全文获取类型
收费全文 | 1098篇 |
免费 | 84篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 116篇 |
地球物理 | 348篇 |
地质学 | 410篇 |
海洋学 | 76篇 |
天文学 | 148篇 |
综合类 | 10篇 |
自然地理 | 61篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 34篇 |
2020年 | 31篇 |
2019年 | 13篇 |
2018年 | 60篇 |
2017年 | 55篇 |
2016年 | 106篇 |
2015年 | 67篇 |
2014年 | 86篇 |
2013年 | 79篇 |
2012年 | 44篇 |
2011年 | 60篇 |
2010年 | 62篇 |
2009年 | 66篇 |
2008年 | 49篇 |
2007年 | 29篇 |
2006年 | 32篇 |
2005年 | 24篇 |
2004年 | 25篇 |
2003年 | 24篇 |
2002年 | 30篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1975年 | 1篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1960年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有1183条查询结果,搜索用时 343 毫秒
951.
952.
953.
J. Perez-Oregon A. Muñoz-Diosdado A. H. Rudolf-Navarro A. Guzmán-Sáenz F. Angulo-Brown 《Journal of Seismology》2018,22(4):1025-1035
The study of the Gutenberg-Richter (GR) parameters a and b has been very important to describe and characterize the seismicity over the different seismic provinces around the world. As far as we know, the possible correlation between the GR parameters a and b has not received enough attention. Bayrak et al. reported the a and b values for 27 active seismic regions around the boundaries of the main tectonic plates of the world. From these data, we found that there exists a positive correlation between the a and b parameters (R =?0.85, R2 =?0.72). On the other hand, we made around 150 computer runs of a spring-block model proposed by Olami et al. (Phys Rev Lett 68(8):1244–1247, 1992). This model roughly emulates the interaction between two fault planes and it reaches a self-organized critical state. With these simulations, we also found that the a and b parameters are positively correlated. Motivated by these results, we propose an analytical demonstration that indeed a and b are positively correlated. In addition, we discuss on other possible applications of the spring-block model to actual seismicity and to frictional experiments made with sandpapers. 相似文献
954.
Castañeda Javiera V. Bronfman Nicolás C. Cisternas Pamela C. Repetto Paula B. 《Natural Hazards》2020,103(2):1881-1904
Natural Hazards - Understanding the culture of preparedness is essential to improve public policies and programs aimed to promote population preparedness to cope with natural hazards. The present... 相似文献
955.
Low‐P melting of metapelitic rocks and the role of H2O: Insights from phase equilibria modelling
下载免费PDF全文
![点击此处可从《Journal of Metamorphic Geology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Alfonso M. Sola Pavlina Hasalová Roberto F. Weinberg Néstor O. Suzaño Raúl A. Becchio Fernando D. Hongn Nilson Botelho 《Journal of Metamorphic Geology》2017,35(9):1131-1159
Water‐fluxed melting has long been thought to have a minor influence on the thermal and chemical structure of the crust. We report here on amphibolite facies metasedimentary rocks from the 490–450 Ma Famatinian Orogen, in northwest Argentina, that have undergone water‐fluxed incongruent biotite melting at relatively low temperature, which have produced and lost a significant volume of melt. The protoliths consist of the turbiditic Puncoviscana Formation (Neoproterozoic to Early Cambrian). The field area exhibits a condensed metamorphic field gradient, from greenschist to amphibolite facies suprasolidus conditions, recording a low pressure almost isobaric path, reaching peak conditions estimated at 700°C at 4 kbar. Thermodynamic modelling in the MnNCKFMASHTO system is applied to investigate melting at such low pressure as a function of water content. Calculations using a typical turbidite composition show how small amounts of added free H2O may increase significantly the melt fraction with little or no change in either the melt or residual phase compositions. They indicate negligible difference in normative An–Ab–Or proportions and ferromagnesian contents between melts derived by dehydration and water‐fluxed melts. The same is true for the content of H2O dissolved in melts, which remains constant and the melt produced is granitic whether or not aqueous fluids are present. Thus, neither the residue nor the melt composition are indicators of the presence of aqueous fluids during anatexis. Recognizing the impact of small additions of H2O to an anatectic terrane may therefore be difficult. The most significant change related to water‐fluxing is the relative proportions of minerals and melt fraction, rather than the actual mineral assemblage. The modal proportion of feldspar decreased while those of cordierite and biotite increased in the residual assemblages, as <5 mol.% of free H2O was added. The impact of this addition is to more than double the proportion of water‐undersaturated melt to 25–30 mol.%. We have also developed a simple way to estimate how much melt a residual rock has lost, if the compositional trends of the protoliths are known. In summary, we find that even though the addition of small amounts of free H2O impacts significantly on rock fertility, there is little obvious record in the field. The combined application of careful petrological investigation and thermodynamic modelling is the key to identify the influence of aqueous fluids, and exploit systems that became open not only to fluid influx but also to the extraction of melt. 相似文献
956.
Sergio M. López-Ramírez Leonardo Sáenz Alex Mayer Lyssette E. Muñoz-Villers Heidi Asbjornsen Z. Carter Berry Nathaniel Looker Robert Manson León Rodrigo Gómez-Aguilar 《水文研究》2020,34(16):3555-3570
Tropical montane cloud forests (TMCF) are recognized for their capacity to maintain high dry-season baseflow and a host of other ecosystem services. Substantial areas of TMCF have been converted to pasture and crops such as coffee, while in other areas TCMF are recovering. However, little is known about the effects of this complex dynamic on catchment hydrology. We investigated the effect of land use on rainfall-runoff response in five neighbouring headwater micro-catchments in central Veracruz, Mexico, dominated by either mature TMCF (MF), young (20 year-old) and intermediate (40 year-old) naturally regenerating TMCF (YF and IF, respectively), shaded coffee (SC), and an intensively grazed pasture (IP). We used a 4-year record of high-resolution rainfall and streamflow (10 min) data collected from 2015 to 2019. These data were analysed via comparison of hydrologic metrics that summarize streamflow responses at various time scales and magnitudes. Results showed no statistical difference in the regulation capacity of high flows in the micro-catchment with 20 years of natural regeneration, compared to the MF. In terms of baseflow sustenance, our results support the hypothesis that MF and IF better promote this hydrologic service than the other land uses. SC exhibited a high capacity to modulate peak flows comparable to that of MF, and an intermediate capacity to sustain baseflow, suggesting that the integrated functioning of this micro-catchment was largely preserved. Finally, 40 years of intense pasture management was found to have degraded the soil hydraulic properties of IP; mainly, reducing its infiltration capacity, causing a fivefold greater peak flow response and a lower baseflow compared to MF. 相似文献
957.
Company Julio Ruiz-Omeñaca José Ignacio Pereda Suberbiola Xabier 《Geologie en Mijnbouw》1999,78(3-4):319-333
Fragmentary remains, including cervical vertebrae and limb bones, of a large pterosaur from the Upper Cretaceous of Tous, province of Valencia (Spain), are described. The material was recovered from lacustrine beds in the upper part of the Calizas y Margas de Sierra Perenchiza Formation, which is probably Maastrichtian in age. Six fragments of vertebrae allow a reconstruction of the anatomy of the mid-series cervicals of the animal. The general morphology of the cervical vertebrae is closely similar to that of the long-necked Azhdarchidae. Compared to other azhdarchids, the Valencia pterosaur shows minor differences from the genera Azhdarcho and Quetzalcoatlus, and is here provisionally referred to as Azhdarchidae indet. A wingspan of about 5.5 m is calculated by comparison with other known azhdarchids. This is the second azhdarchid pterosaur described from the Iberian peninsula. It confirms the wide distribution of this group of large pterosaurs at the end of the Cretaceous. 相似文献
958.
Eighteen sediment samples and six water-column samples were collected in a small (6 km2), coastal embayment (Port Jefferson Harbor, New York) to define a high-resolution spatial distribution of metals and to elucidate sources of contaminants to the harbor. Sediment metal (Ag, Cu, Fe, Ni, Pb, V, and Zn) concentrations varied widely, reflecting differences in sediment grain size, with higher metal concentrations located in the fine-grained inner harbor sediments. Calculated enrichment factors for these sediments show that Ag, Pb, Cu, and Zn are elevated relative to both crustal abundances and their respective abundances in sediments in central Long Island Sound. Metal concentrations were 1.2 to 10 fold greater in water from the inner harbor compared to water from Long Island Sound collected outside the mouth of the harbor. Spatial variations in trace metals in surface waters within the bay parallel the spatial variations of trace metals in sediments within the harbor. Elevated water-column metal concentrations appear to be partially derived from a combination of diagenetic remobilization from contaminated sediments (e.g., Ag) and anthropogenic sources (e.g., Cu and Zn) within the southern portions of the harbor. Although the National Status and Trends Program had reported previously that sediment metal concentrations in Port Jefferson Harbor were low, the results of this study show sediment metals have high spatial variability and are enriched in the inner harbor sediments at levels comparable to more urbanized western north shore Long Island harbors. 相似文献
959.
960.
Geotectonics - Extension parallel to fold axis represents a rarely documented tectonic process that occur in different tectonic settings such as large-scale orogenic belts, mountain ranges, and... 相似文献