全文获取类型
收费全文 | 1834篇 |
免费 | 137篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 65篇 |
大气科学 | 189篇 |
地球物理 | 587篇 |
地质学 | 690篇 |
海洋学 | 117篇 |
天文学 | 224篇 |
综合类 | 21篇 |
自然地理 | 88篇 |
出版年
2023年 | 6篇 |
2022年 | 16篇 |
2021年 | 44篇 |
2020年 | 43篇 |
2019年 | 34篇 |
2018年 | 79篇 |
2017年 | 84篇 |
2016年 | 121篇 |
2015年 | 102篇 |
2014年 | 114篇 |
2013年 | 186篇 |
2012年 | 145篇 |
2011年 | 121篇 |
2010年 | 101篇 |
2009年 | 86篇 |
2008年 | 71篇 |
2007年 | 50篇 |
2006年 | 62篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 39篇 |
2002年 | 45篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 18篇 |
1996年 | 10篇 |
1995年 | 19篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 20篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 14篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1969年 | 7篇 |
排序方式: 共有1981条查询结果,搜索用时 51 毫秒
941.
Rémy Roca Jean-Claude Bergès Hélène Brogniez Michel Capderou Philippe Chambon Olivier Chomette Sophie Cloché Thomas Fiolleau Isabelle Jobard Julien Lémond Mohamed Ly Laurence Picon Patrick Raberanto André Szantai Michel Viollier 《Comptes Rendus Geoscience》2010,342(4-5):390-402
The water and energy cycles are major elements of the Earth climate. These cycles are especially active in the intertropical belt where satellites provide the most suitable observational platform. The history of Earth observations of the water cycle and of the radiation budget viewed from space reveals that the fundamental questions from the early times are still relevant for today's research. The last 2 decades have seen a number of milestones regarding the documentation of rainfall, mesoscale convective systems (MCS), water vapour and radiation at the top of the atmosphere (TOA). Beyond dedicated missions that provided enhanced characterizations of some elements of the atmospheric water cycle and field campaigns that allowed the gathering of validation data, the advent of the long record of meteorological satellites lead to new questioning on the homogenisation of the data time series, etc. The use of this record to document the tropical climate brought new results of the distribution of humidity and reinforced the understanding of some robust features of the African monsoon. Challenges for the immediate future concerns the deepening of the understanding of the role of cloud systems in the monsoon circulation, the downscaling of the documentation of the water and energy cycle at the scale of these cloud systems, the research of better adequation between the users and the satellite estimate of rainfall and finally a much needed methodological effort to build exploitable time series for the estimation of climatic trends in the water and energy cycle in the Tropics. The required observations to address these challenges are rapidly presented with emphasis on the upcoming Megha-Tropiques (MT) mission. 相似文献
942.
943.
Contribution of a sewage sludge application to the short-term carbon sequestration across a wide range of agricultural soils 总被引:1,自引:0,他引:1
José Martín Soriano-Disla J. Navarro-Pedreño I. Gómez 《Environmental Earth Sciences》2010,61(8):1613-1619
The atmospheric levels of carbon dioxide (CO2) and other greenhouse gases (GHGs) have increased dramatically since the industrial revolution. The atmospheric enrichment
with CO2 and other GHGs has resulted in multiple negative consequences: such as the increase in the average temperature and the rise
of the sea level. Hence, there is a growing interest in developing feasible methods to reduce the atmospheric levels of these
gases. One of these strategies is to enhance C sequestration through the increase of soil organic carbon (SOC) pool by the
amendment of agricultural soils with sewage sludge. However, there is considerable uncertainty about the effects (positive
or negative) of sewage sludge applications on the SOC pool. Thus, a simple approach developed under laboratory conditions
is presented to discern the effect of a single sewage sludge application of 50 t ha−1 on the short-term SOC pool in 60 contrasting agricultural soils. The role of soil factors in the C sequestration of the recently
added carbon was also studied. The application of sewage sludge supposed a mean increase of 1.7 ± 1.6 g SOC kg−1, with peak increases of up to 3.8 g SOC kg−1 and decreases of up to 4.6 g SOC kg−1. The initial SOC contents conditioned the C sequestration after sewage sludge application, and no other soil property was
related. 相似文献
944.
Roberto Wagner Lourenço Paulo M. Barbosa Landim André Henrique Rosa José Arnaldo F. Roveda Antonio César Germano Martins Leonardo Fernandes Fraceto 《Environmental Earth Sciences》2010,60(3):495-504
Spatial analysis and fuzzy classification techniques were used to estimate the spatial distributions of heavy metals in soil.
The work was applied to soils in a coastal region that is characterized by intense urban occupation and large numbers of different
industries. Concentrations of heavy metals were determined using geostatistical techniques and classes of risk were defined
using fuzzy classification. The resulting prediction mappings identify the locations of high concentrations of Pb, Zn, Ni,
and Cu in topsoils of the study area. The maps show that areas of high pollution of Ni and Cu are located at the northeast,
where there is a predominance of industrial and agricultural activities; Pb and Zn also occur in high concentrations in the
northeast, but the maps also show significant concentrations of Pb and Zn in other areas, mainly in the central and southeastern
parts, where there are urban leisure activities and trade centers. Maps were also prepared showing levels of pollution risk.
These maps show that (1) Cu presents a large pollution risk in the north–northwest, midwest, and southeast sectors, (2) Pb
represents a moderate risk in most areas, (3) Zn generally exhibits low risk, and (4) Ni represents either low risk or no
risk in the studied area. This study shows that combining geostatistics with fuzzy theory can provide results that offer insight
into risk assessment for environmental pollution. 相似文献
945.
Inés Crespo-Chacón David Montes María José Fernández-Figueroa Javier López-Santiago David GarcÍa-Alvarez Bernard H. Foing 《Astrophysics and Space Science》2004,292(1-4):697-703
We present the results of a high temporal resolution spectroscopic monitoring of the flare (UV Cet type) star V1054 Oph (Wolf 630AB), classified as a dM3.5e visual binary system. Intermediate resolution spectra have been taken during four nights (2–5 April 2001) using the IDS spectrograph of the 2.5 m Isaac Newton Telescope (INT) (La Palma, Canary Islands, Spain). The V1054 Oph spectra show very strong emission lines even in its quiescent state. The analysis of the temporal evolution of the observed emission lines (from Hβ to H11 and the Ca II H and K lines) reveals four strong flares and several weak flares. We have studied in detail the behaviour of the chromospheric lines during the different phases (pre-flare, impulsive and gradual decay) of these flares. The observed flares last from ~25 to 95 min. The equivalent width of the Hβ line changes by a factor up to ~2.3. Broad wings and asymmetric (red-shifted) lines are observed as well. 相似文献
946.
Thierry Montmerle Philippe Claeys Muriel Gargaud Purificatión López-García Hervé Martin Robert Pascal Jacques Reisse Franck Selsis 《Earth, Moon, and Planets》2006,98(1-4):299-312
This concluding chapter is divided into two main parts. The first part is a summary of the main facts and events which constitute the present body of knowledge of the chronology of life in the solar system, in the form of “highlights” in astronomy, geology, chemistry and biology. The second part raises the interrogation “Is life universal?”, and tries to provide answers based on these facts and events. These answers turn out to differ widely among the various disciplines, depending on how far they feel able to extrapolate their current knowledge. 相似文献
947.
Josep M. Trigo‐Rodríguez Jordi Llorca Mona Weyrauch Addi Bischoff Carles E. Moyano‐Cambero Klaus Keil Matthias Laubenstein Andreas Pack José María Madiedo Jacinto Alonso‐Azcárate My Riebe Rainer Wieler Uli Ott Mar Tapia Narcís Mestres 《Meteoritics & planetary science》2014,49(8):1475-1484
We report and describe an L6 ordinary chondrite fall that occurred in Ardón, León province, Spain (longitude 5.5605°W, latitude 42.4364°N) on July 9th, 1931. The 5.5 g single stone was kept hidden for 83 yr by Rosa González Pérez, at the time an 11 yr old who had observed the fall and had recovered the meteorite. According to various newspaper reports, the event was widely observed in Northern Spain. Ardón is a very well‐preserved, fresh, strongly metamorphosed (petrologic type 6), and weakly shocked (S3) ordinary chondrite with well‐equilibrated and recrystallized minerals. The mineral compositions (olivine Fa23.7±0.3, low‐Ca pyroxene Fs20.4±0.2Wo1.5±0.2, plagioclase An10.3±0.5Ab84.3±1.2), magnetic susceptibility (log χ = 4.95 ± 0.05 × 10?9 m3 kg?1), bulk density (3.49 ± 0.05 g cm?3), grain density (3.58 ± 0.05 g cm?3), and porosity (2.5 vol%) are typical for L6 chondrites. Short‐lived radionuclides confirm that the meteorite constitutes a recent fall. The 21Ne and 38Ar cosmic ray exposure ages are both about 20–30 Ma, similar to values for many other L chondrites. The cosmogenic 22Ne/21Ne ratio indicates that preatmospheric Ardón was a relatively large body. The fact that the meteorite was hidden in private hands for 83 yr makes one wonder if other meteorite falls may have experienced the same fate, thus possibly explaining the anomalously low number of falls reported in continental Spain in the 20th century. 相似文献
948.
949.
Abstract An improved definition of the lacustrian thermocline is introduced, allowing a minimization of the random type fluctuations, with the aim of establishing more precise predictive models of the internal energy of lakes. The method consists first of determining the limits of the zone of thermal transition, referred to as the “thermoclinal zone”, and then of defining the plane of the thermocline by calculating its depth, either from the temperatures or from the depths to the limits of this zone. Six new definitions, each borrowing more or less from existing concepts in the literature, are compared with the Brönsted and Wesenburg‐Lund's definition. The best definitions are those for which the plane of the thermocline is defined from the mean temperatures to the limits of the thermoclinal zone. Of these, the most satisfactory is the one obtained from a mean thermal gradient limited to about twice the thermocline depth. 相似文献
950.
Abstract Evaluating horizontal gradients in three‐dimensional shallow water models that use bottom‐following sigma coordinates can lead to large errors near steep bathymetry. A technique that has been proposed to minimize this problem involves computing horizontal gradients in cartesian coordinates, while treating all other terms in a sigma coordinate framework. We study this technique through both truncation error analysis and numerical experimentation, and compare it to the direct application of sigma coordinates. While the Cartesian coordinate method has better convergence properties and generally smaller truncation errors when horizontal gradients are zero, the sigma coordinate method can be more accurate in other physically relevant situations. Also, the Cartesian coordinate method introduces significant numerical diffusion of variable sign near the bottom (where physical diffusion is particularly small), thus potentially leading to instabilities. Overall, we consider the sigma coordinates to be the best approach. 相似文献