全文获取类型
收费全文 | 3016篇 |
免费 | 537篇 |
国内免费 | 703篇 |
专业分类
测绘学 | 378篇 |
大气科学 | 456篇 |
地球物理 | 1298篇 |
地质学 | 1045篇 |
海洋学 | 539篇 |
天文学 | 82篇 |
综合类 | 201篇 |
自然地理 | 257篇 |
出版年
2024年 | 1篇 |
2023年 | 35篇 |
2022年 | 66篇 |
2021年 | 80篇 |
2020年 | 97篇 |
2019年 | 115篇 |
2018年 | 98篇 |
2017年 | 120篇 |
2016年 | 129篇 |
2015年 | 157篇 |
2014年 | 147篇 |
2013年 | 209篇 |
2012年 | 171篇 |
2011年 | 178篇 |
2010年 | 176篇 |
2009年 | 211篇 |
2008年 | 212篇 |
2007年 | 239篇 |
2006年 | 223篇 |
2005年 | 200篇 |
2004年 | 175篇 |
2003年 | 152篇 |
2002年 | 128篇 |
2001年 | 112篇 |
2000年 | 116篇 |
1999年 | 94篇 |
1998年 | 113篇 |
1997年 | 68篇 |
1996年 | 59篇 |
1995年 | 66篇 |
1994年 | 63篇 |
1993年 | 53篇 |
1992年 | 42篇 |
1991年 | 31篇 |
1990年 | 32篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有4256条查询结果,搜索用时 15 毫秒
81.
滑坡定量预测的非线性理论方法 总被引:19,自引:0,他引:19
滑坡时空预测是当前滑坡研究中的难题,特别是滑坡时间预测工作,其进展缓慢。本文基于非线性科学理论,分析了滑坡活动的分形特征及时间分形预测方法,研究了滑坡空间预测的人工神经网络特征,系统介绍了滑坡时间预测的非线性动力学理论。在此基础上,讨论了滑坡定量预测的发展趋势。 相似文献
82.
模拟退火剩余静校正的一步算法 总被引:1,自引:1,他引:1
当地震资料的剩余静校正量大、信噪比低时,利用传统的线性反演方法不能有效地拾取静校正量。本文介绍一种非线性反演方法(一步模拟退火法)来估算炮点和检波点的剩余静校正量。通过对合成地震记录的试算表明,该算法可获得近似于真实的剩余静校正量。 相似文献
83.
判定地下水二维水动力弥散参数的直线图解法 总被引:1,自引:0,他引:1
弥散参数的求得,是正确认识地下水污染运移及对其控制的前提。本文根据极值理论和非线性方程线性化手段,导出了浓度和时间变化的线性关系,得出了确定弥散参数的直线图解法。它可以弥补其它方法的不足。借用实际弥散试验资料对其进行了检验,表明所建数学模型与实际模型之间吻合良好,即所求得的参数结果可信。 相似文献
84.
Oscillation and numerical dispersion limit the reliability of numerical solutions of the convection-dispersion equation when finite difference methods are used. To eliminate oscillation and reduce the numerical dispersion, an optimal upstream weighting with finite differences is proposed. The optimal values of upstream weighting coefficients numerically obtained are a function of the mesh Peclet number used. The accuracy of the proposed numerical method is tested against two classical problems for which analytical solutions exist. The comparison of the numerical results obtained with different numerical schemes and those obtained by the analytical solutions demonstrates the possibility of a real gain in precision using the proposed optimal weighting method. This gain in precision is verified by interpreting a tracer experiment performed in a laboratory column. 相似文献
85.
86.
This paper designs three quasi-geostrophic barotropic models with a radial/horizontal grid length being 2 kin,one in the polar coordinates,one on a stationary typhoon circulation condition and another on a non-stationary typhoon circulation condition in the Cartesian coordinates,to investigate the effects of azimuthal and radial linear advections,and nonlinear advection on the inward propagation of mesoscale vorticity and the changes of typhoon intensity.Results show that the azimuthal linear advection may result in the formation of spiral vorticity bands;the radial linear advection in a certain parameter set is able to transfer vorticity inwards,leading to a slight enhancement of typhoon;the nonlinear advection of perturbation vorticity on a stationary typhoon circulation condition may transfer more vorticities inwards,thus resulting in a distinct enhancement of typhoon;and the nonlinear advection on a non-stationary typhoon circulation condition possesses duality,i.e.on the one hand,the advection increases the vorticity of inward propagation,thus favorable to the intensification of typhoon,and on the other hand,in the inward propagation process of vorticity the originally concentric and axisymmetric structure of typhoon basic flow is damaged,and a complex flow pattern forms,which in turn tends to weaken the circulation of typhoon.At last the paper discusses the possible applications of those results in typhoon intensity prediction. 相似文献
87.
A Simple Parameterisation for Flux Footprint Predictions 总被引:9,自引:6,他引:9
Flux footprint functions estimate the location and relative importance of passive scalar sources influencing flux measurements
at a given receptor height. These footprint estimates strongly vary in size, depending on receptor height, atmospheric stability,
and surface roughness. Reliable footprint calculations from, e.g., Lagrangian stochastic models or large-eddy simulations
are computationally expensive and cannot readily be computed for long-term observational programs. To facilitate more accessible
footprint estimates, a scaling procedure is introduced for flux footprint functions over a range of stratifications from convective
to stable, and receptor heights ranging from near the surface to the middle of the boundary layer. It is shown that, when
applying this scaling procedure, footprint estimates collapse to an ensemble of similar curves. A simple parameterisation
for the scaled footprint estimates is presented. This parameterisation accounts for the influence of the roughness length
on the footprint and allows for a quick but precise algebraic footprint estimation. 相似文献
88.
F. Nguyen G. Van Rompaey H. Teerlynck M. Van Camp D. Jongmans T. Camelbeeck 《Journal of Seismology》2004,8(1):41-56
To provide quantitative information on site effects in the northern part of Belgium, forty-seven H/V microtremor measurements were performed with 5 second seismometers over an area of about 15.000 km2. Most of the results show a northward regular increase of the fundamental period in agreement with the augmentation of the Mesozoic and Cainozoic soft sedimentsthickness from a few meters 40 km south of Brussels to 900 m at the Netherlands-Belgium border. The measured resonance frequency values wereconsistent with theoretical computations performed at different sites onthe basis of existing information and shallow seismic experiments. At oneparticular site (Uccle) where borehole data were available, microtremor measurements using an array of four seismological stations with differentapertures allowed to obtain the low frequency part of the Rayleigh wave dispersion curve, extending the range covered by the analysis of surfacewaves artificially generated. The Vs profile derived from the surface waveinversion corroborates the 1 Hz natural frequency of the site. Comparison of these results with the macroseismic information concerning the MS = 5.0 1938 earthquake which occurred 50 km west of Brussels,confirmed the hypothesis that the geological structure of the Brabant massifis likely to control damage distribution during such an earthquake. Comparisonbetween the intensity map of the 1938 earthquake and the resonance period ofsediments obtained by our microtremor study shows a clear relation betweenthe two parameters. During the 1938 earthquake, site effects played a prominent role due to the dimension of the source whose corner frequency wasabout 1 Hz. 相似文献
89.
Field vibration mitigation by honeycomb WIB for pile foundations of a high-speed train viaduct 总被引:5,自引:0,他引:5
Environmental vibrations from recent high-speed trains are becoming a special concern in the civil and environmental engineering field since they can give detrimental effects to residents, sensitive equipments and high-tech production facilities in the vicinity of train tacks. Herein, aiming at the vibration mitigation for a specific high-tech industrial area, the low-frequency vibrations from a train viaduct are targeted over an anticipated range. A theoretically designed innovative countermeasure, called honeycomb wave impeding barrier (WIB) for a wave impeding barrier, is introduced and its effects are investigated by computer simulation. The present WIB is based on the wave dispersion phenomenon that can modulate the incoming wavelengths into the shorter wavelengths, creating an apparent wave cut-off characteristic in the wave field across WIB installation area. The shorter wavelengths are further impeded due to the impedance ratio of the WIB walls and in-fill materials and absorbed by the in-fills more. The three-dimensional FEM simulation demonstrates a dramatic reduction effect that is difficult to achieve by conventional measures. 相似文献
90.
Shi Shuzhong 《中国地震研究》2004,18(2):105-113
Based on intensity data in Shanghai and its adjacent region, the intensity attenuation relation is determined. Selecting the western United States as a reference area where there are rich strong ground motion records and intensity data, and by determining ground motion attenuation relation in an area lacking in strong ground motion data, we obtain the ground motion attenuation relation in Shanghai and its adjacent region. 相似文献