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821.
822.
ZHANG Guoliang 《《地质学报》英文版》2011,85(6):1286-1298
Major elements of 2202 basalts from the East Pacific Rise (EPR) and 888 basalts from near-EPR seamounts are used to investigate their differences in magma crystallization pressures and mantle melting conditions. Crystallization pressure calculation from basalts with 5.0wt%相似文献
823.
824.
碳酸盐岩中"假纹层构造"的成因分析 总被引:1,自引:1,他引:0
常见于泥微晶碳酸盐岩中的毫米级水平纹层是低能沉积环境特有的相标志.川东北地区长兴组-飞仙关组碳酸盐岩地层无岩芯钻探的岩屑中,通过岩石薄片鉴定发现该层段岩屑样品中,大量岩屑出现纹层构造,甚至水动力条件下不可能形成水平纹层构造的颗粒碳酸盐岩、结晶碳酸盐岩中也有出现,通过对这些现象的薄片鉴定、电子探针及Kα元素面分布等分析手段证实其为非沉积成因、非构造成因的"假纹层构造",研究后将其归因为钻探工艺所使用的钻头(PDC型).为准确对岩石薄片进行鉴定并提升无岩芯钻井地质剖面的解释质量,针对沉积动力学、构造动力学和制片工艺学都无法解释的"假纹层构造"的成因分析具有十分重要的现实意义. 相似文献
825.
826.
北京市地面塌陷特征与致灾因子分析 总被引:1,自引:0,他引:1
年北京地面塌陷呈波动式上升趋势,威胁严重.在讨论其孕灾环境和时空分布特征的基础上,分析引起地面塌陷的因素.研究把此区地面塌陷分为采矿地面塌陷和工程地面塌陷两种类型.采矿地面塌陷主要分布于西山门头沟,致灾因子包括开采深度、矿体倾角、降雨、和大量疏排水.工程地面塌陷主要分布于城区,致灾因子包括管线渗漏与侵蚀、地下水过度开采... 相似文献
827.
以变形作为控制条件的基坑支护结构设计是一个十分复杂的工程问题,由于支点法具有计算模式明确、过程简单的优点,受到广大工程设计人员的欢迎。但是,支点法中土抗力系数卅的选取是工程界的一大难题,在支点法计算中m值选取的准确性直接影响支护结构位移和内力的计算结果,所以将支点法建模及反分析方法应用于实际工程,在开挖过程中考虑了支撑变形的非线性,开发了FORTRAN程序对支护结构进行了反演计算。通过反演分析m值并预测支护结构的变形,实现支护动态设计信息化施工。结果表明,位移反分析法进行深基坑工程中的参数反演与位移预测取得比较好的效果,说明该方法在深基坑开挖反演、预测方面是合理可行的。 相似文献
828.
The Teplá–Barrandian unit (TBU) of the Bohemian Massif exposes a section across the once extensive Avalonian–Cadomian belt, which bordered the northern active margin of Gondwana during late Neoproterozoic. This paper synthesizes the state-of-the-art knowledge on the Cadomian basement of the TBU to redefine its principal component units, to revise an outdated stratigraphic scheme, and to interpret this scheme in terms of a recent plate-tectonic model for the Cadomian orogeny in the Bohemian Massif. The main emphasis of this paper is on an area between two newly defined fronts of the Variscan pervasive deformation to the NW and SE of the Barrandian Lower Paleozoic overlap successions. This area has escaped the pervasive Variscan (late Devonian to early Carboniferous) ductile reworking and a section through the Cadomian orogen is here superbly preserved.The NW segment of the TBU consists of three juxtaposed allochthonous belts of unknown stratigraphic relation (the Kralovice–Rakovník, Radnice–Kralupy, and Zbiroh–?árka belts), differing in lithology, complex internal strain patterns, and containing sedimentary and tectonic mélanges with blocks of diverse ocean floor (meta-)basalts. We summarize these three belts under a new term the Blovice complex, which we believe represents a part of an accretionary wedge of the Cadomian orogen.The SE segment of the TBU exposes the narrow Pi?ín belt, which is probably a continuation of the Blovice complex from beneath the Barrandian Lower Paleozoic, and a volcanic arc sequence (the Davle Group). Their stratigraphic relation is unknown. Flysch units (the ?těchovice Group and Svrchnice Formation) overlay the arc volcanics, and both units contain material derived from volcanic arc. The former was also sourced from the NW segment, whereas the latter contains an increased amount of passive margin continental material. In contrast to the Blovice complex, the flysch experienced only weak Cadomian deformation.The new lithotectonic zonation fits the following tectonic scenario for the Cadomian evolution of the TBU well. The S- to SE-directed Cadomian subduction beneath the TBU led to the involvement of turbidites, chaotic deposits, and 605 ± 39 Ma ocean floor in the accretionary wedge represented by the Blovice complex. The accretionary wedge formation mostly overlapped temporally with the growth of the volcanic arc (the Davle Group) at ~ 620–560 Ma. Upon cessation of the arc igneous activity, the rear of the wedge and some elevated portions of the arc were eroded to supply the deep-water flysch sequences of the ?těchovice Group, whereas the comparable Svrchnice Formation (~ 560 to < 544 Ma) was deposited in a southeasterly remnant basin close to the continental margin. The Cadomian orogeny in the TBU was terminated at ~ 550–540 Ma by slab breakoff, by final attachment of the most outboard ~ 540 Ma oceanic crust, and by intrusion of ~ 544–524 Ma boninite dikes marking the transition from the destructive to transform margin during the early/middle Cambrian. 相似文献
829.
Zhigang Zeng Chen-Tung A. Chen Xuebo Yin Xueying Zhang Xiaoyuan Wang Guoliang Zhang Xiaomei Wang Daigeng Chen 《Journal of Asian Earth Sciences》2011,40(2):661-671
We first report the trace and rare earth element compositions of native sulfur ball with sulfur contents varying from 97.08 wt.% to 99.85 wt.% from the Kueishantao hydrothermal field, off NE Taiwan. We then discuss the sources of trace and rare earth elements incorporated into the native sulfur ball during formation. Comparison of our results with native sulfur from crater lakes and other volcanic areas shows the sulfur content of native sulfur ball from the Kueishantao hydrothermal field is very high, and that the rare earth element (REE) and trace element constituents of the native sulfur balls are very low (∑REE < 35 ppb). In the native sulfur ball, V, Cr, Co, Ni, Nb, Rb, Cs, Ba, Pb, Th, U, Al, Ti and REE are mostly derived from andesite; Mg, K and Mn are mostly derived from seawater; and Fe, Cu, Zn and Ni are partly derived from magma. Based on the sulfur contents, trace and rare earth element compositions, and local environment, we suggest that the growth of the native sulfur ball is significantly slower than that of native sulfur chimneys, which results in the relatively higher contents of trace and rare earth element contents in the native sulfur ball than in the native sulfur chimneys from the Kueishantao hydrothermal field. Finally, we suggest a “glue pudding” growth model for understanding the origin of the native sulfur ball in the Kueishantao hydrothermal field, whereby the native sulfur ball forms from a mixture of oxygenated seawater and acidic, low-temperature hydrothermal fluid with H2S and SO2 gases, and is subsequently shaped by tidal and/or bottom currents. 相似文献
830.
Spatial and temporal analysis of global seismological data 1964–2005 reveals a distinct teleseismic earthquake activity producing
a columnar-like formation in the continental wedge between the Krakatau volcano at the surface and the subducting slab of
the Indo-Australian plate. These earthquakes occur continuously in time, are in the body-wave (m
b) magnitude range 4.5–5.3 and in the depth range 1–100 km. The Krakatau earthquake cluster is vertical and elongated in the
azimuth N30°E, suggesting existence of a deep-rooted fault zone cutting the Sunda Strait in the SSW-NNE direction. Possible
continuation of the fault zone in the SW direction was activated by an intensive 2002/2003 aftershock sequence, elongated
in the azimuth of N55°E. Beneath the Krakatau earthquake cluster, an aseismic gap exists in the Wadati-Benioff zone of the
subducting plate at the depths 100–120 km. We interpret this aseismic gap as a consequence of partial melting inhibiting stress
concentration necessary to generate stronger earthquakes, whereas the numerous earthquakes observed in the overlying lithospheric
wedge beneath the volcano probably reflect magma ascent in the recent plumbing system of the Krakatau volcano. Focal depth
of the deepest events (~100 km) of the Krakatau cluster constrains the location of the primary magma generation to greater
depths. The ascending magmatic fluids stress fault segments within the Sunda Strait fault zone and change their friction parameters
inducing the observed tectonic earthquakes beneath Krakatau. 相似文献