全文获取类型
收费全文 | 2507篇 |
免费 | 115篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 206篇 |
大气科学 | 176篇 |
地球物理 | 670篇 |
地质学 | 883篇 |
海洋学 | 139篇 |
天文学 | 407篇 |
综合类 | 25篇 |
自然地理 | 127篇 |
出版年
2024年 | 5篇 |
2023年 | 12篇 |
2022年 | 22篇 |
2021年 | 43篇 |
2020年 | 58篇 |
2019年 | 45篇 |
2018年 | 144篇 |
2017年 | 112篇 |
2016年 | 178篇 |
2015年 | 152篇 |
2014年 | 168篇 |
2013年 | 198篇 |
2012年 | 168篇 |
2011年 | 162篇 |
2010年 | 138篇 |
2009年 | 133篇 |
2008年 | 104篇 |
2007年 | 82篇 |
2006年 | 76篇 |
2005年 | 51篇 |
2004年 | 65篇 |
2003年 | 47篇 |
2002年 | 50篇 |
2001年 | 44篇 |
2000年 | 32篇 |
1999年 | 20篇 |
1998年 | 45篇 |
1997年 | 29篇 |
1996年 | 19篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 10篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 21篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1985年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1978年 | 6篇 |
1977年 | 4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2633条查询结果,搜索用时 10 毫秒
991.
Metal concentrations (Cd, Cr, Cu, Fe, Mn and Zn) were determined in seawaters and soft tissues of Chthamalus montagui from the northwest coast of Portugal during the four seasons of 2011. The main objectives of this work were to assess seasonal and spatial variations of metals in order to detect hot spots of contamination, to establish correlations between metals in coastal seawaters and C. montagui and to calculate metal bioaccumulation factors (BAFs) in each season. Metal concentrations in coastal seawaters ranged within Cd: 1.2–35 ng L?1; Cr: 15–87 ng L?1; Mn: 77–1763 ng L?1; Cu: 126–1819 ng L?1; Fe: 430–4048 ng L?1 and Zn: 2889–16867 ng L?1 and in C. montagui ranged for Cd: 0.39–1.98 mg kg?1; Cr: 0.45–3.13 mg kg?1; Cu: 0.93–5.70 mg kg?1; Mn: 2.2–20.4 mg kg?1; Fe: 135–707 mg kg?1 and Zn: 119–782 mg kg?1. Significant spatial and seasonal variations were found between: (i) metal concentrations in seawaters and C. montagui tissues; (ii) the distribution of metal concentrations in C. montagui tissues were Fe > Zn > Mn > Cu > Cr > Cd and (iii) C. montagui showed higher bioaccumulation factors for Fe and Cd than for Cu, Mn and Zn in all seasons. Regarding the metal concentrations accumulated in C. montagui tissues during each season of 2011, the ecological quality classifications of the NW coast of Portugal varied from “Class I–Unpolluted” to “Class III–Remarkably Polluted”. 相似文献
992.
Pitra Pavel Schulmann Karel Martínez Catalán José Ramón Ballèvre Michel 《International Journal of Earth Sciences》2017,106(2):395-396
International Journal of Earth Sciences - 相似文献
993.
994.
995.
Raimundo Delgado Aníbal Costa António Arêde Nelson Vila Pouca João Guedes Xavier Romão Pedro Delgado Patrício Rocha 《Bulletin of Earthquake Engineering》2010,8(1):181-199
Research on seismic safety assessment has been the centre of great interest among the scientific community in recent years.
Although the devastating impact of earthquakes on current society should be incentive enough to increase research, the development
of more realistic mechanical behaviour models and the continuous enhancement of computation capabilities are paramount factors
contributing a great deal to the increase of such interest. In this context, three research areas can be identified as currently
leading to important developments: code related research, especially in Europe where new design codes are in the implementation
process; risk analysis, namely concerning the definition of methodologies for safety assessment that involve the evaluation
of the failure probability and could be included in future generations of codes; and experimental characterization of constitutive
laws which provides support for the development and calibration of accurate and realistic numerical models for seismic analysis
and for the adequate characterization of limit state capacities. The paper will present some of the current scientific research
trends on these three seismic safety assessment related topics. Studies addressing the seismic safety assessment of structures,
either probabilistically or based on code provisions, and that consider realistic nonlinear mechanical behaviour models will
be focussed. Reference will also be made to experimental research on the seismic behaviour of structural elements, emphasizing
its crucial role to support the development of numerical models simulating the effects of different seismic strengthening
techniques. Finally, given the development of studies leading to new trends and perspectives for performance based earthquake
engineering, a possible scenario for seismic design in the future is presented, emphasizing the key issues for its implementation. 相似文献
996.
Luis Manuel de Vries Jesus Carrera Oriol Falivene Oscar Gratacós Luit Jan Slooten 《Mathematical Geosciences》2009,41(1):29-42
Simulation of flow and solute transport through aquifers or oil reservoirs requires a precise representation of subsurface
heterogeneity that can be achieved by stochastic simulation approaches. Traditional geostatistical methods based on variograms,
such as truncated Gaussian simulation or sequential indicator simulation, may fail to generate the complex, curvilinear, continuous
and interconnected facies distributions that are often encountered in real geological media, due to their reliance on two-point
statistics. Multiple Point Geostatistics (MPG) overcomes this constraint by using more complex point configurations whose
statistics are retrieved from training images. Obtaining representative statistics requires stationary training images, but
geological understanding often suggests a priori facies variability patterns. This research aims at extending MPG to non-stationary
facies distributions. The proposed method subdivides the training images into different areas. The statistics for each area
are stored in separate frequency search trees. Several training images are used to ensure that the obtained statistics are
representative. The facies probability distribution for each cell during simulation is calculated by weighting the probabilities
from the frequency trees. The method is tested on two different object-based training image sets. Results show that non-stationary
training images can be used to generate suitable non-stationary facies distributions. 相似文献
997.
Ramón Luna Carlos Millán Manuel Domingo Miguel Ángel Satorre 《Astrophysics and Space Science》2008,314(1-3):113-119
CO2 ices are known to exist in different astrophysical environments. In spite of this, its physical properties (structure, density,
refractive index) have not been as widely studied as those of water ice. It would be of great value to study the adsorption
properties of this ice in conditions related to astrophysical environments. In this paper, we explore the possibility that
CO2 traps relevant molecules in astrophysical environments at temperatures higher than expected from their characteristic sublimation
point. To fulfil this aim we have carried out desorption experiments under High Vacuum conditions based on a Quartz Crystal
Microbalance and additionally monitored with a Quadrupole Mass Spectrometer. From our results, the presence of CH4 in the solid phase above the sublimation temperature in some astrophysical scenarios could be explained by the presence of
several retaining mechanisms related to the structure of CO2 ice. 相似文献
998.
Nguyen Dinh Chau Paweł Jodłowski Stefan J. Kalita Paweł Olko Edward Chruściel Adam Maksymowicz Michał Waligórski Paweł Bilski Maciej Budzanowski 《Acta Geophysica》2008,56(2):505-517
The doses of gamma radiation, concentrations of radium isotopes in water and sediments, radon concentration and concentration
of alpha potential energy of radon decay products in the copper ore mine and in the mining region in the vicinity of Lubin
town in Poland are presented. These data served as a basis for the assessment of radiological hazard to the mine workers and
general public. The results of this assessment indicate that radiological hazard in the region does not differ substantially
from typical values associated with natural radiation background. The calculated average annual effective dose for copper
miners is 1.48 mSv. In general, copper ore mines can be regarded as radiologically safe workplaces. 相似文献
999.
Eleazar Padrón Gladys Melián Rayco Marrero Dácil Nolasco José Barrancos Germán Padilla Pedro A. Hernández Nemesio M. Pérez 《Pure and Applied Geophysics》2008,165(1):95-114
Significant changes in the diffuse emission of carbon dioxide were recorded in a geochemical station located at El Hierro,
Canary Islands, before the occurrence of several seismic events during 2004. Two precursory CO2 efflux increases started thirteen and nine days before two seismic events of magnitude 2.3 and 1.7, which took place near
El Hierro Island, Canary Islands, on March 23 and April 15, reaching a maximun value of 51.1 and 46.2 g m−2 d−1, respectively, five and eight days before the two seismic events. Other similar increases started thirteen and five days
before the occurrence of two seismic events of magnitude 1.3 and 1.5 which took place on October 15 and 21 respectively, reaching
the maximum values four and one day before the earthquakes. These changes were not related to variations in atmospheric or
soil parameters. The Material Failure Forecast Method (FFM), which analyzes the rate of precursory phenomena, was successfully
applied to forecast the first seismic event that took place in El Hierro Island in 2004. 相似文献
1000.
The Ter Vell (NE Iberian Peninsula) is a eutrophic coastal lagoon which has been flooded by the excess irrigation water and the agricultural runoff during the last decades. Between 1999 and 2003, restoration measures were applied to improve its water quality. At the same time, but independently, agricultural water management drastically reduced the freshwater inflow. The short-term effects of these management actions on the limnological characteristics of the lagoon were analysed by comparing two hydrological cycles, one before (1999/2000) and the other one after (2002/2003) the actions. The two cycles are illustrative of opposite situations in the hydrological functioning of coastal wetlands. In the first, the lagoon was exorheic, with prolonged flooding periods and a low residence time; in the second, it had a more endorheic character, with scarce water inputs and prolonged periods of confinement. Consequently, nitrogen inputs diminished and organic load and salinity increased as the internal loading and the accumulation effects became more relevant. These effects were actually caused by the drastic reduction in the freshwater inflow which prevented, in turn, the success of the restoration measures. The zooplankton community of the Ter Vell lagoon was not significantly altered by the hydrological change, at least in the short-term, and rotifers and cladocerans, mainly those species indicative of eutrophy, dominated the community. 相似文献