全文获取类型
收费全文 | 1156篇 |
免费 | 54篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 45篇 |
大气科学 | 65篇 |
地球物理 | 327篇 |
地质学 | 446篇 |
海洋学 | 114篇 |
天文学 | 147篇 |
综合类 | 6篇 |
自然地理 | 70篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 19篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 48篇 |
2017年 | 50篇 |
2016年 | 63篇 |
2015年 | 37篇 |
2014年 | 66篇 |
2013年 | 77篇 |
2012年 | 52篇 |
2011年 | 76篇 |
2010年 | 58篇 |
2009年 | 91篇 |
2008年 | 57篇 |
2007年 | 46篇 |
2006年 | 39篇 |
2005年 | 50篇 |
2004年 | 32篇 |
2003年 | 35篇 |
2002年 | 32篇 |
2001年 | 15篇 |
2000年 | 21篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1957年 | 3篇 |
1956年 | 4篇 |
1955年 | 3篇 |
1953年 | 3篇 |
1950年 | 3篇 |
1949年 | 2篇 |
排序方式: 共有1220条查询结果,搜索用时 671 毫秒
971.
Caterina Panzeca Aaron J. Beck Antonio Tovar-Sanchez Jose Segovia-Zavala Gordon T. Taylor Christopher J. Gobler Sergio A. Saudo-Wilhelmy 《Estuarine, Coastal and Shelf Science》2009,85(2):223-230
Distributions of dissolved vitamin B12 and total dissolved Co were measured to gain an understanding of the cycling of these interdependent micronutrients in six marine settings including; an upwelling location, a semi-enclosed bay, two urban coastal systems, and two open ocean locations. Along the coast of Baja California, Mexico, concentrations of B12 and dissolved Co varied from 0.2 to 11 pM and 180 to 990 pM, respectively. At a nearby upwelling station, vitamin B12 and Co concentrations ranged from 0.3 to 7.0 pM and 22 to 145 pM, and concentrations did not correlate with upwelling intensity. Concentrations of B12 were highest within Todos Santos Bay, a semi-enclosed bay off the coast of Baja California, Mexico, during a dinoflagellate bloom, ranging from 2 to 61 pM, while Co concentrations varied between 61 and 194 pM. In the anthropogenically impacted Long Island Sound, NY, U.S.A., B12 levels were between 0.1 and 23 pM and Co concentrations varied from 60 to 1900 pM. However, anthropogenic inputs were not evident in B12 levels in the San Pedro Basin, located outside Los Angeles, Ca, U.S.A., where concentrations of B12 were 0.2–1.8 pM, approximating observed open ocean B12 concentrations. In the Southern Ocean and North Atlantic Ocean, B12 levels were 0.4–4 pM and 0.2–2 pM, respectively. Total Co concentrations in the Southern Ocean and North Atlantic tended to be low; measuring 26–59 pM and 15–80 pM, respectively. These low Co concentrations may limit B12 synthesis and its availability to B12-requiring phytoplankton because the total dissolved Co pool is not necessarily entirely bioavailable. 相似文献
972.
Anderson H. Melo Peryclys R. O. Andrade Antonio J. C. Magalhães Daniel G. C. Fragoso Francisco P. Lima-Filho 《Basin Research》2020,32(5):1054-1080
Five 3rd-order depositional sequences are interpreted from the early Albian to late Campanian interval in the Potiguar Basin. An integrated analysis of seismic interpretations, well logs, cores and biostratigraphic data provides a stratigraphic framework composed by stratigraphic surfaces, systems tracts and sequences. Depositional Sequence 1 and 2 are, respectively, Albian and early to mid-Cenomanian aged and are composed by the falling stage, low stand, transgressive and high stand systems tracts. Depositional Sequence 3 is late Cenomanian to mid-Turonian aged and is composed by the transgressive and high stand systems tracts. Depositional sequences 4 and 5 are, respectively, late Turonian to mid-Santonian and late Santonian to mid-Campanian aged and are composed only by transgressive and high stand systems tracts. The lack of falling stage and low stand systems tracts in depositional sequences 3, 4 and 5, as well the increasing in transgressive and highstand systems tracts thickness as depositional sequences get younger, are reflection of an overall transgressive trend of a 2nd-order sequence. The interpretation proposed in this paper correlates onshore with offshore deposits within a seismic scale (3rd-order) sequence stratigraphy framework. This approach allows a better understanding of the Açu Formation, the primary oil-bearing formation of the Potiguar Basin. The Açu Formation is part of depositional sequences 1, 2 and 3 and is characterized by lateral and vertical variations of depositional systems instead of being associated to a specific depositional system. This sequence stratigraphy analysis can be used as a low-resolution framework for future high-resolution (4th-order scale) studies. 相似文献
973.
The aim was to evaluate the antioxidant defences and the occurrence of oxidative damage in Posidonia oceanica under a stress situation due to the epiphytism of the invasive macroalgae Lophocladia lallemandii. P. oceanica leaves were collected in the absence (control station) and in the presence of the epiphytic algae L. lallemandii and the antioxidant enzyme activities, markers of oxidative damage, and hydrogen peroxide production were determined. Antioxidant enzyme - catalase, glutathione peroxidase and superoxide dismutase - activities were significantly higher in Posidonia epiphytized by L. lallemandii. Malondialdehyde, protein carbonyl derivates, and glutathione levels were also higher in L. lallemandii epiphytized P. oceanica leaves compared to control samples. The production of hydrogen peroxide was also significantly increased when Posidonia was epiphytized by L. lallemandii. The invasion of P. oceanica meadows by L. lallemandii appeared to induce oxidative stress in the seagrass as evidenced by increased levels of oxidative stress markers and antioxidant defences. 相似文献
974.
Cristián Rodrigo Antonio González-Fernández Emilio Vera 《Marine Geophysical Researches》2009,30(1):1-19
Multichannel seismic reflection data recorded between Arauco Gulf (37°S) and Valdivia (40°S), on the Chilean continental margin,
were processed and modeled to obtain seismic images and sub-surface models, in order to characterize the variability of the
bottom-simulating reflector (BSR), which is a geophysical marker for the presence of gas hydrates. The BSR is discontinuous
and interrupted by submarine valleys, canyons, as well as by faults or fractures. The BSR occurrence is more common south
of Mocha Island due to moderate slopes and greater organic matter contribution by rivers in that area. Tectonic uplift and
structural instability change the stability gas hydrate zone and consequently the BSR position, creating in some cases missing
or double BSRs. Our modeling supports the presence of gas hydrate above the BSR and free gas below it. Higher BSR amplitudes
support higher hydrate or free gas concentrations. In the study area, gas hydrate concentration is low (an average of 3.5%)
suggesting disseminated gas hydrate distribution within the sediments. Also higher BSR amplitudes are associated with thrust
faults in the accretionary prism, which serve as conduits for gas flow from deeper levels. This extra gas supply produces
a wider thickness of gas hydrates or free gas. 相似文献
975.
Christian Gorini Bilal U. Haq Antonio Tadeu dos Reis Cleverson Guizan Silva Alberto Cruz Emilson Soares Didier Grangeon 《地学学报》2014,26(3):179-185
The margin of the Foz do Amazonas Basin saw a shift from predominantly carbonate to siliciclastic sedimentation in the early late Miocene. By this time, the Amazon shelf had also been incised by a canyon that allowed direct influx of sediment to the basin floor, thus confirming that the palaeo‐Amazon fan had already initiated by that time (9.5–8.3 Ma). Above this interval, during a prolonged lowstand, Messinian third‐order sequences are preserved only in the incised‐valley fills of the canyon with no equivalent strata on the shelf. Third‐ and fourth‐order sequences younger than Messinian are preserved on the shelf after sea‐level rise above the shelf by the early Pliocene. Sequences younger than 3.8 Ma often show fourth‐order cyclicity with an average duration of 400 ka (larger scale eccentricity cycles) often preserved in high‐sedimentation‐rate areas of river deltas. Mass wasting and transportation of slope sediments to the basin began to play an important role in sediment dispersal at least as far back as the mid‐Pliocene, after rapid progradation had produced steeper slopes more prone to failure. 相似文献
976.
Salvatore Alparone Graziella Barberi Elisabetta Giampiccolo Vincenza Maiolino Antonino Mostaccio Carla Musumeci Antonio Scaltrito Luciano Scarfì Tiziana Tuv Andrea Ursino 《地学学报》2020,32(5):334-344
3D earthquake locations, focal mechanisms and stress tensor distribution in a 16‐month interval covering the 2018 Mt. Etna flank eruption, enabled us to investigate the relationship between magma intrusion and structural response of the volcano and shed light on the dynamic processes affecting the instability of Mt. Etna. The magma intrusion likely caused tension in the flanks of the volcano, leading to significant ground deformation and redistribution of stress on the neighbouring faults at the edge of Mt. Etna's unstable sector, encouraging the ESE sliding of the eastern flank of the volcano. Accordingly, FPSs of the post‐eruptive events show strike slip faulting mechanisms, under a stress regime characterized by a maximum compressive σ1, NE‐SW oriented. In this perspective, any flank eruption could temporarily enhance the sliding process of both the southern and eastern flanks of the volcano. 相似文献
977.
Bonaduce Antonio Staneva Joanna Grayek Sebastian Bidlot Jean-Raymond Breivik Øyvind 《Ocean Dynamics》2020,70(12):1547-1569
Ocean Dynamics - The contribution of sea-state-induced processes to sea-level variability is investigated through ocean-wave coupled simulations. These experiments are performed with a... 相似文献
978.
Irene Novo-Fernández Richard Albert Ricardo Arenas Antonio Garcia-Casco Rubén Díez Fernández Sonia Sánchez Martínez Axel Gerdes Christian De Capitani 《Journal of Metamorphic Geology》2020,38(6):629-653
The Upper Units of the allochthonous complexes of the NW Iberian Massif constitute a terrane with continental affinity. They represent the vestiges of a Cambrian magmatic arc developed in the periphery of Gondwana (West African Craton) which was involved in the Devonian Variscan collision, undergoing high-P, high-T metamorphism. This includes ultramafic rocks, high-P mafic rocks (eclogites and granulites) and high-P migmatitic paragneisses. The latter rocks show an extensive migmatization with the leucosomes oriented parallel to the regional foliation. The migmatitic paragneisses are composed of garnet, kyanite, biotite, quartz, plagioclase, K-feldspar, rutile and Ti-hematite. Thermodynamic modelling using the measured bulk composition in the NCKFMASTHO system indicates metamorphic peak conditions of ~15 kbar and ~800 to 835°C, followed by a significant cooling. The prograde evolution is assessed by means of a melt-reintegration approach, using the composition of the garnet and its inclusions. An appropriate composition of liquid is added to the measured bulk composition to emulate the pre-melting bulk composition. Modelling of this melt-reintegrated composition allows to identify a colder high-P episode below ~500°C. Zircon crystals extracted from the leucosomes show overgrowths crystallized from the partial melt at c. 389 Ma (U–Pb system). The P–T–t path proposed reveals a subduction of the peri-Gondwanan arc-derived section down to mantle depths. An isobaric heating stage occurred as a result of residence at great depths and/or inception of a transient oceanic basin at c. 395 Ma. The ensuing near-isothermal exhumation occurred due to the extension related to the inception of the basin, reaching the thermal peak shortly before c. 389 Ma. Subsequent cooling is related to the underthrusting of colder oceanic and transitional crust below the HP-HT Upper Units. 相似文献
979.
Isotopic and hydrochemistry spatial variation of sulfate for groundwater characterization in karstic aquifers
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)
Antonio González‐Ramón Manuel López‐Chicano Fernando Gázquez Juan José Durán‐Valsero Antonio Pedrera Ana Ruiz‐Constán Elena González‐Egea 《水文研究》2017,31(18):3242-3254
The Sierra Gorda aquifer is one of the most extensive of southern Spain. The main groundwater discharge is produced at its northern boundary through several high‐flow springs. In this study, stable isotopes of dissolved sulfate (δ34S and δ18O) and groundwater chemistry were used to determine the origin of the sulfate and to characterize the groundwater flow. We sampled the main springs, as well as other minor outlets related to perched water tables, in order to determine the different sources of SO42? (e.g., dissolution of evaporites and atmospheric deposition). The substantial difference in the amount of dissolved SO42? between the springs located in its northwestern part (≈25 mg/L) and those elsewhere in the northern part (≈60 mg/L) suggests zones with separate groundwater flow systems. A third group of springs, far from the northeastern boundary of the permeable outcrops, shows higher SO42? content than the rest (≈125 mg/L). The isotopic range of sulfate (?0.3‰ to 14.82‰ V‐CTD) points to several sources, including dissolution of Triassic or Miocene evaporites, atmospheric deposition, and decomposition of organic material in the soil. Among these, the dissolution of Triassic gypsum—which overlies the saturated zone as a consequence of the folds and faults that deform the aquifer—is the main source of SO42? (range from 12.79‰ to 14.82‰ V‐CTD). This range is typical for Triassic gypsum. The higher karstification in the western sector, together with important differences in the saturated thickness between the western and eastern sectors, would also be due to the tectonic structure and could explain the difference in SO42? contents in the water. This singular arrangement may cause a higher residence time of groundwater in the eastern sector; thus, a higher contact time with Triassic evaporitic rocks is inferred. Accordingly, the stable isotopes of SO42? are found to be a valuable tool for identifying areas with different flow systems in the saturated zone of karstic aquifers, as well as for evaluating aspects such as the degree of karstification . 相似文献
980.
Detrital zircon U–Pb provenance and palaeogeography of Triassic rift basins in the Marrakech High Atlas
下载免费PDF全文
![点击此处可从《地学学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The Marrakech High Atlas contains some of the best exposures of the Triassic early‐rift strata related to Atlantic opening in NW Africa. We present the first detrital zircon U–Pb data of five Triassic redbed samples from the Tizi n'Test basin to quantify sediment provenance, transport and dispersal patterns during early rifting. These U–Pb ages document dominant sediment sourcing from the south, the Anti‐Atlas domain, with very limited to absent input from the Variscan Meseta domain to the north. This combined with stratigraphic and thermochronologic information points to a highly asymmetric palaeogeography during Triassic rifting. Furthermore, the occurrence of Archaean detrital zircon grains in Triassic sandstone, likely recycled from the Reguibat shield, suggests the presence of a fully developed regional drainage system with rivers and catchments reaching hundreds of kilometres into the hinterland of the rift flank. 相似文献