全文获取类型
收费全文 | 329篇 |
免费 | 12篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 15篇 |
地球物理 | 77篇 |
地质学 | 154篇 |
海洋学 | 38篇 |
天文学 | 28篇 |
自然地理 | 30篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 17篇 |
2012年 | 28篇 |
2011年 | 23篇 |
2010年 | 17篇 |
2009年 | 22篇 |
2008年 | 21篇 |
2007年 | 19篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 14篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1960年 | 1篇 |
1957年 | 2篇 |
1950年 | 2篇 |
排序方式: 共有346条查询结果,搜索用时 812 毫秒
201.
Jianping Zheng W. L. Griffin Suzanne Y. O’Reilly Ming Zhang Norman Pearson Zhaohua Luo 《Contributions to Mineralogy and Petrology》2006,151(4):457-479
A suite of spinel peridotite xenoliths in Mesozoic basalts of the Tuoyun basin in the Tianshan area of northwest China has a high proportion of amphibole/mica-bearing lherzolites, with high Cpx/Opx ratios (mean 0.74). Many aspects of mineral chemistry in the Tuoyun peridotites are intermediate between those of refractory Archean cratonic mantle and fertile Phanerozoic mantle. These include Ni/Cr and the contents of transition metals and Y in olivine and orthopyroxene and the abundances of elements such as Na, Al, Ti, Y, Sr and LREE in clinopyroxene. The data suggest that the mantle in Tuoyun is moderately depleted in basaltic components relative to both the refractory Archean mantle and the fertile Phanerozoic mantle. The wide variations in the CaO/Al2O3 (0.9–3.5) of whole rocks and LREE/HREE (0.8–14.2) and Ti/Eu (971–5,765) of clinopyroxenes in the Tuoyun peridotites are interpreted as the metasomatism of hydrous carbonatitic and potassic melt or the cumulative effects of mantle metasomatism by different agents (carbonatite and small-volume silicate melts) through time. The Tuoyun mantle shows closer affinity to the type of mantle found beneath the Proterozoic Cathaysia block, and especially to that beneath the East Central Asia Orogenic Belt (ECAOB), than to the mantle beneath the Archean North China Craton. This implies that the Tianshan subcontinental lithospheric mantle may have been generated during the accretion of the ECAOB. The high proportion of fine-grained microstructures, high Cpx/Opx ratio, obvious Ca enrichment and lower overall depletion in the Tuoyun mantle relative to that in other parts of the ECAOB reflect stronger mechanical and chemical modification of the Tuoyun mantle, near the translithospheric Talas-Ferghana strike-slip fault, which played a major role in controlling the strength of the mantle lithosphere and has channeled the upwelling mantle. 相似文献
202.
203.
204.
Origins of Xenolithic Eclogites and Pyroxenites from the Central Slave Craton, Canada 总被引:5,自引:0,他引:5
Aulbach Sonja; Pearson Norman J.; O'Reilly Suzanne Y.; Doyle Buddy J. 《Journal of Petrology》2007,48(10):1843-1873
Major- and trace-element and Sr–Nd–Hf isotopic compositionsof garnet and clinopyroxene in kimberlite-borne eclogite andpyroxenite xenoliths were used to establish their origins andevolution in the subcontinental lithospheric mantle beneaththe central Slave Craton, Canada. The majority of eclogitescan be assigned to three groups (high-Mg, high-Ca or low-Mgeclogites) that have distinct trace-element patterns. Althoughpost-formation metasomatism involving high field strength element(HFSE) and light rare earth element (LREE) addition has partiallyobscured the primary compositional features of the high-Mg andhigh-Ca eclogites, trace-element features, such as unfractionatedmiddle REE (MREE) to heavy REE (HREE) patterns suggestive ofgarnet-free residues and low Zr/Sm consistent with plagioclaseaccumulation, could indicate a subduction origin from a broadlygabbroic protolith. In this scenario, the low REE and smallpositive Eu anomalies of the high-Mg eclogites suggest moreprimitive, plagioclase-rich protoliths, whereas the high-Caeclogites are proposed to have more evolved protoliths withhigher (normative) clinopyroxene/plagioclase ratios plus trappedmelt, consistent with their lower Mg-numbers, higher REE andabsence of Eu anomalies. In contrast, the subchondritic Zr/Hfand positive slope in the HREE of the low-Mg eclogites are similarto Archaean second-stage melts and point to a previously depletedsource for their precursors. Low ratios of fluid-mobile to lessfluid-mobile elements and of LREE to HREE are consistent withdehydration and partial melt loss for some eclogites. The trace-elementcharacteristics of the different eclogite types translate intolower Nd for high-Mg eclogites than for low-Mg eclogites. Withinthe low-Mg group, samples that show evidence for metasomaticenrichment in LREE and HFSE have lower Nd and Hf than a samplethat was apparently not enriched, pointing to long-term evolutionat their respective parent–daughter ratios. Garnet andclinopyroxene in pyroxenites show different major-element relationshipsfrom those in eclogites, such as an opposite CaO–Na2Otrend and the presence of a CaO–Cr2O3 trend, independentof whether or not opx is part of the assemblage. Therefore,these two rock types are probably not related by fractionationprocesses. The presence of opx in about half of the samplesprecludes direct crystallization from eclogite-derived melts.They probably formed from hybridized melts that reacted withthe peridotitic mantle. KEY WORDS: eclogites; pyroxenite xenoliths; mantle xenoliths; eclogite trace elements; eclogite Sr isotopes; eclogite Hf isotopes; eclogite Nd isotopes 相似文献
205.
Olof Zeller Peter Hoffmann Jürgen Bremer Werner Singer 《Journal of Atmospheric and Solar》2009,71(8-9):931-942
VHF Radar echoes in the summer mesosphere at mid- and polar latitudes ([P]MSE—[polar] mesosphere summer echoes) are connected with very cold temperatures where ice particles can exist. Temperature variations can cause conditions for the generation and evaporation of ice particles and affect the [P]MSE occurrence. The impact of temperature and meridional wind oscillations on [P]MSE is described. Generally at mid-latitudes, strong mesosphere summer echoes are strongly affected by meridional wind variations if the mean temperature is near the frost point of water vapor. In contrast, at polar latitudes there is mostly no significant impact of the meridional wind on radar echoes. A mean temperature well below the frost point and a weaker meridional temperature gradient than at mid-latitudes are reasons for this reduced influence. Due to higher temperatures in 2002, long period temperature and meridional wind variations impact the PMSE more than during the other years. 相似文献
206.
Changes in carbon and nitrogen cycling in a floodplain lake over recent decades linked to littoral expansion,declining riverine influx,and eutrophication 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This study aimed to understand changes in the biogeochemical processing of organic matter (OM) in response to multiple stressors (e.g., littoral area expansion, wastewater input, and hydrological regulation) in East Dongting Lake (Central China) over the past 60 years, using analyses of total organic carbon (TOC), total nitrogen (TN), C/N ratios, δ13C, δ15N, and diatoms from 2 sediment cores collected from the littoral and central parts of the lake. OM mainly originated from phytoplankton and C3 plant‐derived soil OM based on the ranges of C/N ratios (from 7 to 11) and δ13C (between ?27‰ and ?23‰). Littoral area expansion due to siltation caused an increasing influx of terrestrial soil OM in the 1980s and the 1990s, subsequently lowering δ13C values and rising C/N ratios in both sediment cores. Meanwhile, higher δ15N was linked to a high influx of isotopically heavy nitrate from urban and agricultural wastewaters. After 2000, slight decreases in TOC and TN in the littoral area were attributable to reducing inputs of external OM, likely linked to declining sediment influx from the upper reaches resulting from the Three Gorges Dam impoundment. Contrasting increases in TOC, TN, and C/N ratios in the central part indicated a high influx of terrestrial soil OM due to the declining distance from the shoreline with littoral area expansion. Declining δ15N values after 2000 indicated an increase in N2‐fixing cyanobacteria with eutrophication. Changes in diatom assemblages in both the littoral and central zones reflected nutrient enrichment and hydrological alterations. These results indicate that littoral expansion, declining riverine influx, and anthropogenic nutrient inputs are potential driving forces for the biogeochemical processing of OM in floodplain lakes. This study provides sedimentary biogeochemical clues for tracking past limnological conditions of floodplain lakes that are subjected to increasing disturbances from hydrological regulation and eutrophication. 相似文献
207.
Suzanne Bull Andrew Nicol Dominic Strogen Karsten F. Kroeger Hannu S. Seebeck 《Basin Research》2019,31(2):253-273
Miocene strata in the southern Taranaki Basin (STB), up to 3 km thick, provide a distal record of erosion associated with plate boundary deformation in New Zealand. 2D and 3D seismic reflection data tied to drillhole stratigraphy have been used to constrain four main phases of basin development. These are: (a) Early Miocene (22–19 Ma) subsidence, dominantly bathyal water depths and deposition of minor submarine fans along the eastern basin margin. (b) Middle Miocene (19–14 Ma) widespread submarine fan deposition on a bathyal basin floor in the central STB. (c) Rapid Middle–Late Miocene (14–7 Ma) progradation of the shelf break northwards across the STB. (d) Widespread uplift and erosion of the STB during the latest Miocene–Pliocene (7–4.5 Ma). Bathyal water depths and fan deposition in the Early Miocene were influenced by vertical motions on major reverse faults and regional subsidence produced by subduction of the Pacific plate beneath northern New Zealand. Subsequent submarine fan deposition and northward shelf‐break progradation reflect increasing input of terrigenous material, primarily eroded from an uplifting region to the south of the STB. Sedimentation patterns in the STB are consistent with the age and locations of conglomerates deposited in onshore West Coast basins, related to this uplift and erosion. Sediment transport in the West Coast region was mainly parallel to NNE trending active reverse faults, and in the STB was perpendicular to the NE‐SW orientated shelf break, especially from ca. 14–7 Ma, when sedimentation rates exceeded fault‐displacement rates. Increases in sedimentation rates in the STB coincide with regional increases in the rates of shortening that appear to reflect plate boundary‐wide events and have been attributed to, or correlated with, increases in the plate convergence rate. Miocene sedimentation patterns in the STB thus reflect both intra‐basinal deformation and tectonic signals from the wider developing New Zealand plate boundary. 相似文献
208.
209.
Colombia has coasts on both the Atlantic and Pacific Oceans, but its marine fisheries are limited by the relatively small size of commercially important stocks. However, diverse fishery resources have traditionally been exploited by coastal communities, and industrial fisheries have grown in recent years with the intensification of tuna fishing in both oceans. The management of Colombia's fisheries has been hampered by frequent administrative changes, which has notably led to the disappearance of a part of the official landings data. We estimated total fisheries removals (reported plus discards and unreported catches) in the Colombian Atlantic and Pacific Oceans for the period 1950–2006. We used secondary sources of information to estimate missing data, and we estimated subsistence fishing and the unreported by-catches of the shrimp and tuna fisheries. We used available information on seafood prices to estimate the relative economic impact (gross revenues) of the small-scale and industrial sectors for the period 2000–2006. Our results suggest that for the period 1950–2006, the Colombian marine fisheries catches may have been almost twice the landings reported by FAO on behalf of the country (2.8 times higher in the Atlantic; 1.3 times higher in the Pacific). Although the total gross revenues of industrial fisheries were higher than those of the small-scale sector, the latter commanded higher gross revenues in the Atlantic in 2006. 相似文献
210.
Sources and fate of nutrients in a subtropical reservoir 总被引:1,自引:0,他引:1
Michele?A.?BurfordEmail author Susanne?A.?Green Andrew?J.?Cook Suzanne?A.?Johnson Jason?G.?Kerr Katherine?R.?O’Brien 《Aquatic Sciences - Research Across Boundaries》2012,74(1):179-190
This study examined the sources and fate of nutrient inputs from two principal tributaries to the eutrophic subtropical Wivenhoe
reservoir: an unregulated river and a dammed river with regular releases, during a period of declining reservoir water levels.
Nutrient budgets were constructed over a period of 6 years, and combined with short-term data on nutrient concentrations and
forms, and δ15N stable isotope data. Our study found that over a 6 year period, there was net retention of phosphorus (P) in the reservoir,
with 60% of inputs retained. Most of the P input load came from the unregulated river, with an agricultural catchment, during
periods of high flow. During one event half of the total TP load from the unregulated river in the study period was delivered
in only 12 days. Much of the P was dissolved inorganic P (DIP) and was derived from high P concentrations in soils and sediments.
This highlights the importance of appropriate catchment management practices to reduce P losses from terrestrial systems because
retention of P in reservoir sediments reduces the availability of this nutrient for agricultural production. In contrast,
there was negligible retention of nitrogen (N). The unregulated river was an important source of N derived from N fixation
in the river and adjacent soils, while the source from the dammed river was mostly reprocessed N. The high retention of P
relative to N is consistent with relatively higher accumulation of P in sediments. 相似文献