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排序方式: 共有371条查询结果,搜索用时 125 毫秒
81.
Gómez-Herrero Raúl RodrÍguez-FrÍas M. Dolores del Peral Luis Sequeiros Juan Müller-Mellin Reinhold Kunow Horst Sierks Holger 《Solar physics》2000,194(2):405-413
An analysis of the hydrogen and helium isotopic composition from EPHIN data, during the quiet-time period from January 1 to June 1, 1996, is presented. An isotopic discrimination and background rejection have been applied and relationships between the abundances of 2H/1H, 3He/4He, and 4He/1H have been calculated. The energy spectra in the 4–50 MeV nucl–1 range have been obtained and the contribution of the different spectral components have been analysed in this energy range. We conclude that the main contribution to the 4He spectrum is of anomalous origin, while the proton and 3He spectra have contributions mainly from particles of solar origin at low energies and from the galactic cosmic radiation modulated by the heliosphere at high energies. The deuterium spectrum is mainly of galactic origin. 相似文献
82.
F. Tosi F. G. Carrozzo A. Raponi M. C. De Sanctis G. Thangjam F. Zambon M. Ciarniello A. Nathues M. T. Capria E. Rognini E. Ammannito M. Hoffmann K. Krohn A. Longobardo E. Palomba C. M. Pieters K. Stephan C. A. Raymond C. T. Russell 《Meteoritics & planetary science》2018,53(9):1902-1924
We investigate the region of crater Haulani on Ceres with an emphasis on mineralogy as inferred from data obtained by Dawn's Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Haulani, which is one of the youngest craters on Ceres, exhibits a peculiar “blue” visible to near‐infrared spectral slope, and has distinct color properties as seen in multispectral composite images. In this paper, we investigate a number of spectral indices: reflectance; spectral slopes; abundance of Mg‐bearing and NH4‐bearing phyllosilicates; nature and abundance of carbonates, which are diagnostic of the overall crater mineralogy; plus a temperature map that highlights the major thermal anomaly found on Ceres. In addition, for the first time we quantify the abundances of several spectral endmembers by using VIR data obtained at the highest pixel resolution (~0.1 km). The overall picture we get from all these evidences, in particular the abundance of Na‐ and hydrous Na‐carbonates at specific locations, confirms the young age of Haulani from a mineralogical viewpoint, and suggests that the dehydration of Na‐carbonates in the anhydrous form Na2CO3 may be still ongoing. 相似文献
83.
G. Thangjam A. Nathues T. Platz M. Hoffmann E. A. Cloutis K. Mengel M. R. M. Izawa D. M. Applin 《Meteoritics & planetary science》2018,53(9):1961-1982
Variations and spatial distributions of bright and dark material on dwarf planet Ceres play a key role in understanding the processes that have led to its present surface composition. We define limits for “bright” and “dark” material in order to distinguish them consistently, based on the reflectance of the average surface using Dawn Framing Camera data. A systematic classification of four types of bright material is presented based on their spectral properties, composition, spatial distribution, and association with specific geomorphological features. We found obvious correlations of reflectance with spectral shape (slopes) and age; however, this is not unique throughout the bright spots. Although impact features show generally more extreme reflectance variations, several areas can only be understood in terms of inhomogeneous distribution of composition as inferred from Dawn Visible and Infrared Spectrometer data. Additional material with anomalous composition and spectral properties are rare. The identification of the composition and origin of the dark, particularly the darkest material, remains to be explored. The spectral properties and the morphology of the dark sites suggest an endogenic origin, but it is not clear whether they are more or less primitive surficial exposures or excavated subsurface but localized material. The reflectance, spectral properties, inferred composition, and geologic context collectively suggest that the bright and dark material tends to gradually change toward the average surface over time. This could be because of multiple processes, i.e., impact gardening/space weathering, and lateral mixing, including thermal and aqueous alteration, accompanied by changes in composition and physical properties such as grain size, surface temperature, and porosity (compaction). 相似文献
84.
Morten Bjerager Finn Surlyk Holger Lykke-Andersen Nicolas Thibault Lars Stemmerik 《Marine and Petroleum Geology》2010
Danian (Paleocene) reefs formed by ahermatypic scleractinian corals in relatively deep water are known in a few localities in southern Scandinavia. Reflection and shallow seismic profiles, and samples from drilling and scuba diving in bridge pier excavations in Øresund, the strait between Denmark and Sweden, for the first time allow interpretation of the factors that controlled the localisation of the reefs. 相似文献
85.
对北京首都机场高速公路旁采集的土壤柱状T01剖面的磁学参数和金属元素分析,探讨了研究区内现代交通导致的土壤磁学性质的变化及其对环境污染的响应.结果表明,磁参数(χ,ARM和SIRM)与重金属含量呈同步垂向变化趋势.来源于交通运输排放的污染物是土壤剖面上部(0~8 cm)磁性和金属含量增强的主要原因,8cm以下,土壤基本未受到污染,磁性矿物和重金属含量较低,磁性颗粒变化稳定,基本代表了该地区土壤的自然背景.尽管土壤岩石磁学分析表明剖面上下部受污染和未受污染样品的磁载体均是粒度较粗的多畴磁铁矿,但是结合磁参数比值曲线,说明底部样品的磁颗粒的粒度较顶部偏细.磁性矿物的含量变化没有影响磁颗粒的粒度特征.指标聚类等相关分析表明,土壤磁参数(χ,ARM和SIRM)与重金属元素(Pb,Zn和Cu)含量显著相关;结合模糊聚类分析,磁参数可用于追踪、识别交通污染物质在土壤剖面中的富集、迁移状态,揭示不同深度土壤的污染程度. 相似文献
86.
The occultation of 136 Tau on May 11, 1988 was observed at the Observatorium Hoher List. The ingress was recorded photoelectrically by the dual beam photometer while the egress was observed visually. A bona fide curve fitting reduction yielded a scale height differing from earlier p.e. occultation results and is in better agreement with theoretical expectations. 相似文献
87.
Mingjie Shen Shouyun Hu Uli. Blaha Haitao Yan Wolfgang. R?sler Ewin. Appel Viktor. Hoffmann 《Frontiers of Earth Science》2008,2(4):400-407
An expressway-side soil profile 22 cm long was sampled from the grassland of the expressway linking Beijing and the Capital
International Airport. Magnetic measurements, geochemical and multivariate statistic analyses were performed on the soil samples.
The results reveal that the soil profile can be divided into two parts with significant difference in magnetic proxies and
heavy metal concentration. The uppermost soil horizon (0–8 cm) represents the pollution-rich layer with higher concentration
of ferrimagnetic phases and metallic elements. The values of xare very high with an average of 141.60 × 10−8 m3·kg−1 in the layer. We explain that the anthropogenic dust input from traffic is the predominant cause for strong signals of magnetic
phases and heavy metals. Below the profile depth of 8 cm, there is minor pollution in the soil with lower concentration of
magnetic minerals and heavy metals compared to the natural background values. χ remains quite stable and relatively low with
an average of 49.44 × 10−8 m3·kg−1. S-ratio also generally decreases with depth, and it changes from 0.93 in the 0–8 cm layer to 0.87 below the depth of 8 cm.
It indicates that the soil samples are overwhelmingly predominated by ferrimagnetic minerals in the upper part soil, while
the contribution of imperfect antiferromagnetic components is stronger in the lower part. Rock magnetic experiments show MD
magnetite as the main magnetic carrier both in the upper and lower parts. Themagnetic grain size in the upper part is, however,
a bit coarser than that in the lower part. Cluster analysis shows a positive correlation between magnetic properties (χ, ARM,
SIRM) and heavy metal pollutants of Pb, Zn, Cu. Fuzzy C-means cluster analysis can clearly help divide the soil profile into
two different layers and distinguish their characteristics. It can be concluded that these magnetic concentration-related
parameters can be used as proxies for pollution investigation in a fast, sensitive, low-cost and highly efficient approach
to screening heavy metal pollution.
__________
Translated from Quaternary Sciences, 2007, 27(6): 1113-1120 [译自:第四纪研究] 相似文献
88.
A space-time discontinuous Galerkin finite element method is proposed and applied to a convection-dominant single-phase flow
problem in porous media. The numerical scheme is based on a coupled space-time finite element discretization allowing for
discontinuous approximations in space and in time. The continuities on the element interfaces are weakly enforced by the flux
treatments, so that no extra penalty factor has to be determined. The resulting space-time formulation possesses the advantage
of capturing the steep concentration front with sharp gradients efficiently. The stability and reliability of the proposed
approach is demonstrated by numerical experiments.
The author is grateful to the DFG (German Science Foundation—Deutsche Forschungsgemeinschaft) for the financial support under
the grant number Di 430/4-2. 相似文献
89.
90.
Ohne Zusammenfassung 相似文献