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D. L. DUNKERLEY 《地球表面变化过程与地形》1996,21(6):573-580
Grid-based samples of surface stone covers are widely employed for the determination of grain properties such as mean diameter. However, this method has an inherent bias that is related to clast size. Studies failing to correct for this effect have inadvertently reported stone diameters weighted by the area that each stone exposed on the sampling plane. Monte Carlo methods are used to generate and sample synthetic veneers of surface stones, like those found on many dryland hillslopes, but having pre-determined population distribution characteristics. Uncorrected grid samples from such stone veneers are shown to yield estimates of mean diameter that are in error by up to several hundred per cent. Formulae are provided which permit accuracy of a few per cent to be obtained with samples of 100–300 stones. Slightly larger samples are required accurately to estimate edge length- and area-weighted mean diameters than for traditional volume-weighted means. 相似文献
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以东方岸外海域为例,计算了极端天气下不同水深条件构建稳定粗化层抛石颗粒的临界粒径;分析了影响粗化层稳定的不同因素,并对人工抛石构建粗化层提出建议。结果显示,在东方岸外30m和60 m水深处,沉积物的中值泥沙粒径至少为30.33 mm和3.99 mm,才能抵御极端浪流的冲刷,且抛石层的厚度应至少为80.9mm和10.8mm,抛石层至少覆盖原始床沙的70%。粗化层的稳定性受颗粒隐蔽暴露效应、砂组分百分比、粗化层颗粒级配、覆盖厚度及覆盖百分比的共同影响,而抛石构建稳定粗化层的实质是对抛石粒径的合理选取及对细粒组分百分比的有效控制。另外,抛石级配的合理选择应受到重视,在施工过程中则需保证覆盖百分数和粗化层的覆盖厚度。粗细混合投放或者分层投放有利于更好地构建稳定粗化层。以上述方法构建稳定粗化层可为海底管道工程设施的维护提供有效支持。 相似文献
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程团结 《地质灾害与环境保护》2006,17(2):95-98
针对浙东某山区危石的危害、规模、分布特征和稳定状况,提出了支撑加固方案,经过比选优化,根据施工反馈信息的调整,最终采用人工挖孔桩支挡柱加固方案,施工后效果良好。本文详细介绍了治理的设计思路与施工过程。 相似文献
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Over the past few years, there has been a steady increase in the interest in dry‐stone walling not only to preserve existing constructions but also to build new ones. Yet, dry masonry's expansion is slowed down by the lack of scientific knowledge to assess its reliability. This study aims at contributing to the construction of this scientific frame using a simplified model based on yield design and homogenization, which can be directly exploited for engineering purposes. A new analytical expression of the ultimate load is thus established. Then, the validity of the method is assessed by comparisons with limit equilibrium analysis, distinct element method, and field trials. Finally, possible improvements of the model are discussed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Sustaining a developed economy and expanding a developing one require the use of large volumes of natural aggregate. Almost all human activity (commercial, recreational, or leisure) is transacted in or on facilities constructed from natural aggregate. In our urban and suburban worlds, we are almost totally dependent on supplies of water collected behind dams and transported through aqueducts made from concrete. Natural aggregate is essential to the facilities that produce energy—hydroelectric dams and coal-fired powerplants. Ironically, the utility created for mankind by the use of natural aggregate is rarely compared favorably with the environmental impacts of mining it. Instead, the empty quarries and pits are seen as large negative environmental consequences. At the root of this disassociation is the philosophy of environmentalism, which flavors our perceptions of the excavation, processing, and distribution of natural aggregate. The two end-member ideas in this philosophy are ecocentrism and anthropocentrism. Ecocentrism takes the position that the natural world is a organism whose arteries are the rivers—their flow must not be altered. The soil is another vital organ and must not be covered with concrete and asphalt. The motto of the ecocentrist is man must live more lightly on the land. The anthropocentrist wants clean water and air and an uncluttered landscape for human use. Mining is allowed and even encouraged, but dust and noise from quarry and pit operations must be minimized. The large volume of truck traffic is viewed as a real menace to human life and should be regulated and isolated. The environmental problems that the producers of natural aggregate (crushed stone and sand and gravel) face today are mostly difficult social and political concerns associated with the large holes dug in the ground and the large volume of heavy truck traffic associated with quarry and pit operations. These concerns have increased in recent years as society's demand for living space has encroached on the sites of production; in other words, the act of production has engendered condemnation. Many other environmental problems that are associated with dust and noise and blasting from quarry and pit operations have been reduced through the efficient use of technology. Recycling concrete in buildings, bridges, and roads and asphaltic pavements will ultimately reduce the demand for virgin natural aggregate. The impact created by the large holes in the ground required for the mining of natural aggregate can be greatly reduced by planning their reclamation before mining begins. 相似文献