全文获取类型
收费全文 | 839篇 |
免费 | 207篇 |
国内免费 | 321篇 |
专业分类
测绘学 | 25篇 |
大气科学 | 164篇 |
地球物理 | 255篇 |
地质学 | 657篇 |
海洋学 | 157篇 |
天文学 | 9篇 |
综合类 | 46篇 |
自然地理 | 54篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 25篇 |
2021年 | 27篇 |
2020年 | 40篇 |
2019年 | 35篇 |
2018年 | 39篇 |
2017年 | 39篇 |
2016年 | 41篇 |
2015年 | 62篇 |
2014年 | 70篇 |
2013年 | 54篇 |
2012年 | 65篇 |
2011年 | 56篇 |
2010年 | 69篇 |
2009年 | 57篇 |
2008年 | 68篇 |
2007年 | 80篇 |
2006年 | 75篇 |
2005年 | 53篇 |
2004年 | 50篇 |
2003年 | 49篇 |
2002年 | 47篇 |
2001年 | 34篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 27篇 |
1997年 | 22篇 |
1996年 | 21篇 |
1995年 | 22篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1367条查询结果,搜索用时 15 毫秒
351.
Bujang B. K. Huat Faisal Hj. Ali F. H. Choong 《Geotechnical and Geological Engineering》2006,24(6):1527-1544
Residual soils occur in most countries of the world but those that occur in greater area and depth are usually found in the
tropical humid areas. This research examines the effects of loading rate of applied or net mean stress on the volume change
behavior of an unsaturated granitic residual soil. Three loading rates were adopted: fast, slow and extra slow loading rate.
It was observed that the loading rate of applied or net mean stress has a pronounced effect on the void ratio and degree of
saturation but has an insignificant effect on the water content of residual soils subjected to constant matric suction. 相似文献
352.
Hisham T. Eid 《Geotechnical and Geological Engineering》2006,24(6):1695-1713
The influence of sample preparation procedure on the measured classification indices such as clay-size fraction, liquid limit,
and plastic limit of shales was investigated. Shale samples covering a wide range of composition and plasticity were tested
using standard and modified preparation procedures to yield quantitative data required for this investigation. The study specifies
the range of shale plasticity in which the measured values of clay-size fraction and liquid limit are sensitive to hydrometer
specimen size and rehydration time, respectively. The study also revealed that the degree of shale particle disaggregation
has an important influence on the measured clay-size fraction and liquid limit. This influence is maximized for shales with
intermediate plasticity and can be interpreted in terms of particle size and shape. Correlations were established between
classification indices derived from standard and modified sample preparation procedures. It is recommended to use these correlations
to adjust shale classification indices derived from standard sample preparation procedures usually utilized by commercial
laboratories. Such correlations help in creating a universally followed procedure for better estimation of shale engineering
properties and reliable interpretation of case histories involving shale formations. 相似文献
353.
Quantifying Damage, Saturation and Anisotropy in Cracked Rocks by Inverting Elastic Wave Velocities 总被引:1,自引:0,他引:1
Alexandre Schubnel Philip M. Benson Ben D. Thompson Jim F. Hazzard R. Paul Young 《Pure and Applied Geophysics》2006,163(5-6):947-973
Crack damage results in a decrease of elastic wave velocities and in the development of anisotropy. Using non-interactive
crack effective medium theory as a fundamental tool, we calculate dry and wet elastic properties of cracked rocks in terms
of a crack density tensor, average crack aspect ratio and mean crack fabric orientation from the solid grains and fluid elastic
properties. Using this same tool, we show that both the anisotropy and shear-wave splitting of elastic waves can be derived.
Two simple crack distributions are considered for which the predicted anisotropy depends strongly on the saturation, reaching
up to 60% in the dry case. Comparison with experimental data on two granites, a basalt and a marble, shows that the range
of validity of the non-interactive effective medium theory model extends to a total crack density of approximately 0.5, considering
symmetries up to orthorhombic. In the isotropic case, Kachanov's (1994) non-interactive effective medium model was used in
order to invert elastic wave velocities and infer both crack density and aspect ratio evolutions. Inversions are stable and
give coherent results in terms of crack density and aperture evolution. Crack density variations can be interpreted in terms
of crack growth and/or changes of the crack surface contact areas as cracks are being closed or opened respectively. More
importantly, the recovered evolution of aspect ratio shows an exponentially decreasing aspect ratio (and therefore aperture)
with pressure, which has broader geophysical implications, in particular on fluid flow. The recovered evolution of aspect
ratio is also consistent with current mechanical theories of crack closure. In the anisotropic cases—both transverse isotropic
and orthorhombic symmetries were considered—anisotropy and saturation patterns were well reproduced by the modelling, and
mean crack fabric orientations we recovered are consistent with in situ geophysical imaging.
Our results point out that: (1) It is possible to predict damage, anisotropy and saturation in terms of a crack density tensor
and mean crack aspect ratio and orientation; (2) using well constrained wave velocity data, it is possible to extrapolate
the contemporaneous evolution of crack density, anisotropy and saturation using wave velocity inversion as a tool; 3) using
such an inversion tool opens the door in linking elastic properties, variations to permeability. 相似文献
354.
煤矸石浸泡污染物溶解释放规律研究--阜新市新邱露天煤矿不同风化煤矸石在不同固液比条件下浸泡实验 总被引:2,自引:0,他引:2
论文对新邱露天矿不同风化程度的煤矸石在不同固液比条件下溶解释放污染物的规律进行了浸泡实验研究。结果表明:煤矸石溶解释放的主要污染物为总硬度(CaCO3)、硫酸盐(SO42-)、钠(Na )、总溶解性固体(TDS)、氟化物(F-)、耗氧量(OC)和总铁(Fe)等,氯化物(Cl-)、锰(Mn)、锌(Zn)等少量,其它重金属和砷等微量。pH值接近中性。煤矸石风化程度越高,溶解释放的无机盐类污染物量越多,新鲜混合煤矸石溶解释放出较高的氟化物(F-)、耗氧量(OC)和总铁(Fe);固液比对煤矸石中污染物的溶解释放有重要影响。固液比越小,浸泡液中污染物浓度越低,越有利于煤矸石中污染物的溶解释放,单位质量煤矸石溶解释放的污染物量越多,煤矸石中污染物的溶解释放规律受扩散控制;在同一固液比条件下,各污染物浓度变化与浸泡时间成对数曲线关系,即Ct=a bLogt。 相似文献
355.
NUMERICAL STUDY OF REMOTE SENSING OF CLOUD LIQUID WATER CONTENT BY SPACE-BORNE COMBINED RADAR-RADIOMETER*
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A retrieval method of microwave(MW) space-borne remote sensing of cloud liquid water content by the combined radar-radiometer is suggested.A three-layer cloud model is chosen to represent the typical stratified precipitating cloud.The retrieval method mainly follows our previously suggested scheme with some modifications.Numerical comparative study shows that in space-borne remote sensing of cloud liquid water content by the combined method is much better than by radar only;Also the retrieval accuracy of cloud liquid water content may be improved when using the three-layer cloud model in the combined method. 相似文献
356.
近源地震动峰值加速度衰减关系影响因素分析 总被引:6,自引:1,他引:5
本文收集了丰富的强震资料, 以峰值加速度为例, 采用简单且体现近场峰值加速度PGA震级饱和和距离饱和特性的衰减模型, 研究了表征震级与距离饱和效应的R0(M)的性质。R0与震级相关, 同时与震源性质、地震波频谱有关。在单个地震的R0(M)的求取中, 由于R0与系数d几乎呈线性关系, 所以要求单个地震R0的值, 必须先根据理论约束确定d的大小。在检验衰减方程的预测效果时, 不仅要判断衰减曲线是否反映了实测资料的平均变化趋势, 而且要判断实测资料是否绝大多数落在84%及16%概率水平的预测曲线之内(之间). 相似文献
357.
On the dynamical effects of a heterogeneous and compressible liquid core in the theory of Chandler wobble 总被引:1,自引:0,他引:1
The general 3-D scalar equations of motion of the liquid core (with respect to the radial components of displacements and cubic dilatation) are constructed as a superposition of the solutions of ordinary differential equations describing the dynamics of a stably stratified, heterogeneous, compressible and inviscid rotating fluid inside thin spherical layers ( Molodensky & Sasao 1995 ). The estimation of dynamical effects of a homogeneous and incompressible liquid core on the Chandler period (Groten, Lenhardt & Molodensky 1991) is generalized for the case of a heterogeneous, compressible, inviscid and neutrally stratified liquid core. 相似文献
358.
359.
本文研究高层建筑利用调液阻尼器(TLD)减小地震反应的方法。首先探讨了激励频率比、调谐频率比对减震效果的影响。在此基础上建立了具有不同TLD设置方式的高层建筑体系的学模型和运动方程,首次提出了利用多个TLD减小高层建筑多个振型的方法。最后通过数值算例验证了本文方法的有效性。 相似文献
360.
湘中锑矿深源流体的地幔柱成矿演化 总被引:16,自引:0,他引:16
深源流体在地幔柱热驱动下,历经长期壳幔循环,形成高浓度古水热成矿流体,为湘中锑的成矿蓄积丰沛的矿源。 相似文献