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111.
K-Ar Geochronology of Mesozoic Mafic Dikes in Shandong Province, Eastern China: Implications for Crustal Extension 总被引:3,自引:0,他引:3
LIU Shen HU Ruizhong ZHAO Junhong FENG Caixia Institute of Geochemistry Chinese Academy of Sciences Guiyang Guizhou 《《地质学报》英文版》2004,78(6):1207-1213
Based on K-Ar isotope analyses, Mesozoic mafic (and alkali ultramafic) dikes from western and eastern Shandong Province, China, are dated at 88.2±1.70 Ma to 169.5±3.7 Ma with the majority of ages ranging from 90 Ma to 140 Ma. The emplacement of the dikes suggests a major Yanshanian (Cretaceous) crustal extension in Shandong province. Together with other available age data, this study suggests four periods of crustal extension at about 80 Ma, 100 Ma, 120 Ma and 140 Ma, respectively. Besides the effect of collapse of the Yanshanian orogenic belt on the emplacement of the mafic dikes in Shandong in the Cretaceous, the mantle plume and the extensive left-lateral advection and extension of the Tanlu fault also have controlled the crustal extension and the emplacement of the mafic dikes in eastern Shandong and western Shandong, respectively. 相似文献
112.
Current glacier recession under the global warming has aroused world-wide attention. Initiated from 1958, the observations of Urumqi Glacier No. 1 at the headwaters of Urumqi River in eastern Tianshan promise the best datasets of the glacier and the climate changes in China. Taking Urumqi Glacier No. 1 as an example, we analyzed the response of the glacier to the climate change. The results show that over the past 50 years, the glacier has changed remarkably in the aspects of snow-firn stratigraphy, ice formation zone, ice temperature, area and terminus position, etc. These changes are apparently the results of temperature rise in this area. The glacier recession continued throughout the entire observed time period, and showed an accelerated tendency since 1985. Meltwater runoff also increased 84.2% over the last 20 years. 相似文献
113.
对粤东后江岬间海岸1992年和1992年7条重复地形剖面分析结果表明,当前各剖面年净冲淤变化很小,剖面分别与Bodge和Lee平衡剖面模式符合良好,拟合的平衡剖面闭合水深反映了在海区波候条件作用下泥沙运动的临界水深。 相似文献
114.
The impact of human activities on the flushing properties of a semi-enclosed lagoon: Xiaohai, Hainan, China 总被引:1,自引:0,他引:1
In this study, a Lagrangian particle tracking model driven by hydrodynamic fields was used to investigate the changes of flushing properties in Xiaohai Lagoon resulting from natural evolution and influences of human activities. Comparisons of residence times between 1936 and 2001 indicate that the flushing efficiency of the lagoon has deteriorated greatly during the past seven decades. Over this period, the average residence time of the lagoon has increased from 45 to 71 days, an increase of 59%. The Lagrangian residual velocity has decreased from 1936 to 2001 in the large portions of the lagoon, and the spatial distribution pattern of the residual current has changed significantly. The well-developed horizontal circulations in 1936 disappeared. Instead, the horizontal Lagrangian residual velocity showed uniformly seaward motion with reduced velocity in 2001. Human activities have incurred great impacts on the deterioration of flushing efficiency. The reduction of river inflow imposed the most significant impact, causing an increase of average residence time by 33%. The land reclamation in the lagoon came as the second most significant factor, causing an increase of 15%. Closure of the North Opening had posed minor impact. The model results suggest that restoring the river inflow, as well as the dredging of the tidal channel and the inner lagoon, should be the top proprieties for future water quality management. 相似文献
115.
116.
1 IntroductionThemodernspacegeodesytechnology (GPSes pecially)israpidlydeveloping ,andisabletoprecise lymonitorongoingsurfacechangeprocessatun precedentedspatialandtemporalresolution .Soithasgraduallybecomethemostsuitabletooltoob servegeodynamicalphenomena[1 - 5] .Theearthquakepreparationandoccurrencearecloselyrelatedtofaultanditsmovement.Activefaultanditsquantitativeanalysisisstillthepredomi nantfieldofseismologicalresearch[6,7] .Faultdislo cationmaycausecrustaldeformationaroundit.Onthebas… 相似文献
117.
维向切变流中的非线性对称不稳定 总被引:1,自引:0,他引:1
讨论了维向切变流中的非线性对称不稳定问题。中采用绝热无粘的非线性对称扰动方程组,利用多尺度摄动方法分析其不稳定波动的有限振幅特性。研究结果表明:不稳定波的有限振幅在强度上呈现出振荡趋势。无论是超临界切变情况,还是次临界切变情况,对称扰动振幅都随时间呈现出周期性的变化,振荡周期的大小不仅与基本场稳定度参数及波的特性有关,而且还与初始扰动的振幅及其增长率有关。 相似文献
118.
CONCLUSION The analysis of air parcel trajectories affecting Shanghai indicates that the coming-direction of air parcel is different
in various months. The transport track of trajectory (backward and forward) is closely related to the synoptic system, and
also related to acid rain occurring in Shanghai region.
Air pollution and acid rain in Shanghai region have relationship with both the influence of local pollutants and the influence
of external pollutants from southwest and northeast. 相似文献
119.
In this paper, four problems are discussed: (1) the monsoon circulation over southern Asia; (2) the seasonal variation of the general circulation of the atmosphere; (3) the influence of the monsoon on the rainfall in southwestern China; and (4) the source region of water vapor for the rainfall in the Changjiang valley. 相似文献
120.
Spatial distribution and source apportionment of PAHs in surficial sediments of the Yangtze Estuary, China 总被引:3,自引:0,他引:3
Spatial distribution and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the Yangtze Estuary, especially the North Branch, have been fully investigated. PAH concentrations increased with the descending distance from the inner estuary to the adjacent sea, and varied significantly in various estuarine regions. Water currents (e.g., river runoff and ocean current) greatly affected the distribution pattern. In addition, ambient sewage and traffic also contributed to the PAH pollution in the estuary. In the adjacent sea, PAH values along the -20m isobath were higher than those along the -10m isobath due to the "marginal filter" phenomenon formed by different water currents. In most sites, PAHs had poor correlations with sediment size, but had positive correlations with total organic carbon. Based on the qualitative and quantitative analysis results, PAH sources were proved to be mainly from a mixture of petroleum combustion, biomass, and coal combustion. 相似文献