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991.
Sameh A. Sakr 《Hydrogeology Journal》1999,7(2):155-160
The problem of seawater intrusion is considered for the case of a confined coastal aquifer in which there is steady seaward
flow of fresh water. Using the GWCH2O model, the problem is solved first for the case of no dispersion where a distinct interface
exists separating the fresh water from the salt water. The problem is solved next by taking into account dispersion and diffusion
of the salt-water component, along with the density effect. In this respect, a two-dimensional finite-element model, 2D-VDTRAN,
is developed to simulate density-dependent solute transport.
To investigate the limitation of the sharp-interface approach in coastal aquifers for conditions of both steady state and
unsteady state, the problem is solved twice using the two models with different parameter values. These parameters are combined
in dimensionless form, resulting in four named parameters: seepage factor (A); dispersion-to-advection ratio (B); geometry
ratio (C); and time-scale factor (T). Using the density-dependent model, the dimensionless width of the transition zone (W/L)
is determined for different values of A, B, C, and T. Steady-state simulations show that the sharp-interface approach is valid
only when the system is dominated by advection, i.e., when 0<B≤5% for all values of A and C, or when A≥65% for all values
of B and C. However, the unsteady-state analysis shows that the applicability of the sharp-interface approach is sufficiently
accurate at early times.
Received, October 1997 Revised, June 1998, October 1998 Accepted, November 1998 相似文献
992.
T. N. Narasimhan 《Journal of Earth System Science》1999,108(3):117-148
The equation describing the conduction of heat in solids has, over the past two centuries, proved to be a powerful tool for
analyzing the dynamic motion of heat as well as for solving an enormous array of diffusion-type problems in physical sciences,
biological sciences, earth sciences, and social sciences. This equation was formulated at the beginning of the nineteenth
century by one of the most gifted scholars of modern science, Joseph Fourier of France. A study of the historical context
in which Fourier made his remarkable contribution and the subsequent impact his work has had on the development of modern
science is as fascinating as it is educational. This paper is an attempt to present a picture of how certain ideas initially
led to Fourier’s development of the heat equation and how, subsequently, Fourier’s work directly influenced and inspired others
to use the heat diffusion model to describe other dynamic physical systems. Conversely, others concerned with the study of
random processes found that the equations governing such random processes reduced, in the limit, to Fourier’s equation of
heat diffusion. In the process of developing the flow of ideas, the paper also presents, to the extent possible, an account
of the history and personalities involved.
Reprinted by permission from theAmerican Geophysical Union, @ 1999. Originally published inReviews of Geophysics as “Fourier’s Heat Conduction Equation: History, Influence and Connections,” Vol. 37, issue 1, pages 151–172, February 1999.
Appended here are eight figures of historical importance. 相似文献
993.
线性扩散波洪水演算模型研究 总被引:2,自引:0,他引:2
扩散波概念的提出至今已有近半个世纪。在前人研究的基础上,着重讨论如何把扩散波解析解用到天然河道的洪水演算中去,即通过把入流过程离散成带常系数的单位矩形入流之和,将单位线概念引入具有自由下边界的线性扩散波洪水演算模型,并给出了确定天然河道Ck和μ的实用方法。用于黄河下游6个河段的洪水演算获得了令人满意的成果。扩散波洪水演算模型,继承了水力学方法的长处,又具有水文学方法的优点,可能有罗好的开发应用前景 相似文献
994.
IntroductionEarthquakemonitoringandpredictionisstillatthestageofexplorationandempiricalprediction.Thebasisistheanomalyvariationconsistingofseismometryindexandtheobservedresultsusingtheprecursoryapproaches.Althoughthesevariationshowsvarietyandcomplexityanditsrelationwithearthquakesisnotcertain,throughcarefullystudyingonMs>7earthquakeswecanfindthattheanomalyvariationbeforeearthquakestillshowssteadyreappearanceandhasregularity.Theyareallrelativetotheseismogenicprocess.Inthispaperwefocusonstronge… 相似文献
995.
As an alternative approach to classical turbulence modelling using a first or second order closure, the data assimilation method of optimal control is applied to estimate a time and space-dependent turbulent viscosity in a three-dimensional oceanic circulation model. The optimal control method, described for a 3-D primitive equation model, involves the minimization of a cost function that quantifies the discrepancies between the simulations and the observations. An iterative algorithm is obtained via the adjoint model resolution. In a first experiment, a k ± L model is used to simulate the one-dimensional development of inertial oscillations resulting from a wind stress at the sea surface and with the presence of a halocline. These results are used as synthetic observations to be assimilated. The turbulent viscosity is then recovered without the k + L closure, even with sparse and noisy observations. The problems of controllability and of the dimensions of the control are then discussed. A second experiment consists of a two-dimensional schematic simulation. A 2-D turbulent viscosity field is estimated from data on the initial and final states of a coastal upwelling event. 相似文献
996.
近年我国文化地理学研究的新进展 总被引:16,自引:0,他引:16
以改革开放以来中国文化地理学的进展作了综述,在评述了其理论体系构建及主要通论性菱的基础上,按文化景观,文化生态、等几个主要对我国文化地理学的发展进行了全面阐述。 相似文献
997.
Hongguang Sun Shiqian Nie Aaron I.Packman Yong Zhang Dong Chen Chengpeng Lu Chunmiao Zheng 《国际泥沙研究》2023,38(1):12-23
The Rouse formula and its variants have been widely used to calculate the steady-state vertical concentration distribution for suspended sediment in steady sediment-laden flows, where the diffusive flux is assumed to be Fickian. Turbulent flow, however, exhibits fractal properties, leading to non-Fickian diffusive flux for sediment particles. To characterize non-Fickian dynamics of suspended sediment, the current study proposes a Hausdorff fractal derivative based advection-dispersion equation(H... 相似文献
998.
太湖、琵琶湖中水平扩散系数的探讨 总被引:1,自引:0,他引:1
根据1992年和1993年在太湖和日本琵琶湖观测到的长序列湖流资料,依据Taylor扩散理论计算了太湖和琵琶湖中的水平扩散系数,计算结果与通过浓度扩散方程计算基本一致。 相似文献
999.
1000.
海洋天然气水合物的类型及特征 总被引:12,自引:0,他引:12
根据天然气水合物的产出条件,海洋环境水合物可以分为二类扩散系统水合物和渗漏系统水合物。扩散系统水合物分布广泛,在水合物稳定带内是水-水合物两相共存的热力学平衡体系,游离气仅发育于稳定带之下,在地震剖面上发育有指示水合物底界的强反射面(BSR)。该类水合物含量低,埋藏深。除温度和压力外,水合物的沉淀受甲烷溶解度和扩散速度的控制,并与气体组分、孔隙水盐度、天然气供应和有机碳转化等有关。渗漏系统与断层等通道相伴生,水合物发育于渗漏系统整个水合物稳定带,是水-水合物-游离气三相共存的热力学非平衡体系,水合物的沉淀受动力学控制。该类水合物含量高,埋藏浅,但一般不发育BSR。而且,天然气渗漏活动在海底沉积物和上覆水体中形成了一系列特殊的地质、地球物理、地球化学和特异生物群异常。 相似文献