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101.
102.
Cui Xingfu Li Hongbing Hu Ying Liang Hong Qi Li 《应用地球物理》2007,4(2):94-100
When topography and low velocity zone differences vary greatly, conventional vertical static time shifts will cause wavefield distortion and influence wave equation seismic imaging for seismic data acquired on a complex near surface. In this paper, we propose an approach to datum correction that combines a joint tomography inversion with wavefield continuation to solve the static problem for seismic data on rugged acquisition topography. First, the near surface model is obtained by refracted wave tomography inversion. Second, the wavefield of sources and receivers are continued downward and upward to accomplish datum correction starting from a flat surface and locating the datum above topography. Based on the reciprocal theorem, Huygens' and Fresnel principles, the location of sources and receivers, and regarding the recorded data on the surface as a secondary emission, the sources and receivers are upward-continued to the datum above topography respectively. Thus, the datum correction using joint tomography inversion and wavefield continuation with the condition of a complex near surface is accomplished. 相似文献
103.
104.
Observed pollutants are of both primary and secondary origins, influenced by local topography and meteorology. Identifying
sources and relative contribution often require vast detailed data collection and complicated models. This study applied a
statistical time series analysis to two selected pollution events, spring and fall, at two sites in northern Taiwan. Vector
moving average representations were used to quantitatively examine relationships among chemical pollutants and estimate their
lifetimes. Results from impulse responses show that wind direction change alters the characteristic of pollution observed
in opposite sites of Taipei City, from chemical dominant system to transport dominant one and vice versa. Chemicals are clearly
separated into photochemical pollutants and primary pollutants. Results pointed out that Taipei City is the major source of
photochemical smog, but not these primary pollutants. Derived chemical lifetimes at same location vary from 20% to four times
under different meteorological condition. Estimated concentrations of hydroxyl radical range between 2 to 8 × 107 cm−3. Photochemical pollutants are responsible for parts of PM10 collected in both station observed. Oxidation of SO2 is only important in PM10 observed at one station. This study provides a simpler tool to derive information usually from
complex models, therefore, is suitable as complement in decision-making process. 相似文献
105.
整数模糊度参数的快速检索算法 总被引:1,自引:0,他引:1
GPS快速定位中,由于模糊度参数之间的强相关性,模糊度参数置信区间定义的检索区域比相应的置信椭球大得多。本文通过模糊度参数向量的正交变换,定义出包含模糊度参数置信椭球的最小正交多面体,借助在其中构造的均匀正交网格点,找出置信椭球中的所有整数模糊度参数向量。该方法显著地减少了整数模糊度参数的检索范围,提高了计算效率。 相似文献
106.
图象重建是一个求逆过程具有不适定性。本文介绍的是一种从少数投影数据进行图象重建的线性代数法-Phillips-Tikhonov正则化方法,同时选择优化工具GCV确定最优的正则参数。为验证该方法,我们对日本Yohkoh卫星上塔载的硬X射线望远镜(HXT)拍摄的太阳图象进行重建。 相似文献
107.
This paper treats the upscaling of the absolute permeability in a heterogeneous reservoir. By replacing the fine scale permeability tensor with an upscaled, or effective permeability tensor, a modelling error is introduced. An a posteriori error estimate on this modelling error is formulated and tested. An implementation of the theory, based on domain decomposition coupled with a hierarchical representation of the absolute permeability field, is given. As hierarchical basis functions we have chosen the Haar system, which leads to a wavelet representation of the permeability. The wavelet representation offers a natural upscaling technique which resembles the highcut filters commonly used in signal analysis. This procedure represents an adaptive upscaling method. The numerical results show that this method conserves both the dissipation and the mean velocity in the problem fairly well. The a posteriori error estimate on the modelling error coupled with domain decomposition methods constitutes a powerful modelling tool. 相似文献
108.
A new single-station model (SSM) for monthly median values of the ionospheric parameters foF2 and M(3000)F2 has been developed. Fourier analysis provides a tool for decomposing the time-varying ionospheric parameters. The 12–month smoothed sunspot number R
12
was used as an external solar characteristic because of its availability and predictability. However, for the first time, the solar activity is described not only by R
12
, but also by the linear coefficient K
R
representing the tendency of the change of solar activity. A general non-linear approximation of the influence of the solar-cycle characteristics R
12
and K
R
and ionospheric parameters foF2 and M(3000)F2 was accepted. The new SSM is applied to several European stations and its statistical evaluation shows better results than the other two SSMs used in the paper. The approach described in the paper does not contradict the use of different synthetic ionospheric indices (as the T-index, MF2–index); the basic aim is to show only that using one additional new characteristic of the solar-cycle variations, such as K
R
, improves the monthly median model. 相似文献
109.
Some methods for statistical analysis of multimodal distributions and their application to grain-size data 总被引:1,自引:0,他引:1
Malcolm W. Clark 《Mathematical Geology》1976,8(3):267-282
Some of the methods used in the resolution of mixed normal distributions are discussed under three headings: analytical, graphical, and numerical methods. Attention is given to their applicability in the analysis of grain-size data as derived from sieving. Comparisons are made by applying several methods to published data. It is concluded that the numerical methods offer most scope, especially the method of nonlinear least squares. Some analyses of beach sediments, using this method, are presented. The adoption of a convention for the number of individuals in the sample increases ease of interpretation. 相似文献
110.
YOSHIKATSU MIYASHITA TOSHIAKI ITOZAWA HIROYUKI KATSUMI SHIN-ICHI SASAKI Department of Knowledge-Based Information Engineering Toyohashi University of Technology Tempaku.Toyohashi Japan 《地理学报(英文版)》1990,(1)
The Non-linear lterative Partial Least Squares(NIPALS)algorithm is used in principal componentanalysis to decompose a data matrix into score vectors and eigenvectors(loading vectors)plus a residualmatrix.N1PALS starts with some guessed starting vector.The principal components obtained by NIPALSdepends on the starting vector;the first principal component could not always be computed.Wold hassuggested a starting vector for NIPALS,but we have found that even if this starting vector is used,thefirst principal component cannot be obtained in all cases.The reason why such a situation occurs isexplained by the power method.A simple modification of the original NIPALS procedure to avoid gettingsmaller eigenvalues is presented. 相似文献