全文获取类型
收费全文 | 4468篇 |
免费 | 903篇 |
国内免费 | 1241篇 |
专业分类
测绘学 | 300篇 |
大气科学 | 789篇 |
地球物理 | 1141篇 |
地质学 | 2155篇 |
海洋学 | 905篇 |
天文学 | 236篇 |
综合类 | 605篇 |
自然地理 | 481篇 |
出版年
2024年 | 33篇 |
2023年 | 68篇 |
2022年 | 206篇 |
2021年 | 237篇 |
2020年 | 224篇 |
2019年 | 248篇 |
2018年 | 313篇 |
2017年 | 273篇 |
2016年 | 284篇 |
2015年 | 217篇 |
2014年 | 270篇 |
2013年 | 264篇 |
2012年 | 354篇 |
2011年 | 305篇 |
2010年 | 296篇 |
2009年 | 280篇 |
2008年 | 227篇 |
2007年 | 251篇 |
2006年 | 201篇 |
2005年 | 189篇 |
2004年 | 131篇 |
2003年 | 124篇 |
2002年 | 96篇 |
2001年 | 109篇 |
2000年 | 157篇 |
1999年 | 213篇 |
1998年 | 145篇 |
1997年 | 169篇 |
1996年 | 120篇 |
1995年 | 110篇 |
1994年 | 103篇 |
1993年 | 98篇 |
1992年 | 69篇 |
1991年 | 53篇 |
1990年 | 45篇 |
1989年 | 31篇 |
1988年 | 20篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1958年 | 4篇 |
1957年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有6612条查询结果,搜索用时 15 毫秒
131.
珊瑚礁工程地质研究的内容和方法 总被引:3,自引:0,他引:3
珊瑚礁工程地质研究的主要内容为珊瑚礁自然地质条件、珊瑚礁岩土物理力学性质和珊瑚礁混凝土料问题。除了通常的工程地质研究方法外, 着重介绍珊瑚礁工程地质研究的钻探、触探和地球物理勘测方法。 相似文献
132.
地球内核快速旋转的发现与全球变化的轨道效应 总被引:3,自引:0,他引:3
科里奥利效应是产生内核快速旋转的主要原因。科氏力使上升物质向西漂移,下降物质向东漂移;造成地球外层自转减速,地球内层自转加速。所以,自旋体中的垂直运动可以产生大规模的水平运动——圈层差异旋转。地震波测量结果表明,内核旋转速度每年比地壳地幔快1°。对于一个内核差异旋转的地球,太阳辐射不仅形成地磁场的内外磁尾和地壳与内核的反向振动,而且影响核幔角动量交换和电磁耦合,从而控制了地球内能的释放,形成天文周期与地质旋回的一一对应关系。地球轨道和太阳轨道的全球变化响应,为太阳辐射量变化控制地球内能释放提供了证据 相似文献
133.
物探方法在岩溶勘查中的应用综述 总被引:7,自引:0,他引:7
简要介绍了岩溶勘察中常用物探方法的基本原理和技术,并举例说明其在岩溶地区进行水利水电工程地质勘察、岩溶地下水寻找、环境保护和溶洞探测时的有效性。 相似文献
134.
135.
Kela 2 Gas Field, with high formation pressure (74.35MPa), high pressure coefficient (2.022) and difficulty of potential test and evaluation, is the largest integrated proved dry gas reservoir in China so far and the principal source for West-East Gas Development Project. In order to correctly evaluate the elastic-plastic deformation of rocks caused by the pressure decline during production, some researches, as the experiment on reservoir sensitivity to stress of gas filed with abnormal high pressure, are made. By testing the rock mechanic properties, porosities and permeabilities at different temperature and pressure of 342 core samples from 5 wells in this area, the variations of petro-physical properties at changing pressure are analyzed, and the applicable inspection relationship is concluded. The average productivity curve with the reservoir sensitivity to stress is plotted on the basis of the research, integrated with the field-wide productivity equation. The knowledge lays a foundation for the gas well productivity evaluation in the field and the gas field development plan, and provides effective techniques and measures for basic research on the development of similar gas fields. 相似文献
136.
Introduction Based on the elastic theory of the hard inclusion (Dobrovolskii, 1991), we developed an inclusion theory of rheologic medium, and applied the results of bulk-strain field of a rheologic inclusion model to explain the spatial-temporal evolution process of earthquake precursors (SONG, et al, 2000). In the former paper (SONG, et al, 2003), we derived the viscoelastic displacement field of the rheologic inclusion model on the basis of the analytic expression of displacement field o… 相似文献
137.
Seepage driving effect on deformations of San Fernando dams 总被引:2,自引:0,他引:2
In the process of flow deformation of an earth dam, the seepage force inside the dam plays a role as a driving force. The seepage force acts just like the gravitational force in terms of pushing soils away from their original locations after liquefaction is triggered. This paper draws attention to this seepage driving effect by presenting a set of fully coupled finite element analyses on the well-known San Fernando dams, with the objective of evaluating the impact of this seepage effect. The results indicate that while this effect is always there, its practical significance depends on a number of factors. In the case of the upper San Fernando dam, which experienced a significant, but restricted, downstream movement during the 1971 earthquake, the seepage driving effect was indeed significant. On the contrary, for the lower dam, which failed and slid into the upstream reservoir during the same earthquake, this seepage effect was relatively less pronounced. The detailed results of the analyses reveal the likely mechanisms of failure and deformation of the two dams and the likely cause behind the difference between their responses during the earthquake. 相似文献
138.
Cross-sensor calibration between Ikonos and Landsat ETM+ for spectral mixture analysis 总被引:1,自引:0,他引:1
Conghe Song 《Geoscience and Remote Sensing Letters, IEEE》2004,1(4):272-276
Spectral mixture analysis is an algorithm that is developed to overcome the weakness in traditional land-use/land-cover (LULC) classification where each picture element (pixel) from remote sensing is assigned to one and only one LULC type. In reality, a remotely sensed signal from a pixel is often a spectral mixture from several LULC types. Spectral mixture analysis can derive subpixel proportions for the endmembers from remotely sensed data. However, one frequently faces the problem in determining the spectral signatures for the endmembers. This study provides a cross-sensor calibration algorithm that enables us to obtain the endmember signatures from an Ikonos multispectral image for spectral mixture analysis using Landsat ETM+ images. The calibration algorithm first converts the raw digital numbers from both sensors into at-satellite reflectance. Then, the Ikonos at-satellite reflectance image is degraded to match the spatial resolution of the Landsat ETM+ image. The histograms at the same spatial resolution from the two images are matched, and the signatures from the pure pixels in the Ikonos image are used as the endmember signatures. Validation of the spectral mixture analysis indicates that the simple algorithm works effectively. The algorithm is not limited to Ikonos and Landsat sensors. It is, in general, applicable to spectral mixture analysis where a high spatial resolution sensor and a low spatial resolution sensor with similar spectral resolutions are available as long as images collected by the two sensors are close in time over the same place. 相似文献
139.
顶空气相色谱法测定地层水中的苯系物 总被引:10,自引:2,他引:10
利用极性聚乙二醇弹性石英毛细管柱分离苯系物,在线顶空气相色谱法测定地层水中的苯系物。讨论了色谱柱、载气压力、液相体积、顶空压力、顶空加热温度等因素对测定的影响。该方法实现了地层水中苯、甲苯、乙苯、对二甲苯、间二甲苯、邻二甲苯、异丙苯、苯乙烯等各组分的完全分离,方法的检出限在0.07—0.23μg/L,8次测定相对标准偏差在2.98%-4.91%,加标回收率为95.2%-104%。方法可用于地层水等液体样品中苯系物的测定。 相似文献
140.
铜陵地区中生代中酸性侵入岩的地球化学特征及其成矿-地球动力学意义 总被引:24,自引:21,他引:24
本文对铜陵地区晚侏罗世-早白垩世高钾钙碱性中酸性侵入岩进行了研究,发现该类岩体具有埃达克岩的地球化学特征,具体表现为:SiO2≥56%,Al2O3含量高(>15%),Na2O/K2O>1,亏损HREE,(La/Yb)N>12,负Eu异常不明显(Eu*/Eu=0.71-0.96),Sr含量高(>750μg/g),Sr/Y比值高(>38)。但是,由于岩石的K2O含量较高、εNd(t)较低和ISr值较高,又不同于典型的与板块俯冲有关的埃达克岩,而与中国东部中生代的C型埃达克岩比较类似,暗示铜陵地区的高钾钙碱性岩可能是加厚的下地壳底部基性岩部分熔融的产物。本文主要依据铜陵埃达克质岩的HREE特征,将其分为三类:第一类岩体为HREE平坦型,Yb含量较高(>1.8μg/g);第二类为HREE平坦型,Yb<1.8μg/g,(Ho/Yb)N≈1;第三类岩体HREE亏损,Yb<1.8μg/g,(Ho/Yb)N<1.2。上述三类岩石地球化学性质上的差异不太可能是分离结晶作用或地壳混染的 结果,而可能是由于幔源岩浆与下地壳物质混合的程度不同引起源区成分不同形成的。铜陵地区及中国东部埃达克质岩石可能代表了中国东部中生代时的地壳增生和加厚过程。铜陵埃达克岩主要是古老下地壳和底侵玄武岩不同比例混合部分熔融形成的,在岩浆演化过程中可能还不同程度地叠加了分离结晶作用和岩浆混合作用的影响。铜陵埃达克岩具岛弧特征,但并不表明其 相似文献