全文获取类型
收费全文 | 236篇 |
免费 | 20篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 5篇 |
地球物理 | 71篇 |
地质学 | 80篇 |
海洋学 | 41篇 |
天文学 | 46篇 |
综合类 | 2篇 |
自然地理 | 9篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 16篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 19篇 |
2012年 | 14篇 |
2011年 | 16篇 |
2010年 | 10篇 |
2009年 | 17篇 |
2008年 | 20篇 |
2007年 | 17篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有259条查询结果,搜索用时 15 毫秒
251.
A brief summary about the composition and origins of the U deposit is present. The mineralization is composed by secondary uranium phosphates (saleeite and meta-saleeite). The precipitation was probably the main responsible factor for U retention within the quartz veins leading to the uranium phosphate mineralization of Vale de Abrutiga. 相似文献
252.
Simon Damien Carrière Konstantinos Chalikakis Chloé Ollivier Tom Heath Marie Mangin Jean Kempf Jacques Bablon Randriatsitohaina Marina Gillon Théodore Razakamanana Jean Lapègue 《Environmental Earth Sciences》2018,77(21):734
Southwestern Madagascar is a semi-arid region and a hot-spot of global change. On the Mahafaly plateau, people live with quasi-permanent water stress and groundwater, the only available resource, is difficult to exploit due to a complex hydrogeological environment. A methodology (suitable for humanitarian projects; <?40 k€) was developed in four phases to assess the sustainable exploitation of the water resource: (A) regional scale exploration, (B) village scale exploration, (C) drilling campaign, and (D) hydro-climatic monitoring. This integrated hydrogeophysical approach involves geophysical measurements (262 TEM-fast soundings, 2588 Slingram measurements, 35 electrical soundings), hydrochemical analyses (112 samples), and a piezometric survey (127 measurements). Two groundwater resources were identified, one deep (below 150 m) and one shallow (<?20 m). Hydrochemical results highlighted the vulnerability of both resources: anthropic contamination for the shallower and seawater intrusion for the deeper. Therefore, subsequent geophysical surveys supported the siting of six boreholes and three wells in the shallow aquifer. This methodological approach was successful in this complex geological setting and requires testing at other sites in and outside Madagascar. The study demonstrates that geophysical results should be used in addition to drilling campaigns and to help monitor the water resource. In fact, to prevent over-exploitation, piezometric and meteorological sensors were installed to monitor the water resource. This unique hydro-climatic observatory may help (1) non-governmental organization and local institutions prevent future water shortages and (2) scientists to understand better how global change will affect this region of the world. 相似文献
253.
Marina Tagliaferro María Laura Miserendino Ana Liberoff Analia Quiroga Miguel Pascual 《Limnologica》2013,43(6):500-509
Three large rivers have their headwaters in the Patagonian Ice Fields (PIFs) in the Andes Mountains, the largest mid-latitude ice masses on Earth: Santa Cruz, Baker and Pascua. They are the last large free flowing rivers in Patagonia, but plans are advanced for building dams for hydroelectric power generation. The three PIF rivers, with a discharge dominated by ice melt, share a common, unique hydrograph compared to that of the other eight large rivers in the region: a distinct seasonal cycle, and an extremely stable discharge, with much lower variability than other rivers. In this study we present the first extensive survey of habitats and benthic macroinvertebrates in the least studied system, the Santa Cruz River. We assess how much of the natural capital provided and sustained by benthic invertebrates are expected to be lost by flooding and discuss how dams would affect riverine habitat and biota. In the Santa Cruz River, we conducted an intensive field survey during September 2010; a total of 52 sites located at regular 6 km intervals were sampled along the 310 river-km for macroinvertebrates and seventeen habitat variables. Although some habitat structure is apparent at the local scale, the Santa Cruz River could be described as very homogeneous. Macroinvertebrate density and the richness (38 genera) found in the Santa Cruz River resulted to be one of the lowest in comparison with 42 other Patagonian rivers. Albeit weak, the structure of the macroinvertebrates assemblages was successfully described by a reduced set of variables. The reduced flow variation and the lack of bed scouring flows have a direct and negative effect on the heterogeneity of riverbeds and banks. The high turbidity of the Santa Cruz River may also contribute to shorter food webs, by affecting autotrophic production, general trophic structure, and overall macroinvertebrate productivity and diversity. Dams will obliterate 51% of the lotic environment, including the most productive sections of the river according to our macroinvertebrate data. Since Santa Cruz River has a naturally homogeneous flow cycle, dams may provide more variable flows and more diverse habitat. Our data provide critically valuable baseline information to understand the effects of dams on the unique set of glacial driven large rivers of Patagonia. 相似文献
254.
Landscape curvature evolves in response to physical, chemical, and biological influences that cannot yet be quantified in models. Nonetheless, the simplest models predict the existence of equilibrium hillslope profiles. Here, we develop a model describing steady‐state regolith production caused by mineral dissolution on hillslopes which have attained an equilibrium parabolic profile. When the hillslope lowers at a constant rate, the rate of chemical weathering is highest at the ridgetop where curvature is highest and the ridge develops the thickest regolith. This result derives from inclusion of all the terms in the mathematical definition of curvature. Including these terms shows that the curvature of a parabolic hillslope profile varies with distance from the ridge. The hillslope model (meter‐scale) is similar to models of weathering rind formation (centimeter‐scale) where curvature‐driven solute transport causes development of the thickest rinds at highly curved clast corners. At the clast scale, models fit observations. Here, we similarly explore model predictions of the effect of curvature at the hillslope scale. The hillslope model shows that when erosion rates are small and vertical porefluid infiltration is moderate, the hill weathers at both ridge and valley in the erosive transport‐limited regime. For this regime, the reacting mineral is weathered away before it reaches the land surface: in other words, the model predicts completely developed element‐depth profiles at both ridge and valley. In contrast, when the erosion rate increases or porefluid velocity decreases, denudation occurs in the weathering‐limited regime. In this regime, the reacting mineral does not weather away before it reaches the land surface and simulations predict incompletely developed profiles at both ridge and valley. These predictions are broadly consistent with observations of completely developed element‐depth profiles along hillslopes denuding under erosive transport‐limitation but incompletely developed profiles along hillslopes denuding under weathering limitation in some field settings. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
255.
The origin of chromitites and related PGE mineralization in the Bushveld Complex: new mineralogical and petrological constraints 总被引:2,自引:0,他引:2
Naldrett A. J. Wilson Allan Kinnaird Judith Yudovskaya Marina Chunnett Gordon 《Mineralium Deposita》2012,47(3):209-232
This article reports a study of chromitites from the LG-1 to the UG-2/3 from the Bushveld Complex. Chromite from massive chromitite
follows two compositional trends on the basis of cation ratios: trend A—decreasing Mg/(Mg + Fe) with increasing Cr/(Cr + Al);
trend B—decreasing Mg/(Mg + Fe) with decreasing Cr/(Cr + Al). The chromitites are divided into five stages on the basis of
which trend they follow and the data of Eales et al. (Chemical Geology 88:261–278, 1990) on the behaviour of the Mg/Fe ratio of the pyroxene and whole rock Sr isotope composition of the environment in which they
occur. Following Eales et al. (Chemical Geology 88:261–278, 1990), the different characteristics of the stages are attributed to the rate at which new magma entered the chamber and the effect
of this on aAl2O3 and, in the case of stage 5, the appearance of cumulus plagioclase buffering the aAl2O3. The similarity of PGE profiles across the MG-3 and MG-4 chromitites that are separated laterally by up to 300 km and the
variation in V in the UG-2 argue that the chromitites have largely developed in situ. Modelling using the programme MELTS
shows that increase in pressure, mixing of primitive and fractionated magma, felsic contamination of primitive magma or addition
of H2O do not promote crystallization of spinel before orthopyroxene (in general they hinder it) and that the Cr2O3 content of the magma was of the order of 0.25 wt.%. Less than 20% of the chromite in the magma is removed before orthopyroxene
joins chromite, which implies a >13-km thickness of magma for the Critical Zone. It is suggested that the large excess of
magma has escaped up marginal structures such as the Platreef. The PGE profile of chromitites depends on whether sulphide
accumulated or not along with chromite. Modelling shows that contamination of Critical Zone magma with a felsic melt will
induce sulphide immiscibility, although not chromite precipitation. The LG-1 to LG-4 chromitites developed without sulphide,
whilst those from the LG-5 upwards had associated liquid sulphide. Much of the sulphide originally in the LG-5 and above has
been destroyed as a result of reaction with the chromite. 相似文献
256.
正1 Introduction On the territory Kulunda Plain,located to the south-west of the Ob’plateau,there are more than 3,000 fresh and salt lakes with water TDS range from 1 to 430 g/L.The interest in these lakes was associated mainly with the study of 相似文献
257.
Ostreopsis ovata is an epiphytic potentially toxic dinoflagellate. It has a world-wide distribution, normally associated with other epiphytic or benthic dinoflagellates. In tropical seas O. ovata is often associated with the genera Gambierdiscus, Coolia and Prorocentrum, causing cinguatera fish poisoning. Recently, Ostreopsis spp. blooms in the Tyrrhenian and southern Adriatic Sea have been related to human health problems, such as breathing and skin irritation. Here we report the first record of Ostreopsis cfr. ovata in the Northern Adriatic Sea. O. cfr. ovata was isolated from macroalgae in two areas, the Gulf of Trieste (Italy) and close to Rovinj (Croatia). The microalga was identified by scanning electron microscopy and by fluorescence light microscopy. Size range and thecal pore structure were similar to those described for O. cfr. ovata in previous studies. Ostreopsis cfr. ovata was present on all the macroalgae collected, particularly browns and reds. The microalgal association on macroalgae was mostly composed of Ostreopsis sp., Coolia monotis and Coscinodiscus sp. 相似文献
258.
The regional distribution and chemical composition of massive and disseminated chromitites through a Platreef sequence and
along a strike distance of over ∼20 km were investigated to correlate them both within the framework of the northern limb
and to the eastern and western limbs of the Bushveld Complex. The chromitite layers and seams of the Platreef form two main
chromite-bearing zones: the Upper Chromitite that occurs as two to three discontinuous seams in feldspathic pyroxenite at
approximately 20 m below the Platreef top contact and the Lower Chromitite that is composed of multiple seams in feldspathic
harzburgite, pyroxenite and norite close to the bottom contact of the Platreef with footwall. Electron micro-probe analyses
reveal that the chemical composition of chromite depends on the host rock type. Norite and pyroxenite host chromite with the
highest Cr2O3 content while harzburgite-hosted chromites are Cr and Mg poor. The wide range in chromite compositions is explained by the
influence of late-magmatic processes including post-cumulus growth and re-equilibration, interaction with fluid- and sulphide-saturated
magmatic liquid and contact metamorphism. Each of these processes is characterised by its own distinct geochemical signature,
but generally they lead to a decrease in Mg and Al and an increase in both di- and tri-valent Fe in the chromite. The occurrence
of chromitite locally on the different distance from the contact between the upper Platreef sills and the overlying Main Zone
magma suggests erosion of the upper Platreef by the Main Zone as it was emplaced. The localisation of chromitites supports
an independent development of the northern limb during the Critical Zone emplacement although the chemical composition of
chromite and co-existing silicates from ultramafic rocks suggest a Critical Zone affinity with the eastern and western limbs
of the Bushveld Complex. 相似文献
259.
Nissrine Maad Pascal Le Roy Mohamed Sahabi Marc-André Gutscher M. Hssain Nathalie Babonneau Marina Rabineau Brigitte Van Vliet Lanoë 《Comptes Rendus Geoscience》2010,342(9):731-740
A recent high resolution seismic survey was carried out along the North-West Moroccan Atlantic continental shelf to perform sequence stratigraphy and to better understand the link between the onshore observations across the western termination of the Rif front and the multibeam bathymetric data previously collected across the Gulf of Cadiz. Seismic interpretation clearly shows evidence of deformation affecting the Pleistocene sedimentary cover. This is mainly located between the Lalla Zahra ridge and the Neogene nappes that outcrop at the seabed to the North of Larache, where the identified structures bound the upper part of a gravitationally spreading lobe and are interpreted to be developed by activation of the major tectonic structures located at the southern front of the Rif Cordillera. The offshore extension of the Lalla Zahra Ridge is characterised by an east-west trending major folded and faulted corridor. This structure marks the active front of Prerifan area and corresponds to a major Quaternary kinematic boundary in the western prolongation of the ENE-WSW trending Jebha fault. 相似文献