全文获取类型
收费全文 | 555篇 |
免费 | 76篇 |
国内免费 | 310篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 3篇 |
地球物理 | 31篇 |
地质学 | 779篇 |
海洋学 | 4篇 |
综合类 | 26篇 |
自然地理 | 92篇 |
出版年
2024年 | 10篇 |
2023年 | 18篇 |
2022年 | 36篇 |
2021年 | 31篇 |
2020年 | 47篇 |
2019年 | 45篇 |
2018年 | 26篇 |
2017年 | 56篇 |
2016年 | 37篇 |
2015年 | 22篇 |
2014年 | 31篇 |
2013年 | 110篇 |
2012年 | 52篇 |
2011年 | 38篇 |
2010年 | 31篇 |
2009年 | 37篇 |
2008年 | 48篇 |
2007年 | 39篇 |
2006年 | 40篇 |
2005年 | 24篇 |
2004年 | 26篇 |
2003年 | 25篇 |
2002年 | 18篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1973年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有941条查询结果,搜索用时 15 毫秒
71.
Guochun ZHAO LIU Shuwen Min SUN LI Sanzhong Simon WILDE Xiaoping XIA Jian ZHANG Yanhong HE 《《地质学报》英文版》2006,80(6):790-806
The Trans-North China Orogen (TNCO) was a Paleoproterozic continent-continent collisional belt along which the Eastern and Western Blocks amalgamated to form a coherent North China Craton (NCC). Recent geological, structural, geochemical and isotopic data show that the orogen was a continental margin or Japan-type arc along the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction of the oceanic lithosphere beneath the western margin of the Eastern Block. At 2550-2520 Ma, the deep subduction caused partial melting of the medium-lower crust, producing copious granitoid magma that was intruded into the upper levels of the crust to form granitoid plutons in the low- to medium-grade granite-greeustone terranes. At 2530-2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, which led to underplating of mafic magma in the lower crust and widespread mafic and minor felsic volcanism in the arc, forming part of the greenstone assemblages. Extension driven by widespread mafic to felsic volcanism led to the development of back-arc and/or intra-arc basins in the orogen. At 2520-2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of tonalitic-trondhjemitic-granodioritic (TTG) magmatism. At this time following further extension of back-arc basins, episodic granitoid magmatism occurred, resulting in the emplacement of 2360 Ma, -2250 Ma 2110-21760 Ma and -2050 Ma granites in the orogen. Contemporary volcano-sedimentary rocks developed in the back-arc or intra-are basins. At 2150-1920 Ma, the orogen underwent several extensional events, possibly due to subduction of an oceanic ridge, leading to emplacement of mafic dykes that were subsequently metamorphosed to amphibolites and medium- to high-pressure mafic granulites. At 1880-1820 Ma, the ocean between the Eastern and Western Blocks was completely consumed by subduction, and the dosing of the ocean led to the continent-arc-continent collision, which caused large-scale thrusting and isoclinal folds and transported some of the rocks into the lower crustal levels or upper mantle to form granulites or eclogites. Peak metamorphism was followed by exhumation/uplift, resulting in widespread development of asymmetric folds and symplectic textures in the rocks. 相似文献
72.
REGULARITYANDESTIMATIONOFMETHANEEMISSIONFROMMARSHLANDINTHESANJIANGPLAIN①CuiBaoshan(崔保山)MaXuehui(马学慧)ChangchunInstituteofGeogr... 相似文献
73.
74.
75.
A reprocessing program to enhance the correlation between the surface geology and the seismic data has been completed for seismic line 9 (eastern 100 km) and line 10 in the central region of the Trans-Hudson Orogen of Saskatchewan, Canada. The new seismic images through lateral continuity of reflectivity provide sufficient detail to resolve the discrepancy between the low-dipping, layer-parallel and dextral-reverse nature of the Sturgeon-Weir shear zone (line 9) observed in the field and its steeply dipping (apparent) normal displacement character interpreted on the basis of the initial processing. Furthermore, the new interpretation provides a strong confirmation of the role of Pelican Thrust as a major detachment zone — the main `sole thrust' — along which juvenile allochthons have been carried across the Archaean microcontinental block. The images are also refined enough to suggest: (a) a boundary within the Pelican Thrust between its internal and external suites; (b) a possible boundary separating a lower (older?) Archaean basement from its upper (younger?) counterpart; and (c) sub-Moho events (M2) which reveal possible involvement of the upper mantle in the collisional tectonic process in addition to the well defined Moho (M1) which probably represents the youngest of the post-collisional detachments. 相似文献
76.
J. R. MUHLING 《Journal of Metamorphic Geology》1990,8(1):47-64
The Narryer Gneiss Complex of the Yilgarn Block is a key segment of the Western Australian Precambrian Shield. It is a regional granulite facies terrain comprised of predominantly quartzo-feldspathic gneisses derived from granitic intrusions c. 3.6–3.4 Ga old. Granulite facies metamorphism occurred c. 3.3 Ga ago, and conditions of 750–850°C and 7–10 kbar are estimated for the Mukalo Creek Area (MCA) near Errabiddy in the north. The P–T path of the MCA has been derived from metamorphic assemblages in younger rocks that intruded the gneisses during at least three subsequent events, and this path is supported by reaction coronas in the older gneisses. There is no evidence for uplift immediately following peak metamorphism of the MCA, and a period of isobaric cooling is inferred from the pressures recorded in younger rocks. Pressures and temperatures estimated from metadolerites, which intruded the older gneisses during ‘granite–greenstone’tectonism at about 2.6 Ga and during early Proterozoic thrusting show that the Errabiddy area remained in the lower crust, although it was probably reheated during the younger events. Isothermal uplift to upper crustal levels occurred at c. 1.6 Ga ago, and was followed by further deformation and patchy retrogression of high-grade assemblages. The effects of younger deformation, cooling and reheating can be discerned in the older gneisses, but as there has been no pervasive deformation or rehydration, the minerals and microstructures formed during early Archaean granulite facies metamorphism for the most part are retained. The MCA remained in the lower crust for about 1700 Ma following peak metamorphism and some event unrelated to the original metamorphism was required to exhume it. Uplift occurred during development of the Capricorn Orogen, when some 30–35 km were added to the crust beneath the Errabiddy area. The recognition of early Proterozoic thrusting, plus crustal thickening, suggests that the Capricorn Orogen is a belt of regional compression which resulted from convergence of the Yilgarn and Pilbara Cratons. 相似文献
77.
滇西地区二叠纪—三叠纪岩浆岩展布还不清楚,导致相关古特提斯构造演化模型还存在争议。本文对兰坪-思茅盆地西缘水泄地区的辉长岩开展了LA-ICP-MS锆石U-Pb定年、锆石Hf同位素、全岩主微量元素及Sr-Nd同位素分析,探讨了岩石成因及地质意义。水泄辉长岩2件样品的锆石U-Pb年龄分别为237.8±3.4 Ma和240.8±3.3 Ma,代表其结晶年龄,属于中三叠世。样品具有较高的Na2O/K2O(3.81~49.14),明显富集Ba、Rb、Th、U等大离子亲石元素,相对亏损Nb、Ta等高场强元素,稀土元素弱分馏,轻稀土弱富集,δEu值为0.87~1.07,无明显的Eu异常。锆石εHf(t)值全为正值,主要介于+5.67~+15.75,全岩初始87Sr/86Sr比值为0.70453~0.70776,εNd(t)值全为正值,介于+4.9~+5.2。地球化学特征显示水泄辉长岩来源于亏损地幔的部分熔融,在岩浆演化过程中发生了镁铁质矿物和铁钛矿物的分离结晶作用。水泄... 相似文献
78.
广西新元古代BIF的铁同位素特征及其地质意义 总被引:10,自引:1,他引:9
通过分析广西三江地区新元古代条带状含铁建造的Fe同位素和主量元素组成,对海水的氧化还原状态提供了制约,为富禄期的地球处于间冰期提供了证据。相对于标准物质IRMM-014,新元古代含铁建造不同条带全岩样品的δ57Fe值变化范围1.60‰~2.20‰,平均值为1.85‰,表明BIF样品富集铁的重同位素。条带状含铁建造主要由Fe2O3和SiO2组成,但却具有较高的Al2O3含量。这表明条带状含铁建造样品不是纯净的化学沉积物,而是具有一定的碎屑物质输入。碎屑输入量的不同引起深色和浅色条带之间铁同位素组成存在着0.4‰的差别。剔除碎屑的影响,新元古代BIF从海水中沉淀的赤铁矿δ57Fe的平均值在2‰左右,略高于太古代条带状铁建造的Fe同位素组成,这表明当时海水的氧逸度可能比太古代还低。这说明在富禄期绝大部分海洋仍旧被冰盖覆盖,只在局部出现融化。因此,富禄期的地球可能出于冰期的相对温暖阶段,而不是间冰期。 相似文献
79.
Effects of Nitrogen Addition on Plant Functional Traits in Freshwater Wetland of Sanjiang Plain,Northeast China 总被引:1,自引:0,他引:1
To clarify the responses of plant functional traits to nitrogen(N) enrichment, we investigated the whole-plant traits(plant height and aboveground biomass), leaf morphological(specific leaf area(SLA) and leaf dry mass content(LDMC)) and chemical traits(leaf N concentration(LNC) and leaf phosphorus(P) concentration(LPC)) of Deyeuxia angustifolia and Glyceria spiculosa following seven consecutive years of N addition at four rates(0 g N/(m^2·yr), 6 g N/(m^2·yr), 12 g N/(m^2·yr) and 24 g N/(m^2·yr)) in a freshwater marsh in the Sanjiang Plain, Northeast China. The results showed that, for both D. angustifolia and G. spiculosa, N addition generally increased plant height, leaf, stem and total aboveground biomass, but did not cause changes in SLA and LDMC. Moreover, increased N availability caused an increase in LNC, and did not affect LPC. Thus, N addition decreased leaf C∶N ratio, but caused an increase in leaf N∶P ratio, and did not affect leaf C∶P ratio. Our results suggest that, in the mid-term, elevated N loading does not alter leaf morphological traits, but causes substantial changes in whole-plant traits and leaf chemical traits in temperate freshwater wetlands. These may help to better understand the effects of N enrichment on plant functional traits and thus ecosystem structure and functioning in freshwater wetlands. 相似文献
80.
Magnetotelluric studies over the igneous arc of the Indo Burman range in the Sagaing province of Myanmar have delineated the high resistivity Indian plate subducting westwards beneath the Burmese block to depths of 30 km and beyond. The thick moderately resistive (20–100 Ω m) layer overlying the subducting Indian plate may be due to the low resistivity sediments. The entire region is covered with prominent sedimentary layer with a conductance varying between 20 and 3000 S showing a general increase from the east to west, suggesting that their thickness increases toward the west. The large unsystematic variations in the conductance are indicative of the widely varying depositional environments and also possible vertical block movements during the course of their deposition. A west dipping low resistivity zone to the east of Burmese block seems to demarcate its eastern limit, suggesting the possibility of a hitherto unknown deep seated fault, which is also supported by the several earthquake foci located over this zone. The nature of the crustal movements over this fault is not immediately apparent. Possibility exists that the Sagaing fault is an en echelon fault and the present feature observed here is a part of this en echelon fault. The possibility of channel flows of the weakened rocks in the deep crust observed in the vicinity of the eastern Himalayan syntaxis may also cause such low resistivity zones. 相似文献