全文获取类型
收费全文 | 1670篇 |
免费 | 199篇 |
国内免费 | 204篇 |
专业分类
测绘学 | 434篇 |
大气科学 | 172篇 |
地球物理 | 516篇 |
地质学 | 355篇 |
海洋学 | 219篇 |
天文学 | 87篇 |
综合类 | 116篇 |
自然地理 | 174篇 |
出版年
2024年 | 9篇 |
2023年 | 9篇 |
2022年 | 39篇 |
2021年 | 55篇 |
2020年 | 53篇 |
2019年 | 77篇 |
2018年 | 49篇 |
2017年 | 71篇 |
2016年 | 77篇 |
2015年 | 89篇 |
2014年 | 90篇 |
2013年 | 111篇 |
2012年 | 100篇 |
2011年 | 66篇 |
2010年 | 66篇 |
2009年 | 88篇 |
2008年 | 89篇 |
2007年 | 118篇 |
2006年 | 92篇 |
2005年 | 74篇 |
2004年 | 84篇 |
2003年 | 85篇 |
2002年 | 47篇 |
2001年 | 42篇 |
2000年 | 54篇 |
1999年 | 50篇 |
1998年 | 46篇 |
1997年 | 30篇 |
1996年 | 39篇 |
1995年 | 27篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 18篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2073条查询结果,搜索用时 46 毫秒
31.
32.
针对三维地震数据插值,提出采用Laplacian算子进行光滑约束的插值方法,并借鉴Mallet研究的离散光滑插值思路,采用预条件共轭梯度法,直接生成网格节点上的值,从而回避寻求满足插值方程的函数. 为了实现其中Laplacian算子的快速求逆,文中引入Claerbout螺旋坐标系谱因式分解理论. 在螺旋坐标系下,Laplacian算子的表示矩阵具有Toeplitz结构,其快速求逆可由谱法LU分解实现. 基于二维离散光滑插值,文中还给出共轭梯度法与NMO相结合的沿时间切片逐层处理的离散光滑插值流程. 最后,应用该方法对模型数据和实际三维地震数据进行了处理. 相似文献
33.
Masao Komazawa Hitoshi Morikawa Kajuro Nakamura Junpei Akamatsu Keiichi Nishimura Sumio Sawada Ayfer Erken Akin Onalp 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):829-836
The 1999 Kocaeli earthquake brought serious damage to downtown of Adapazari. To study why strong motions were generated at the town, a bedrock structure was investigated on the basis of Bouguer gravity anomaly, and SPAC and H/V analyses of microseisms. It was revealed that, the basin consists of three narrow depressions of bedrock with very steep edges, extending in E–W or NE–SW directions along the North Anatolia faults, and the depth to bedrock reaches 1000 m or more. Downtown of Adapazari is located 1–2 km apart from the basin-edge. It is considered that, the specific configuration of bedrock amplifies ground motions at the downtown area by focusing of seismic waves and/or interference between incident S-waves and surface-waves secondarily generated at the basin-edge. Studying 3D bedrock structure is an urgent issue for microzoning an urban area in a sedimentary basin. 相似文献
34.
35.
In continent Lg is usually one of the predominant phases recorded by short-period or broad-band seismometers. A ray-theoretical approach shows that Lg wave is the superposition of higher-mode surface waves propagating in the continental crust[1—4]. The g… 相似文献
36.
A method, based on the Hilbert–Huang spectral analysis, has been proposed by the authors to identify linear structures in which normal modes exist (i.e., real eigenvalues and eigenvectors). Frequently, all the eigenvalues and eigenvectors of linear structures are complex. In this paper, the method is extended further to identify general linear structures with complex modes using the free vibration response data polluted by noise. Measured response signals are first decomposed into modal responses using the method of Empirical Mode Decomposition with intermittency criteria. Each modal response contains the contribution of a complex conjugate pair of modes with a unique frequency and a damping ratio. Then, each modal response is decomposed in the frequency–time domain to yield instantaneous phase angle and amplitude using the Hilbert transform. Based on a single measurement of the impulse response time history at one appropriate location, the complex eigenvalues of the linear structure can be identified using a simple analysis procedure. When the response time histories are measured at all locations, the proposed methodology is capable of identifying the complex mode shapes as well as the mass, damping and stiffness matrices of the structure. The effectiveness and accuracy of the method presented are illustrated through numerical simulations. It is demonstrated that dynamic characteristics of linear structures with complex modes can be identified effectively using the proposed method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
37.
时间谱电阻率法中的剩余电磁效应研究 总被引:2,自引:0,他引:2
根据频谱激电(SIP)法或复电阻率(CR)法中研究剩余电磁(REM)效应的思想,通过分析时间谱电阻率(TSR)法中场的基本特征,在TSR法中建立了与SIP(或CR)法中参数Φmax/Φ0max相类似的参数-Emax/E0,用来描述了TSR法中的REM效应。通过对一维可极化大地模型的REM效应的理论计算,验证了用Emax/E0表示的REM异常可用来形象地反映地电断面电阻率的高低。 相似文献
38.
39.
40.
The basic concepts of spectral and multiscale selective reconstruction of (geophysically relevant) vector fields on the sphere from error-affected data is outlined in detail. The reconstruction mechanism is formulated under the assumption that spectral as well as multiscale approximation is well-representable in terms of only a certain number of expansion coefficients at the various resolution levels. It is shown that spectral denoising by means of orthogonal expansions in terms of vector spherical harmonics reflects global a priori information of the noise (e.g., in form of a covariance tensor field), whereas multiscale signal-to-noise thresholding can be performed under locally dependent noise information within a multiresolution analysis in terms of spherical vector wavelets. An application of the multiscale formalism to Earth's magnetic field determination is presented. 相似文献