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901.
902.
宁镇中段燕山期中酸性侵入岩的稀土和微量元素地球化学研究 总被引:1,自引:0,他引:1
与铜多金属成矿相关的宁镇中段地区岩浆活动主要发生在燕山晚期,形成多个中酸性侵入岩体.文章在开展野外调查的基础上,主要从稀土元素和微量元素的实测资料,结合常量元素进行分析,探讨岩浆来源、结晶分异过程及铜多金属矿化特点.研究结果表明,宁镇中段岩浆为壳幔混合型,具有相同的演化趋势.并确定了6大岩体结晶分异程度的高低,提出了岩浆分异程度与矿化特点的关系. 相似文献
903.
通过对孙吴-嘉荫盆地淘淇河组、永安村组、太平林场组、鱼亮子组、乌云组和孙吴组露头剖面详细的沉积学研究,查明该盆地从淘淇河组到孙吴组发育的沉积相类型有冲积扇、辫状河、曲流河、扇三角洲、辫状河三角洲、曲流河三角洲、湖底扇和湖泊。冲积扇及扇三角洲主要发育于淘淇河组和孙吴组;辫状河及辫状河三角洲主要发育于鱼亮子组和乌云组;曲流河及曲流河三角洲主要发育于永安村组和太平林场组,各组均有湖泊相沉积发育。孙吴-嘉荫盆地从淘淇河组到乌云组,具有冲积扇-扇三角洲-湖泊→曲流河-曲流河三角洲-湖泊→辫状河-辫状河三角洲-湖泊→冲积扇-扇三角洲-湖泊的沉积演化规律,反映晚白垩-古新世构造活动性减弱,中-上新世孙吴组沉积时重又趋于活动。 相似文献
904.
The 1.78 Ga Xiong'er Volcanic Province (XVP) and coeval North China giant mafic Dyke Swarm (NCDS) are the most important magmatic events occurring after the amalgamation of the North China craton (NCC). The XVP consists of 3–7 km of extrusive volcanics and some feeder dykes/sills located along the southern margin of the NCC and extending over an area > 0.06 M km2. Compositions vary from basalt to rhyolite, but are predominantly intermediate in terms of silica content. There are also minor sedimentary intercalations and pyroclastic units. The sedimentary interlayers indicate an environment changing from continental-facies to oceanic-facies up-section. The XVP is characterized by fractional crystallization from an EM I type mantle source, and both continental arc (Andean-type) and rift environments have been proposed. The NCDS is widespread in the central NCC with an outcrop area > 0.1 M km2, and are exposed at variable depths up to 20 km (deepest in the north). Dyke compositions vary from basalt to andesite and dacite, but are dominantly mafic, and comprise two series of magmatism. Previous studies revealed that the NCDS recorded assimilation and fractional crystallization of an EM I type magma source, with a minor DM contribution in the younger magmas. Both syn-collisional and intra-continental anorogenic environments have been proposed. Spatial and petrogenic correlations suggest a cogenetic relationship between the NCDS and XVP, and considered together, they define a Large Igneous Province (LIP) of > 0.1 M km2 in area and > 0.1 M km3 in volume, which is also notable for its continuous compositional range from mafic to felsic (with no gap at intermediate compositions). The petrology is explained by a common magma source that undergoes a silica-poor and iron-enriched fractionation trend at depth followed by a silica-rich and iron-poor fractionation trend in shallow-level magma conduits (dykes) and surface lavas. A mantle plume is favored as the cause of this 1.78 Ga North China LIP. 相似文献
905.
The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated
with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the
deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe
intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have
intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly
different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental
liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization
is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal
contacts with sedimentary footwall. The δ
34S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement
of external S with elevated δ
34S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of picrites
associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than
that of sulfide liquid expected to segregate from undepleted picrite magma. Cr-spinel and olivine are present in the Limahe
ultramafic rocks as well as in the picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble
those of the picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust,
are present in the intrusion but absent in the picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher
degrees of contamination with the upper crust than did the picrites. The results of this study permit us to suggest that the
parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging
chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide
segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage
sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent
to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying
unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose
that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills
or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second,
relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine
crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were
then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit
in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe
deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential
of economic Ni–Cu sulfide deposits. 相似文献
906.
907.
908.
909.
台前金矿床是一产于韧性剪切带中的中型金矿床,该矿床位于NE向西林-陡崖断裂带中段.从该矿的矿床地质特征入手,通过分析研究前人地质工作成果,解析了地层、构造、岩浆岩等控矿因素与成矿的关系,总结了矿化富集规律,预测了找矿前景. 相似文献
910.
针对当前县域尺度城镇化研究不足,以及传统数理统计模型无法描述城镇化空间集聚特征的薄弱点,从空间自相关视角来探讨县域尺度城镇化空间集聚特征。基于人口、经济、空间及社会4个维度构建县域城镇化体系,运用投影寻踪模型测度县域尺度城镇化,较科学地评价县域城镇化水平;采用空间自相关模型分析县域城镇化空间集聚,并解释其影响因素,实现了对县域城镇化空间集聚规律有效揭示。研究结果表明:安徽县域城镇化水平呈上升态势,存在"南高北低"区域分异;县域城镇化具有显著全局空间集聚,局部H-H区集聚"合-芜-马",L-L区集聚皖北地区;地理区位条件、交通网络改善、中心城市作用及发展政策倾向是影响安徽县域城镇化空间集聚主要因素。 相似文献