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981.
非饱和土热力学参数确定的探讨 总被引:2,自引:1,他引:1
研究非饱和土热力学的力学性质,必须建立能量守恒方程,表征能量的两个基本物理力学参数(体积比热系数和热传导系数)的确定是求解能量守恒方程的重要因素。对于不同颗粒组成的土体,对其干燥颗粒有效热力学参数进行了分析,对固体、液体和气体三相共存的热力学参数进行了研究,并对计算结果进行了对比分析,在此基础上,提出了较适合计算热传导系数的方法,并将此方法和体积平均法、自洽法及Hashin-Strikman方法进行了比较。经与试验结果对比表明:提出的方法能较好地描述非饱和土的热力学参数特性。 相似文献
982.
The summit cone of the Erebus volcano contains two craters. The Main crater is roughly circular (∼ 500 m diameter) and contains an active persistent phonolite lava lake ∼ 200 m below the summit rim. The Side Crater is adjacent to the southwestern rim of the Main Crater. It is a smaller spoon-shaped Crater (250–350 m diameter, 50–100 m deep) and is inactive. The floor of the Side Crater is covered by snow/ice, volcanic colluvium or weakly developed volcanic soil in geothermal areas (a.k.a. warm ground). But in several places the walls of the Side Crater provide extensive vertical exposure of rock which offers an insight into the recent eruptive history of Erebus. The deposits consist of lava flows with subordinate volcanoclastic lithologies. Four lithostratigraphic units are described: SC 1 is a compound lava with complex internal flow fabrics; SC 2 consists of interbedded vitric lavas, autoclastic and pyroclastic breccias; SC 3 is a thick sequence of thin lavas with minor autoclastic breccias; SC 4 is a pyroclastic fall deposit containing large scoriaceous lava bombs in a matrix composed primarily of juvenile lapilli-sized pyroclasts. Ash-sized pyroclasts from SC 4 consist of two morphologic types, spongy and blocky, indicating a mixed strombolian-phreatomagmatic origin. All of the deposits are phonolitic and contain anorthoclase feldspar. 相似文献
983.
Modeling radar-rainfall estimation uncertainties using parametric and non-parametric approaches 总被引:1,自引:0,他引:1
Gabriele Villarini Francesco Serinaldi Witold F. Krajewski 《Advances in water resources》2008,31(12):1674-1686
There are large uncertainties associated with radar estimates of rainfall, including systematic errors as well as the random effects from several sources. This study focuses on the modeling of the systematic error component, which can be described mathematically in terms of a conditional expectation function. The authors present two different approaches: non-parametric (kernel-based) and parametric (copula-based). A large sample (more than six years) of rain gauge measurements from a dense network located in south-west England is used as an approximation of the true ground rainfall. These data are complemented with rainfall estimates by a C-band weather radar located at Wardon Hill, which is about 40 km from the catchment. The authors compare the results obtained using the parametric and non-parametric schemes for four temporal scales of hydrologic interest (5 and 15 min, hourly and three-hourly) by means of several different performance indices and discuss the strengths and weaknesses of each approach. 相似文献
984.
Diffusion in stratified porous media is common in the natural environment. The objective of this study is to develop analytical solutions for describing the diffusion in layered porous media with a position-dependent diffusion coefficient within each layer. The orthogonal expansion technique was used to solve a one-dimensional multi-layer diffusion equation in which the diffusion coefficient is expressed as a segmented linear function of positions in the porous media. The behavior of the solutions is illustrated using several examples of a three-layer system, with constant diffusion coefficient α1 in layer 1 (0 < x < l1), α3 in layer 3(l2 < x < l3), and a linearly position-dependent diffusion coefficient α1(1 + Δ(x − l1)/(l2 − l1)) in the center layer (Δ = α3/α1 − 1). Because of the asymmetry of the layered system, the diffusion and related concentration distributions are also asymmetrical. For a given Δ value, the smaller the value of (l2 − l1)/l3, the more significant the accumulation of concentration in the middle transition zone (l1 < x < l2), the sharper the change in the concentration profile of spatial distribution. Therefore, transition between two layers has significant effects on diffusion. 相似文献
985.
根据建筑物地基的层位关系,土性和力学特征暨上部建筑的结构受力特点,并考虑了造价和施工方法,在对大直径冲击钻孔施工和其它方法进行了分析对比的基础上,论述了选择大直径冲孔灌注方案的依据及该类典型摩擦端承桩的设计计算方法 。 相似文献
986.
This paper points out two numerical problems linked to the resolution of compositional multiphase flow models for porous media
with the finite‐volume technique. In particular, we consider fluid mixtures featuring fast mass transfers between the phases,
hence stiff. In this context, we show how the computation of mass exchange kinetics can be expensive and that erroneous saturation
front locations arise. A numerical splitting method is developed which is proven to be stable with advection‐type time steps,
whatever the stiffness of the mass transfer. The erroneous front location problem is illustrated and shown to be intrinsically
linked to the numerical diffusion. If we assume that the fluids are in thermodynamical equilibrium, we find that spurious
solutions can be avoided by deriving and solving a new uncoupled hyperbolic equation for the saturation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
987.
988.
Deborah Sporton 《The Professional geographer》1999,51(1):68-76
Fertility research in population geography is rooted in a spatial demography tradition which places emphasis on the use of quantitative methodologies to analyse, model and project fertility. As data sources have become more sophisticated and abundant some have questioned whether research within the discipline is now too data-oriented resulting in a reluctance to embrace new methods and concepts. Alternative conceptualisations of fertility and reproduction are outlined which represent a shift away from general explanation to more differentiated understandings of reproductive behaviour and favour the use of qualitative methodologies in combination or in a multi-level framework. The paper illustrates, with reference to a research project in the Kalahari of Botswana, the potential for methodological pluralism in the study of fertility. 相似文献
989.
A method is developed for the reconstruction of a non-uniform distribution of scattering properties in the upper layers of the Earth using data on broadening of an incoherent body-wave group or pulse along a number of rays. The theoretical basis for this reconstruction is a linear integral formula after Bocharov (1985, 1988), which is employed to design a linear inversion procedure. The inversion is performed in terms of a single scalar parameter of effective turbidity. This parameter presents an adequate generalization of the common turbidity parameter used in the isotropic scattering case; it describes, simultaneously, scattering attenuation, pulse broadening and backscattering or coda formation. As a preliminary step, necessary conditions of applicability of the transport equation approach for the analysis of regional high-frequency seismic waves are verified. A new compact derivation of Bocharov's formula is then presented. A linear least-squares inversion procedure for recovering a layered turbidity structure is proposed and tested on synthetic data of onset-to-peak delays of incoherent body-wave pulses. A few practical aspects of the application of the general approach to seismological data are analysed, including the correctness of the low-angle approximation, the use of peak delay observations instead of pulse centroid, the effects of a realistic spatial spectrum of inhomogeneity field, the potential bias produced by intrinsic loss, and the distortions produced by a non-spherical (double dipole) source radiation pattern. The latter point is considered as critically important, as one can expect significant data contamination by nodal arrivals. An efficient robust estimation procedure is designed and tested that is capable of suppressing distortions from nodal and near-nodal data. 相似文献
990.
In the frequency range from millihertz to hundreds of megahertz, many different physical and physico-chemical processes contribute to the electrical polarization of porous water-bearing rocks. This makes the interpretation of their electrical spectra a complicated problem and requires both elaborate theories and model experiments. At high frequencies, the Maxwell–Wagner–Bruggeman–Hanai (MWBH) theory of effective media, which takes into account only bulk properties, shape and partial volume of components, is very appropriate. At low frequencies, surface films, polarization of the electrical double layer (EDL) and clustering of conductive components can produce very strong polarization; corresponding theoretical models are considered in a companion paper ( Chelidze & Gueguen 1999 , hereafter referred to as Paper I). This paper is devoted to the review of experimental data and their comparison with theoretical models.
Experiments on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water-bearing rocks and the dominance of this contribution over MWBH values at low frequencies. The effective dielectric constant of porous saturated rocks increases with the surface-to-volume ratio of the system and strongly depends on the surface charge ( ζ potential). At ζ potential, equal to zero, the low-frequency dielectric permittivity (DP) is minimal. The experimental data on relaxation times and the magnitude of the surface polarization of water-bearing porous systems can be satisfactorily explained by theories of film polarization, diffusional polarization generated by deformation of an 'open' electrical double layer (EDL) and percolation. 相似文献
Experiments on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water-bearing rocks and the dominance of this contribution over MWBH values at low frequencies. The effective dielectric constant of porous saturated rocks increases with the surface-to-volume ratio of the system and strongly depends on the surface charge ( ζ potential). At ζ potential, equal to zero, the low-frequency dielectric permittivity (DP) is minimal. The experimental data on relaxation times and the magnitude of the surface polarization of water-bearing porous systems can be satisfactorily explained by theories of film polarization, diffusional polarization generated by deformation of an 'open' electrical double layer (EDL) and percolation. 相似文献