全文获取类型
收费全文 | 2887篇 |
免费 | 711篇 |
国内免费 | 913篇 |
专业分类
测绘学 | 82篇 |
大气科学 | 1449篇 |
地球物理 | 734篇 |
地质学 | 1338篇 |
海洋学 | 525篇 |
天文学 | 23篇 |
综合类 | 160篇 |
自然地理 | 200篇 |
出版年
2024年 | 18篇 |
2023年 | 28篇 |
2022年 | 88篇 |
2021年 | 100篇 |
2020年 | 107篇 |
2019年 | 152篇 |
2018年 | 101篇 |
2017年 | 113篇 |
2016年 | 103篇 |
2015年 | 136篇 |
2014年 | 191篇 |
2013年 | 163篇 |
2012年 | 162篇 |
2011年 | 181篇 |
2010年 | 156篇 |
2009年 | 224篇 |
2008年 | 222篇 |
2007年 | 288篇 |
2006年 | 207篇 |
2005年 | 219篇 |
2004年 | 175篇 |
2003年 | 151篇 |
2002年 | 165篇 |
2001年 | 120篇 |
2000年 | 117篇 |
1999年 | 114篇 |
1998年 | 123篇 |
1997年 | 104篇 |
1996年 | 93篇 |
1995年 | 60篇 |
1994年 | 69篇 |
1993年 | 45篇 |
1992年 | 54篇 |
1991年 | 55篇 |
1990年 | 28篇 |
1989年 | 18篇 |
1988年 | 29篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有4511条查询结果,搜索用时 156 毫秒
971.
972.
Global estimates of wind energy input to subinertial motions in the Ekman-Stokes layer 总被引:1,自引:0,他引:1
By incorporating the wave-induced Coriolis-Stokes forcing into the classical Ekman model, the wind energy input to the Ekman-Stokes
layer is investigated, with an emphasis on the surface wave effects when the direction of Stokes drift deviates from that
of wind stress. Theoretical analysis of the kinetic energy balance of the Ekman-Stokes layer shows that the total wind energy
input consists of the direct wind energy input and the wave-induced energy input. Details of the direct wind and wave-induced
energy input are discussed. Based on the ECMWF ERA-40 Re-Analysis wind stress and surface wave data, the global total wind
energy input to subinertial motions in the Ekman-Stokes layer is estimated at 2.19 TW, including 0.26 TW (12%) wave-induced
energy input and 1.93 TW (88%) direct wind energy input. The effect of sea-ice coverage on the energy input to the Ekman-Stokes
layer is also considered. It is shown that the global total energy input could be overestimated by 0.08 TW (about 4%) without
taking the sea-ice coverage into account. 相似文献
973.
A case study for the energy saving in the powering characteristics of a river going general cargo ship has been carried out. Two different hull forms were generated from the original hull form of the vessel to optimise the stern flow of the vessel. A possible energy saving concept, such as partial wake equalizing duct was investigated in this manner. Resistance, self-propulsion and flow visualization measurements were performed with the hull models to explore the effect of partial wake equalizing ducts on the powering characteristics of the hull form. Analysis of the results indicates that the partial wake equalizing duct concept with an appropriate stern design affect not only the flow characteristics at aft-end, but also the propulsion characteristics. In order to identify effect of each component (partial wake equalizing duct and stern form) a further investigation is needed. 相似文献
974.
春季南海北部上混合层的数值模拟与数值实验 总被引:5,自引:0,他引:5
根据 1 998年南海季风实验 (SCSMEX)北部“实验 3号”调查船的观测资料 ,采用一维湍动能模式 (TKE模式 ) ,对春季南海北部的SST及混合层随时间变化特征进行了数值模拟和数值试验。结果表明 ,TKE模式能够很好地模拟南海北部的海表面温度SST和上混合层深度随时间变化基本特征。在南海 5— 6月 ,SST的日振荡主要依赖于短波辐射的日变化 ,短波辐射是SST的主要维持机制 ;短波辐射会使SST升高 1— 4℃ ;风的垂直混合作用主要是抑制了SST的日周期振荡。春季南海海面潜热通量和感热通量与短波辐射和风应力相比较 ,是一个对SST影响较小的量。南海北部 5月份混合层深度的变化趋势和振荡特征受风应力和短波辐射共同控制 ,风应力使混合层深度加深 5— 1 0m ,短波辐射使混合层深度平均变浅 5— 1 0m。而 6月份南海北部 ,在夏季风爆发后短波辐射较小 ,短波辐射的作用只能使混合层深度变浅1— 2m ,潜热通量和感热通量对混合层的作用会使混合层的深度加深 1— 2m ,混合层深度主要受风应力控制。 相似文献
975.
长江三角洲第一硬土层中微结核的矿物化学特征及其成因 总被引:4,自引:0,他引:4
长江三角洲第一硬土层是古土壤层,是长江河漫滩型沉积物,其形成经历多次沉积和成土过程.硬土层中的铁锰结核以菱铁矿、菱锰矿和褐铁矿为主,通过铁锰元素离子和矿物Eh-pH稳定关系分析,最有利于菱锰矿和菱铁矿结核生成的条件是:Eh<0且pH>8.成土期处于末次冰期低海面、气候寒冷干燥期,土壤的化学过程是以氧化作用为主,是褐铁矿等氧化性矿物形成时期;冰后期海相层的沉积覆盖使土壤层进入成岩阶段,土壤层的化学过程以还原作用为主,成岩过程是铁锰碳酸盐结核的主要生成期. 相似文献
976.
Hydrography of the eastern tropical Pacific: A review 总被引:3,自引:10,他引:3
977.
A new set of Boussinesq-type equations describing the free surface evolution and the corresponding depth-integrated horizontal velocity is derived with the bottom boundary layer effects included. Inside the boundary layer the eddy viscosity gradient model is employed to characterize Reynolds stresses and the eddy viscosity is further approximated as a linear function of the distance measured from the seafloor. Boundary-layer velocities are coupled with the irrotational velocity in the core region through boundary conditions. The leading order boundary layer effects on wave propagation appear in the depth-integrated continuity equation to account for the velocity deficit inside the boundary layer. This formulation is different from the conventional approach in which a bottom stress term is inserted in the momentum equation. An iterative scheme is developed to solve the new model equations for the free surface elevation, depth-integrated velocity, the bottom stress, the boundary layer thickness and the magnitude of the turbulent eddy viscosity. A numerical example for the evolution of periodic waves propagating in one-dimensional channel is discussed to illustrate the numerical procedure and physics involved. The differences between the conventional approach and the present formulation are discussed in terms of the bottom frictional stress and the free surface profiles. 相似文献
978.
979.
Numerical Simulations of Sea Surface Cooling by a Mixed Layer Model during the Passage of Typhoon Rex 总被引:3,自引:0,他引:3
In order to investigate the formation mechanism of rapid decrease of maritime sea surface temperature (SST) observed by R/V Keifu Maru, the ocean response to Typhoon Rex is simulated using a mixed layer model. The rapid decrease of the maritime SST is successfully simulated with realistic atmospheric forcing and an entrainment scheme of which sources of turbulent kinetic energy (TKE) are production due to wind stress, generation during free convection, and production due to current shear. The rapid decrease at the observed station by R/V Keifu Maru is not produced by instant atmospheric forcing but is mainly produced by entrainment on the right side of the running typhoon as a part of cooling area during its passage, and remained during a few days. The sea surface cooling (SSC) is evident along the track and on the right side of the running typhoon, which is similar to the SSC of satellite observation by TRMM/TMI. The conspicuous SSC produced by both entrainment and upwelling is situated just under the track of typhoon when the typhoon moves slower. Intercomparison of entrainment schemes of the mixed layer model is implemented. Frictional velocity and buoyancy effects are effective for a gradual SSC covering the wide region. In contrast, the effect of current shear at the mixed layer base is related to the amount of SSC and the sharp horizontal gradient of SSC. The entrainment scheme including all three TKE sources has the best performance for SSC simulation. 相似文献
980.
福建九龙江口入海泥沙的扩散和河口湾的现代沉积 总被引:15,自引:1,他引:15
本文阐述了40年来九龙江入海泥沙量增加了两倍,入海泥沙在海门岛—鸡屿一带的浅滩区,其年平均淤积8—10cm,一次洪水流域搬来悬浮泥沙,使河口湾新淤积层厚2—3cm.并指出、进入河口湾的三条汉河各有独立的扇形粗粒冲积浅滩;悬移质的粉砂、粘土粒扩散至鼓浪屿以南海域;构成三角洲沉积主体的河口浅滩区的沉积速度由入海泥沙倍增而相应地加快进行. 相似文献