全文获取类型
收费全文 | 2130篇 |
免费 | 559篇 |
国内免费 | 437篇 |
专业分类
测绘学 | 200篇 |
大气科学 | 395篇 |
地球物理 | 827篇 |
地质学 | 717篇 |
海洋学 | 520篇 |
天文学 | 109篇 |
综合类 | 168篇 |
自然地理 | 190篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 35篇 |
2021年 | 47篇 |
2020年 | 59篇 |
2019年 | 75篇 |
2018年 | 57篇 |
2017年 | 77篇 |
2016年 | 83篇 |
2015年 | 85篇 |
2014年 | 107篇 |
2013年 | 150篇 |
2012年 | 128篇 |
2011年 | 139篇 |
2010年 | 133篇 |
2009年 | 141篇 |
2008年 | 142篇 |
2007年 | 210篇 |
2006年 | 168篇 |
2005年 | 136篇 |
2004年 | 129篇 |
2003年 | 106篇 |
2002年 | 107篇 |
2001年 | 93篇 |
2000年 | 67篇 |
1999年 | 90篇 |
1998年 | 73篇 |
1997年 | 70篇 |
1996年 | 70篇 |
1995年 | 54篇 |
1994年 | 62篇 |
1993年 | 45篇 |
1992年 | 46篇 |
1991年 | 36篇 |
1990年 | 17篇 |
1989年 | 25篇 |
1988年 | 8篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3126条查询结果,搜索用时 15 毫秒
991.
The equivalent operator equation is derived from the full primitive nonlinear equations of the atmospheric motion and the properties and physical senses of the operators are studied.In the infinite dimensional Hilbert space,the global asymptotic behavior of the atmosphere system with the non-stationary external forcing is studied under the assumption of the bounded external forcing.The existence theorems of the global absorbing set and the global attractor are obtained.Thus,the conclusions deduced from the large-scale atmosphere(Li and Chou 1996a;1996b) are extended to the general atmosphere. 相似文献
992.
Helmholtz's equation with a variable wavenumber is solved for a point force through use of a first-order differential equation system approach. Since the system matrix in this formulation is non-constant, an eigensolution is no longer valid and recourse has to be made to approximate techniques such as series expansions and Picard iterations. These techniques can accommodate in principle any variation of the wavenumber with position and are applicable to scalar wave propagation in one, two and three dimensions, with the latter two cases requiring radial symmetry. As shown in the examples, good solution accuracy can be achieved in the near field region, irrespective of frequency, for the particular case examined, namely a wavenumber which increases (or decreases) as the square root of the radial distance from source to receiver. Finally, the resulting Green's functions can be used as kernels within the context of boundary element type solutions to study scalar wave scattering in inhomogeneous media. 相似文献
993.
利用六面体单元和三线性插值函数,推导出在任意弹性各向异性介质中三维三分量波动方程所满足的有限元方程.给出用时域有限差分求解该有限元方程时,时间、空间采样率和弹性参数应满足的稳定性条件.提出避免每一时间步都求解一大型线性代数方程组的方法.在开始求波场前,先求质量矩阵的逆的因子形式,以后每时间步只需作刚度矩阵的逆的因子形式与向量的乘积运算,可大大提高有限元素法在微机上进行波动方程数值模拟的运算速度.结合两个数值模拟算例,说明该方法的可行性,并与伪谱法作了计算速度的比较,有限元法的计算速度高于伪谱法的计算速度. 相似文献
994.
Laplace变换边界积分方程与Schapery数值反演法模拟溶质运移问题 总被引:3,自引:0,他引:3
王晓红 《水文地质工程地质》1997,24(6):19-22
本文将对流-弥散方程化为纯尔散方程,采用Laplace变换,Schapery数值反演法求解,通过裕列计算对选取不同的Laplace变换参数的计算结果进行比较,分析Laplace变换参数对计算精度的影响,给出P值的选取方法式。 相似文献
995.
本文发展了积分方程法用于层状介质中三维不均匀体的大地电磁模拟算法(简称MT).分为二个步骤:第一步,异常体用等效的散射电流代替,通过层状介质中的格林函数,建立以散射电流为未知参数的积分方程;第二步,把求得的散射电流乘上相应的格林函数,即得地面上的二次电磁场,由此而计算出各种MT响应. 文中采用了数值滤波与插值、群变换以及格林矩阵带状化三个方面的数值处理方法,提高了计算效率.通过与已发表的三维MT计算结果对比及格林函数互易性检验,表明了该算法的正确性.在此基础上,进行了数值模拟,初步讨论了三维MT曲线的畸变特点. 相似文献
996.
An estimate of the magnitudes of the absolute vorticity advection terms and the terms in the balance equation suggest that
the use of the barotropic vorticity equation within 5 degrees of latitude of the equator is not very good and that the linear
balance equation is as good as the nonlinear balance equation in the equatorial region.
Zonal Fourier analysis has revealed that the contribution from planetary scale waves is much larger than that from synoptic
scale waves, being more in the winter hemisphere than in the summer hemisphere.
In classical scale analysis there must be a distinction in wavelength between the zonal and the meridional directions for
planetary scale waves. This distinction does not appear to be necessary for synoptic scale waves. 相似文献
997.
An extention of our previous theory for trace gas absorption into freely-falling cloud and raindrops is presented. This theory describes the convective diffusion of a trace gas through air and into a water drop with internal circulation, the drop falling at its terminal velocity. Using flow fields for the circulating water inside and for the moving air outside the drop, obtained by numerical solutions to the Navier—Stokes equation of motion, we numerically solved the convective diffusion equation to determine the uptake of SO2 by water drops of various sizes, time exposure to the gas phase, and concentration of SO2 in the gas phase. It was found that for drops of radius larger than 1 mm and relatively low gas concentrations (10 ppb (v)), resistance to gas diffusion lies mainly in the gas phase; while for drops of radius less than 500 m and gas concentrations larger than those found in the atmosphere (1% (v)), the resistance to diffusion lies primarily in the liquid phase. With drop sizes and gas concentrations between these limits, the rate of SO2 uptake is controlled by a coupled resistance to diffusion inside and outside the drop. In addition to our general model, a simplified version was formulated which allows considerable savings in computer time for evaluation and improved ease of handling without significant loss of accuracy. A comparison between our simplified model and that of Barrie (1978) shows that the boundary-layer approach of Barrie may be a useful alternate approach to estimating trace gas absorption by water drops, provided appropriate values are chosen for the thickness of the boundary layers involved. 相似文献
998.
999.
文中导得了N层模式的KdV方程,作为例子计算了三层模式的孤立Rossby波流型。基本气流的垂直切变、水平切变和Froude数对孤波流型都有重要影响;不同模态的孤波具有不同流型,不同高度位面上的孤波流型一般是不同的。 相似文献
1000.
In this paper,the local potential of nondivergent flow on beta plane is derived from the motion equa-tion.The conservation principle for vorticity is obtained when the local potential tends to be minimumwith the variational technique.Some other properties st,ch as Lagrangian of vorticity equation,energyetc.are also discussed briefly in the paper. 相似文献