of HgT (14.4±6.5 pM), HgR (8.9±4.5 pM) and MMHg (<50 fM) found in equatorial Pacific rain were less than the average concentrations found in Wisconsin. In general, the results indicate that although particulate Hg is a small fraction of the total atmospheric Hg burden, it is the major contributor to Hg in precipitation. Furthermore, deposition could be an important source of HgR to the equatorial Pacific Ocean. In contrast, deposition is not a significant source of MMHg to either the equatorial Pacific Ocean or the remote seepage lakes of Wisconsin. This implies that methylated mercury is formedin situ in these systems. 相似文献