全文获取类型
收费全文 | 8229篇 |
免费 | 1398篇 |
国内免费 | 2195篇 |
专业分类
测绘学 | 857篇 |
大气科学 | 1725篇 |
地球物理 | 1670篇 |
地质学 | 3895篇 |
海洋学 | 1505篇 |
天文学 | 400篇 |
综合类 | 743篇 |
自然地理 | 1027篇 |
出版年
2024年 | 72篇 |
2023年 | 169篇 |
2022年 | 402篇 |
2021年 | 447篇 |
2020年 | 436篇 |
2019年 | 420篇 |
2018年 | 441篇 |
2017年 | 391篇 |
2016年 | 473篇 |
2015年 | 442篇 |
2014年 | 496篇 |
2013年 | 553篇 |
2012年 | 549篇 |
2011年 | 571篇 |
2010年 | 494篇 |
2009年 | 486篇 |
2008年 | 441篇 |
2007年 | 421篇 |
2006年 | 363篇 |
2005年 | 343篇 |
2004年 | 275篇 |
2003年 | 210篇 |
2002年 | 225篇 |
2001年 | 241篇 |
2000年 | 240篇 |
1999年 | 275篇 |
1998年 | 236篇 |
1997年 | 220篇 |
1996年 | 215篇 |
1995年 | 189篇 |
1994年 | 183篇 |
1993年 | 154篇 |
1992年 | 141篇 |
1991年 | 127篇 |
1990年 | 86篇 |
1989年 | 83篇 |
1988年 | 65篇 |
1987年 | 52篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 29篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1973年 | 4篇 |
1958年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Lin Y. Hu 《Mathematical Geology》2002,34(8):953-963
Gradual deformation is a parameterization method that reduces considerably the unknown parameter space of stochastic models. This method can be used in an iterative optimization procedure for constraining stochastic simulations to data that are complex, nonanalytical functions of the simulated variables. This method is based on the fact that linear combinations of multi-Gaussian random functions remain multi-Gaussian random functions. During the past few years, we developed the gradual deformation method by combining independent realizations. This paper investigates another alternative: the combination of dependent realizations. One of our motivations for combining dependent realizations was to improve the numerical stability of the gradual deformation method. Because of limitations both in the size of simulation grids and in the precision of simulation algorithms, numerical realizations of a stochastic model are never perfectly independent. It was shown that the accumulation of very small dependence between realizations might result in significant structural drift from the initial stochastic model. From the combination of random functions whose covariance and cross-covariance are proportional to each other, we derived a new formulation of the gradual deformation method that can explicitly take into account the numerical dependence between realizations. This new formulation allows us to reduce the structural deterioration during the iterative optimization. The problem of combining dependent realizations also arises when deforming conditional realizations of a stochastic model. As opposed to the combination of independent realizations, combining conditional realizations avoids the additional conditioning step during the optimization process. However, this procedure is limited to global deformations with fixed structural parameters. 相似文献
962.
对冬季较少出现的天气现象及其引伸的现象的资料处理情况进行概括,有助于台站处理审核原始资料。 相似文献
963.
随着计算机技术的不断进步,用户界面设计---有效的人机交互策略变得更加重要。地理信息系统的发展要求其系统软件的设计者与开发者设计开发出更加人性化的用户界面,以提高不同领域、不同层次软件使用者的满意度。 相似文献
964.
Jialin Zhou Xin Zhang Lin Zhang Fang Dong Erwin Oh 《Geomechanics and Geoengineering》2020,15(3):159-171
ABSTRACT This paper describes compressive static load tests of concrete driven piles confined by Carbon Fibre Reinforced Polymer (CFRP). The tested piles include one concrete pipe pile and one concrete rectangular pile which are all partially confined by CFRP, and other two piles with the same dimensions without CFRP application. Tests program was performed to obtain the behaviours of these composite piles. Four Static Loading Tests (SLTs) were conducted and the results shown that those two types of composite pile demonstrate less vertical displacement with the same loading of traditional concrete piles. Furthermore, the traditional methods of Load-settlement (Q-s) curves, Settlement-lg (Load) (s-lgQ) curves and Settlement-lg (Time) curves are analysed. Due to un-plunging condition, the interpretation methods of Davisson’s, DeBeers, Double-Tangent as well as Chin’s methods are demonstrated for the ultimate bearing capacity of these four piles. It is concluded that the CFRP confinement increased the ultimate bearing capacity and this composite material can be perfectly applied in geotechnical condition. 相似文献
965.
966.
967.
Permafrost on the Qinghai-Tibet Plateau (QTP) is widespread, thin, and thermally unstable. Under a warming climate during the past few decades, it has been degrading extensively with generally rising ground temperatures, the deepening of the maximum summer thaw, and with lessening of the winter frost penetration. The permafrost has degraded downward, upward and laterally. Permafrost has thinned or, in some areas, has totally disappeared. The modes of permafrost degradation have great significance in geocryology, in cold regions engineering and in cold regions environmental management. Permafrost in the interior of the QTP is well represented along the Qing-hai-Tibet Highway (QTH), which crosses the Plateau through north to south and traverses 560 km of permafrost-impacted ground. Horizontally, the degradation of permafrost occurs more visibly in the sporadic permafrost zone in the vicinity of the lower limit of permafrost (LLP), along the margins of taliks, and around permafrost islands. Downward degradation develops when the maximum depth of seasonal thaw exceeds the maximum depth of seasonal frost, and it generally results in the formation of a layered talik disconnecting the permafrost from the seasonal frost layer. The downward degrada- tion is divided into four stages: 1) initial degradation, 2) accelerated degradation, 3) layered talik and 4) finally the conversion of permafrost to seasonally frozen ground (SFG). The upward degradation occurs when the geothermal gradient in permafrost drops to less than the geothermal gradients in the underlying thawed soil layers. Three types of permafrost temperature curves (stable, degrading, and phase-changing transitory permafrost) illustrate these modes. Although strong differentiations in local conditions and permafrost types exist, the various combinations of the three degradation modes will ultimately transform permafrost into SFG. Along the QTH, the downward degradation has been proceeding at annual rates of 6 to 25 cm, upward degradation at 12 to 30 cm, and lateral degradation in the sporadic permafrost zone at 62 to 94 cm during the last quarter century. These rates exceed the 4 cm per year for the past 20 years reported for the discontinuous permafrost zone in subarctic Alaska, the 3 to 7 cm per year reported in Mongolia, and that of the thaw-stable permafrost in subarctic Yakutia and Arctic Alaska. 相似文献
968.
969.
基于自适应四叉树分割的遥感图像压缩算法 总被引:6,自引:0,他引:6
遥感图像具有不同于一般图像的特点,针对遥感图像对压缩算法的特殊要求,提出了自适应四叉树分割算法实现图像的分块,以各像块的均值近似表示该像块的灰度值,从而以尺量少的数值获得对原始图像的最佳逼近,再对辐近误差进行自适应分割和基于像块方差的自适应量化,最后对各分量进行Huffman编码.实验表明,本算法能表现出良好的实用性能,比JPEG算法更适用于遥感图像的压缩. 相似文献