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991.
992.
青藏高原夏季臭氧低谷形成的机理-臭氧输送和化学过程 总被引:6,自引:0,他引:6
利用三维化学输送模式(OSLO CTM2)模拟青藏高原夏季臭氧低谷。结果表明:在青藏高原夏季臭氧低谷的形成和变化过程中,动力输送过程起着最主要作用,化学过程部分补偿了输送过程引起的臭氧减少。在动力输送过程中,水平输送在5月份是造成臭氧减少的主要原因,可在6月和7月成为使臭氧增加;垂直平流的作用不断增强,在6月和7月成为臭氧减少的主要因素;对流输送的作用在7月份大幅增加,其引起的臭氧减少可以与净的变化相比,其作用也不可忽视。气相的化学过程引起的臭氧增加的量值有时超过了臭氧的净变化的大小,因此它也起着重要作用。 相似文献
993.
使用1998年夏季高分辨率的GAME再分析资料,通过计算热量和水汽收支,分析了江淮梅雨的热力和动力特征。梅雨期间,江淮整个地区为强热源及水汽汇控制,并伴有强上升运动。热量和水汽收支计算表明,非绝热加热主要是降水产生的凝结潜热释放,地面感热和蒸发耗热均较小。江淮梅雨降水是对流云和层状云共同产生的混合性降水。子波分析显示,热源、水汽汇和垂直运动有相似的时间变化和多尺度特征。江淮梅雨期间,周期约为6天的天气尺度扰动以及周期约为2天和12小时的中尺度扰动同时发展,使江淮地区产生暴雨,亚引起了热源、水汽汇和上升运动的最大值,对此中尺度扰动起了主要作用。 相似文献
994.
The mid-Cenomanian Dunvegan Formation represents a delta complex deposited on a foreland basin ramp over about 2 my. The Dunvegan is divided into 10 transgressive–regressive allomembers, labelled J–A in ascending order, each defined by regional marine transgressive surfaces. Parasequences within allomembers show an aggradational to offlapping stacking pattern that reflects alternate generation and removal of accommodation. The upper surfaces of allomembers H–E are incised by extensive valley systems traceable for up to 320 km and over about 50 000 km2. Valley depths range up to 41 m and can change significantly over short distances. However, the average depth of incision (mean 21 m) shows no systematic variation in longitudinal profiles and no evidence of headward shallowing. Valleys are typically 1–2 km wide, but locally widen to about 8 km. Widening is sometimes associated with confluence zones, but elsewhere it is not. Updip reaches of valleys are dominated by cross-bedded fluvial sandstone forming multistorey point-bar deposits. Sandstones contain widespread but uncommon paired carbonaceous drapes recognizable as tidal bundles. Inclined heterolithic stratification is locally well developed at the top of the valley fill. Downdip reaches of valleys, typically within 50 km of the lowstand shoreline, have a sandstone-dominated lower part and, locally, a mud-rich upper portion consisting of a variety of laminated heterolithic facies with a clear tidal signature. These heterolithic deposits may represent central basin, tidal flat, bayhead delta and point-bar environments. Valley filling took place mainly during the transgressive systems tract (TST) when tidally influenced environments migrated upvalley. Semi-diurnal tidal backwater effects extended at least 30 km landward of the regional maximum transgressive marine shoreline. The aggradational late TST and highstand systems tract (HST) includes deltaic and coastal plain deposits comprising lake and anastomosed river deposits that suggest a very low gradient (≈ 1:3000). Delta parasequences of the falling stage systems tract (FSST) offlap seaward and have no equivalent coastal plain deposits. The FSST has an average width of 60 km and an inferred gradient of 1:2500. The upper surfaces of the HST and FSST are extensively incised by valleys. The lowstand systems tract (LST) is subtly aggradational, lacks valleys and is characterized by large delta lobes fed by major distributaries. The width and inferred slope of the FSST, coupled with the thickness of aggradational TST and HST deposits on the coastal plain, suggest a vertical accommodation of about 35 m per transgressive event. About 11 m of this is attributed to isostatic subsidence resulting from water and sediment loads; the residual 24 m is attributed to eustatic rise. This sea-level change is of the same order of magnitude as the valley depths. The length of valleys, however, does not seem to be explicable solely in terms of downstream forcing by sea-level change, and an additional, upstream-forcing mechanism, possibly related to precipitation cycles in the Milankovitch band, might be inferred. 相似文献
995.
996.
层状饱水软土地基三维非轴对称动力响应分析方法 总被引:1,自引:0,他引:1
将饱水软土地基视为两相介质、考虑水的渗流和土骨架9变形的耦合作用,用Fourier展开和Hankel积分变换分析三维非称对称饱和弹性土层波动方程,用刚度矩阵方法,建立了层状饱和软土地基三维非轴对称动力响应的解析分析方法。以数值算例对比分析了单相土介质与两相饱和土介质三维非轴对称稳态动力响应,结果表明:在饱水软土地基动力响应分析中应该考虑土体中孔隙流体的影响。 相似文献
997.
998.
999.
A new simplified modelling strategy to simulate the non‐linear behaviour of reinforced concrete shear walls under dynamic loading is presented. The equivalent reinforced concrete (ERC) model is derived from the framework method and uses lattice meshes for concrete and reinforcement bars and uniaxial constitutive laws based on continuum damage mechanics and plasticity. Results show the capacity of the model to analyse structures having different slenderness and boundary conditions. For low reinforcement ratios however, results are sensitive to the angle formed by the diagonals of the concrete lattice and the horizontal bars. The method is compared with the shear multi‐layered beam model that uses Timoshenko multi‐layered 2D beam elements and biaxial constitutive laws. Comparisons for both models with experimental results of two research programs (one organized by NUPEC and the other by COGEMA and EDF) are provided. ERC is a simplified method that intends to save computer time and allows parametrical studies. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
1000.
Martin Thorp Peter Glanville Stephen Stokes Richard Bailey 《Comptes Rendus Geoscience》2002,334(12):903-908
This paper presents the first results of a 14C and optical luminescence dating project on extensive alluvial silt formations in the southern Anti Atlas Mountains in southern Morocco. The silts comprise three members: basal silts, an inter-silt fluvial gravel member and a top silt member and are incised by the rivers. Top silt dates are: 11 340–11 940, 12 670–13 130 cal. yr BP, and 10.6±0.7 ka (OSL). OSL dates for the inter-silt gravels are 29.6±2.0 ka and for the bottom silts is 45.0±3.7 ka. The sediments correlate with Soltanian stratigraphies known elsewhere in Morocco. To cite this article: M. Thorp et al., C. R. Geoscience 334 (2002) 903–908. 相似文献