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A Strontium and Neodymium Isotopic Investigation of the Fongen--Hyllingen Layered Intrusion, Norway 总被引:1,自引:0,他引:1
The FongenHyllingen Intrusion, situated 60 km SE of Trondheim,Norway, is a synorogenic layered mafic intrusion of Caledonianage . The intrusion is divided into four evolutionary stages based on cryptic variations: StageIa basal reversal; Stage IIunchanged mineral chemistryor slight normal evolution; Stage IIIa gradual regression;Stage IV a strong normal fractionation trend Magma replenishmentdominated during most of the crystallization, i.e. during StagesI, II and III Replenishing magma was more dense than resident,evolved magma, and continuing influx eventually caused a compositionallystratified magma column to form. Cryptic lateral variation isan important feature in the southern part of the complex andformed by in situ crystallization from a stratified magma alongan inclined floor, where modal layering formed parallel to thecrystallization front. Initial Sr- and Nd-isotopic ratios inthe cumulates vary as a result of assimilation of country rockand subsequent mixing between uncontaminated, replenishing magmaand contaminated, resident magma. The parental magma had a moderatelydepleted isotope composition, relative to Bulk Earth, with Nd=584and Sri=070308, whereas the main contaminant was a partialmelt of metapelitic country rock with Nd=-874 and Sri=07195(Sri is the initial 87Sr/86Sr). Sri in the analysed cumulatewhole-rock samples ranges from 070308 to 070535 and initialNd ranges from. 158 to 584. There is a strong correlationbetween mineralogical composition and isotopic trends in mostof the cumulates: the most primitive samples are the least contaminated,as reflected by relatively high ed and low Sr,, and more evolvedsamples have progressively lower eNi and higher Sry A gradualregression of several hundred metres thickness characterizesStage III; stratigraphically upwards mineral compositions becomemore primitive and isotope compositions more depleted (higherNd and lower Sri), implying a process of. progressive mixing-inof replenishing, primitive and uncontaminated magma. Magma influxin Stage III took place by fountaining, whereas magma additionwas more tranquil in the earlier stages. The fountaining influxentrained resident, relatively evolved and contaminated magma,resulting in a hybrid magma which ponded at the floor. Duringprolonged magma addition with concomitant crystallization, thelowermost magma layer was replaced by progressively more primitivehybrid magma, creating a gradual regression in the crystallizingcumulate sequence. A detailed two-dimensional study revealslateral variations in mineral compositions both at the baseand top of Stage III, whereas lateral variations in Sr- andNd-isotopic compositions are present at the top, but not atthe base. This implies that the lowest crystallizing part ofthe magma column was essentially isotopically homogeneous, butcompositionally stratified, before influx in Stage III. Isotopicgradients in the magma were strong close to the roof, wheremost of the assimilation occurred, and decreased downwards,merging into isotopically homogeneous magma. This stratifiedsystem was destroyed by turbulent mixing between replenishingand resident magma during fountaining influx in Stage III, anda new stratification was established with both an isotopic anda compositional gradient. After the final influx, crystallizationcontinued in an essentially closed system, in which the remainingmagma column eventually became homogenized, as magma layersmixed when their densities converged owing to release of buoyant,residual liquid during fractional crystallization.
Corresponding author 相似文献
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运用高分辨率层序地层学原理和方法,通过对钻井和地震资料的综合分析,在二连盆地吉尔嘎朗图凹陷下白垩统中识别出1个超长期基准面旋回(二级层序)SSC1和5个长期基准面旋回(三级层序):LSC1,LSC2,LSC3,LSC4,LSC5,分析了各旋回的发育特征。识别出五种类型的沉积体系:滨浅湖近岸水下扇、较深水湖浊积扇、滨浅湖扇三角洲、滨浅湖辫状河三角洲和河流沉积体系,并在等时地层格架内分析了各基准面旋回的沉积体系构成和储层砂体的发育情况。综合分析生、诸、盖条件后认为,在垂向上,LSC3旋回为本区最有利的储集层段,在平面上,本区的油气勘探应主要寻找宝饶构造带辫状河三角洲前缘砂体,主要储层砂体类型为前缘分流水道砂和前缘席状砂。 相似文献
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北京地区城市化过程与机制研究 总被引:84,自引:13,他引:84
在长时间序列高分辨率Landsat TM/MSS数据的支持下,对北京地区1975-1997年城市化基本过程和驱动机制进行了分析研究,基本结论如下;(1)北京地区城市化过程主要表现为中心大区和边缘次级中心区的面状城市化,中心大区和边缘次级中心区之间沿交通干线的线状城市化以及中心大区与边缘次级中心区之间的点状城市化3种基本模式,其中,中心大区、在城市边缘区的面状成都市化过程在区域内居于优势地位。(2)北京地区城市化过程和城市格局的形成是地形,交通等内在适应性因素和经济因素,政府行为,文化传统,突发事件等外在驱动因素共同作用的结果。其中,城市规划,产业发展政策等政府行为和3000年城市发展形成的旧有城市格局和古都风貌从根本上决定了现代北京城市发展的基本过程。 相似文献
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This study applies theories of systems and system dynamics to ecological economic systems in the oasis environment, with the intention of finding the basic characteristics of the oasis environment and its feedback structures. This study explores the inner mechanisms of economic development in the oasis environment and its relationship to policy variables. This model is applied to economic development in the Manas oasis of the Xinjiang Uygur Autonomous Region of China. System dynamics method starts from studying feedback structure within the system study and then searches for the best solution through identifying the right "policy point" and through model simulation in the computer. It embodies the cream of "systems cybernetics theory". This study is justified because the nature of the oasis system and the simulation results are scientifically sound and practically feasible. 相似文献
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云南省防洪空间信息系统构建 总被引:4,自引:1,他引:4
通过讨论应用地理信息系统(GIS)技术,立足现实对相关空间数据进行集成和整合处理,实现防洪空间信息的数字化、标准化,为优化防汛指挥工作手段提供基础。系统数据库饭知不同比例尺精度的空间基础数据以满足不同目的的需求,对相关水文、防洪设施、全省洪涝风险和重点区风险图、土地利用等图件进行系统整合。系统有较强的管理功能和分析功能,可提高云南省防洪空间信息的共享度和系统有效管理,为政府统一组织和指挥抗洪救灾提供重要的辅助决策支持手段。 相似文献
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栖霞组沉积地球化学特征及其环境意义 总被引:2,自引:1,他引:2
沉积环境的古氧相特征是沉积环境和古海洋特征恢复的重要内容。岩石地球化学特征是判断其形成环境氧化还原条件的重要手段之一。本文以来宾地区铁桥面为重点.通过对栖霞组灰岩的地球化学分析,结合沉积学、古生态学特征.认为栖霞组沉积于贫氧的沉{只背景.是在海水深度和海域的局限程度等沉积条件发生周期性变化的情况下形成的。古氧相地球化学指标V(V十Ni)、Cc/La、U/Th值都适用于该组以钙质沉积为主的沉积物。黄铁矿矿化程度(DOP值)变。化较大.眨映该区多变的古氧相特征。 相似文献
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