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41.
发育于内蒙古东乌旗地区的泥鳅河组,属于早中泥盆世沉积,厚度约1000m,主要发育泥岩、粉砂岩和灰岩沉积,粉砂岩中常常发育大量腕足类和珊瑚生物化石。首次在本区发现风暴沉积和Beaconites遗迹化石:风暴沉积由下至上包括粒序层理段、平行层理段、丘状交错层理段和浪成波纹层理段4个层段;Beaconites遗迹化石具管壁和内部水平“V”字型的回填纹构造。通过对岩相、生物化石、风暴沉积和Beaconites遗迹化石的研究显示,东乌旗地区泥鳅河组为浅海相沉积。 相似文献
42.
针对ZY-3多光谱影像各谱段共视场扫描成像特点,提出基于在轨检校内方位元素的虚拟CCD重成像算法,通过虚拟CCD重成像技术实现单谱段CCD影像的无缝拼接及多谱段的高精度谱段配准。采用河南登封区域及天津区域的ZY-3多光谱影像对ZY-3多光谱相机进行在轨几何检校,利用河北安平区域的30个高精度靶标控制点验证了检校结果的正确性;进一步利用检校后的内方位元素对河北安平区域、兰州区域的ZY-3多光谱影像进行虚拟CCD重成像,采用靶标点验证方法以及高精度配准验证方法对虚拟CCD重成像影像的谱段配准精度验证,谱段配准精度均优于0.2像元。 相似文献
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陕北地区退耕还林还草工程土壤保护效应的时空特征 总被引:3,自引:0,他引:3
以中国退耕还林生态工程重点区域陕北地区作为研究区,基于耕地遥感监测数据集,分析了陕北地区2000-2013年耕地的时空变化特征;基于梯田空间分布,对RUSLE模型进行改进,模拟生成陕北地区土壤侵蚀模数栅格数据并进行精度验证;最后结合耕地变化数据集对陕北地区退耕还林(草)地及未退耕地的土壤侵蚀变化特征进行对比分析,以明确工程对全区土壤侵蚀变化的影响。结果表明,2000-2010年,陕北退耕农田内部侵蚀模数减少了22.70 t/hm 2,是退耕农田区2000年土壤侵蚀模数的47.08%。同期,陕北地区未退耕农田侵蚀模数减少了10.99 t/hm 2,占未退耕农田区域2000年土壤侵蚀模数的28.60%。从陕北全区的角度看,各种土地利用类型2000-2010年土壤侵蚀模数平均减少了14.51 t/hm 2,占2000年全区土壤侵蚀模数的41.87%。由此可见,退耕还林还草工程可以有效减少土壤侵蚀模数,达到土壤保护的作用。其中,由耕地转为林草所导致的侵蚀减少最为显著,对土壤保护的贡献作用最大。但是,2010年以后(2010-2013年)为退耕还林还草巩固时期,因此该阶段陕北地区土壤侵蚀模数和土壤侵蚀量变化较前10年显著降低。 相似文献
48.
Visible gold in arsenian pyrite at the Shuiyindong Carlin-type gold deposit, Guizhou, China: Implications for the environment and processes of ore formation 总被引:13,自引:0,他引:13
Wenchao Su Bin Xia Hongtao Zhang Xingchun Zhang Ruizhong Hu 《Ore Geology Reviews》2008,33(3-4):667-679
Carlin-type gold deposits are best known for the scarcity of visible gold in their ores. It has long been recognized that the majority of gold is “invisible”, such that it cannot be resolved by conventional microscopy, and resides in arsenian pyrite. Shuiyindong differs in that sub-μm to μm-sized native gold is present in arsenian pyrite veinlets and disseminations. It is also the largest (55 tonnes) and highest grade (7 to 18 ppm), stratabound, Carlin-type gold deposit in Guizhou, China and has produced 5 tonnes of gold from sulfide refractory ores extracted by underground mining methods. In this study, an electron microprobe analyzer (EMPA) was used to map the spatial distribution of “invisible” gold and sub-μm to μm-size visible gold particles in arsenian pyrite in high-grade ore samples from the Shuiyindong. The samples studied are hosted in Permian bioclastic ferroan limestone of the Longtan Formation and exhibit evidence of decarbonation, silicification and sulfidation. Arsenian pyrite with detectable Au (> 400 to 3800 ppm) is disseminated in altered limestone and was deposited in two stages separated by an episode of corrosion in a veinlet.The results show that there are two populations of native gold in arsenian pyrite. One is comprised of sub-μm size gold particles (0.1 to 0.2 μm) that are occasionally present in the gold-bearing arsenian pyrite disseminated in the host rocks. This arsenian pyrite is interpreted to have been formed by sulfidation of ferroan calcite and dolomite. Another is comprised of coarser (1 to 6 μm) native gold grains present in the arsenian pyrite veinlet, either on the first stage where it has been corroded or on the second stage. The lack of fluid inclusion or other evidence of boiling and the low iron content of fluid inclusions in quartz, suggest the veinlet formed by sulfidation of another fluid containing Fe. The Fe-bearing fluid may be a depleted ore fluid that gained Fe by dissolution of ferroan limestone after H2S had been consumed. The association of the largest visible gold grains with an episode of corrosion suggests that fluids episodically became undersaturated with arsenian pyrite while remaining saturated with gold (e.g., pH decrease or an increase in the oxidation state). This may have resulted from incursion of relatively acidic or oxidized fluids that were able to dissolve arsenian pyrite and remain saturated with gold. In this case, sulfidation of iron from the host rock, was the most important depositional mechanism for Au-bearing arsenian pyrite with, or without, grains of native gold. 相似文献
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Emplacement ages, geochemical characteristics and analysis of continental dynamics on gabbroic intrusions in Luodian County, Guizhou Province, have been discussed based on studies of isotopic chronology (the whole-rock Sm-Nd and Rb-Sr isochron methods), major elements, trace elements and PGE. Intrusive activities of the gabbroic intrusions in the study area took place during the Late Yanshanian Orogenic Movement (the Cretaceous Period), as indicated by the Sm-Nd isochron ages (t)=(99.6±4.5) (2σ) Ma and by the Rb-Sr isochron ages t=(97±1.6) (2σ) Ma. The gabbroic intrusions are attached to mafic rocks in cal-alkaline basaltic series. They occurred as dikes and might be formed under an extensional background of the continent. Differentiation of their magmatic crystallization resulted in obvious zonation of petrography. In the gabbroic intrusions of this study, large ion lithophile elements and LREE are enriched, and the chondrite-normalized REE distribution pattern is leftward inclined without anomalies of JCe or JEu, and there are high concentrations of PGE and ratios of Pd/Ir (averaging 4.21). All of these imply that their source areas may be basaltic magma in the upper mantle with high-level partial melting, derived from EMl-type enriched mantle. It is different from Emeishan basalt, which may be related to the upper mantle at low-grade partial melting. Emplacement mechanism of the gabbroic intrusions in this study may suppose to be asthenosphere upheaving as an isolated hot wave in the presence of mantle fluid, resulting in basaltic magma intruded into the continental crust as a diapiric intrusion. Therefore, uplifting of faulting-block and extensional deformation could take place in the shallow part of the continental crust while vertical amassing and accretion of magmatic materials in the deep part of the continental crust. These special processes could supposed to be a special background of continental dynamics for this large-scale epithermal metallogenic domain, such as Au 相似文献
50.
2030年,非洲人口总量预期将达16亿.在当前的经济社会发展模式下,非洲难以建立起自主的粮食生产机制,人口的快速增长将使非洲粮食缺口进一步扩大.这一问题将对我国的粮食安全和能源资源安全造成负面影响,进而对我国际政治空间造成挤压.本文针对非洲人口增长将引发的粮食需求增长问题,分析了非洲本土粮食生产的局限性及风险,指出非洲缺粮源于发达国家操纵贸易规则,预测了非洲可能面临的系统性缺粮风险,研判了非洲缺粮对中国的粮食安全、国际政治安全及能源资源安全带来的风险,提出了我国解决非洲粮食安全问题外溢的应对措施——建立大型跨国粮食贸易集团,提升周边国家粮食供应能力,进而论证了“一带一路”、自贸区建设及人民币国际化战略的必要性和重要战略意义. 相似文献