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排序方式: 共有133条查询结果,搜索用时 156 毫秒
31.
现行黄河口水下三角洲海底形貌及不稳定性 总被引:4,自引:0,他引:4
杨作升 G.H.Keller 陆念祖 D.B.Prior 林天充 B.D.Bornhold 许卫东 L.D.Wright J.Suhayda 曹立华 W.J.Wisenman 《中国海洋大学学报(自然科学版)》1990,(1)
高分辨力的声学仪器调查表明,现行黄河口水下三角洲海底的形貌十分复杂,由于高浓度巨量黄河泥沙快速沉积的结果,使河口底坡出现了大量的不稳定性现象,如塌陷冲沟,高密度沉积物重力流,切割—充填结构海底,V形水下河谷、滑塌等。根据海底扰动程度作了分区,划分了地形单元,并对不同的海底形态的成因作了分析。比较了1985和1986年两个航次考查结果的变动,分析了原因。 相似文献
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Robert E. Rhoades Virginia Nazarea 《山地科学学报》2006,3(4):334-346
Introduction In tracing the pioneering influences which created the 1980s participatory research movement in international agriculture, health and conserva- tion, the experiences of Latin America must be highlighted. Activist participatory research itselfwas originally inspired by Paulo Freire, the influential Brazilian educator whose pedagogical teachings have been commonplace throughout South America since the 1960s (Freire 1968, Chambers 1994a). Due to a multitude of social forces betwe… 相似文献
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Kideok D. Kwon Virginia Vadillo-Rodriguez James D. Kubicki 《Geochimica et cosmochimica acta》2006,70(15):3803-3819
Pull-off forces were measured between a silica colloid attached to an atomic force microscope (AFM) cantilever and three homopolymer surfaces representing constituents of extracellular polymeric substances (EPS). The pull-off forces were −0.84 (±0.16), −0.68 (±0.15), and −2.37 (±0.31) nN as measured in water for dextran, phosphorylated dextran, and poly-l-lysine, respectively. Molecular orbital and density functional theory methods (DFT) were applied to analyze the measured pull-off forces using dimer clusters representing interactions between the three polymers and silica surfaces. Binding energies for each dimer were calculated with basis set superposition error (BSSE) and interpolated using corrections for silica surface hydroxyl density and silica charge density. The binding energies were compared with the normalized pull-off forces with the effective silica surface area contacting the polymer surfaces. The predicted binding energies at a −0.064 C/m2 silica surface charge density corresponding to circum-neutral pH were −0.055, −0.029, and −0.338 × 10−18 J/nm2 for the dimers corresponding to the silica surface with dextran, phosphorylated dextran, and poly-l-lysine, respectively. Polarizable continuum model (PCM) calculations with different solvents, silanol vibrational frequency calculations, and orbital interaction analysis based on natural bonding orbital (NBO) showed that phosphate groups formed stronger H-bonds with neutral silanols than hydroxyl and amino functional groups of polymers, implying that phosphate containing polymers would play important roles in EPS binding to silica surfaces. 相似文献
35.
Virginia M. Oversby 《Earth and Planetary Science Letters》1980,49(2):252-258
The choice of diagrammatic representation for Pb isotope data should be determined by clarity of presentation and ability of the chosen diagram to highlight significant differences between samples. The conventionally used [α, β] diagram is shown to be superior to the recently proposed [I, S] diagram in both these respects. Transformation of Pb data to achieve parametric forms which can be treated by linear statistical methods causes a loss of diagnostic sensitivity, particularly for relatively young events. This loss of sensitivity argues against use of the parametric [I, S] diagram. 相似文献
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Virginia M Oversby 《Geochimica et cosmochimica acta》1973,37(12):2693-2696
Redetermination of the lead isotopic composition in Canyon Diablo troilite shows that the original analysis was overcorrected for analytical fractionation. The new analysis indicates that the lead in nodule CDN-1 is a mixture of primordial lead plus a small amount of common lead. 相似文献
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Andrew Steele David t. Goddard Dave Stapleton Jan k. w. Toporski Vanessa Peters Virginia Bassinger George Sharples David d. Wynn‐Williams David s. Mckay 《Meteoritics & planetary science》2000,35(2):237-241
Abstract— Examination of fracture surfaces near the fusion crust of the martian meteorite Allan Hills (ALH) 84001 have been conducted using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and has revealed structures strongly resembling mycelium. These structures were compared with similar structures found in Antarctic cryptoendolithic communities. On morphology alone, we conclude that these features are not only terrestrial in origin but probably belong to a member of the Actinomycetales, which we consider was introduced during the Antarctic residency of this meteorite. If true, this is the first documented account of terrestrial microbial activity within a meteorite from the Antarctic blue ice fields. These structures, however, do not bear any resemblance to those postulated to be martian biota, although they are a probable source of the organic contaminants previously reported in this meteorite. 相似文献
38.
Ferretti JA Tran HV Cosgrove E Protonentis J Loftin V Conklin CS Grant RN 《Marine pollution bulletin》2011,62(5):1066-1072
Currently, densities of Enterococcus in marine bathing beach samples are performed using conventional methods which require 24 h to obtain results. Real-time PCR methods are available which can measure results in as little as 3 h. The purpose of this study was to evaluate a more rapid test method for the determination of bacterial contamination in marine bathing beaches to better protect human health. The geometric mean of Enterococcus densities using Enterolert® defined substrate testing and membrane filtration ranged from 5.2 to 150 MPN or CFU/100 mL and corresponding qPCR results ranged from 6.6 to 1785 CCE/100 mL. The regression analysis of these results showed a positive correlation between qPCR and conventional tests with an overall correlation (r) of 0.71. qPCR was found to provide accurate and sensitive estimate of Enterococcus densities and has the potential to be used as a rapid test method for the quantification of Enterococcus in marine waters. 相似文献
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