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651.
Weiguo Wang Kenneth J. Davis Chuixiang Yi Edward G. Patton Martha P. Butler Daniel M. Ricciuto Peter S. Bakwin 《Boundary-Layer Meteorology》2007,124(2):305-314
The dimensionless bottom-up and top-down gradient functions in the convective boundary layer (CBL) are evaluated utilizing
long-term well-calibrated carbon dioxide mixing ratio and flux measurements from multiple levels of a 447-m tall tower over
a forested area in northern Wisconsin, USA. The estimated bottom-up and top-down functions are qualitatively consistent with
those from large-eddy simulation (LES) results and theoretical expectations. Newly fitted gradient functions are proposed
based on observations for this forested site. The integrated bottom-up function over the lowest 4% of the CBL depth estimated
from the tower data is about five times larger than that from LES results for a ‘with-canopy’ case, and is smaller than that
from LES results for a ‘no-canopy’ case by a factor of 0.7. We discuss the uncertainty in the evaluated gradient functions
due to stability, wind direction, and uncertainty in the entrainment flux and show that while all of these have a significant
impact on the gradient functions, none can explain the differences between the modelled and observed functions. The effects
of canopy features and atmospheric stability may need to be considered in the gradient function relations. 相似文献
652.
John D. Wilson 《Boundary-Layer Meteorology》2007,125(1):39-47
Well-mixed, first-order Lagrangian stochastic (LS) particle trajectory models are derived from several idealized (“toy”) turbulent
velocity distributions, and their performance is compared against the observations of Project Prairie Grass, i.e., the case
of a continuous point source of tracer near the ground, in the horizontally homogeneous and neutrally stratified surface layer.
Although in a context of limited information a Gaussian distribution is the preferred choice, and although the Gaussian corresponds
to the simplest of this set of LS models (namely, the Langevin equation), models stemming from other velocity distributions
give similar, albeit distinguishable, predictions. 相似文献
653.
基于小波萎缩方法的图像小波去噪的研究 总被引:1,自引:0,他引:1
小波方法越来越广泛地应用到图像处理当中。小波萎缩方法是小波图像去噪方法中较为重要的方法之一。本文主要介绍了图像小波去噪中较常用的小波萎缩方法,并主要针对Bayes阈值,使用噪声方差邻域估计法加以研究和实现,并将几种阈值函数的去噪效果进行了对比。 相似文献
654.
Sensible (H) and latent (LvE) heat fluxes are obtained by a combined energy budget – similarity model applied to observations from Melle in Belgium and Cabauw in The Netherlands. The sensitivity to both the stability functions and the accuracy of input data is investigated. In a first step, fluxes are calculated for a selection of stability functions and compared to values obtained with pre-defined (reference) functions. For the diurnal fluxes higher than 10 W m−2 in 1996 at Melle, the root-mean-square rmsreaches 9 W m−2 for H and 6 W m−2 for LvE, depending on the chosen functions. A lesser sensitivity is obtained at Cabauw and can be explained by lower absolute values of the stability parameter ζ (L involving the Obukhov length) mainly induced by higher mean wind speeds. Different stability bins are also considered. It is concluded that a more accurate assessment of the stability functions is already desirable for absolute values of L above a few metres. These values are not so scarce at Melle and should be captured in the future by an increasing number of new developing long-term measurement stations. In a second step, a statistical approach is proposed with errors depicted by both systematic biases and random fluctuations represented by means of Gaussian distributions. The results show that very accurate measurements are needed in order to maintain the mean annual value of the bias and rms below 5–10 W m−2, and thus to allow the discrimination between the sensitivity to errors on input data and to the stability functions selection. 相似文献
655.
The weight-percent values of four mineralogic variables (quartz, K feldspar, color index, and muscovite) for 10 sets of granitic rocks (20–50 samples in each set) from magmatic units of the Singhbhum granite were used for (1) computation of the Mahalanobis' generalized distance functions (D
2) between all pairs of the 10 sets, (2) testing significance of the difference between the multivariate means, and (3) computation of the linear discriminant functions between all possible pairs of the sets. The 10 data sets are for six magmatic units which belong to three successive but closely related phases of emplacement. The multivariate means for all sets are significantly different except for those between two of the sets of phase I. Cluster analysis on the basis of theD
2 values enables the 10 sets to be placed into four distinct groups. Group A includes two subgroups, one of which consists of two sets representing typical members of phase I; the other subgroup includes two sets which are typical of phase II. Group B includes two sets which are typical of phase III. The other four sets do not group with the typical representatives of the three phases, probably because of certain special conditions of their emplacement. A separate series ofD
2 computation from the same data, but excluding the color index, was unsuccessful in making the four aberrant sets group with the typical members of the respective phases. Efficient LDF's could be determined for discrimination between most pairs of the 10 sets of granite rocks. 相似文献
656.
The response of a realistic earth to ocean tide loading 总被引:3,自引:0,他引:3
Spiros D. Pagiatakis 《Geophysical Journal International》1990,103(2):541-560
657.
Helmut Mayer 《Mathematical Geology》1993,25(7):975-1001
The importance of time-series analysis in cyclic stratigraphy is evaluated by comparing three different methods (adaptive multiple taper spectral analysis, auto-/cross-correlation analysis, cova functions) applied to stratigraphic time series from the Early Cretaceous Cismon section in northern Italy. Carbonate content and magnetic susceptibility vary in a quasi-cyclic fashion in this pelagic limestone section and are almost perfectly negatively correlated. The spectral technique requires a high degree of preprocessing of the original data (interpolation and resampling at a regular interval, filtering, inversion) which introduces smoothing and rounding errors. The statistical correlation analysis also requires evenly and (for cross-correlation) correspondingly spaced series. The geostatistical cova functions (a generalization of the cross-variogram) prove to be the most versatile and robust of the methods compared. Cova functions can be calculated from unevenly and noncor-respondingly spaced time series without any preprocessing. This method also retains relatively more of the signal if noise and extreme outliers obscure the picture. The periodicities detected in the Cismon time series fall in the range of Milankovitch cycles. Cycle periods of 45 cm and 80 cm likely correspond to dominant precession and obliquity cycles. Due to the inaccuracy of the Cretaceous time scale periods cannot be matched exactly yet, but cycle ratios are close to expected ratios so that there is great potential for future cyclostratigraphic work to contribute to a substantial improvement of the geologic time scale. 相似文献
658.
The effects of partial frequency redistribution on the formation of spectral lines have been studied. We considered the angle-averaged
RII, RIII andR
v
types of redistribution with isotropic phase function, Transfer equation with plane-parallel geometry is solved in isothermal
atmospheres. For an atmosphere with constant thermal sources, the frequency-dependent source function SL (R
v) lies below SL (RIII) but above SL(R
III) in the line wings. 相似文献
659.
The X-ray luminosity function of low-mass binaries constructed from the observations of point like X-ray sources in galactic bulges can be explained in terms of the main evolutionary relations for the rate of mass transfer onto a compact object. The observed scatter of luminosities for individual low-mass X-ray sources in our Galaxy is shown to be satisfactorily described by a symmetric quasi-Lorentz curve with a dispersion proportional to the mean luminosity. Such a form of the mean luminosity function for individual sources does not affect the power-law pattern of the luminosity function for the entire population of sources that is expected for a power-law dependence of the mass transfer rate in a close binary on the mass of the Roche lobe—filling optical component. 相似文献
660.
应用1985年5~9月南亚地区OLR格点资料和同期该范围500hPa位势高度格点资料,通过自然正交函数(EOF)展开和功率谱、交叉谱分析,研究了南亚地区夏季风期间对流发展空间分布的两种主要类型及其和天气系统活动的关系、时间演变特征等。 相似文献