全文获取类型
收费全文 | 1522篇 |
免费 | 97篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 102篇 |
地球物理 | 364篇 |
地质学 | 651篇 |
海洋学 | 107篇 |
天文学 | 270篇 |
综合类 | 3篇 |
自然地理 | 111篇 |
出版年
2023年 | 10篇 |
2022年 | 17篇 |
2021年 | 27篇 |
2020年 | 42篇 |
2019年 | 31篇 |
2018年 | 56篇 |
2017年 | 55篇 |
2016年 | 90篇 |
2015年 | 58篇 |
2014年 | 78篇 |
2013年 | 114篇 |
2012年 | 80篇 |
2011年 | 103篇 |
2010年 | 78篇 |
2009年 | 92篇 |
2008年 | 74篇 |
2007年 | 44篇 |
2006年 | 49篇 |
2005年 | 71篇 |
2004年 | 64篇 |
2003年 | 31篇 |
2002年 | 28篇 |
2001年 | 22篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 18篇 |
1995年 | 22篇 |
1994年 | 13篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 16篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1969年 | 8篇 |
排序方式: 共有1629条查询结果,搜索用时 15 毫秒
41.
Márian Urban Rainer Thomas Vratislav Hurai Patrik Koneèný Martin Chovan 《Mineralium Deposita》2006,40(8):867-873
CO2 inclusions with density up to 1,197 kg m−3 occur in quartz–stibnite veins hosted in the low-grade Palaeozoic basement of the Gemericum tectonic unit in the Western Carpathians. Raman microanalysis corroborated CO2 as dominant gas species accompanied by small amounts of nitrogen (<7.3 mol%) and methane (<2.5 mol%). The superdense CO2 phase exsolved from an aqueous bulk fluid at temperatures of 183–237°C and pressures between 1.6 and 3.5 kbar, possibly up to 4.5 kbar. Low thermal gradients (∼12–13°C km−1) and the CO2–CH4–N2 fluid composition rule out a genetic link with the subjacent Permian granites and indicate an external, either metamorphogenic (oxidation of siderite, dedolomitization) or lower crustal/mantle, source of the ore-forming fluids.According to microprobe U–Pb–Th dating of monazite, the stibnite-bearing veins formed during early Cretaceous thrusting of the Gemeric basement over the adjacent Veporic unit. The 15- to 18-km depth of burial estimated from the fluid inclusion trapping PT parameters indicates a 8- to 11-km-thick Upper Palaeozoic–Jurassic accretionary complex overlying the Gemeric basement and its Permo-Triassic autochthonous cover. 相似文献
42.
Emmanuel Causse 《Geophysical Prospecting》2002,50(3):317-327
Seismic inversion by modelling and data fitting depends on the criterion chosen to measure the misfit between observed and modelled data. The popular least‐squares error criterion has an important drawback: it is sensitive both to the shape of the recording surface and to velocity variations along this surface. Tests on synthetic seismic reflection data show that least‐squares inversion may work surprisingly poorly in situations where (i) the range of angles between reflected rays and the acquisition surface is large, (ii) the velocity varies significantly along this surface, or (iii) a compensation for the effects of dissipation is applied to the gradients. In these situations, the gradients may contain important artefacts and have incorrect amplitudes. The outgoing flux of energy of the residual wavefield across the acquisition surface provides an alternative measure of the data misfit which is independent of the recording surface, provided this surface is closed, and which is only sensitive to the aperture in the practical situation of an open surface or line of receivers. Energy‐flux inversion presents a strong resemblance to reverse‐time migration, but with the additional possibility of iteratively improving the images. In all the tests, energy‐flux inversion provided better images than least‐squares inversion. 相似文献
43.
Frédérick Delay Hélène Housset-Resche Gilles Porel Ghislain de Marsily 《Mathematical Geology》1996,28(1):45-71
A new method for solving the transport equation based on the management of a large numbe of particles in a discretized 2-D domain is presented. The method uses numerical variables to represent the number of particles in a given mesh and is more complex than the 1-D problem. The first part of the paper focuses on the specific management of particles in a 2-D problem. The method also would be valid for three dimensions as long as the medium can be modeled similar to a layered system. As the particles are no longer tracked individually, the algorithm is fast and does not depend on the number of particles present. The numerical tests show that the method is nearly numerical dispersion free and permits accurate calculations even for simulations of low-concentration transport. Because each mesh is considered as a closed system between two successive time steps, it is easy to add adsorption phenomenon without any problem of numerical stability. The model is tested under conditions that are extremely demanding for its operating mode and gives a good fit to analytical solutions. The conditions in which it can be used to best advantage are discussed. 相似文献
44.
Emmanuel Damien Rivière Michel Pirre Gwenaël Berthet Jean-Baptiste Renard Franck Lefèvre 《Journal of Atmospheric Chemistry》2004,48(3):261-282
Two cases of simultaneous nighttime measurements of NO2 and OClO in the winter polar stratosphere are analyzed in order to test our present knowledge of halogen chemistry in the presence of high amount of NO2 at low temperature. Comparisons with Lagrangian model calculations using several hypotheses are performed. First simulations, using the admitted constant rates of chemical reaction, strongly underestimate the measured OClO while the NO2 profiles are correctly reproduced. If uncertainties in actinic fluxes calculations are taken into account, simulation results do not show a significant reduction of the underestimation. A better agreement can be achieved if the formation of unstable isomers of ClONO2 and of BrONO2 occurs in the cold conditions of the polar stratosphere. An approximate value of the branching ratios of the channels leading to ClONO2 and ClOONO, and to BrONO2 and BrOONO, necessary to reproduce both OClO and NO2 is given and discussed. 相似文献
45.
A Reflection on Mg, Cd, Ca, Li and Si Isotopic Measurements and Related Reference Materials 总被引:6,自引:1,他引:6
Jean Carignan Damien Cardinal Anton Eisenhauer Albert Galy Mark Rehkamper Frank Wombacher Nathalie Vigier 《Geostandards and Geoanalytical Research》2004,28(1):139-148
This contribution aims to report the reflections we had with the scientific community during two international workshops on reference materials for stable isotopes in Davos (2002) and Nice (2003). After evaluating the isotopic homogeneity of some existing reference materials, based on either certificates, literature data or specific inter-laboratory rounds, we confirm these as primary reference materials or propose new ones relative to which stable isotope compositions should be reported. We propose DSM-3 for Mg, NIST SRM 915a for Ca, L-SVEC for Li and NBS28 for Si. Cadmium does not yet have a well identified delta zero material, although three commercial mono-elemental Cd solutions have yielded the same isotopic composition relative to one another. In order to scale the linearity of any mass spectrometer, some secondary reference materials are also proposed: Cambridge-1 solution for Mg, the "Münster-Cd" and JEPPIM Cd solutions for Cd and the "Big Batch" silicate for Si. The team from Nancy propose to prepare a mixed spike solution for Li isotopes. Well-characterised natural samples such as ocean or continental waters, diatoms, sponges, rocks and minerals are needed to validate the entire analytical procedure, particularly to take into account the effect of sample mineralisation and of chemical manipulations for elemental separation prior to analysis. 相似文献
46.
Nicolas Domange Caroline Grégoire Véronique Gouy Michèle Tremolières 《Comptes Rendus Geoscience》2004,336(1):49-58
The soil solution sampling by ceramic cups allows pesticide transfer monitoring in the soil during long times. The ageing of material involves a bias in the sampling results. In laboratory, the comparison of two types of ceramic suction cups, new and installed in situ during four years, shows a modification of the hydrodynamic properties and a possible evolution of the adsorption capacity of the matrix. The passage rate, as well qualitative as quantitative, is better for the old material. Recommendations about site management are finally exposed. To cite this article: N. Domange et al., C. R. Geoscience 336 (2004). 相似文献
47.
In the Gran Paradiso massif (western Alps), the boundary between the Erfaulet orthogneiss and the overlying metasediments (Money Complex) is interpreted as a Late Palaeozoic intrusive contact. Major arguments in favour of this hypothesis are: (i) the obliquity of the sedimentary layering with respect to the contact; (ii) the presence of aplitic dykes within the Money Complex; (iii) the lack of a mylonitic zone; and (iv) rare relics of an early generation of garnet in the Money metasediments, interpreted as evidence of the contact metamorphism of the Erfaulet granite. To cite this article: B. Le Bayon, M. Ballèvre, C. R. Geoscience 336 (2004). 相似文献
48.
Jean-Marie Dautria Jean-Michel Liotard Danièle Briot 《Comptes Rendus Geoscience》2004,336(11):971-981
Sr and Nd isotopic compositions of one trachyte, eight phonolites and five basalts have been measured. The isotopic characteristics of the trachyte can be explained by a combined assimilation–fractional crystallization process within an upper crustal magmatic chamber. Some phonolites display isotopic signatures identical to basalts, suggesting that they have been protected against any crustal assimilation during their formation. Some others have low Sr contents, whereas they are enriched in radiogenic Sr (0.70451<87Sr/86Sri<0.71192), and display basaltic 143Nd/144Nd ratios. Both observations could be explained by very strong alkali feldspar fractionation and by subsequent very low assimilation of surrounding rocks (between 0.3 and 4%) during intrusion. To cite this article: J.-M. Dautria et al., C. R. Geoscience 336 (2004). 相似文献
49.
Weights of Evidence Modeling of Mineral Potential: A Case Study Using Small Number of Prospects,Abra, Philippines 总被引:9,自引:1,他引:9
Weights of evidence (WofE) modeling usually is applied to map mineral potential in areas with large number of deposits/prospects. In this paper, WofE modeling is applied to a case study area measuring about 920 km2 with 12 known porphyry copper prospects. A pixel size of 100 m × 100 m was used in the spatial data analyses to represent in a raster-based GIS lateral extents of prospects and of geological features considered as spatial evidence. Predictor maps were created based on (a) estimates of studentized values of positive spatial association between prospects and spatial evidence; (b) proportion of number of prospects in zones where spatial evidence is present; and (c) geological interpretations of positive spatial association between prospects and spatial evidence. Uncertainty because of missing geochemical evidence is shown to have an influence on tests of assumption of conditional independence (CI) among predictor maps with respect to prospects. For the final predictive model, assumption of CI is rejected based on omnibus test but is accepted based on a new omnibus test. The final predictive model, which delineates 30% of study area as zones with potential for porphyry copper, has 83% success rate and 73% prediction rate. The results demonstrate plausibility of WofE modeling of mineral potential in large areas with small number of mineral prospects. 相似文献
50.
Rainfall thresholds for landsliding in the Himalayas of Nepal 总被引:5,自引:0,他引:5
Emmanuel J. Gabet Douglas W. Burbank Jaakko K. Putkonen Beth A. Pratt-Sitaula Tank Ojha 《Geomorphology》2004,63(3-4):131-143
Landsliding of the hillslope regolith is an important source of sediment to the fluvial network in the unglaciated portions of the Himalayas of Nepal. These landslides can produce abrupt increases of up to three orders of magnitude in the fluvial sediment load in less than a day. An analysis of 3 years of daily sediment load and daily rainfall data defines a relationship between monsoonal rainfall and the triggering of landslides in the Annapurna region of Nepal. Two distinct rainfall thresholds, a seasonal accumulation and a daily total, must be overcome before landslides are initiated. To explore the geomorphological controls on these thresholds, we develop a slope stability model, driven by daily rainfall data, which accounts for changes in regolith moisture. The pattern of rainfall thresholds predicted by the model is similar to the field data, including the decrease in the daily rainfall threshold as the seasonal rainfall accumulation increases. Results from the model suggest that, for a given hillslope, regolith thickness determines the seasonal rainfall necessary for failure, whereas slope angle controls the daily rainfall required for failure. 相似文献