全文获取类型
收费全文 | 1427篇 |
免费 | 291篇 |
国内免费 | 370篇 |
专业分类
测绘学 | 63篇 |
大气科学 | 394篇 |
地球物理 | 394篇 |
地质学 | 687篇 |
海洋学 | 135篇 |
天文学 | 71篇 |
综合类 | 125篇 |
自然地理 | 219篇 |
出版年
2024年 | 7篇 |
2023年 | 22篇 |
2022年 | 66篇 |
2021年 | 56篇 |
2020年 | 73篇 |
2019年 | 67篇 |
2018年 | 84篇 |
2017年 | 67篇 |
2016年 | 74篇 |
2015年 | 67篇 |
2014年 | 76篇 |
2013年 | 72篇 |
2012年 | 77篇 |
2011年 | 81篇 |
2010年 | 87篇 |
2009年 | 73篇 |
2008年 | 64篇 |
2007年 | 73篇 |
2006年 | 72篇 |
2005年 | 77篇 |
2004年 | 46篇 |
2003年 | 70篇 |
2002年 | 62篇 |
2001年 | 49篇 |
2000年 | 58篇 |
1999年 | 89篇 |
1998年 | 56篇 |
1997年 | 43篇 |
1996年 | 34篇 |
1995年 | 50篇 |
1994年 | 32篇 |
1993年 | 41篇 |
1992年 | 25篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1958年 | 8篇 |
排序方式: 共有2088条查询结果,搜索用时 31 毫秒
991.
狼山—武威—共和断裂带是近年来根据重力、航磁资料解释发现的规模仅次于郯庐断裂的大型走滑隐伏断裂带。该断裂带沿狼山—武威—共和一线呈NEE向延伸 ,横切了北大山、龙首山、祁连山和西秦岭造山带 ,使蒙甘青地区在地球物理场和区域构造格架上具有EW分块的基本格局。沿该断裂 ,温泉、地热异常成群、成带分布 ,与其南段亚东—羊八井—那曲走滑断裂 ,构成中国西部一条近SN向导热、控震断裂构造。 相似文献
992.
-- Rupture in the heterogeneous crust appears to be a catastrophe transition. Catastrophic rupture sensitively depends on the details of heterogeneity and stress transfer on multiple scales. These are difficult to identify and deal with. As a result, the threshold of earthquake-like rupture presents uncertainty. This may be the root of the difficulty of earthquake prediction. Based on a coupled pattern mapping model, we represent critical sensitivity and trans-scale fluctuations associated with catastrophic rupture. Critical sensitivity means that a system may become significantly sensitive near catastrophe transition. Trans-scale fluctuations mean that the level of stress fluctuations increases strongly and the spatial scale of stress and damage fluctuations evolves from the mesoscopic heterogeneity scale to the macroscopic scale as the catastrophe regime is approached. The underlying mechanism behind critical sensitivity and trans-scale fluctuations is the coupling effect between heterogeneity and dynamical nonlinearity. Such features may provide clues for prediction of catastrophic rupture, like material failure and great earthquakes. Critical sensitivity may be the physical mechanism underlying a promising earthquake forecasting method, the load-unload response ratio (LURR). 相似文献
993.
994.
995.
Qiang Wang Zhen-Hua Zhao Zhi-Wei Bao Ji-Feng Xu Wei Liu Chao-Feng Li Zheng-Hua Bai Xiao-Lin Xiong 《Resource Geology》2004,54(2):137-152
Abstract. The late Jurassic Tongshankou and Yinzu plutons in southeast Hubei have been investigated for their contrasting metal mineralization features. The former is closely associated with porphyry Cu‐Mo mineralization, while the latter is barren of metal mineralization, althouth both are located very close to each other. The Tongshankou granodiorite porphyries and the Yinzu granodiorites are geochemically similar to adakites, e.g., high Al2O3 and Sr contents and La/Yb and Sr/Y ratios, enriched in Na2O, depleted in Y and Yb, very weak Eu anomalies and positive Sr anomalies. However, different geochemi‐cal characteristics exist between the two plutons: the Tongshankou adakitic rocks (1) are relatively enriched in SiO2, K2O, MgO, Cr, Ni, and Sr and depleted in Y and Yb; (2) have higher degree REE differentiation; (3) have positive Eu anomalies in contrast with very weak negative or unclear Eu anomalies in the Yinzu rocks; and (4) isotopically have relatively higher ePNd(t) values (‐5.19 to ‐5.38) and lower initial 87Sr/86Sr ratios (0.7060 to 0.7062), while the Yinzu adakitic rocks have relatively lower ePNd(t) values (‐7.22 to ‐8.67) and higher initial 87Sr/86Sr ratios (0.7065 to 0.7074). The trace element and isotopic data demonstrate that the Tongshankou adakitic rocks were most probably originated from partial melting of delaminated lower crust with garnet being the main residual mineral whereas little or no plagioclase in the source. On the contrary, the Yinzu adakitic rocks were likely derived from partial melting of thickened lower crust, with residual garnet and a small quantity of plagioclase and hornblende in the source. Interactions between the adakitic magmas and mantle peridotites possibly took place during the ascent of the Tongshankou adakitic magmas through the mantle, considering that MgO, Cr, and Ni contents and ePNd(t) values of the adakitic magmas were possibly elevated and initial 87Sr/86Sr ratios were possibly lowered due to the contamination of mantle peridotites. In addition, the Fe2O3 of the adakitic magmas was likely released into the mantle and the oxygen fugacities (?o2) of the latter were obviously possibly raised, which made metallic sulfide in the mantle oxidized and the chalcophile elements such as Cu were incorporated into the adakitic magmas. The ascent of the adakitic magmas enriched in Cu and Mo will lead to the formation of porphyry Cu‐Mo deposit. Nevertheless, the Yinzu adakitic magmas were possibly lack of metallogenetic materials due to not interacting with mantle peridotite, and thus unfavorable to metal mineralization. 相似文献
996.
基于WebGIS的中国湿地信息系统研究 总被引:1,自引:2,他引:1
湿地被称为“地球之肾”,具有独特的生态结构与功能。中国湿地面积约占全球湿地面积的10%,但近年来湿地面积逐渐萎缩,已造成了极为严重的生态恶果。因此总结以往湿地研究成果,确立包括遥感在内的各种湿地信息提取方法,形成包含各种湿地信息的湿地数据子库和管理操作这些数据的湿地信息系统,并确立湿地信息的共享与发布机制,从而加快湿地科研步伐,成为湿地与遥感科技工作者共同关注的问题。WebGIS技术是GIS融合Internet技术发展起来的新技术,具有对大批量数据进行有效的分析管理和快速的查询检索功能。基于WebGIS技术的中国沼泽信息系统的建立有效地满足了湿地科研和开发保护的需要。 相似文献
997.
The silicon isotope abundance ratios and atomic weights of NBS-28 and several other silicon isotope reference materials were determined in this study. For the calibration of the measurement procedure, two new synthetic isotope mixtures were prepared gravimetrically from highly enriched silicon isotope materials in the form of SiO2. All materials were converted into SiF4 gas and subsequently their silicon isotope ratios were measured on the SiF3+ species by using a gas source mass spectrometer MAT-253. The calibrated isotope abundance ratios of NBS-28 are 0.0507446 (26) for 29Si/28Si and 0.0341465 (15) for 30Si/28Si. The corresponding isotopic abundances are 92.17515(28)% for f(28Si), 4.67739(24)% for f(29Si) and 3.14746(14)% for f(30Si). The silicon molar mass of NBS-28 is determined to be 28.08653(11), which is 0.001 larger than previously reported values. In the meanwhile, the 29Si/28Si and 30Si/28Si isotope abundance ratios and atomic weights of SRM-990, IRMM-017, IRMM-018, GBW-04421 and GBW-04422 are also calibrated. These new calibrated data can improve the reliability and comparability of silicon isotope results using above calibrators. 相似文献
998.
Yilong Bai Zhaoke Jia Xiaohui Zhang Fujiu Ke Mengfen Xia 《Pure and Applied Geophysics》2004,161(9-10):1841-1852
— It has been shown in CA simulations and data analysis of earthquakes that declustered or characteristic large earthquakes may occur with long-range stress redistribution. In order to understand long-range stress redistribution, we propose a linear-elastic but heterogeneous-brittle model. The stress redistribution in the heterogeneous-brittle medium implies a longer-range interaction than that in an elastic medium. Therefore, it is surmised that the longer-range stress redistribution resulting from damage in heterogeneous media may be a plausible mechanism governing main shocks. 相似文献
999.
Helmert方差分量估计在跨河水准测量中的应用 总被引:7,自引:0,他引:7
采用测距三角高程法进行跨河水准测量,可以不量取仪器高,但观测值中有两类不同的观测量。利用Helmert方差分量估计,通过若干次迭代计算,可以更准确地确定两类观测值权的关系,提高了跨河水准测量的平差精度。 相似文献
1000.
基于椭球面三角格网的数字高程建模 总被引:7,自引:2,他引:7
针对传统的DEM在模拟表达大面积地形时具有存在裂缝、地理分析不精确、数据冗余等问题,在椭球面四元三角格网QTM层次剖分的基础上,提出了一种基于椭球面三角格网层次剖分的数字高程建模方法,该方法避免了上述缺陷。应用全球GTOP030数据对该方法进行了验证。 相似文献