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591.
During the ascent, emplacement and post-emplacement deformation of igneous rocks, two or more phases of deformation that overprint
each other are often depicted. These overprints, when magnetic minerals are present, are recorded in magnetic fabric. In this
contribution, overprints are studied by means of numerical modeling, following several basic scenarios common to igneous rocks.
Biotite and amphibole that occur often together in igneous rocks are considered as carriers of the anisotropy of magnetic
susceptibility. Modeling shows that (1) a constrictional fabric with a low degree of anisotropy as commonly recorded in magmatic
rocks may result from a deformation overprint and not necessarily from an extensional/transtensional regime, and (2) that
the constrictional AMS fabrics originates from orthogonal superimposition of a deformation event on an AMS fabric inherited
from earlier magma emplacement history. Therefore, the interpretation of a constrictional fabric must be performed with caution.
Numerical modeling may provide a suitable help in strengthening the interpretation of real magnetic fabric data. 相似文献
592.
Knut–Andreas Lie Stein Krogstad Ingeborg Skjelkv?le Ligaarden Jostein Roald Natvig Halvor M?ll Nilsen B?rd Skaflestad 《Computational Geosciences》2012,16(2):297-322
Accurate geological modelling of features such as faults, fractures or erosion requires grids that are flexible with respect
to geometry. Such grids generally contain polyhedral cells and complex grid-cell connectivities. The grid representation for
polyhedral grids in turn affects the efficient implementation of numerical methods for subsurface flow simulations. It is
well known that conventional two-point flux-approximation methods are only consistent for K-orthogonal grids and will, therefore, not converge in the general case. In recent years, there has been significant research
into consistent and convergent methods, including mixed, multipoint and mimetic discretisation methods. Likewise, the so-called
multiscale methods based upon hierarchically coarsened grids have received a lot of attention. The paper does not propose
novel mathematical methods but instead presents an open-source Matlab? toolkit that can be used as an efficient test platform for (new) discretisation and solution methods in reservoir simulation.
The aim of the toolkit is to support reproducible research and simplify the development, verification and validation and testing
and comparison of new discretisation and solution methods on general unstructured grids, including in particular corner point
and 2.5D PEBI grids. The toolkit consists of a set of data structures and routines for creating, manipulating and visualising
petrophysical data, fluid models and (unstructured) grids, including support for industry standard input formats, as well
as routines for computing single and multiphase (incompressible) flow. We review key features of the toolkit and discuss a
generic mimetic formulation that includes many known discretisation methods, including both the standard two-point method
as well as consistent and convergent multipoint and mimetic methods. Apart from the core routines and data structures, the
toolkit contains add-on modules that implement more advanced solvers and functionality. Herein, we show examples of multiscale
methods and adjoint methods for use in optimisation of rates and placement of wells. 相似文献
593.
Memory-Efficient Categorical Multi-point Statistics Algorithms Based on Compact Search Trees 总被引:1,自引:1,他引:0
Tuanfeng Zhang Stein Inge Pedersen Christen Knudby David McCormick 《Mathematical Geosciences》2012,44(7):863-879
Multi-point statistics (MPS) has emerged as an advanced geomodeling approach. A practical MPS algorithm named snesim (simple normal equations simulation), which uses categorical-variable training images, was proposed in 2001. The snesim algorithm generates a search tree to store the occurrence statistics of all patterns in the training image within a given set of search templates before the simulation proceeds. The snesim search tree concept makes MPS simulation central processing unit efficient but consumes large amounts of memory, particularly when three-dimensional training images contain complex patterns and when a large search template is required to ensure optimal reproduction of the image patterns. To crack the memory-restriction bottleneck, we have developed a compact search tree that contains the same information but reduces memory cost by one order of magnitude. Furthermore, the compact structure also accelerates MPS simulation significantly. Such remarkable improvement makes MPS a more practical tool to use in building the large and complex three-dimensional facies models required in the oil and gas industry. 相似文献
594.
Vera Potop Pavel Zahraniček Luboš Türkott Petr Štěpánek Josef Soukup 《Natural Hazards》2014,71(1):1-19
This study has, for the first time, analysed in detail the risk occurrences of the last spring frost, first fall frost and the length of the frost-free period during the growing season of vegetable crops at a high horizontal resolution of 10 km in the Elbe River lowland in the Czech Republic. The daily minimum air temperature from 116 grid points throughout the studied area for the period 1961–2011 was used. The daily values of minimum air temperature ranges of 0 to ?1.1 °C, ?1.2 to ?2.2 °C and below ?2.2 °C were considered to constitute mild, moderate and severe frost intensities, respectively. Firstly, the spatiotemporal variability of the date of the last spring frost, the date of the first fall frost and the length of the frost-free period in the Elbe River lowland is provided. Secondly, the estimation of the probability of a later date in the spring and an earlier date in the fall for various severe frost events and the length of the frost-free period is determined. Third, the changes in the timing of the last and first frosts of the three severities, as well as the length of the frost-free period, are evaluated. From 1961 to 2011, the Elbe River lowland has experienced a decrease in the number of frost days, while the length of the frost-free period between the last spring frost and the first fall frost has increased. The temporal evolution of the frost-free period anomalies displays two distinct periods: a shortening of the frost-free period in the 1960s and an intensified lengthening of the frost-free period since the 1980s. Whereas the latest spring frost has ended on an earlier date across the Elbe River lowland, the first frost date in the fall has generally been delayed to a later date. The dates of the last spring frost have advanced by ?0.21 days per year on average. The fall dates are delayed up to 0.18 days per year, whereas the frost-free period is lengthening by up to 0.39 days per year on average. However, regional frost series suggests that the frost-free period exhibits a large amount of inter-annual variability. In terms of the growth of field vegetables, a late spring frost remains a risk factor, but the degree of risk has decreased. There is a 25 % chance of the occurrence of dangerous spring frosts during the planting of field vegetables after 3rd May, but after 15th May, the risk is only 10 %. 相似文献
595.
Jan Jelínek František Staněk Lukáš Vebr Josef Honěk 《International Journal of Earth Sciences》2014,103(4):1113-1123
The aim of this article is to inform about the spatial distribution of the lignite qualitative parameters and total lignite reserves in the Czech Part of the Vienna Basin—The South Moravian Lignite Coalfield (SMLC). The total reserves were estimated on the basis of several composed variant digital models of individual seams in four partial area of SMLC. Calculations of the reserves resulted from the identified spatial distribution of chemical-technological parameters obtained from the thousands analysis of samples taken from more than 4,000 exploration works. The basic model of the deposit was so-called geological model characterising genetic evolution of the deposit and defines the spatial positions of the coal seams. Subsequently developed variant economical models spatially define the selected areas by the quality of lignite expressed by the limits of ash yield. Based on the created models, it was found that in the past just 3–7 % (depending on the variant model) of the total lignite reserves SMLC had been extracted. The presented geological reserves are currently using the existing mining technologies only partially mineable. 相似文献
596.
597.
Günther Josef Redhammer Anatoliy Senyshyn Gerold Tippelt Clemens Pietzonka Georg Roth Georg Amthauer 《Physics and Chemistry of Minerals》2010,37(5):311-332
CoGeO3 was synthesized at 1,273 and 1,448 K using ceramic sintering techniques in the monoclinic and orthorhombic modification,
respectively. The two compounds were analysed by magnetic susceptibility measurements and neutron diffraction in order to
study magnetic ordering and spin structures at low temperature. The monoclinic form of CoGeO3 has C2/c symmetry and orders magnetically below 36 K with a small negative paramagnetic Curie temperature θ
P = −4.6 (2) K. The magnetic structure can be described with k = (1, 0, 0) in the magnetic space group C2′/c′ having a ferromagnetic spin arrangement within the chains of M1 sites, but a dominating antiferromagnetic coupling between
the chains. At the M1 sites the magnetic spins are aligned within the a–c plane forming an angle of 120° with the +a-axis and they are not parallel to the spins at M2. Here spins are also ferromagnetically coupled within, but antiferromagnetically
coupled between the M1/M2 site bands. The orthorhombic phase of CoGeO3 displays Pbca symmetry and transforms to an antiferromagnetically ordered state [θ
P = −18.6(2) K] below 33 K. The magnetic spin structure can be described with k = (0, 0, 0) in space group Pbca′ and it is similar to the one of the C2/c phase except that it is non-collinear in nature, i.e. there are components of the magnetic moment along all three crystallographic
axes. Small magneto-elastic coupling is observed in the orthorhombic phase. 相似文献
598.
In this study the global coupled atmosphere-ocean general circulation model ECHAM2/OPYC and its performance in simulating the present-day climate is presented. The model consists of the T21-spectral atmosphere general circulation model ECHAM2 and the ocean general circulation model OPYC with a resolution corresponding to a T42 Gaussian grid, with increasing resolution towards the equator. The sea-ice is represented by a dynamic thermodynamic sea-ice model with rheology. Both models are coupled using the flux correction technique. With the coupled model ECHAM2/OPYC a 210-year integration under present-day greenhouse gas conditions has been performed. The coupled model simulates a realistic mean climate state, which is close to the observations. The model generates several ENSO events without external forcing. Using traditional and advanced (POP-technique) methods these ENSO events have been analyzed. The results are consistent with the delayed action oscillator theory. The model simulates both a tropical and an extra-tropical response to ENSO, which are in good agreement with observations. 相似文献
599.
600.
Tom Kol Petr Dobrovolný Pter Szab Tom Mikita Tom Kyncl Josef Kyncl Irena Sochov Ale Flídr David Merta Michal Rybní
ek 《第四纪科学杂志》2022,37(1):123-132
The development of settlement and building activity is the result of socioeconomic, political and demographic changes in the past. However, accurate information on temporal variation in building activity is rather limited. Dendrochronological databases containing dated historical wooden constructions provide an important resource. We used 6514 tree-felling dates to reconstruct building activity in the Czech lands for the period 1450–1950. Comparing felling dates with historical events demonstrated that building activity was negatively associated with intense wars, particularly during the Thirty Years' War (1618–1648). After the Peace of Westphalia (1648), socioeconomic renewal and demographic growth were reflected in an upsurge of building activity, especially ecclesiastical buildings. While the construction of ecclesiastical and noble buildings culminated around the 1720s, rural buildings peaked in the 1780s and the 1820s. Although no direct effect of climate was demonstrated, adverse climatic conditions leading to harvest failures and subsequent famines (e.g. the ‘Hunger Years’ 1770–1772) significantly contributed to declines in building activity. In contrast, a higher number of felling dates were detected when strong and/or frequent windstorms occurred. This study provides a comprehensive understanding of building activity in Central Europe and advocates the use of dendrochronological databases for the investigation of human activities in history. 相似文献