全文获取类型
收费全文 | 6024篇 |
免费 | 1175篇 |
国内免费 | 1610篇 |
专业分类
测绘学 | 848篇 |
大气科学 | 1058篇 |
地球物理 | 1179篇 |
地质学 | 3194篇 |
海洋学 | 1021篇 |
天文学 | 230篇 |
综合类 | 525篇 |
自然地理 | 754篇 |
出版年
2024年 | 52篇 |
2023年 | 139篇 |
2022年 | 361篇 |
2021年 | 426篇 |
2020年 | 335篇 |
2019年 | 412篇 |
2018年 | 397篇 |
2017年 | 350篇 |
2016年 | 370篇 |
2015年 | 363篇 |
2014年 | 417篇 |
2013年 | 451篇 |
2012年 | 467篇 |
2011年 | 418篇 |
2010年 | 417篇 |
2009年 | 361篇 |
2008年 | 368篇 |
2007年 | 333篇 |
2006年 | 285篇 |
2005年 | 254篇 |
2004年 | 207篇 |
2003年 | 178篇 |
2002年 | 229篇 |
2001年 | 205篇 |
2000年 | 131篇 |
1999年 | 143篇 |
1998年 | 96篇 |
1997年 | 113篇 |
1996年 | 90篇 |
1995年 | 73篇 |
1994年 | 67篇 |
1993年 | 51篇 |
1992年 | 62篇 |
1991年 | 44篇 |
1990年 | 30篇 |
1989年 | 30篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1958年 | 2篇 |
1957年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有8809条查询结果,搜索用时 62 毫秒
991.
Subduction is the core process of plate tectonics. The mantle wedge in subduction-zone systems represents a key tectonic unit, playing a significant role in material cycling and energy exchange between Earth's layers. This study summarizes research progresses in terms of subduction-related peridotite massifs, including supra-subduction zone(SSZ) ophiolites and mantle-wedge-type(MWT) orogenic peridotites. We also provide the relevant key scientific questions that need be solved in the future. The mantle sections of SSZ ophiolites and MWT orogenic peridotites represent the mantle fragments from oceanic and continental lithosphere in subduction zones, respectively. They are essential targets to study the crust-mantle interaction in subduction zones. The nature of this interaction is the complex chemical exchanges between the subducting slab and the mantle wedge under the major control of physical processes. The SSZ ophiolites can record melt/fluid-rock interaction, metamorphism,deformation, concentration of metallogenic elements and material exchange between crust and mantle, during the stages from the generation of oceanic lithosphere at spreading centers to the initiation, development, maturation and ending of oceanic subduction at continental margins. The MWT orogenic peridotites reveal the history of strong metamorphism and deformation during subduction, the multiple melt/fluid metasomatism(including silicatic melts, carbonatitic melts and silicate-bearing C-HO fluids/supercritical fluids), and the complex cycling of crust-mantle materials, during the subduction/collision and exhumation of continental plates. In order to further reveal the crust-mantle interaction using subduction-zone peridotites, it is necessary to utilize high-spatial-resolution and high-precision techniques to constrain the complex chemical metasomatism, metamorphism,deformation at micro scales, and to reveal their connections with spatial-temporal evolution in macro-scale tectonics. 相似文献
992.
We report 7 mammalian and 16 pollen species from the top of the Shimagou Formation in Kumkol Basin of northern Qinghai-Xizang Plateau, whose age is latest Middle Miocene(about 12.5 Ma). We erect a new species of fossil rodent,Spermophilinus kumkolensis sp. nov. The micromammalian fauna from the Kumkol Basin shares high similarities with contemporary faunas from Europe and northern China, indicating the existence of active zoogeographic exchange between Europe and northern Asia. Trees are dominant in pollen fossils, and herbs and shrubs are minorities. Broadleaved Quercus and Fagus predominate in tree pollens. The flora reconstructed by pollens displays a mixture of evergreen broadleaved forest and dry and warm steppe landscape. Compared to the modern vegetation in Yunnan region, the latest Middle Miocene flora in the Kumkol Basin represents a distinct vertical distribution. The ecotypes of the latest Middle Miocene fauna and flora in the Kumkol Basin,as a whole, are markedly different from those of modern animals and vegetation, the past climate being more suitable than today. 相似文献
993.
Chen Dongyu Lian Ergang Shu Yeqiang Yang Shouye Li Yalong Li Chao Liu Pengfei Su Ni 《中国科学:地球科学(英文版)》2020,63(10):1564-1576
Oxygen isotope(δ~(18)O) of seawater is an excellent proxy for tracing the origins of water masses and their mixing processes. Combining with hydrographic observation, hybrid coordinate ocean model(HYCOM) analysis data, and seawater oxygen isotope, we investigated the source of the South China Sea Warm Current(SCSWC) in the southwestern Taiwan Strait and its underlying mechanism. Results show that the Kuroshio subsurface water(KSSW) can intrude the continental slope in the southwestern Taiwan Strait, and thereby climb up the continental slope coupled with upwelling. The δ~(18)O-salinity relationship further indicates that in spring, the SCSWC in the southwestern Taiwan Strait originates from the upslope deflection of the slope current formed by the KSSW intrusion into the South China Sea, rather than from the west segment of the SCSWC formed to the east of Hainan Island. In addition, the southward flowing Zhe-Min Coastal Current(ZMCC) can reach as far as the Taiwan Bank(TB) and deflects offshore over the western TB at approximately 23.5°N, to some extent affecting the SCSWC. Moreover, this study reveals that seawater δ~(18)O is exquisitely sensitive to the determination of the origin and transport of water masses as compared with traditional potential temperature-salinity plot(θ-S) and HYCOM analysis data. In addition, their coupling can more reliably interpret the mixing processes of shelf water masses. 相似文献
994.
Science China Earth Sciences - Subducting oceanic slabs undergo metamorphic dehydration with the increase of temperature and pressure during subduction. Dehydration is an essential step for element... 相似文献
995.
渤东凹陷东营组烃源岩评价 总被引:1,自引:1,他引:0
渤东凹陷是渤海海域下一步油气勘探的重点地区之一。本文通过对渤东凹陷单井烃源岩的有机地球化学分析和与渤中凹陷烃源岩的对比研究,结合渤东凹陷盆地模拟成果,得出以下认识:渤东凹陷南部东营组半深湖深湖相泥岩的有机质丰度高,有机质类型好,有机质演化已处于成熟阶段,因而东营组暗色泥岩具有较高的生烃潜力,是一套良好的烃源岩层。 相似文献
996.
997.
Seamounts are ubiquitous topographic units in global oceans, and their influences on local oceanic circulation have attracted great attention in physical oceanography; however, previous efforts were less made in paleoclimatology and paleoceanography. The Caiwei Guyot in the Magellan Seamounts of the western Pacific is a typical seamount, and in this study, we investigate a well-dated sediment core by magnetic properties to reveal the relationship between deep-sea sedimentary processes and global climate changes. The principal results are as follows: (1) the dominant magnetic minerals in the sediments are low-coercivity magnetite in pseudo-single domain range, probably including a biogenic contribution; (2) the variabilities of magnetic parameters can be clustered into two sections at ~500 ka, and the differences between the two units are evident in amplitudes and means; (3) changes in the grainsize-dependent magnetic parameters can be well correlated to records of global ice volume and atmospheric CO2 in the middle Pleistocene. Based on these results, a close linkage was proposed between deep-sea sedimentary processes in the Caiwei Guyot and global climate changes. This linkage likely involves different roles of biogenic magnetite in the sediments between interglacial and glacial intervals, responding to changes in marine productivity and deep-sea circulation and displaying a major change in the Mid-Brunhes climate event. Therefore, we proposed that the sedimentary archives at the bottom of the Caiwei Guyot record some key signals of global climate changes, providing a unique window to observe interactions between various environmental systems on glacial-interglacial timescales. 相似文献
998.
根据相同土地利用类型景观格局特征相似的原理,在传统遥感分类方法的基础上,结合景观生态学理论,建立了土地利用分类新方法; 应用SPOT遥感图像提取了北京市五环内的居民用地和非居民用地类型,总分类精度达到了85.9%,Kappa系数为71.1%.本研究结合学科交叉的优势,为遥感技术应用和土地利用信息提取提供了新思路. 相似文献
999.
大量城市建筑使得高分影像中含有许多阴影区。这些阴影区在土地利用分类、植被绿度调查等遥感应用中会较大地影响结果精度,降低数据使用效率并增加研究成本。基于同一地物阴影区与临近非阴影区反射率相等这一辐射特征关系,通过建立辐射传输方程,发展了一种新的城市高分遥感影像阴影校正方法 RERB(Reflectance Equality Relationship Based Method)。利用RERB对不同城市(北京和荷兰Enschede)不同高分多光谱影像(Geo Eye-1和Quick Bird)进行阴影校正,并对比分析其与被广泛采用的均值方差变换法MVT(Mean and Variance Transformation)的校正结果,通过定性和定量精度评价发现:(1)RERB能很好地将城市阴影区影像视觉特征(颜色、纹理、色调等)信息恢复到与非阴影区同一水平上;(2)RERB恢复后的阴影区具有丰富的细节信息且在视觉上与临近非阴影区具有良好的一致性;(3)RERB恢复后的城市柏油路面和水泥路面阴影区辐射信息具有较低的误差,可见光-近红外波段的平均误差分别为7%和9%。同时RERB能较好地恢复城市阴影区植被波谱特征信息。 相似文献
1000.
祖母绿是一种名贵彩色宝石,其产地来源对祖母绿价值的评定具有重要影响。祖母绿的产地鉴别因而成为宝石实验室的重要技术,也是宝石学领域的研究热点。祖母绿的包裹体、谱学特征和化学成分是常用且关键的产地鉴别信息,但随着祖母绿产地研究数据的积累,传统的产地鉴别方法备受挑战。文章系统整理和归纳分析了全球各产地祖母绿的宝石学特征、包裹体信息、谱学特征和主微量成分数据,在综述前人研究结果的基础上,系统阐明了目前祖母绿产地鉴别的研究现状,总结了不同产地祖母绿的宝石学特征和包裹体特征,划分了紫外-可见光-近红外(UV-VIS-NIR)光谱类型,揭示了各产地祖母绿的成分指纹信息,并以案例的形式阐明区分祖母绿常见重要产地的方法。全球尺度的对比虽然表明不同产地祖母绿包裹体种类多数雷同、光谱趋同、成分含量范围重叠明显,但也从包裹体出现频率、UV-VIS-NIR光谱样式类型、重水吸收样式和成分投图参数的选择上提供了产地鉴别的新思路。综上所述,文章旨在促进祖母绿鉴别技术的发展,为祖母绿的产地溯源提供科学依据。 相似文献