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301.
《地震研究进展(英文)》2021,1(1):100005
Seismic anisotropy is an effective feature to study the inner structure of the Earth. In complex tectonic area, the assumption of single-layer anisotropy is sometimes not well consistent with the observed data; thus, the assumption of multi-layered (i.e. stratified) anisotropy should be considered. At present, the main methods to study anisotropy include receiver functions, shear wave splitting from local and teleseismic events (SKS, SKKS, and PKS, hereafter collectively called XKS), P- and Pn wave travel time inversion, surface wave inversion from far-field earthquakes and ambient noise. Each of the above method has its own advantages and limitations. Thus, one or more of the above methods are often combined to characterize multi-layered anisotropy, of which the depth range of anisotropic layers are different. This paper reviews the research progress of multi-layered anisotropy for the purpose of providing a basis for future seismic anisotropy investigations. 相似文献
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303.
Biodiversity mapping in extensive tropical forest areas poses a major challenge for the interpretation of Landsat images, because floristically clearly distinct forest types may show little difference in reflectance. In such cases, the effects of the bidirectional reflection distribution function (BRDF) can be sufficiently strong to cause erroneous image interpretation and classification. Since the opening of the Landsat archive in 2008, several BRDF normalization methods for Landsat have been developed. The simplest of these consist of an empirical view angle normalization, whereas more complex approaches apply the semi-empirical Ross–Li BRDF model and the MODIS MCD43-series of products to normalize directional Landsat reflectance to standard view and solar angles. Here we quantify the effect of surface anisotropy on Landsat TM/ETM+ images over old-growth Amazonian forests, and evaluate five angular normalization approaches. Even for the narrow swath of the Landsat sensors, we observed directional effects in all spectral bands. Those normalization methods that are based on removing the surface reflectance gradient as observed in each image were adequate to normalize TM/ETM+ imagery to nadir viewing, but were less suitable for multitemporal analysis when the solar vector varied strongly among images. Approaches based on the MODIS BRDF model parameters successfully reduced directional effects in the visible bands, but removed only half of the systematic errors in the infrared bands. The best results were obtained when the semi-empirical BRDF model was calibrated using pairs of Landsat observation. This method produces a single set of BRDF parameters, which can then be used to operationally normalize Landsat TM/ETM+ imagery over Amazonian forests to nadir viewing and a standard solar configuration. 相似文献
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305.
Polarimetric reflectance measurements have been made at a wavelength of for a suite of predominantly lunar regolith simulants in support of development efforts for the BepiColombo Laser Altimeter (BELA). Measurements were made using an instrument at the University of Bern, Switzerland, that has been modified to accommodate photometric characterizations of laboratory samples down to 0° phase angle (g) with linearly polarized illumination and a linearly polarized receiver. The data reveal opposition surges that are dominated by polarization state-conserving reflectance terms for all samples. Relative strengths of the trans-state reflectance terms are lowest for the darkest samples, suggesting that multiple scattering is responsible for state conversions. Normal albedo measurements of the lunar simulants range from 0.13 to 0.22 at zero illumination angle (i=0°). The total reflectance of the regolith simulants at g=0° were found to decrease with increasing i, which is inconsistent with predictions of reflectance models for Mercury. However, the g=0° reflectance remains higher at i>0° than would be expected for a gray Lambert surface that is scaled to the g=i=0° reflectance value. Polarization ratios for reflectance under polarized illumination but unconstrained emission show that the samples scatter light in the in-plane polarization state more efficiently than in the transverse state at g=0° and i>0°. The opposite is true for g>0° polarization ratios, which indicate that transverse polarized illumination scatters more efficiently at high g. The polarization effect appears to correlate with the sample's characteristic grain size, but the statistical basis of this trend is weak. The implications of these measurements upon the performance of the BELA instrument are discussed. 相似文献
306.
Based on the observation of a complete hydrological year from June 2014 to May 2015, the temporal and spatial variations of the main inorganic nitrogen(MIN, referring to NO_3~--N, NO_2~--N, NH_4~+-N) in surface water and groundwater of the Li River and the Yuan River wetland succession zones are analyzed. The Li River and the Yuan River are located in agricultural and non-agricultural areas, and this study focus on the influence of surface water level and groundwater depth and precipitation on nitrogen pollution. The results show that NO_3~-N in surface water accounts for 70%-90% of MIN, but it does not exceed the limit of national drinking water surface water standard. Groundwater is seriously polluted by H_4~+-N. Based on the groundwater quality standard of H_4~+-N, the groundwater quality in the Li River exceeds Class III water standard throughout the year, and the exceeding months' proportion of Yuan River reaches 58.3%. Compared with the Yuan River, MIN in groundwater of the Li River shows significant temporal and spatial variations owing to the influence of agricultural fertilization. The correlation between the concentrations of MIN and surface water level is poor, while the fitting effect of quadratic correlation between H_4~+-N concentration and groundwater depth is the best(R~2=0.9384), NO_3~-N is the next(R~2=0.5128), NO_2~--N is the worst(R~2=0.2798). The equation of meteoric water line is δD =7.83δ~(18) O+12.21, indicating that both surface water and groundwater come from atmospheric precipitation. Surface infiltration is the main cause of groundwater H_4~+-N pollution. Rainfall infiltration in non-fertilization seasons reduces groundwater nitrogen pollution, while rainfall leaching farming and fertilization aggravate groundwater nitrogen pollution. 相似文献
307.
《China Geology》2019,2(3):325-332
Based on the 39 surface sediment samples collected in the flood season and the dry season in 2012 respectively and the measured hydrological data in October 2012, the sediment grain size characteristics has been analyzed and the response mechanism of surface sediments to estuarine hydrodynamics was revealed by calculating the range of waves and tidal currents. The results show that: (1) The grain size of the surface sediment samples decreased gradually from land to sea in the flood season. The fine sediment was redistributed under marine hydrodynamics in the dry season and the sediments showed coarser tendency ingeneral; (2) tidal current stirring sediment was very obvious in Dagu River estuary area, and wave stirring sediments mainly occurred in the tidal flat area and estuary sand bar area; (3) in the flood season, surface sediment sat the estuary were transported towards south and southeast. In the dry season, surface sediments were transported towards southwest at the north area of Jiaozhou Bay Bridge, and sediments were transported towards northeast area at the south of Jiaozhou Bay Bridge. 相似文献
308.
采用不同样本集合同化地面观测对一次飑线过程的影响 总被引:2,自引:1,他引:1
针对夏季黄淮地区一次飑线过程,利用WRF (Weather Research and Forecasting) 模式及其Hybrid ETKF-3DVAR同化系统,考察不同生成方案的样本对同化地面观测的影响。集合样本创建方式包括3类:扰动初始背景场的方案 (RCV)、使用不同的物理参数化方案 (PPMP) 以及前两者集成方案 (BLE)。基于增量场分析,同化地面观测主要调整850 hPa以下水平风和水汽混合比的空间结构,其中RCV方案侧重于改变水平风的空间分布,PPMP方案侧重于改变水汽混合比的空间结构,BLE方案兼具二者特征。同化地面观测可以间接改善6 h降水预报,其中PPMP试验的降水预报最好,尤其是对降水位置和强度的预报。对比雷达回波观测,RCV试验和BLE试验对弓状回波模拟得较好,BLE试验的模拟较多体现RCV特征。PPMP试验和RCV试验还可改变冷池的位置和强度,同时影响飑线出现和消亡时间,相对而言,PPMP试验影响更大。 相似文献
309.
310.
Simulation of the spontaneous growth of a dynamic crack without constraints on the crack tip path 总被引:2,自引:0,他引:2
The spontaneous growth of a dynamic in-plane shear crack is simulated using a newly developed method of analysis in which no a priori constraint is required for the crack tip path, unlike in other classical studies. We formulate the problem in terms of boundary integral equations; the hypersingularities of the integration kernels are removed by taking the finite parts. Our analysis shows that dynamic crack growth is spontaneously arrested soon after the bending of the crack tips, even in a uniformly stressed medium with homogeneously distributed fracture strengths. This shows that the dynamics of crack growth has a significant effect on forming the non-planar crack shape, and consequently plays an essential role in the arrest of earthquake rupturing. 相似文献