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991.
Upper Cretaceous oceanic red beds in southern Tibet:Lithofacies,environments and colour origin 总被引:6,自引:0,他引:6
Jansa Luba 《中国科学D辑(英文版)》2006,49(8):785-795
992.
D. Karátson K. Németh B. Székely Zs. Ruszkiczay-Rüdiger Z. Pécskay 《International Journal of Earth Sciences》2006,95(5):929-944
A new model for the formation and relief evolution of the Danube Bend, northern Hungary, is discussed on geomorphological and volcanological grounds. We propose that the present-day U-shaped loop of the Danube Bend was partly inherited from the horseshoe caldera morphology of Keserűs Hill volcano, a mid-Miocene (ca 15 Ma) lava dome complex with an eroded central depression open to the north. According to combined palaeogeographical data and erosion rate calculations, the drainage pattern in the Danube Bend region was formed when Pleistocene tectonic movements resulted in river incision and sedimentary cover removal. Formation of the present curvature of the river was due to the exhumation of the horseshoe-shaped caldera as well as the surrounding resistant volcaniclastic successions (i.e. Visegrád Castle Hill) and a hilltop lava dome (Szent Mihály Hill). The process accelerated and the present narrow gorge of the Danube Bend was formed by very rapid, as young as late Quaternary differential tectonic uplift, also enhancing the original volcanic morphology. On the basis of comparative long-term erosion-rate calculations, we estimated successive elevation changes of the volcanic edifice, including partial burial in late Miocene time. In comparison with various order-of-magnitude changes, the mid-to-late Quaternary vertical movements show increased rates and/or base level drop in the Pannonian Basin. 相似文献
993.
This paper extends the scope of seismic isolation by introducing an innovative uplift‐restraining Friction Pendulum system. Termed the XY‐FP isolator, the new isolation device consists of two orthogonal opposing concave beams interconnected through a sliding mechanism that permits tension to develop in the bearing, thereby preventing uplift. Owing to its distinct configuration, the XY‐FP isolator possesses unique properties for a seismic isolator, including uplift restraint, decoupling of the bi‐directional motion along two orthogonal directions, and capability of providing independent stiffness and energy dissipation along the principal horizontal directions of the bearing. The study concentrates on introducing the concept and establishing the underlying principles of operation of the new XY‐FP isolator, formulating the mathematical model for the XY‐FP isolator, and presenting its mechanical behaviour through a displacement‐control testing program on a single XY‐FP isolator. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
994.
Previous studies have suggested that rocking vibration accompanied by uplift motion might reduce the seismic damage to buildings subjected to severe earthquake motions. This paper reports on the use of shaking table tests and numerical analyses to evaluate and compare the seismic response of base‐plate‐yielding rocking systems with columns allowed to uplift with that of fixed‐base systems. The study is performed using half‐scale three‐storey, 1 × 2 bay braced steel frames with a total height of 5.3 m. Base plates that yield due to column tension were installed at the base of each column. Two types of base plates with different thicknesses are investigated. The earthquake ground motion used for the tests and analyses is the record of the 1940 El Centro NS component with the time scale shortened by a factor of 1/√2. The maximum input acceleration is scaled to examine the structural response at various earthquake intensities. The column base shears in the rocking frames with column uplift are reduced by up to 52% as compared to the fixed‐base frames. Conversely, the maximum roof displacements of the fixed and rocking frames are about the same. It is also noted that the effect of the vertical impact on the column associated with touchdown of the base plate is small because the difference in tensile and compressive forces is primarily due to the self‐limiting tensile force in the column caused by yielding of the base plate. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
995.
996.
通过分析青藏高原东部的活动断裂资料和GPS速度场数据,试图阐述活动地块的几何学、运动学和形变特征。初步认为:(1)第四纪特别是晚更新世以来的活动地块边界带与早期的构造单元边界密切相关,但也具有明显的新生性;(2)根据两种资料推导出的各个活动地块的运动学特征基本上是吻合的,其中鲜水河-玉树-玛尼断裂带是一条重要的分界线,其南、北部活动地块的运动方式差异明显;(3)除了活动地块的边界带强烈活动外,各个地块内部也显示出很强的变形;(4)晚更新世以来,青藏高原地壳的运动学和形变特征表现为在印度板块挤压力作用下,活动地块在向NE方向的运动过程中遇到稳定地块阻挡,调节方式是地壳增厚以及南、北部地块分别向SE-SSE和NWW-W方向的构造软弱部位水平侧向迁移。 相似文献
997.
998.
西藏西南部达巴-休古嘎布蛇绿岩带的形成与演化 总被引:16,自引:0,他引:16
:该蛇绿岩带的岩体由地幔橄榄岩组成,主要岩石类型是方辉橄榄岩和纯橄榄岩,缺少典型蛇绿岩剖面中的洋壳单元.微量元素和稀土元素特征显示蛇绿岩形成于类似洋中脊的构造环境.笔者提出该区蛇绿岩来源于印度大陆北缘洋盆的洋壳碎片,这个陆缘洋盆与新特提斯洋主体的形成和演化准同步.洋盆的演化模式是:早三叠世,随着印度(冈瓦纳)大陆向南漂移,其北部边缘因引张裂解产生裂谷,于晚三叠世向东开口与新特提斯洋主体连通,洋盆初具洋壳性质,北侧形成阿依拉-仲巴微陆块.侏罗-白垩纪为洋盆洋壳演化期,处于类似洋中脊的构造环境.晚白垩世末洋盆开始闭合.在新特提斯洋板块向北俯冲消减过程中,阿依拉-仲巴微陆块、陆缘洋盆和印度大陆一起随着向北漂移,在印度大陆向北挤压作用下洋盆逐渐收缩以致最终闭合. 相似文献
999.
1000.