全文获取类型
收费全文 | 591篇 |
免费 | 25篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 90篇 |
地球物理 | 123篇 |
地质学 | 247篇 |
海洋学 | 51篇 |
天文学 | 69篇 |
自然地理 | 32篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 16篇 |
2014年 | 30篇 |
2013年 | 46篇 |
2012年 | 35篇 |
2011年 | 46篇 |
2010年 | 28篇 |
2009年 | 62篇 |
2008年 | 38篇 |
2007年 | 34篇 |
2006年 | 33篇 |
2005年 | 34篇 |
2004年 | 21篇 |
2003年 | 8篇 |
2002年 | 32篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 9篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有627条查询结果,搜索用时 125 毫秒
211.
A global ocean circulation model is coupled to a particle-tracking model to simulate the transport of floating debris washed into the North Pacific Ocean by the Tohoku tsunami. A release scenario for the tsunami debris is based on coastal population and measured tsunami runup. Archived 2011/2012 hindcast current data is used to model the transport of debris since the tsunami, while data from 2008 to 2012 is used to investigate the distribution of debris on timescales up to 4 years. The vast amount of debris pushed into ocean likely represents thousands of years worth of ‘normal’ litter flux from Japan’s urbanized coastline. This is important since a significant fraction of the debris will be comprised of plastics, some of which will degrade into tiny particles and be consumed by marine organisms, thereby allowing adsorbed organic pollutants to enter our food supply in quantities much higher than present. 相似文献
212.
Martial Haeffelin Jean-Charles Dupont Neda Boyouk Darrel Baumgardner Laurent Gomes Greg Roberts Thierry Elias 《Pure and Applied Geophysics》2013,170(12):2283-2303
Fog is an atmospheric phenomenon that has important environmental consequences related to visibility, air quality and climate change on local and regional scales. The formation of radiation fog results from a complex balance between surface radiative cooling, turbulent mixing in the surface layer, aerosol growth by deliquescence and activation of fog droplets. During the ParisFog field experiment, out of 16 events forecasted for radiation fog, activated fog materialized in seven events, while in five other events the visibility dropped to 1–2 km but haze particle size remained below the critical size of activation. To better understand the conditions that lead to or do not lead to sustained fog droplet activation, we performed a comparative study of dynamic, thermal, radiative and microphysical processes occurring between sunset and fog (or quasi-fog) onset. We selected two radiation fog events and two quasi-radiation fog events that occurred under similar large-scale conditions for this comparative study. We identified that aerosol growth by deliquescence and droplet activation actually occurred in both quasi-fog events, but only during <1 h. Based on ParisFog measurements, we found that the main factors limiting sustained activation of droplets at fog onset in the Paris metropolitan area are (1) lack of mixing in the surface layer (typically wind speed <0.5 ms?1), (2) relative humidity exceeding 90 % throughout the residual layer, (3) low cooling rate in the surface layer (typically less than ?1 °C per hour on average) due to weak radiative cooling (0 to ?30 Wm?2) and near zero sensible heat fluxes, and (4) a combination of the three factors listed above during the critical phase of droplet activation preventing the transfer of cooling from the surface to the liquid layer. In addition, we found some evidence of contrasted aerosol growth by deliquescence under high relative humidity conditions in the four events, possibly associated with the chemical nature of the aerosols, which could be another factor impacting droplet activation. 相似文献
213.
Bruna Raquel Wolfarth Naziano Filizola Wanderli Pedro Tadei Laurent Durieux 《水文科学杂志》2013,58(7):1495-1504
AbstractThis work comprises a spatial, temporal and statistical analysis of the epidemiology of malaria occurrence in four municipalities of the State of Amazonas, Brazil: Coari, Codajás, Manacapuru and Manaus, for the period 2003–2009. The number of malaria cases, precipitation, water level and temperature data were analysed in this study. The strength of the relationship between these hydrological/meteorological variables and the occurrence of malaria was determined by employing the Spearman rank correlation coefficient. Seasonal peaks of malaria were registered, on average, about 1–2 months before the annual maximum temperature and after the river’s seasonal high-water level. The phenomenon called repiquete (notable variations in the water level) was observed during periods of between 9 and 56 days. The results showed a statistically significant correlation between malaria, temperature, precipitation and water level. Temperature influenced malaria occurrence the least, while rainfall was the most important factor, especially in the municipality of Coari. Water level had an important influence on the records of malarial occurrence in the municipality of Manacapuru.Editor Z.W. KundzewiczCitation Wolfarth, B.R., Filizola, N., Tadei, W.P., and Durieux, L., 2013. Epidemiological analysis of malaria and its relationships with hydrological variables in four municipalities of the State of Amazonas, Brazil. Hydrological Sciences Journal, 58 (7), 1495–1504. 相似文献
214.
Violette Marchais Gauthier Schaal Jacques Grall Anne Lorrain Caroline Nerot Pierre Richard Laurent Chauvaud 《Estuaries and Coasts》2013,36(4):808-819
This study aimed at characterizing the diet of the oyster Crassostrea gigas along an estuarine gradient in the Bay of Brest (France), through stable isotope (δ13C and δ15N) measurements in primary producers and wild oysters. The contribution of different potential food sources to the diet of C. gigas was estimated at high spatial resolution (over a gradient of 40 km with samplings every 2 km) to identify ecological transition zones and highlighted the dominance of resuspended biofilm in oysters diet. Although the different primary producers did not display any obvious pattern along the estuarine gradient, the stable isotope signatures of C. gigas differed among estuarine, inner Bay, and open sea sites. In particular, a striking 15N depletion pattern was found along the gradient which allowed to identify seven homogeneous groups. Moreover, some unexpected values found at two stations within the estuary revealed localized anthropogenic disturbances. Overall, our results suggest that suspension feeders might be better indicators of ecosystem functioning than primary producers and reflect the different ecological processes occurring along estuarine gradients, including localized anthropogenic inputs. We suggest that the usefulness of suspension feeders as indicators of ecosystem functional typology lies in the dominance of benthic material in their diet, which results in locally occurring processes being reflected in oysters’ stable isotope ratios. 相似文献
215.
We tackle here the question of past and future climate change at sub-regional or country scale with the example of France. We assess France climate evolution during the 20th and 21st century as simulated by an exhaustive range of global climate simulations. We first show that the large observed warming of the last 30 years can be simulated only if anthropogenic forcings are taken into account. We also suggest that human influence could have made a substantial contribution to the observed 20th century multi-decadal temperature fluctuations. We then show that France averaged annual mean temperature at the end of the 21st century is projected to be on the order of 4.5 K warmer than in the early 20th century under the radiative concentration pathways 8.5 (RCP8.5) scenario. Summer changes are greater than their winter counterpart (6 K versus 3.7 K). Near-future (2020–2049) changes are on the order of 2.1 K (with 2.6 K in summer and 1.8 K in winter). Model projections also suggest a substantial summer precipitation decrease (−0.6 mm/day), in particular over southern France, and a moderate winter increase, (0.3 mm/day), mostly over the northernmost part of France. Uncertainties about the amplitude of these precipitation changes remain large. We then quantify the various sources of uncertainty and study how their ranking varies with time. We also propose a physically-based metric approach to reduce model uncertainty and illustrate it with the case of summer temperature changes. Finally, timing and amplitude of France climate change in case of a global average 2-K warming are investigated. Aggressive mitigation pathways (such as RCP2.6) are absolutely required to avoid crossing or barely exceeding the 2-K global threshold. However, France climate change requiring adaptation measures is still to be expected even if we achieve to remain below the 2-K global target. 相似文献
216.
Aur��lien Bideaud Benoit Belier Alain Benoit Laurent Berg�� Philippe Camus Sophie Collin Louis Dumoulin Christian Hoffmann Stefanos Marnieros Alessandro Monfardini 《Experimental Astronomy》2011,32(2):179-191
Microbolometers are at present the most sensitive detectors for mm and sub-mm Astronomy. They are in use in most of the present instruments in that bandwidth. We have developed filled arrays of NbSi-based planar antenna coupled microbolometers. The fabrication details are given, together with characterization of the NbSi thermometers and optical results. The optical performances are potentially good for ground-based mm-wave astronomy applications, while the overall detectors performances are limited by low-frequency excess noise in the thermometric NbSi high-impedance sensors (Anderson insulator). 相似文献
217.
Jean-Pierre Roques Elisabeth Jourdain Loredana Bassani Angela Bazzano Renaud Belmont A. J. Bird E. Caroli M. Chauvin D. Clark N. Gehrels U. Goerlach F. Harrisson P. Laurent J. Malzac P. Medina A. Merloni S. Paltani J. Stephen P. Ubertini J. Wilms 《Experimental Astronomy》2012,34(2):489-517
We are proposing a mission devoted to high energy X-ray astronomy that is based on a focusing telescope operating in the 1?C200?keV energy range but optimized for the hard X-ray range. The main scientific topics concern: Physics of compact objects: The proximity of compact objects provides a unique laboratory to study matter and radiation in extreme conditions of temperature and density in strong gravitational environment. The emission of high energy photons from these objects is far from being understood. The unprecedented sensitivity in the high energy domain will allow a precise determination of the non-thermal processes at work in the vicinity of compact objects. The full 1?C200?keV energy coverage will be ideal to disentangle the emission processes produced in the spacetime regions most affected by strong-gravity, as well as the physical links: disk?Cthermal emission?Ciron line?Ccomptonisation?Creflection?Cnon-thermal emission?Cjets. Neutron stars?Cmagnetic field?Ccyclotron lines: Time resolved spectroscopy (and polarimetry) at ultra-high sensitivity of AXP, milliseconds pulsars and magnetars will give new tools to study the role of the synchrotron processes at work in these objects. Cyclotron lines?Cdirect measurement of magnetic filed?Cequation of state constraints?Cshort bursts?Cgiant flares could all be studied with great details. AGN: The large sensitivity improvement will provide detailed spectral properties of the high energy emission of AGN??s. This will give a fresh look to the connection between accretion and jet emission and will provide a new understanding of the physical processes at work. Detection of high-redshift active nuclei in this energy range will allow to introduce an evolutionary aspect to high-energy studies of AGN, probing directly the origin of the Cosmic X-ray Background also in the non-thermal range (> 20?keV). Element formation?CSupernovae: The energy resolution achievable for this mission (<0.5?keV) and a large high energy effective area are ideally suited for the 44Ti line study (68 and 78?keV). This radioactive nuclei emission will give an estimate of their quantities and speed in their environment. In addition the study of the spatial structure and spectral emission of SNR will advance our knowledge of the dynamics of supernovae explosions, of particles acceleration mechanisms and how the elements are released in the interstellar medium. Instrumental design: The progress of X-ray focusing optics techniques allows a major step in the instrumental design: the collecting area becomes independent of the detection area. This drastically reduces the instrumental background and will open a new era. The optics will be based on depth-graded multi-layer mirrors in a Wolter I configuration. To obtain a significant effective area in the hundred of keV range a focal length in the 40?C50 meters range (attainable with a deployable mast) is needed. In addition such a mission could benefit from recent progress made on mirror coating. We propose to cover the 1?C200?keV energy range with a single detector, a double-sided Germanium strip detector operating at 80?K. The main features will be: (a) good energy resolution (.150?keV at 5?keV and <.5?keV at 100?keV), (b) 3 dimensional event localization with a low number of electronic chains, (c) background rejection by the 3D localization, (d) polarisation capabilities in the Compton regime. 相似文献
218.
Laurent Koechlin Jean-Pierre Rivet Paul Deba Denis Serre Truswin Raksasataya René Gili Jules David 《Experimental Astronomy》2012,33(1):129-140
This paper presents high contrast images of sky sources, obtained from the ground with a novel optical concept: Fresnel arrays. We demonstrate the efficiency of a small 20?cm prototype Fresnel array for making images with high brightness ratios, achieving contrasts up to 4 × 105 on sky sources such as Mars and its satellites, and the Sirius?A?CB couple. These validation results are promising for future applications in space, for example the 4 m array we have proposed to ESA in the frame of the ??Call for a Medium-size mission opportunity for a launch in 2022??. Fresnel imagers are the subject of a topical issue of Experimental Astronomy published in 2011, but only preliminary results were presented at the time. Making images of astronomical bodies requires an optical component to focus light. This component is usually a mirror or a lens, the quality of which is critical for sharp and high contrast images. However, reflection on a mirror and refraction through a lens are not the only ways to focus light: an alternative is provided by diffraction through binary masks (opaque foils with multiple precisely etched sub-apertures). Our Fresnel arrays are such diffractive focusers, they offer weight, price and size advantages over traditional optics in space-based astronomical instruments. This novel approach requires only void apertures of special shapes in an opaque material to form sharp images, thus avoiding the wavefront distortion, diffusion and spectral absorption associated with traditional optical media. In our setup, lenses and/or mirrors are involved only downstream (at small sizes) for focal instrumentation and chromatic correction. Fresnel arrays produce high contrast images, the resolution of which reaches the theoretical limit of diffraction. Unlike mirrors, they do not require high precision polishing or positioning, and can be used in a large domain of wavelengths from far IR to far UV, enabling the study of many science cases in astrophysics from exoplanet surfaces and atmospheres to galaxy evolution. 相似文献
219.
Mélanie Béguer Julien Bergé Caroline Gardia-Parège Laurent Beaulaton Gérard Castelnaud Michel Girardin Philippe Bo?t 《Estuaries and Coasts》2012,35(4):1082-1099
Spanning 20?years (1979?C2007), this study is the longest time series pertaining to the resident shrimp species Palaemon longirostris in a European estuary. Data from monthly faunal surveys undertaken across the middle part of the Gironde estuary from April 1979 along with data from a statistical analysis of the commercial catches throughout the entire estuary and river were considered in order to explore their inter and intra-annual variability and long-term trends. Long-term densities series as well as environmental series (salinity, discharge, temperature and NAO) were decomposed and the effects of environmental variables were also examined using statistical models (GAMs). This revealed important spatio-temporal variability and a significant overall decrease in abundance of this species in the Gironde estuary since the beginning of the 1980s. This long-term decrease in abundance corresponded significantly to long-term decreases in both discharge and the NAO index, as well a long-term increase in temperature and salinity in the middle part of the estuary. However, models showed that environmental factors explained only a small part of the variability. The upstream shift of the population highlighted in this study, probably due to the intrusion of marine waters into the middle section of the estuary, may also have contributed to its decrease in abundance. Inter-annual variability of densities was also significantly linked with inter-annual fecundity fluctuations, and a significant decrease in both mean female size and fecundity was shown for preserved samples from 1992. Moreover, the breeding period has been temporally stretched out and began earlier in more recent years, potentially due to the increase in spring temperature. 相似文献
220.
Marion Garçon Catherine Chauvel Emmanuel Chapron Xavier Faïn Mingfang Lin Sylvain Campillo Sarah Bureau Marc Desmet Marie-Christine Bailly-Maître Laurent Charlet 《Applied Geochemistry》2012
High-altitude lake sediments are often used as archives for environmental changes and their chemical and isotopic compositions provide significant constraints on natural and anthropogenic long-term changes that have occurred in their catchment area. Here, trace-element concentrations and Pb isotopes are presented for two sedimentary cores from Lake Blanc Huez in the French Alps, to trace the impact of climate changes and human activities over the Holocene. Lead and Ag contents are very high and clearly dominated by input from a Pb–Ag vein located a few meters from the lakeshore, a vein that also buffers the Pb isotopes. Mining of this vein in medieval times is recorded in the corresponding lake sediments with high Ag content coupled with high Pb/U ratio. These chemical characteristics can be used to constrain the major Holocene climate changes. Significant advances of glaciers next to the lake produced sediments with Ag and Pb concentration peaks and high Pb/U ratios due to accelerated erosion of the Pb–Ag vein, similar to the effects of the medieval mining. In contrast, reduced glacier activity led to the formation of organic-rich sediments with high U and As contents and low Pb/U ratios. More generally, the observed combination of chemical changes could be used elsewhere to decipher environmental changes over long periods of time. 相似文献