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131.
An investigation of the geotechnical properties of sediments from 57 boreholes drilled in West Delta and South Pass OSC Lease Areas, offshore Louisiana, indicated that sediment texture, shear strength, water content, and liquid limit vary significantly laterally and with depth. Samples are predominantly soft, fine‐grained sediments with high water content and medium to high plasticity. Firm, coarser‐grained sediments were obtained near the shoreline in South Pass OCS Lease Area and in the northern and eastern parts of West Delta OCS Lease Area. Trends in the distribution of geotechnical properties appear to be influenced by sediment texture and rate of sedimentation. 相似文献
132.
We developed habitat suitability curves (HSC) using generalised additive models (GAMs) for nine benthic macroinvertebrate taxa from a small New Zealand river for hydraulic-habitat modelling assessments of instream flow requirements. We included interaction terms between the primary variables (water depth, velocity, substrate) when significant, to address a longstanding criticism of univariate HSC. To date, only large-river univariate HSC have been available and these have been used in hydraulic-habitat applications on small rivers, despite doubt over the transferability of HSC between rivers of different size and type. We tested the outcome on the predicted abundance–flow relationship of applying the small-river habitat suitability GAMs versus large-river GAMs for two taxa on the same small river. We found the effects of flow allocation were overestimated by the large-river GAMs relative to the small-river GAMs. Further research to develop general HSC for categories of river size and type is needed to better inform hydraulic-habitat modelling applications. 相似文献
133.
针对异源遥感影像由于辐射水平差异导致地物在相邻图像上亮度值存在差异的现象,分析了造成影像间色调差异的各种原因以及现有处理方法在进行影像间色彩平衡处理时存在的问题,实现了基于Wallis滤波器进行匀光的相关算法,并通过多组匀光实验取得了较好的色彩平衡效果。 相似文献
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CHEN Lan XU Guiwen DA Xuejuan YI Haisheng ZHU Zhangxiong HUANG Zhaohui LI Xiaogang 《《地质学报》英文版》2017,91(2):630-643
The marine oil shales of the Qiangtang Basin, northern Tibet, exposed in the Biluo Co, Tuonamu, Shenglihe and Changsheshan areas are believed to be important petroleum source rocks. This work comprehensively analyzed the carbon isotopes, trace elements, and calcareous nannofosills, ammonites and bivalves of the Biluo Co section in the Qiangtang Basin. The organic carbon isotopes show a positive excursion close to 2.17‰(relative to PDB), which, albeit significantly smaller, may also be associated with other Early Toarcian Oceanic Anoxic Events(T-OAE) in the European epicontinental seas and the Tethyan continental margins. Coinciding with the Early Toarcian transgression, the oxygen deficiency in bottom water had led to dysoxic-anoxic conditions and deposition of black shales lacking benthic fauna. Under such condition, the redox-sensitive trace metals such as Mo, V, Ni, Cr, and U were enriched, in conjunction with high planktonic productivity of Watznaueriaceae calcareous nannofossils. Comparison of the results with the records of chemo-and biostratigraphy, as well as the palaeogeography during the Early Jurassic suggests that the anoxia linked to the Early Toarcian oceanic anoxic event was mainly caused by the high surface water temperature, sea-level rise and an increase of surface water productivity. 相似文献
136.
James A. Kingsbury Jeannie R. B. Barlow Bryant C. Jurgens Peter B. McMahon John K. Carmichael 《Hydrogeology Journal》2017,25(6):1661-1678
Wells along two regional flow paths were sampled to characterize changes in water quality and the vulnerability to contamination of the Memphis aquifer across a range of hydrologic and land-use conditions in the southeastern United States. The flow paths begin in the aquifer outcrop area and end at public supply wells in the confined parts of the aquifer at Memphis, Tennessee. Age-date tracer (e.g. SF6, 3H, 14C) data indicate that a component of young water is present in the aquifer at most locations along both flow paths, which is consistent with previous studies at Memphis that documented leakage of shallow water into the Memphis aquifer locally where the overlying confining unit is thin or absent. Mixtures of young and old water were most prevalent where long-term pumping for public supply has lowered groundwater levels and induced downward movement of young water. The occurrence of nitrate, chloride and synthetic organic compounds was correlated to the fraction of young water along the flow paths. Oxic conditions persisted for 10 km or more down dip of the confining unit, and the presence of young water in confined parts of the aquifer suggest that contaminants such as nitrate-N have the potential for transport. Long-term monitoring data for one of the flow-path wells screened in the confined part of the aquifer suggest that the vulnerability of the aquifer as indicated by the fraction of young water is increasing over time. 相似文献
137.
Alessandro Batezelli Francisco Sergio Bernardes Ladeira Diego Luciano do Nascimento Mrcio Luiz DA Silva 《Sedimentology》2019,66(2):699-735
The Upper Cretaceous Bauru Group in south‐east Brazil consists of alluvial strata whose characteristics and distribution indicate a fluvial system developed in a semi‐arid to arid climate. Sections exposed within a 90 000 km2 study area in Minas Gerais State (in south‐eastern Brazil) were evaluated using facies and palaeosol analysis to formulate depositional and pedogenic models that may account for geomorphic and climate features. From east to west, the study succession records a gradual decrease in grain size, an increase in the width/thickness ratio in channels, a decrease in the lateral and vertical connectivity of channel deposits, and an increase in overbank deposits. The fluvial architecture indicates a braided channel belt, ephemeral ribbon–channels, and an unconfined fluvial facies from east to west in the study area. The lateral and vertical distribution of facies, stratigraphic architecture and palaeocurrent data suggest proximal, medial and distal portions of a progradational distributive fluvial system. The sedimentary dynamics were marked by the building and abandonment of channels related to processes of aggradation, vegetation growth and palaeosol generation. Macromorphological and micromorphological analyses have identified pedological and mineralogical features that indicate an arid to semi‐arid climate with a provenance from the north‐eastern part of the basin (Alto Paranaiba Uplift). From the proximal to the distal portions of the distributive fluvial system, the palaeosol development is different. In the proximal portion, the palaeosols are absent or poorly developed, allowing a possible general comparison with the present soil order: Inceptisols and Aridisols. In the medial portion of the fluvial system, the palaeosols are well‐developed and characterized by Bt, Btk, C and Ck horizons (Alfisols, Aridisols, Inceptisols and Entisols). Poorly drained to well‐drained palaeosols from the base to the top in the distal plain (Aridisols and Inceptisols) are associated with geomorphic and hydromorphic changes in the fluvial system due to progradational evolution. The genetic relationship between the fluvial architecture and the palaeosols enhances the understanding that the sedimentation and pedogenesis that occurs in different portions of the distributive fluvial system are related to the tectonic and climatic evolution of the basin. 相似文献
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139.
Steven L. Bryant 《Computational Geosciences》2001,5(3):203-223
We present an overview of several applications of reactive flow and transport in which interesting mathematical issues and computational challenges arise. The topics include front propagation through porous media in the presence of dispersion; numerical simulation of large-scale reactive transport problems; the reliability of processes that involve in-situ generation of viscosifying agents; methods for describing pore-scale geometry in granular media; and the information content of reactive tracer experiments. The intent of this survey is to heighten awareness of underlying mathmetical aspects and, it is hoped, to stimulate new contributions in these areas. 相似文献
140.
Raymond L. Bryant 《Singapore journal of tropical geography》2001,22(1):15-37
This paper explains how the notion of “critical engagement” has been a popular basis for NGO‐state relations in the Philippines and Indonesia. It has been used, moreover, in both liberal democratic (post‐1985 Philippines) and authoritarian (late 1960s to late 1990s Indonesia) political regimes. For both states and reform‐minded NGOs, critical engagement has represented a flexible means by which to pursue assorted political, economic and social ends. In a context of regional political and economic upheaval, it is likely to remain popular with both states and many NGOs for the foreseeable future. 相似文献