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151.
Jacques Bourgois Yves Lagabrielle Hervé Martin Jérôme Dyment Jose Frutos Maria Eugenia Cisternas 《Pure and Applied Geophysics》2016,173(10-11):3217-3246
152.
153.
FEM × DEM modelling of cohesive granular materials: Numerical homogenisation and multi-scale simulations 总被引:2,自引:0,他引:2
The article presents a multi-scale modelling approach of cohesive granular materials, its numerical implementation and its results. At microscopic level, Discrete Element Method (DEM) is used to model dense grains packing. At the macroscopic level, the numerical solution is obtained by a Finite Element Method (FEM). In order to bridge the micro- and macro-scales, the concept of Representative Elementary Volume (REV) is applied, in which the average REV stress and the consistent tangent operators are obtained in each macroscopic integration point as the results of DEM’s simulation. In this way, the numerical constitutive law is determined through the detailed modelling of the microstructure, taking into account the nature of granular materials. We first elaborate the principle of the computation homogenisation (FEM × DEM), then demonstrate the features of our multiscale computation in terms of a biaxial compression test. Macroscopic strain location is observed and discussed. 相似文献
154.
Groundwater plays an important role in New Zealand water supplies and hence monitoring activities are conducted regularly. Most monitoring programmes aim to evaluate groundwater chemistry and almost completely overlook the microbial component in this ecosystem. In our present study, the bacterial community structure of groundwater in the Wairarapa Valley was examined using the terminal restriction fragment length polymorphism (T-RFLP), and relationships between bacterial community structure and groundwater chemistry, aquifer confinement and groundwater usage were explored. In addition, the results from this study were compared with a previous T-RFLP survey of the same area in an attempt to detect changes in bacterial community structure over time. The data obtained suggested that bacterial community structure was related to groundwater chemistry, especially to redox conditions. Species composition showed minimal variation over time if groundwater chemistry remained unchanged. These findings reflect the potential of using bacterial communities as biological indicators to evaluate the health of groundwater ecosystems. We suggest that it is important to include this type of broad bacterial diversity assessment criteria into regular groundwater monitoring activities. 相似文献
155.
A new formulation is proposed for the electrical potential developed inside a horizontally‐layered half‐space for a direct current point‐source at the surface. The recursion formula for the kernel coefficient in the potential integral is simpler than the generally used two‐coefficient recursion. The numerical difficulties that may occur during the computation of the integrals and near the source axis are examined and solutions are proposed. The set of equations permits a stable and accurate computation of the tabular potential everywhere in the medium. 相似文献
156.
Jeannine-Marie St. Jacques Brian F. Cumming John P. Smol 《Journal of Paleolimnology》2008,40(2):733-744
We developed a fast, inexpensive, statistically rigorous method of varve verification that uses prospective varve layer-splitting
and seasonal pollen deposition. This method can be used on any sediment that contains seasonally deposited pollen, and avoids
the need for radio-isotopic, optical, or thermoluminescence dating. The method uses a χ2 test and non-parametric regression, together with recorded plant bloom times from pollen traps, to assess the differences
in pollen abundances in light/dark (i.e. summer/winter-spring) sediment layers. A statistical test is required because such
seasonally deposited data are inherently noisy, with a low signal-to-noise ratio. To illustrate this approach, visible laminations
of Lake Mina, Minnesota, USA, were assessed in two separate regions of a core spanning 900 years. Results show that the laminations
were deposited annually. 相似文献
157.
Vortex merger is a phenomenon characterizing the whole class of geophysical vortices, from atmospheric storms and large oceanic eddies up to small scale turbulence. Here we focus on the merger of subsurface oceanic anticyclones in an idealized primitive equations model. This study has been motivated by past and recent observations of colliding lens-like anticyclones off of Gibraltar Strait. The critical conditions for merger (critical merger distance and time needed for merger) are determined. We will show that the predictions of classical two-dimensional merger are not verified for subsurface isolated vortices. For instance, critical merger distances will be reduced because of the vortex potential vorticity (PV) structure. The post-merger characteristics of the vortex (radius, extension and PV), are also determined. Merger-related effects, like production of peripheral filaments and small-scale eddies are also investigated and suggest the contribution of merger in both direct and inverse energy cascades. 相似文献
158.
Hedia Chakroun Goze B. Benie Norman T. O'Neill Jacques Desilets 《International journal of geographical information science》2013,27(4):319-336
Data layers that represent geographical constraints in a multidimensional GIS model must be appropriately weighted to effectively account for the diversity as well as the functional and spatial interrelationships between the constraints. This paper presents a spatial analysis weighting algorithm (SAWA) using Voronoi diagrams. The basic functions of the SAWA are defined so that the spatialization of weights is done according to two approaches: a global spatialization method based on the statistical distribution of the original data and a contextual approach where neighbourhood defined by Voronoi diagrams is integrated into the weighting functions. Different simulations on artificial and real maps applied to the problem of shortest path optimisation are analysed. The results show that the effective integration of the spatial dimension in a weighting process is not only possible but also improves the optimisation of shortest paths. Research is continuing to improve the contextual phase of the algorithm. 相似文献
159.
We present a theoretical weakly nonlinear analysis of the dynamics of an inviscid flow submitted to both rotation and precession of an unbounded cylindrical container, by considering the coupling of two Kelvin (inertial) waves. The parametric centrifugal instability known for this system is shown to saturate when one expands the Navier–Stokes equation to higher order in the assumed small precession parameter (ratio of precession to rotation frequencies) with the derivation of two coupled Landau equations suitable to describe the dynamics of the modes. It is shown that an azimuthal mean flow with differential rotation is generated by this modes coupling. The time evolution of the associated dynamical system is studied. These theoretical results can be compared with water experiments and also to some numerical simulations where viscosity and finite length effects cannot be neglected. 相似文献
160.
Carole Gaüzère Marina Moletta‐Denat Faisl Bousta Stéphane Moularat Geneviève Orial Sébastien Ritoux Jean‐Jacques Godon Enric Robine 《洁净——土壤、空气、水》2013,41(3):226-234
Biological aerosols from air constitute a significant source of exposure to microorganisms in public places. Airborne microorganisms are involved in the development of certain respiratory symptoms, allergies, or infections among users and occupants. Various sampling instruments have commonly been used in aerobiology to collect bacteria and fungi suspended in the air. The objective of this study was to develop a reliable procedure for sampling in indoor public environments presenting different levels of occupancy, airborne bacteria and fungi to be subjected to molecular analysis (bacteria and fungi quantitative PCR, capillary electrophoresis single strand conformation polymorphism fingerprinting). Four different sampling devices were tested in situ in an office building (open‐plan type) and the sampling strategy chosen was tested in two museum contexts. In accordance with the drawbacks involved to our study (quantitative and qualitative aspects, cost, and overcrowding), cyclone device appeared to be most suitable. The results underline the effectiveness of this high‐volume aerosol sampling device for both qualitative and quantitative molecular analysis. Four in situ sampling collections were carried out in 1 day in the Louvre Museum to study quantitative and qualitative variations of airborne bacterial and fungal diversity. The quantitative results revealed a similar order of magnitude for the numbers of both bacteria and fungi. In the Louvre Museum, the samples yielded between 3.7 × 104 and 4.1 × 104 genome equivalent (GE) bacteria/m3 air and between 5.0 × 104 and 5.9 × 104 GE fungi/m3 air and in the Decorative Arts Museum between, 2.1 × 104 and 2.5 × 104 GE bacteria/m3 air and between 1.4 × 104 and 1.7 × 104 GE fungi/m3 air. The results also indicate that the dominant bacterial community displayed a stable structure over a short period of time whereas dominant eukaryotic airborne community appeared more variable. 相似文献