全文获取类型
收费全文 | 6732篇 |
免费 | 1447篇 |
国内免费 | 2435篇 |
专业分类
测绘学 | 1303篇 |
大气科学 | 1078篇 |
地球物理 | 1211篇 |
地质学 | 4370篇 |
海洋学 | 1102篇 |
天文学 | 86篇 |
综合类 | 589篇 |
自然地理 | 875篇 |
出版年
2024年 | 54篇 |
2023年 | 143篇 |
2022年 | 382篇 |
2021年 | 473篇 |
2020年 | 354篇 |
2019年 | 483篇 |
2018年 | 455篇 |
2017年 | 397篇 |
2016年 | 468篇 |
2015年 | 439篇 |
2014年 | 500篇 |
2013年 | 588篇 |
2012年 | 585篇 |
2011年 | 611篇 |
2010年 | 619篇 |
2009年 | 558篇 |
2008年 | 548篇 |
2007年 | 535篇 |
2006年 | 494篇 |
2005年 | 359篇 |
2004年 | 293篇 |
2003年 | 228篇 |
2002年 | 206篇 |
2001年 | 219篇 |
2000年 | 174篇 |
1999年 | 99篇 |
1998年 | 58篇 |
1997年 | 58篇 |
1996年 | 44篇 |
1995年 | 29篇 |
1994年 | 25篇 |
1993年 | 26篇 |
1992年 | 33篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1957年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
521.
宝泉滑坡体方量巨大 ,且处于宝泉抽水蓄能电站工程的关键部位。通过极限平衡法和三维有限元模拟计算 ,模拟了宝泉滑坡体的稳定性和工程处理方案。削坡减载是工程处理的最有效措施。将滑坡体开挖至 770m高程后 ,滑坡体稳定性将大大提高 ,即使在Ⅶ度地震条件下仍将保持稳定。 相似文献
522.
The Upper Permian Sedimentary Facies and Its Role in the Dajing Cu-Sn Deposit, Linxi County, Inner Mongolia, China 总被引:3,自引:1,他引:3
Gongjiong QIN Yosuke KAWACHI Liqing ZHAO Yongzheng WANG Qiang OU 《Resource Geology》2001,51(4):293-305
Abstract: Exhaustive investigations were launched for confirming the upper Permian host rocks of the Dajing Cu-Sn Deposit, probing into the possibility that Dajing is a Sedex type deposit during cosedimentation, complementing the deficiency of previous researches and going further into substantiating the role of the upper Permian strata in the control of ore distribution. After more than two years work, we reclassified the sedimentary facies in the Dajing area and its periphery as shallow fresh water lake and delta. Indicative sedimentary structures, such as ripple marks, rain marks, and mud cracks combined with contemporary fossils, were revealed. Having measured the flow directions, performed chemical comparison, and analyzed various sediments from sourceland in the Dajing area by XRF, we consequently redivided the strata into four sedimentary members, among which P2 l1 and P2 l2 were concluded as significant ore-hosted strata. The upper Permian basin was a lateral rift basin. The water and sediments in the basin are much deeper and thicker in the north than those in the south.
The indicators of special sedimentary facies, such as gravity flow, brine pool and synchronogenic stratiform structure of the ore cannot be found in the Dajing area. There was no growth fault, assemblage of sulfide and sulfate, and no zonation as well.
On the basis of study in this area, taking into account the paleosedimentary environment as capriciously flowing shallow lake, which approximated the state of oxidation, we figured that the paleogeography made it prohibitively difficult to form stratiform sulfide deposits which are prone to form in deoxidized environment. It can be ruled out the possibility that the Dajing deposit is a syngenetic deposit during sedimentation. 相似文献
The indicators of special sedimentary facies, such as gravity flow, brine pool and synchronogenic stratiform structure of the ore cannot be found in the Dajing area. There was no growth fault, assemblage of sulfide and sulfate, and no zonation as well.
On the basis of study in this area, taking into account the paleosedimentary environment as capriciously flowing shallow lake, which approximated the state of oxidation, we figured that the paleogeography made it prohibitively difficult to form stratiform sulfide deposits which are prone to form in deoxidized environment. It can be ruled out the possibility that the Dajing deposit is a syngenetic deposit during sedimentation. 相似文献
523.
524.
THE CHARACTERS OF ENERGY BUDGET ON THE GOBI AND DESERT SURFACE IN HEXI REGION 总被引:23,自引:0,他引:23
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)
In the paper,the characters of surface energy budget on Huayin(Gobi)and the desert surface during the periodfrom 26 June to 31 August 1990 in the HEIFE have been analyzed,then have been compared with the observed resultsduring 4—19 September 1988 in the Pilot Observation Period of the HEIFE.The results show that the atmosphere is insuperadiabatic unstable state and there is a phenomenon of inverse humidity to form negative water vapour flux.Thesensible heat flux on the surface energy budget is in majority,but the latent heat flux may be neglected over the Gobi anddesert surface in the cloudless daytime in the summer. 相似文献
525.
In the paper,the characters of surface energy budget on Huayin(Gobi)and the desert surface during the period from 26 June to 31 August 1990 in the HEIFE have been analyzed,then have been compared with the observed results during 4-19 September 1988 in the Pilot Observation Period of the HEIFE.The results show that the atmosphere is in superadiabatic unstable state and there is a phenomenon of inverse humidity to form negative water vapour flux.The sensible heat flux on the surface energy budget is in majority,but the latent heat flux may be neglected over the Gobi and desert surface in the cloudless daytime in the summer. 相似文献
526.
527.
528.
Many observations and studies indicate that pore fluid pressure in the crustal rocks plays an important role in deformation, faulting, and earthquake processes. Conventional models of pore pressure effects often assume isotropic porous rocks and yield the nondeviatoric pressure effects which seem insufficient to explain diverse phenomena related to pore pressure variation, such as fluid-extraction induced seismicity and crustal weak faults. We derive the anisotropic effective stress law especially for transversely-isotropic and orthotropic rocks, and propose that the deviatoric effects of pore fluid pressure in anisotropic rocks not only affect rock effective strength but also cause variation of shear stresses. Such shear stress variations induced by either pore pressure buildup or pore pressure decline may lead to faulting instability and trigger earthquakes, and provide mechanisms for the failure of crustal weak faults with low level of shear stresses. We believe that the deviatoric effects of pore fluid pressure in anisotropic rocks are of wide application in studies of earthquake precursors and aftershocks, oil and gas reservoir characterization, enhanced oil recovery, and hydraulic fracturing. 相似文献
529.
突变理论在工程地质中的应用 总被引:28,自引:2,他引:28
本文说明了突变理论应用于工程地质中的一般方法。着重通过实例介绍尖点突变理论在工程地质中的应用现状,其中包括用突变理论评价层状结构斜坡、地下洞室的顶板冒落及活断层的稳定性,以及斜坡失稳的时间预报等问题。同时对其应用前景作了展望。 相似文献
530.
刘宝珺 余光明 徐强 G. Einsele W. Frisch 刘光华 J. Wendt A. Wetzel L. Ratschbacher H. P. Luterbacher 《沉积与特提斯地质》1993,(1):32-49
通过对喜马拉雅三叠纪到第三纪区域沉积特征分析,阐明了雅鲁藏布喜马拉雅特提斯造山带从裂谷—被动大陆边缘—前陆盆地的沉积盆地演化史。随着以雅鲁藏布带为代表的喜马拉雅特提斯打开,三叠纪到早侏罗世为特提斯早期裂开的大陆边缘裂谷盆地。早期裂谷中心部位不是现在大陆缝合线的雅鲁藏布一带,而在低分水岭带。晚侏罗世到早白垩世,雅鲁藏布江南测为典型被动大陆边缘,其沉积盆地沉降、海平面变化与沉积作用相吻合。晚白垩世到第三纪为前陆盆地演化阶段,从沉积作用可以识别出晚白垩世晚期为造山第一暮,第三纪初为第二幕。 相似文献