全文获取类型
收费全文 | 2171篇 |
免费 | 118篇 |
国内免费 | 97篇 |
专业分类
测绘学 | 118篇 |
大气科学 | 125篇 |
地球物理 | 565篇 |
地质学 | 1131篇 |
海洋学 | 99篇 |
天文学 | 167篇 |
综合类 | 35篇 |
自然地理 | 146篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 67篇 |
2021年 | 90篇 |
2020年 | 91篇 |
2019年 | 99篇 |
2018年 | 195篇 |
2017年 | 171篇 |
2016年 | 234篇 |
2015年 | 109篇 |
2014年 | 218篇 |
2013年 | 224篇 |
2012年 | 129篇 |
2011年 | 141篇 |
2010年 | 80篇 |
2009年 | 93篇 |
2008年 | 65篇 |
2007年 | 45篇 |
2006年 | 57篇 |
2005年 | 32篇 |
2004年 | 26篇 |
2003年 | 27篇 |
2002年 | 23篇 |
2001年 | 19篇 |
2000年 | 16篇 |
1999年 | 6篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1975年 | 6篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有2386条查询结果,搜索用时 9 毫秒
101.
Important mafic–ultramafic masses have been located for the first time in the intersection area between the Keraf Shear Zone and the Nakasib Suture Zone of the Nubian Shield. The masses, comprising most of the members of the ophiolite suite, are Sotrebab and Qurun complexes east of the Nile, and Fadllab complex west of the Nile. The new mafic–ultramafic masses are located on the same trend of the ophiolitic masses decorating the Nakasib Suture. A typical complete ophiolite sequence has not been observed in these complexes, nevertheless, the mafic–ultramafic rocks comprise basal unit of serpentinite and talc chlorite schists overlain by a thick cumulate facies of peridotites, pyroxenites and layered gabbros overlain by basaltic pillow lavas with dolerite dykes and screens of massive gabbros. Associated with pillow lavas are thin layers of carbonates and chert. The best section of cumulate mafic–ultramafic units has been observed in Jebel Qurun and El Fadlab complexes, comprising peridotites, pyroxenites and layered gabbros. Dolerite dykes and screens of massive gabbros have been observed with basaltic pillow lava sections in Wadi Dar Tawaiy. The basal ultramafic units of the complexes have been fully or partly retrograded to chlorite magnetite schist and talc to talc-carbonate rocks (listowenites), especially in the Jebel Qurun and Sotrebab complexes. Petrographically, the gabbros (layered and massive) and the basaltic pillow lavas show mineral assemblages of epidote amphibolite facies. The mafic members from the three complexes show a clear tholeiitic trend and oceanic floor affinity. The pillow lavas plot in the field of oceanic floor basalt, namely in the back arc field. Primitive mantle normalized spider diagram of the pillow lavas reveals a closer correspondence to Enrich-Mid-Oceanic Ridge Basalt (E-MORB) type, which is confirmed by the flat chondrite normalized Rare Earth Elements (REE) pattern. Field, petrographical and geochemical evidence supports ophiolitic origin of the three complexes. The newly discovered ophiolitic complexes mark the western continuation of the Nakasib Suture Zone. 相似文献
102.
Ullah Farman Saqib Shahab E. Ahmad Mokbul Morshed Fadlallah Mahmoud Ali 《Natural Hazards》2020,104(1):225-247
Natural Hazards - Risk perception plays a vital part in flood risk management and mitigation strategies. Therefore, this study aims at first to measure the risk perception of the vulnerable... 相似文献
103.
M. Ishaq F. Akbar Jan M. Shakirullah I. Ahmad Hina Ali 《Arabian Journal of Geosciences》2013,6(11):4109-4118
In the present study, coal from Chakwal (Pakistan) was leached with an aqueous solutions of iodine monochloride (ICl) and diethylenetriamine pentaacetic acid (DPTA) of different concentrations. The effect of stirring time, concentration and pH was studied on the leaching of different metals from coal. The physicochemical parameters indicated that the coal was of reasonably good quality. The results indicated that with increase in time duration, the extraction of metals increased. In most of the cases, metal concentration increased in the leachate with increasing the concentration of the leaching agents. DPTA was found to be the best leaching agent for most of the metals. Higher extraction of metals from coal fly ash indicated that coal organic matter has a pronounced effect on the leaching. Higher concentration of metals was extracted from virgin coal and coal fly ash at low pH (p?>?0.00) as compared to high pH. DPTA extracted metals in higher concentration from virgin coal and coal fly ash at low pH as compared to ICl. Based on the present study, the most leached metals were Fe, Cu, Mn and the least were Pb, Ni, Cd and Cr. 相似文献
104.
Alireza Garakaninezhad Morteza Bastami Mohammad Reza Soghrat 《Journal of Seismology》2017,21(6):1505-1516
The evaluation of seismic risk of spatially distributed systems requires the spatial correlation model for ground motion intensity measures. This study investigates the spatial correlation of four earthquakes recorded in northern Iran. The intra-event spatial correlation for both horizontal and vertical components of spectral acceleration at eight periods in the range of 0.0–3.0 s is estimated using geostatistical tools. An exponential form is chosen to fit experimental semivariograms, and the correlation ranges of spectral accelerations as a function of period are derived. The results show similar trend of correlation ranges for both components. It should be mentioned that the ranges for the vertical component, in general, are higher than those observed for the horizontal one. For both components, the correlation ranges as a function of period are divided into three segments. The first and the third one are increasing while the second one is decreasing with increasing period. 相似文献
105.
Seyedeh Fatemeh NEMATI Naser HAFEZI MOGHADAS Gholam Reza LASHKARIPOUR Hosein SADEGHI 《山地科学学报》2021,18(12):3261-3274
Characterizing the subsurface structure is an important parameter for the improvement of seismic hazard assessment.Due to the tectonic complexity of the earth,s... 相似文献
106.
Ali Mohammadi Mohssen Moazzen Anna Lechmann Oscar Laurent 《International Geology Review》2020,62(15):1931-1948
ABSTRACT We present zircon U-Pb crystallization ages combined with bulk rock major and trace element geochemistry and Sr-Nd-Pb and zircon in-situ Hf isotopic compositions of the Amand and Moro granitoid intrusions in northwest Iran. The Amand and Moro plutons include granite and syeno-diorite with LA-ICP-MS U-Pb zircon ages of 367 ± 6.8 Ma and 351 ± 1.3 Ma, respectively, representative of Late Devonian-Early Carboniferous magmatic activity in NW Iran. Geochemical characteristics such as typical enrichments in alkalis, Nb, Zr, Ga and Y, depletion in P and Sr and fractionated REE patterns with high Ga/Al ratios and Eu negative anomalies are consistent with A-type magmatic signatures. The granitoids are classified as A2-type and within-plate granitoids. The bulk rock geochemistry (enrichments in Th, Nb and, high Th/Yb, Zr/Y ratios) along with low variation of 143Nd/144Nd(i) and 87Sr/86Sr(i) ratios and positive zircon εHf(t) support the role of a mantle plume component for the evolution of the Amand and Moro A-type granitoids in an extensional tectonic environment. In fitting with wider regional knowledge, this magmatism occurred during Paleo-Tethys opening in northern Gondwana. 相似文献
107.
108.
Data on 12 variables in 98 thin sections from 150 carbonate core samples of the Mauddud Formation (early Middle Cretaceous) in 13 well locations distributed throughout the Greater Burgan Oil Field, Kuwait, are re-examined using two correlation coefficients, distance similarity and product-moment, for data comparison and the weighted-pair group clustering technique with simple arithmatic averages for clustering of coefficients. The analysis shows results compatible with those obtained with subjective appraisal of the same data. The method can be utilized for sedimentary microfacies recognition and can be profitably applied in frontier areas where data are limited. 相似文献
109.
110.
地貌特征对约旦南部阿尔阿加河(WadiAl-Arja)流域产沙影响分析(英文) 总被引:1,自引:0,他引:1
Ali Hamdi ABU SALIM 《地理学报(英文版)》2014,24(3):457-474
This study addresses the morphometric variables that determine the sediment yield in Wadi Al-Arja through the analysis of the impact of different morphometric characteristics along the course of the valley on its sediment yield, as well as the analysis of spatial and formal dimensions and morphologies of the basin and its relationship to the sediment yield. The study also addresses the size of variation in the volume of sediment yield of the river tributaries that make up the water network of the valley under the differences of its morphometric and hydrological characteristics. The study found several results, most notably: The classification of Wadi Al-Arja basin according to the hypsometric integral value(72.1%) within an uneven topography, which increases the force of the erosive activity and the size of the sediment yield if the basin was exposed to moist climatic periods. The study also showed the presence of convergence in the intra-spaces between the river tributaries in the water network. This increases the volume of water flows when these tributaries meet with each other and thus increasing their erosive ability and sediment yield. The study also showed the presence of marked variation in the sediment yield of the river tributaries depending on the differences in its morphometric characteristics. The results of the step-wise regression analysis confirmed the importance of the morphometric and hydrological variables, and plant coverage in interpreting the variation in the size of the sediment yield of the river tributaries of different stream order in Wadi Al-Arja basin, where these variables interpreted 43% of the total variation, with statistical significance less than 0.05. 相似文献