全文获取类型
收费全文 | 203篇 |
免费 | 16篇 |
国内免费 | 48篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 23篇 |
地球物理 | 53篇 |
地质学 | 74篇 |
海洋学 | 24篇 |
天文学 | 20篇 |
综合类 | 24篇 |
自然地理 | 25篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 16篇 |
2012年 | 8篇 |
2011年 | 10篇 |
2010年 | 14篇 |
2009年 | 9篇 |
2008年 | 12篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 8篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1984年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有267条查询结果,搜索用时 15 毫秒
11.
主要研究了分数阶混合随机泛函微分方程的能控性.在无限维空间下,假设所考虑方程线性部分生成半群不是紧的,使用非紧性测度技术和Mönch不动点定理,给出了方程能控性充分条件,并通过一个例子说明了结论的有效性. 相似文献
12.
By virtue of the generalised Hermann--Feynmam theorem we re-derive the energy average formula of photon gas. This is another useful application of the theorem. 相似文献
13.
主要研究了非齐次马氏链的强极限定理.首先应用鞅差序列收敛定理给出了关于非齐次马氏链的任意k元函数一类平均值的极限定理.最后得到一系列相关状态序偶出现频率的推论. 相似文献
14.
Precise, automatic and fast method for vanishing point detection 总被引:1,自引:0,他引:1
A new automated approach for vanishing point detection in images of urban scenes is described. This method is based on the theorem of Thales. The main contribution of this paper is the automatic and simultaneous detection of all vanishing points of the image, achieved by converting this problem into the detection of circles in a complex cloud of points, in which each point corresponds to a segment and is associated with an uncertainty. This extraction of circles uses a RANSAC method, modified to improve its speed by using accumulation techniques (Hough transform or otherwise). This robust estimation is then refined by least squares error propagation using the individual variances of each segment. The algorithm is robust, its accuracy is optimised and it is entirely automatic. Its successful operation has been tested on a large number of images of varied urban scenes. 相似文献
15.
Abstract Experimental investigations of the surface discharge of two-dimensional heated saline jets into surroundings with stable, constant salt gradients were carried out. The discharge conditions were parameterized with the densimetric Froude number, and the Reynolds number. The evolution of the discharge was monitored by flow visualization methods, and by the measurements of temperature and salinity distributions. For comparison, experiments of the surface discharge of heated water into homogeneous surroundings at the corresponding discharge conditions were also conducted. The results clearly showed that while in the former case, the region away from the vicinity of the discharge manifold was marked by the presence of salt-finger convection, in the latter case this region exhibited stable thermal stratification. Furthermore the occurrence of salt-finger convection considerably retarded the motion of the jet, and increased the penetration depth of temperature and salinity fields. 相似文献
16.
本文推广了经典的抽样定理,并据此导出了函数有限离散傅里叶变换误差方程(简称DFT误差方程,下同)。该方程把有限离散傅里叶变换中固有的离散效应和有限效应表示为确切的数学形式。离散效应被表示为一个含整参变量(参变量取0,1,…,N-1)的复无穷级数;有限效应被表示为一个含整参变量(参变量取0,1,…,N-1)的复无穷级数的DFT。 基于DFT误差方程和位函数特点,作者提出了两种位场数值傅里叶变换新算法--移样法和等效源续尾叠样法。移样法可近百倍地提高位场数值傅里叶反变换的精度,等效源续尾叠样法可数十倍地提高正变换精度。两种算法都不需要增加资料长度和取样密度,因而基本不需要增加计算机时间和内存。文中给出了算例。 相似文献
17.
Theoretical background for the inversion of seismic waveforms including elasticity and attenuation 总被引:3,自引:0,他引:3
Albert Tarantola 《Pure and Applied Geophysics》1988,128(1-2):365-399
To account for elastic and attenuating effects in the elastic wave equation, the stress-strain relationship can be defined through a general, anisotropic, causal relaxation function
ijkl
(x, ). Then, the wave equation operator is not necessarily symmetric (self-adjoint), but the reciprocity property is still satisfied. The representation theorem contains a term proportional to the history of strain. The dual problem consists of solving the wave equation withfinal time conditions and an anti-causal relaxation function. The problem of interpretation of seismic waveforms can be set as the nonlinear inverse problem of estimating the matter density (x) and all the functions
ijkl
(x, ). This inverse problem can be solved using iterative gradient methods, each iteration consisting of the propagation of the actual source in the current medium, with causal attenuation, the propagation of the residuals—acting as if they were sources—backwards in time, with anti-causal attenuation, and the correlation of the two wavefields thus obtained. 相似文献
18.
Reciprocity theorem to compute the static deformation due to a point dislocation buried in a spherically symmetric earth 总被引:4,自引:0,他引:4
Shuhei Okubo 《Geophysical Journal International》1993,115(3):921-928
Intriguing reciprocity relations exist between the static deformation excited by a point dislocation in a SNREI earth and those generated by external forces, such as tidal force, surface loading and surface shear forces. Coseismic deformations can be rewritten as follows: (1) potential change in terms of the tide deformation field, (2) radial displacement in terms of the load and tidal deformation fields, and (3) tangential displacement in terms of shear and torsional deformation fields. The relations greatly reduce the effort to compute the coseismic crustal deformation in a spherically symmetric earth. 相似文献
19.
20.
A non-hydrostatic numerical model, the Regional Atmospheric Modeling System (RAMS), has been used to investigate the development of katabatic jumps in Coats Land, Antarctica. In the control run with a 5 m s-1downslope directed initial wind, a katabatic jump develops near the foot of the idealized slope. The jump is manifested as a rapid deceleration of the downslope flow and a change from supercritical to subcritical flow, in a hydraulic sense, i.e., the Froude number (Fr) of the flow changes from Fr > 1 to Fr> 1. Results from sensitivity experiments show that an increase in the upstream flow rate strengthens the jump, while an increase in the downstream inversion-layer depth results in a retreat of the jump. Hydraulic theory and Bernoulli's theorem have been used to explain the surface pressure change across the jump. It is found that hydraulic theory always underestimates the surface pressure change, while Bernoulli's theorem provides a satisfactory estimation. An analysis of the downs balance for the katabatic jump indicates that the important forces are those related to the pressure gradient, advection and, to a lesser extent, the turbulent momentum divergence. The development of katabatic jumps can be divided into two phases. In phase I, the t gradient force is nearly balanced by advection, while in phase II, the pressure gradient force is counterbalanced by turbulent momentum divergence. The upslope pressure gradient force associated with a pool of cold air over the ice shelf facilitates the formation of the katabatic jump. 相似文献