全文获取类型
收费全文 | 2607篇 |
免费 | 148篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 215篇 |
大气科学 | 188篇 |
地球物理 | 712篇 |
地质学 | 931篇 |
海洋学 | 150篇 |
天文学 | 418篇 |
综合类 | 25篇 |
自然地理 | 129篇 |
出版年
2023年 | 13篇 |
2022年 | 24篇 |
2021年 | 45篇 |
2020年 | 63篇 |
2019年 | 48篇 |
2018年 | 154篇 |
2017年 | 116篇 |
2016年 | 185篇 |
2015年 | 164篇 |
2014年 | 175篇 |
2013年 | 207篇 |
2012年 | 173篇 |
2011年 | 171篇 |
2010年 | 146篇 |
2009年 | 146篇 |
2008年 | 113篇 |
2007年 | 85篇 |
2006年 | 82篇 |
2005年 | 55篇 |
2004年 | 70篇 |
2003年 | 47篇 |
2002年 | 47篇 |
2001年 | 46篇 |
2000年 | 31篇 |
1999年 | 22篇 |
1998年 | 49篇 |
1997年 | 27篇 |
1996年 | 17篇 |
1995年 | 23篇 |
1994年 | 25篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 21篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1972年 | 9篇 |
1968年 | 3篇 |
1965年 | 3篇 |
1950年 | 4篇 |
排序方式: 共有2768条查询结果,搜索用时 515 毫秒
951.
J. A. Grande T. Valente M. L. de la Torre M. Santisteban J. C. Cerón E. Pérez-Ostalé 《Environmental Earth Sciences》2014,71(6):2729-2738
The present work aims to propose a methodology for quantifying the sources of acid mine drainage (AMD) and to characterize the magnitude of the affected areas in the Iberian Pyrite Belt (SW Spain). Such an approach allows the creation of a support tool for managing land and natural resources valorization, which may be easily applied in similar mining regions. The motivation and usefulness of this work can be realized by focusing on two main emerging strategic issues: (1) water resources management, with the example of Alcolea dam that will receive water from affected areas in the Iberian Pyrite Belt; and (2) mineral resources valorization, especially, regarding copper exploration due to increasing market prices. The used methodology included the following general steps: it started with an inventory of the mines in the Iberian Pyrite Belt, followed by field cartography campaigns and finally the quantification of affected areas and contaminant discharges. The results of the present work serve to confirm and quantify the magnitude of the AMD pollution in the Pyrite Belt. A total affected area of about 4,847 ha was estimated. Taking into account this figure and combining it with the annual average precipitation (650 L/m2) results in an estimation of 31,503,680 m3/year of discharging water affected by the presence of sulphides. In this scenario, a total annual contribution of 260,056 tonnes/year was obtained for sulphates, which means more than 712 tonnes a day. In the case of arsenic, a toxic element, the total annual contribution is more than 20 tonnes, or close to 55 kg/day. Regarding copper, this economically interesting metal translates into total contributions of 10,364 tonnes/year in the generating medium. This gave more than 28 tonnes/day, which today sits at 8,200 dollars/tonne. This result suggests that solutions aimed at recovering this resource should be searched. It may represent a financial return at the same time that it would mean overcome environmental liabilities. 相似文献
952.
Juan Antonio Pascual Aguilar Vicente Andreu Pablo Vázquez Yolanda Picó 《Environmental Earth Sciences》2014,71(1):31-37
The Mediterranean wetlands are unique in biological diversity and provide multiple benefits, constituting a great water reserve for the planet and producing biomass and nutrients for the trophic chain. However, the increasing human impact and socio-economic development in recent decades have caused important losses in these ecosystems. This work was carried out in the Natural Park of L’Albufera (Valencia, Spain), which includes a coastal lagoon, marshlands, dunes and pinewoods, surrounded by rice fields and orchard in its non-urbanized part. Despite this great ecological value, it suffers impacts derived from the high human and industrial occupation and the hydrological contributions of the connected irrigation systems. The study focused on the development of a combined methodology, based on environmental forensics principles, with the aim of identifying the presence, flow paths and spatial distribution of illicit drugs entering the Natural Park. It is organized around two major procedures: analysis of 16 water samples and application of Geographical Information Systems (GIS) integrating different sources and data formats, as analysis of 14 drugs of abuse by Liquid Chromatography-Mass Spectrometry techniques, and social and environmental data in either GIS layers or tabular digital formats. Results show that, at present, most analyzed drugs have been identified in all sample points. Besides the population distribution pattern, the traditional irrigation system connected to sewage treatment plant (STP) locations is the way by which illicit substances are introduced into the Natural Park waters. 相似文献
953.
Distribution and origin of nitrate in groundwater in an urban and suburban aquifer in Mar del Plata,Argentina 总被引:2,自引:1,他引:1
Daniel Martínez Eleonora Moschione Emilia Bocanegra Melisa Glok Galli Ramón Aravena 《Environmental Earth Sciences》2014,72(6):1877-1886
The impact of urbanization on groundwater quality is of special concern for water managers dealing with the provision of drinking water to large urban centers. Nitrate is one of the most common contaminants found in urban aquifers. This paper presents a case study aiming at evaluating the distribution and sources of nitrate in an urban aquifer in the city of Mar del Plata, Argentina. Four study zones under different land uses, including a pristine, a semi-rural, an intermediate, and an urban area, were evaluated as a part of this study. The three latter zones are linked by the groundwater flow system. The average nitrate concentration in the pristine area is 6.7 mg/L as nitrate and is over the permissible level of 50 mg/L for drinking water in the other areas. In the semi-rural area it ranges from 39.2 to 107.1 mg/L with an average value of 38.2 mg/L and the nitrate concentration tends to decrease in the intermediate zone to an average value of 38.2 mg/L; however, values above 60 mg/L are also observed there. Then the nitrate concentration in the urban area water is higher than that in the intermediate zonewater ranging from 48.2 to 100.3 mg/L with an average value of 67.3 mg/L. Data on the stable isotopes 15N and 18O in nitrate show that the main sources of nitrate in the study area are manure associated to agriculture uses and cesspools in the semi-rural area, and leakage of the sewage distribution network in the urban area, respectively. This is supported by a previous study which found that 20 % of the water flooding many underground structures in the city came from leakage of the sewage network. No evidence of nitrate attenuation by denitrification was found in the groundwater. This study has shown that aquifers in urban areas can be affected by agricultural activity in the upstream areas and leakage of the sewage network in the urban area. 相似文献
954.
955.
This paper describes the development of a Livelihood Vulnerability Index (LVI) that estimates the relative ability of California commercial sea urchin fishermen to cope with the change associated with proposed marine protected areas. A key goal in establishing marine protected areas is to maximize conservation benefits while minimizing the potential negative impacts to local fishing communities. However, current impact analyses largely assume a linear relationship between percent of fishing area or revenue lost with the magnitude of impact to fishermen. The LVI described in this paper aims to provide an additional dimension to impact analyses in which the adaptive capacity of individual fishermen is examined to estimate the differential abilities of fishermen to cope with the loss of fishing areas or revenue. This paper advances vulnerability assessments as it develops a novel framework for identifying and measuring drivers of vulnerability for understudied fishing populations whose livelihoods depend upon marine resources. This vulnerability assessment is intended to inform the design of marine protected areas by enabling researchers to incorporate the adaptive capacity of fishermen into socioeconomic impact analyses. The LVI was developed for the California commercial sea urchin fishery in the context of proposed marine protected area networks develop through the California Marine Life Protected Act planning process. As climate change advances there is an increasing need to identify vulnerable and resilient populations and ways to bolster adaptive capacity given the environmental and economic changes ahead. 相似文献
956.
James McCarthy Chery Chen David López-Carr Barbara Louise Endemaño Walker 《GeoJournal》2014,79(6):665-675
We have reached a crucial turning point in debates around climate change. A well established scientific consensus regarding the physical causes, dynamics, and at least many likely implications of anthropogenic climate change has thus far failed to result in any substantial movement towards mitigation. For many, then, the most urgent questions regarding climate change are now socio-cultural ones, such as: how do people come to hold and act on certain beliefs regarding environmental conditions and processes; how do institutional forms and histories shape and constrain the views and options of various sorts of actors; and what are relationships among fossil fuels, climate change, and the historical geographies and future trajectories of capitalism? Far from being simpler than physical and life science questions, these social science questions introduce entirely new sorts of actors, dynamics, and methodological challenges into this already complex and dynamic domain. This special issue takes up these topics. In this essay, we chart some of the major contours of contemporary social science thinking regarding climate change and introduce the articles in the special issue. We begin by examining work, from political science and scholarship on the commons, that foregrounds questions of sovereignty, territoriality, and cooperation with respect to environmental governance. Then we examine work from neoclassical economics and radical political economy, which frame climate change in terms of externalities, or contradiction and crisis, respectively. Finally, we examine the rapidly proliferating work exploring how individuals think and feel about these issues, emphasizing concepts of risk, communication, and governmentality. 相似文献
957.
J. L. Justo J.-C. García-Núñez M. Vázquez-Boza E. Justo P. Durand J. M. Azañón 《Rock Mechanics and Rock Engineering》2014,47(4):1277-1290
This paper presents calculations of displacements and bending moments in a 2-m-thick reinforced-concrete foundation slab using three-dimensional finite-element software. A preliminary paper was presented by Justo et al. (Rock Mech Rock Eng 43:287–304, 2010). The slab is the base of a tower of 137 m height above foundation, supported on jointed and partly weathered basalt and scoria. Installation of rod extensometers at different depths below foundation allowed comparison between measured displacements and displacements calculated using moduli obtained from rock classification systems and three material models: elastic, Mohr–Coulomb and hardening (H). Although all three material models can provide acceptable results, the H model is preferable when there are unloading processes. Acceptable values of settlement may be achieved with medium meshing and an approximate distribution of loads. The absolute values of negative bending moments (tensions below) increase as the rock mass modulus decreases or when the mesh is refined. The paper stresses the importance of adequately representing the details of the distribution of loads and the necessity for fine meshing to obtain acceptable values of bending moments. 相似文献
958.
Vaduvescu O. Aznar Macias A. Wilson T. G. Zegmott T. Pérez Toledo F. M. Predatu M. Gherase R. Pinter V. Pozo Nunez F. Ulaczyk K. Soszyński I. Mróz P. Wrona M. Iwanek P. Szymanski M. Udalski A. Char F. Salas Olave H. Aravena-Rojas G. Vergara A. C. Saez C. Unda-Sanzana E. Alcalde B. de Burgos A. Nespral D. Galera-Rosillo R. Amos N. J. Hibbert J. López-Comazzi A. Oey J. Serra-Ricart M. Licandro J. Popescu M. 《Earth, Moon, and Planets》2022,126(2):1-26
Earth, Moon, and Planets - The Perseverance rover (Mars 2020) mission, the first step in NASA’s Mars Sample Return (MSR) program, will select samples for caching based on their potential to... 相似文献
959.
Adamiec-Wójcik Iwona Brzozowska Lucyna Drąg Łukasz Wojciech Stanisław 《Boundary-Layer Meteorology》2022,184(3):423-440
Boundary-Layer Meteorology - Space–time correlations are fundamental to statistical theories and turbulence modelling. However, experimental studies of space–time correlations are often... 相似文献
960.
Amaral Genilda Canuto Pezzopane José Eduardo Macedo de Souza Nóia Júnior Rogério Martínez Manuel Fernández Fonseca Mariana Duarte Silva Gibson Elbya Leão Toledo João Vitor Pezzopane José Ricardo Macedo Klippel Valéria Hollunder Xavier Talita Miranda Teixeira 《Theoretical and Applied Climatology》2022,147(1-2):347-361
Theoretical and Applied Climatology - The climate change endangers many species of the Amazon Forest. An example, in the endangered medicinal species Pilocarpus microphyllus (popularly known as... 相似文献