全文获取类型
收费全文 | 6613篇 |
免费 | 1688篇 |
国内免费 | 2416篇 |
专业分类
测绘学 | 450篇 |
大气科学 | 2184篇 |
地球物理 | 1924篇 |
地质学 | 3677篇 |
海洋学 | 1254篇 |
天文学 | 104篇 |
综合类 | 440篇 |
自然地理 | 684篇 |
出版年
2024年 | 31篇 |
2023年 | 89篇 |
2022年 | 237篇 |
2021年 | 256篇 |
2020年 | 293篇 |
2019年 | 390篇 |
2018年 | 335篇 |
2017年 | 326篇 |
2016年 | 331篇 |
2015年 | 396篇 |
2014年 | 533篇 |
2013年 | 557篇 |
2012年 | 529篇 |
2011年 | 555篇 |
2010年 | 420篇 |
2009年 | 567篇 |
2008年 | 539篇 |
2007年 | 624篇 |
2006年 | 542篇 |
2005年 | 410篇 |
2004年 | 422篇 |
2003年 | 342篇 |
2002年 | 317篇 |
2001年 | 245篇 |
2000年 | 235篇 |
1999年 | 211篇 |
1998年 | 184篇 |
1997年 | 166篇 |
1996年 | 150篇 |
1995年 | 106篇 |
1994年 | 108篇 |
1993年 | 54篇 |
1992年 | 50篇 |
1991年 | 36篇 |
1990年 | 26篇 |
1989年 | 12篇 |
1988年 | 19篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1971年 | 3篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Modified PIC Method for Sea Ice Dynamics 总被引:1,自引:0,他引:1
The sea ice cover displays various dynamical characteristics such as breakup, rafting, and ridging under external forces. To model the ice dynamic process accurately, the effective numerical modeling method should be established. In this paper, a modified particle-in-cell (PIC) method for sea ice dynamics is developed coupling the finite difference (FD) method and smoothed particle hydrodynamics (SPH). In this method, the ice cover is first discretized into a series of lagrangian ice particles which have their own sizes, thicknesses, concentrations and velocities. The ice thickness and concentration at Eulerian grid positions are obtained by interpolation with the Gaussian function from their surrounding ice particles. The momentum of ice cover is solved with FD approach to obtain the Eulerian cell velocity, which is used to estimate the ice particle velocity with the Gaussian function also. The thickness and concentration of ice particles are adjnsted with particle mass density and smooth length, which are adjusted with the redistribution of ice particles. With the above modified PIC method, numerical simulations for ice motion in an idealized rectangular basin and the ice dynamics in the Bohai Sea are carried out. These simulations show that this modified PIC method is applicable to sea ice dynamics simulation. 相似文献
62.
本文在作者另文数值模拟得到的三维海浪基础上 ,进一步分析给出了三维波峰长度、高度及方向角度等特征量的统计分布。发现考虑海浪的方向性质后波峰分布不再是均匀连续的 ;波峰的长度分布受方向函数影响 ,方向分布越宽 ,波峰的平均长度越短 ,波峰的方向角分布越宽 ;波峰高度和长度在波峰高度较小时有很大的相关性 ,而在波峰高度很大时无关 相似文献
63.
在洋浦近岸海域计算潮流场基础上,计算预选排污口附近海水质点运动轨迹及预测污染物浓度分布,最后,从环保角度出发,推荐了洋浦地区各开发区的排污口位置,为洋浦近岸海域污染控制规划方案的制定及其优化提供了依据。 相似文献
64.
环台湾岛海域半日潮波特征的三维模拟 总被引:10,自引:0,他引:10
用1997版POM海洋模式,首次应用于环台湾岛海域的潮波数值研究.得到该海域的半日潮波主要为23°N以南西太平洋传来的胁振潮.影响台湾海峡的半日潮波分别由海峡南北口传入的两支潮波,且北支强于南支.福建沿岸湄州湾-兴化湾为最强潮区,其M2分潮最大振幅可达240cm.最强潮流区位于澎湖水道,M2分潮最大潮流达196cm/s.环台湾岛海域潮波潮流水平结构上除海峡北部原有一个圆流点外,还发现另外存在4个新的圆流点.潮流垂直结构上主要为右偏,接近底层处为左偏. 相似文献
65.
Two commonly used methods of simulating random time series, given a target power spectrum, are discussed. Wave group statistics, such as the mean length of runs of high waves, produced by the different simulation schemes are compared. The target spectra used are obtained from ocean measurements, and cover a wide range of ocean conditions. For a sufficiently large number of spectral components, no significant differences are found in the wave group statistics produced by the two simulation techniques. 相似文献
66.
67.
In this paper, the characteristics of different forms of mild slope equations for non-linear wave are analyzed, and new non-linear theoretic models for wave propagation are presented, with non-linear terms added to the mild slope equations for non-stationary linear waves and dissipative effects considered. Numerical simulation models are developed of non-linear wave propagation for waters of mildly varying topography with complicated boundary, and the effects are studied of different non-linear corrections on calculation results of extended mild slope equations. Systematical numerical simulation tests show that the present models can effectively reflect non-linear effects. 相似文献
68.
The working group Mathematical Geology of the Freie Universität Berlin was formed in 1971. We review quantitative methods used by the working group since 1983 to treat mineral exploration problems. The methods applied vary from elementary statistical analysis of multivariate exploration data to optimal strategies for selecting favorable targets, and from multiobjective decision-making for additional drill hole locations to expert systems in exploration.The methods applied are directly related to the level of information at each stage of the exploration process. Special emphasis was placed on the relationship between and evaluation of subjective and objective data. Case studies illustrating the various methods are presented for different kinds of mineral deposits and exploration environments. 相似文献
69.
70.
J A Vargas-Guzmán 《中国地质大学学报(英文版)》2008,19(1):85-92
An analysis of statistical expected values for transformations is performed in this study to quantify the effect of heterogeneity on spatial geological modeling and evaluations. Algebraic transformations are frequently applied to data from logging to allow for the modeling of geological properties. Transformations may be powers, products, and exponential operations which are commonly used in well-known relations (e.g., porosity-permeability transforms). The results of this study show that correct computations must account for residual transformation terms which arise due to lack of independence among heterogeneous geological properties. In the case of an exponential porosity-permeability transform, the values may be positive. This proves that a simple exponential model back-transformed from linear regression underestimates permeability. In the case of transformations involving two or more properties, residual terms may represent the contribution of heterogeneous components which occur when properties vary together, regardless of a pair-wise linear independence. A consequence of power- and product-transform models is that regression equationswithin those transformations need corrections via residual cumulants. A generalization of this result isthat transformations of multivariate spatial attributes require multiple-point random variable relations. This analysis provides practical solutions leading to a methodology for nonlinear modeling using correct back transformations in geology. 相似文献