全文获取类型
收费全文 | 250篇 |
免费 | 60篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 70篇 |
大气科学 | 9篇 |
地球物理 | 108篇 |
地质学 | 20篇 |
海洋学 | 23篇 |
天文学 | 31篇 |
综合类 | 8篇 |
自然地理 | 50篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 1篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 9篇 |
2013年 | 12篇 |
2012年 | 9篇 |
2011年 | 8篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 14篇 |
2005年 | 26篇 |
2004年 | 11篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 13篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有319条查询结果,搜索用时 15 毫秒
61.
2002年在京津冀地区进行了45个测点的地磁三分量测量,对测量资料进行通化处理,通化时间为2002年5月5日16~18时(世界时). 通化后的观测均方差分别优于1.5nT(地磁场总强度F),0.5′(磁偏角D和磁倾角I). 将国际参考地磁场(IGRF2000)作为地磁正常场,建立了京津冀地区地磁异常场的球冠谐模型(BTHASCH). 球冠极的空间位置坐标为39.5°N和117.0°E,球冠半角为4°. 在模型计算过程中,球冠谐函数的截断阶数分别取为1~10. 经综合比较, 最终采用的截断阶数为5. 建立了京津冀地区参考地磁场的球冠谐模型(BTHGRF).根据模型,绘制了京津冀地区地磁异常场图(ΔX、ΔY、ΔZ、ΔF、ΔD、ΔI)和京津冀地区地磁图(X、Y、Z、F、D、I). 相似文献
62.
The aim of this paper is to understand the seismic anisotropy of the overburden shale in an oilfield in the North West Shelf of Western Australia. To this end, we first find the orientation of the symmetry axis of a spherical shale sample from measurements of ultrasonic P‐wave velocities in 132 directions at the reservoir pressure. After transforming the data to the symmetry axis coordinates, we find Thomsen's anisotropy parameters δ and ? using these measurements and measurements of the shear‐wave velocity along the symmetry axis from a well log. To find these anisotropy parameters, we use a very fast simulated re‐annealing algorithm with an objective function that contains only the measured ray velocities, their numerical derivatives and the unknown elasticity parameters. The results show strong elliptical anisotropy in the overburden shale. This approach produces smaller uncertainty of Thomsen parameter δ than more direct approaches. 相似文献
63.
球体位错理论计算程序的总体设计与具体实现 总被引:3,自引:0,他引:3
本文详细介绍了球体位错理论计算程序的总体设计思想、 各类配套文件的具体内涵以及各类输出文件的物理含义, 同时介绍了程序的使用方法和注意事项, 为读者独立使用该程序提供参考。 球体位错理论计算程序主要由三部分组成: ① 位错格林函数计算程序, 基于具体的球对称地球模型提供离散的二维格林函数数值框架; ② 积分计算程序, 对离散的格林函数数值框架进行双二次样条插值运算, 并对四类独立位错源对应的格林函数进行适当组合, 从而计算出任意位置任意类型震源在地表产生的同震变形(含位移、 应变、 重力变化和大地水准面变化); ③ 辅助文件, 用于提供发震断层模型和计算点位信息。 一般情况下, 读者不需要理解位错格林函数计算程序和积分计算程序, 只需要对辅助文件提供的信息进行针对性改动, 就可以计算目标地震在目标观测站引起的同震变形。 相似文献
64.
针对目前地基GNSS台站在全球分布不均匀,导致南半球海洋和中高纬地区出现与实际不符的VTEC为负值的问题,利用IGS前1 d的最终GIM作为虚拟观测值对TEC可能为负值的地区进行约束,结合GNSS数据建立全球电离层模型(称为SGG模型),并用2014年200多个IGS台站数据对模型进行验证。结果表明,各台站VTEC的RMS优于3 TECu(赤道异常区域RMS在5~7 TECu)。同时SGG能有效消除南半球海洋(40°~90°S)VTEC为负的情况,且对原有非负VTEC几乎没有影响(其变化小于2 TECu)。SGG的卫星DCB与CODE 相比,RMS和MEAN分别优于0.2 ns和0.04 ns,不同纬度带SGG与CODE的接收机DCB估值变化基本一致,两者之差基本在1 ns以内。 相似文献
65.
A variable mesh finite element model of the Irish and Celtic Sea regions with/without the inclusion of the Mersey estuary is used to examine the influence of grid resolution and the Mersey upon the higher harmonics of the tide in the region. Comparisons are made with observations and published results from finite difference models of the area. Although including a high resolution representation of the Mersey had little effect upon computed tides in the western Irish Sea it had a significant effect upon tidal currents in the eastern Irish Sea. In addition the higher harmonics of the M2 tide in near-shore regions of the eastern Irish Sea particularly the Solway and Mersey estuary together with Morecambe Bay showed significant small scale variability. The Mersey was used to test the sensitivity to including estuaries because high resolution accurate topography was available. The results presented here suggest that comparable detailed topographic data sets are required in all estuaries and near-shore regions. In addition comparisons clearly show the need for an unstructured grid model of the region that can include all the estuaries. Such an unstructured grid solution was developed here within a finite element approach, although other methods in particular the finite volume, or coordinate transformations/curvilinear grids and nesting could be applied. 相似文献
66.
Nonmodal growth (NG) and unstable normal mode growth are considered in spherical geometry. Two groups of initial conditions (IC) are studied: "connected" IC (common in Cartesian studies) and "separated" IC (based on observed conditions prior to cyclogenesis). Time series of growth rates are emphasized in conjunction with eigenmode projections. Projections show that early on normal mode growth was much stronger for connected IC and that NG caused negative growth early on of some variables for separated IC. Projections explain why amplitude, kinetic energy (KE), and potential vorticity have more NG than available potential energy (APE). Though varying between ICs and with initial phase shift, NG increases with wavenumber. For middle wavelengths, NG is significant and positive using connected IC but negative or small using separated IC. Total energy and KE growth rates of short waves are very similar during the first 2 days for both ICs. Amplitude time series closely follow KE in all cases studied. APE has less overlap than does KE between the main modes present, so less NG occurs for APE than for KE. In separated IC cases, APE growth rates evolve consistent with emergence of an unstable normal mode and little NG. 相似文献
67.
The Cartesian moments of the mass density of a gravitating body and the spherical harmonic coefficients of its gravitational
field are related in a peculiar way. In particular, the products of inertia can be expressed by the spherical harmonic coefficients
of the gravitational potential as was derived by MacCullagh for a rigid body. Here the MacCullagh formulae are extended to
a deformable body which is restricted to radial symmetry in order to apply the Love–Shida hypothesis. The mass conservation
law allows a representation of the incremental mass density by the respective excitation function. A representation of an
arbitrary Cartesian monome is always possible by sums of solid spherical harmonics multiplied by powers of the radius. Introducing
these representations into the definition of the Cartesian moments, an extension of the MacCullagh formulae is obtained. In
particular, for excitation functions with a vanishing harmonic coefficient of degree zero, the (diagonal) incremental moments
of inertia also can be represented by the excitation coefficients. Four types of excitation functions are considered, namely:
(1) tidal excitation; (2) loading potential; (3) centrifugal potential; and (4) transverse surface stress. One application
of the results could be model computation of the length-of-day variations and polar motion, which depend on the moments of
inertia.
Received: 27 July 1999 / Accepted: 24 May 2000 相似文献
68.
G. Metris P. Exertier Y. Boudon F. Barlier 《Celestial Mechanics and Dynamical Astronomy》1993,57(1-2):175-188
The main effects of tesseral harmonics of a gravity potential expansion on the motion of a satellite, are short period variations as well as long period variations due to resonances. However, other smaller long period and secular variations can arise from interactions between tesseral terms of the same order. The analytical integration of these effects is developed, using numerical evaluation of Kaula eccentricity and inclination functions. Examples for some Earth's geodetic satellites show that secular effects can reach a few decameters per year. The secular variations can even reach several hundred of meters per year for the Mars natural satellite Phobos. 相似文献
69.
J. A. López Ortí A. López García R. López Machí 《Celestial Mechanics and Dynamical Astronomy》1992,53(4):311-322
The equilibrium configurations of close binary systems are analyzed. The autogravitational, centrifugal and tidal potentials are expanded in Clairaut's coordinates. From the set of the total potential angular terms an integral equations system is derived. The reduction of them to ordinary differential equations and the determination of the boundary conditions allow a formulation of the problem in terms of a single variable. 相似文献
70.
V. M. Hamza R. R. Cardoso C. F. Ponte Neto 《International Journal of Earth Sciences》2008,97(2):205-226
A reappraisal of the international heat flow database has been carried out and the corrected data set was employed in spherical
harmonic analysis of the conductive component of global heat flow. Procedures used prior to harmonic analysis include analysis
of the heat flow data and determination of representative mean values for a set of discretized area elements of the surface
of the earth. Estimated heat flow values were assigned to area elements for which experimental data are not available. However,
no corrections were made to account for the hypothetical effects of regional-scale convection heat transfer in areas of oceanic
crust. New sets of coefficients for 12° spherical harmonic expansion were calculated on the basis of the revised and homogenized
data set. Maps derived on the basis of these coefficients reveal several new features in the global heat flow distribution.
The magnitudes of heat flow anomalies of the ocean ridge segments are found to have mean values of less than 150 mW/m2. Also, the mean global heat flow values for the raw and binned data are found to fall in the range of 56–67 mW/m2, down by nearly 25% compared to the previous estimate of 1993, but similar to earlier assessments based on raw data alone.
To improve the spatial resolution of the heat flow anomalies, the spherical harmonic expansions have been extended to higher
degrees. Maps derived using coefficients for 36° harmonic expansion have allowed identification of new features in regional
heat flow fields of several oceanic and continental segments. For example, lateral extensions of heat flow anomalies of active
spreading centers have been outlined with better resolution than was possible in earlier studies. Also, the characteristics
of heat flow variations in oceanic crust away from ridge systems are found to be typical of conductive cooling of the lithosphere,
there being little need to invoke the hypothesis of unconfined hydrothermal circulation on regional scales. Calculations of
global conductive heat loss, compatible with the observational data set, are found to fall in the range of 29–34 TW, nearly
25% less than the 1993 estimate, which rely on one-dimensional conductive cooling models. 相似文献