全文获取类型
收费全文 | 380篇 |
免费 | 10篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 14篇 |
地球物理 | 72篇 |
地质学 | 217篇 |
海洋学 | 18篇 |
天文学 | 24篇 |
综合类 | 1篇 |
自然地理 | 34篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 12篇 |
2018年 | 14篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 15篇 |
2014年 | 16篇 |
2013年 | 19篇 |
2012年 | 20篇 |
2011年 | 23篇 |
2010年 | 28篇 |
2009年 | 32篇 |
2008年 | 29篇 |
2007年 | 18篇 |
2006年 | 22篇 |
2005年 | 6篇 |
2004年 | 13篇 |
2003年 | 4篇 |
2002年 | 10篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有396条查询结果,搜索用时 15 毫秒
171.
多接收电感耦合等离子体质谱(MC-ICP-MS)的广泛应用使过渡金属元素同位素地球化学的研究近年来获得蓬勃发展.利用元素双稀释剂法对钼同位素值进行校正,目前可以获得±0.1‰(2σ)的测试精度.自然界中钼同位素分馏δ98/95Mo可达~3‰,其分馏机制与环境的氧化-还原状态有关.在氧化环境下钼以MoO2/4-的形式与锰... 相似文献
172.
Philipp Bluszcz Emiliya Kirilova André F. Lotter Christian Ohlendorf Bernd Zolitschka 《Aquatic Geochemistry》2008,14(1):73-98
A 2-year (October 2003–October 2005) high-resolution sediment trap study was conducted in Sacrower See, a dimictic hardwater
lake in northeastern Germany. Geochemical and diatom data from sediment trap samples were compared with a broad range of limnological
and meteorological parameters to quantify the impact of single parameters on biochemical calcite precipitation and organic
matter production. Our goals were to disentangle how carbonaceous varves and their sublaminae form during the annual cycle
to better understand the palaeorecords and to detect influences of dissolution, resuspension as well as of global radiation
and stratification on lake internal particle formation. Total particle fluxes in both investigated years were highest during
spring and summer. Sedimentation was dominated by autochthonous organic matter and biochemically precipitated calcite. Main
calcite precipitation occurred between April and July and was preceded and followed by smaller flux peaks caused by resuspension
during winter and blooms of the calcified green algae Phacotus lenticularis during summer. In some of the trap intervals during summer up to 100% of the precipitated calcite was dissolved in the hypolimnion.
High primary production due to stable insolation conditions in epilimnic waters began with stratification of the water column.
Start and development of stratification is closely related to air and water surface temperatures. It is assumed that global
radiation influences the onset and stability of water column stratification and thereby determining the intensity of primary
production and consequently of timing and amount of calcite precipitation which is triggered by phytoplanktonic CO2 consumption. Sediment fluxes of organic matter and calcite are also related to the winter NAO-Index. Therefore these fluxes
will be used as a proxy for ongoing reconstruction of Holocene climate conditions. 相似文献
173.
Helama S Schöne BR Kirchhefer AJ Nielsen JK Rodland DL Janssen R 《Marine environmental research》2007,63(3):185-199
Annual growth increments were examined from shells of the ocean quahog (Arctica islandica L.) from northwest Norway and from tree-ring samples of the Scots pine (Pinus sylvestris L.) from nearby coastal areas. The reconstructed annual growth increments were used to compare growth variability in marine and terrestrial ecosystems. Spatiotemporal comparison of the growth records showed statistically significant correlation during the 19th century A.D., indicative of ecosystem-independent response to pre-anthropogenic climate variations. Geographical correlation between marine and terrestrial records was only observed at the local scale. Years with particularly low winter or high summer North Atlantic Oscillation (NAO) indices showed the best synchronization of marine and terrestrial growth. Despite strong correlation during historical time, our palaeoecological evidence suggests that marine and terrestrial ecosystems may show dissimilar growth reaction to recently observed positive winter-NAO phases. 相似文献
174.
Several occurrences of gold-bearing quartz veins are situated along the east–northeast-trending Barramiya–Um Salatit ophiolitic belt in the central Eastern Desert of Egypt. In the Barramiya mine, gold mineralization within carbonaceous, listvenized serpentinite and adjacent to post-tectonic granite stocks points toward a significant role of listvenitization in the ore genesis. The mineralization is related to quartz and quartz–carbonate lodes in silicified/carbonatized wallrocks. Ore minerals, disseminated in the quartz veins and adjacent wallrocks are mainly arsenopyrite, pyrite and trace amounts of chalcopyrite, sphalerite, tetrahedrite, pyrrhotite, galena, gersdorffite and gold. Partial to complete replacement of arsenopyrite by pyrite and/or marcasite is common. Other secondary phases include covellite and goethite. Native gold and gold–silver alloy occur as tiny grains along micro-fractures in the quartz veins. However, the bulk mineralization can be attributed to auriferous arsenopyrite and arsenic-bearing pyrite (with hundreds of ppms of refractory Au), as evident by electron microprobe and LA-ICP-MS analyses.The mineralized quartz veins are characterized by abundant carbonic (CO2 ± CH4 ± H2O) and aqueous-carbonic (H2O–NaCl–CO2 ± CH4) inclusions along intragranular trails, whereas aqueous inclusions (H2O–NaCl ± CO2) are common in secondary sites. Based on the fluid inclusions data combined with thermometry of the auriferous arsenopyrite, the pressure–temperature conditions of the Barramiya gold mineralization range from 1.3 to 2.4 kbar at 325–370 °C, consistent with mesothermal conditions. Based on the measured δ34S values of pyrite and arsenopyrite intimately associated with gold, the calculated δ34SΣs values suggest that circulating magmatic, dilute aqueous-carbonic fluids leached gold and isotopically light sulfur from the ophiolitic sequence. As the ore fluids infiltrated into the sheared listvenite rocks, a sharp decrease in the fluid fO2 via interaction with the carbonaceous wallrocks triggered gold deposition in structurally favorable sites. 相似文献
175.
Wiese Bernd 《GeoJournal》1981,2(2):51-58
Richards Bay and Saldanha were officially opened in 1976 as new deep water ports, primarily for the export of coal and iron ore respectively. The heavy investment in both infrastructure and industrial development by the South African government led to considerable urban and industrial growth in Richards Bay, whereas the port of Saldanha was initiated by one big concern and failed to produce a far reaching multiplier effect. The development of ports as growth centres has to be considered in terms of the location relative to the Pretoria-Witwatersrand-Vereeniging complex, which dominates the economy of the subcontinent, and within the context of the official decentralisation-growth point policy. 相似文献
176.
In order to establish a reliable chronology for lacustrine sediments of the Frickenhauser See (central Germany) different dating methods have been applied. A total of 17 AMS 14C dates, all within the last 2000 years, were supplemented with 137Cs/210Pb dating and varve counting of the uppermost sediments (131 years). The age–depth model for the Frickenhauser See has to cope with highly variable sedimentation rates and overlapping probability distributions of calibrated 14C dates. The uncertainty of calibrated 14C dates could be considerably reduced by including the stratigraphic relationship of the dated samples, the age information derived from short-lived isotopes and varve counting as well as an upper and lower limit of realistic sedimentation rates as ‘a priori’ information in the calibration procedure. Sets of possible age combinations obtained by repeated sampling from the modified probability distributions were used to calculate continuous age–depth relationships based on monotonic smoothing splines. The obtained age–depth model for the sediment record of the Frickenhauser See represents the average of over 16,000 such model runs and suggests a drastic increase in sedimentation rates from around 1–2 mm a−1 (200–1000 AD) to over 25 mm a−1 for the period between 1100 and 1300 AD. From then on, sedimentation rates exhibit relatively stable values around 3–9 mm a−1. ‘Conventional’ age–depth models such as general polynomial regression or cubic splines either do not include the obtained age-information in a satisfying manner (the model being too “stiff”) or exhibit “swings” causing age-reversals in the model. Although the age–depth relationships obtained for monotonic smoothing splines and mixed-effect regression are generally very similar, they differ in their respective sedimentation rates as well as in their uncertainties. Mixed-effect regression resulted in much higher sedimentation rates of more than 37 mm a−1. These results suggest that monotonic smoothing splines give better control of the age–depth model characteristics and are well suited in situations, where the integrity of 14C dates is high, i.e. the dated material represents the age of the respective layer. 相似文献
177.
The southern Peruvian coastal desert around Palpa, southern Peru (14.5°S) is currently characterized by hyper-arid conditions. However, the presence of two species of molluscs (Scutalus, Pupoides) and desert-loess deposits indicates the past development of semi-desert and grassland ecosystems caused by a displacement of the eastern desert margin due to hydrological changes. Radiocarbon dating shows that the transition to a semi-arid climate in the southern Peruvian coastal desert took place during the Greenland interstadial 1, ∼ 13.5 cal ka BP. At the beginning of the Holocene, the mollusc fauna vanished due to increasing humidity and the development of grasslands. Dust particles were fixed by the grasses, as indicated by abundant Poaceae phytoliths, and desert loess was formed. The humid period we observe here is out of phase with the palaeoenvironmental records from the Titicaca region, which indicates dry conditions at that time. This paper offers a new idea for this contradiction: an orbitally driven meridional shift of the Bolivian high might have altered the moisture supply across the Andes. 相似文献
178.
Irina Shtangeeva Antti Vuorinen Bernd Rietz Liisa Carlson 《Geostandards and Geoanalytical Research》2001,25(2-3):299-306
A detailed characterisation was carried out for soil sampled from sites with different levels of contamination before and after the cultivation of oats and barley. Mineralogical composition, concentration of exchangeable cations, dynamics of soil pH and acid neutralisation buffer capacity of the soil were studied. A total of 21 elements in the soil and 28 elements in the plants were determined by instrumental neutron activation analysis. Distribution of Al, Cr, Mn, Fe, Co, Ni, Cu, Zn and Pb in soil leachates was studied by sequential leaching procedure and ICP-AES. It was found that plants significantly affect most of the soil characteristics including the leaching of heavy metals. 相似文献
179.
A detailed study of the lipids of selected zooplankton species and scavenging amphipods in the near-bottom water layer (15–100 m above bottom, mab) was carried out at the BENGAL site in late summer 1998. Copepoda were the main contributors to the zooplankton, comprising 75% of the total abundance, followed by Ostracoda and Chaetognatha. Calanoid copepods of the family Metridinidae were predominant and accounted for more than 50% of all copepods.Two types of storage lipids were distinguished: triacylglycerols and wax esters. Ostracoda and the polychaete Vanadis sp. stored exclusively triacylglycerols whilst the bulk of the Copepoda accumulated wax esters, with the exception of the family Aetideidae. In the amphipods both lipid classes were found: Eurythenes gryllus stored wax esters and Paralicella spp. and Orchomene sp. triacylglycerols.The fatty acid composition was characterized by a high level of monounsaturated 18:1 (n—9), which is described as characteristic for animals living in the deeper layers of the water column, and to a lesser degree by 16:1 (n—7) and 20:5 (n—3), which are typical components of diatom lipids, and 22:6 (n—3), typical of dinoflagellates. The ratio of 18:1 (n—9):18:1 (n—7) fatty acids was between 5 and 10 in the copepods and indicates a carnivorous/omnivorous feeding behaviour in this group, whereas the higher ratios of 8–18 in the amphipods confirm their necrophagy. The fatty alcohols of the animals storing wax esters were dominated by the monounsaturated isomers 18:1 (n—9) and 18:1 (n—7).The predominance of wax esters as storage lipids in the deep-sea copepods indicates a strong seasonality in the availability of food. This is supported by the high levels of 16:1 (n—7), 20:5 (n—3) and 22:6 (n—3) fatty acids, which point to there being a direct link between the surface primary production and deep-sea copepods, probably via the rapid deposition of phytodetritus. 相似文献
180.
Roy H. Gabrielsen Jan Inge Faleide Christophe Pascal Alvar Braathen Johan Petter Nystuen Bernd Etzelmuller Sejal O'Donnell 《Marine and Petroleum Geology》2010
The regional resultant stress field of the northeastern North Atlantic has shifted significantly throughout the Phanerozoic. In Fennoscandian parts of the Caledonian orogen, mountain building, which was characterized by NW-SE contraction (reference to present North), was followed by a collapse with transport both parallel and transverse to the mountain chain. The Late Palaeozoic – Mesozoic saw several stages of E-W to NW-SE extension, varying in time and position. Local episodes of inversion are traceable in some cases, particularly in connection with deep-seated and long-lived zones of weakness. The Cenozoic has to a larger degree been affected by compression, including folding and basin inversion. Again some of the more pronounced effects of local inversion are related to pre-existing fault systems. Neogene uplift of the western mountainous area in Scandinavia can be unravelled by potential field study, AFT data and reflection seismic sections. Assuming that the region is close to isostatic equilibrium, the uplifted areas must be supported at depth by substantial volumes of low-density material within the crust or the mantle, close to the crust/mantle interface or close to the lithosphere/asthenosphere interfaces. 相似文献