全文获取类型
收费全文 | 4452篇 |
免费 | 987篇 |
国内免费 | 823篇 |
专业分类
测绘学 | 403篇 |
大气科学 | 801篇 |
地球物理 | 2094篇 |
地质学 | 2234篇 |
海洋学 | 251篇 |
天文学 | 15篇 |
综合类 | 368篇 |
自然地理 | 96篇 |
出版年
2024年 | 4篇 |
2023年 | 38篇 |
2022年 | 89篇 |
2021年 | 124篇 |
2020年 | 154篇 |
2019年 | 148篇 |
2018年 | 133篇 |
2017年 | 154篇 |
2016年 | 171篇 |
2015年 | 210篇 |
2014年 | 277篇 |
2013年 | 245篇 |
2012年 | 299篇 |
2011年 | 305篇 |
2010年 | 224篇 |
2009年 | 260篇 |
2008年 | 214篇 |
2007年 | 289篇 |
2006年 | 263篇 |
2005年 | 276篇 |
2004年 | 262篇 |
2003年 | 256篇 |
2002年 | 209篇 |
2001年 | 186篇 |
2000年 | 191篇 |
1999年 | 194篇 |
1998年 | 181篇 |
1997年 | 151篇 |
1996年 | 169篇 |
1995年 | 149篇 |
1994年 | 108篇 |
1993年 | 101篇 |
1992年 | 73篇 |
1991年 | 44篇 |
1990年 | 22篇 |
1989年 | 35篇 |
1988年 | 27篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有6262条查询结果,搜索用时 421 毫秒
991.
992.
沧13井数字化地热资料自2010年12月13日开始出现上升异常变化,之后高值持续.在排除环境因素无明显的变化外,通过一系列的分析方法,诸如地热与水位、气压相关资料的对比分析,地热变化与观测系统的电信号的相关分析,调取分析存储的原始记录.综合分析认为:该地热异常变化不是地震前兆异常. 相似文献
993.
通过对1980年以来至今14个指标的全时间扫描,并使用祁连山西段地区Ms5.0地震进行对应。结果表明,选取A值、AC值、A(b)值、b值、Mf值和地震活动度S值进行同步异常分析,能显著提高祁连山西段地区的有震报震率,但有漏报。对目前地区异常集中区进行时间扫描,结果显示,祁连山西段地区出现同步异常,认为2012年或稍长时期有发生Ms≥5.0中强震的可能。 相似文献
994.
采用非均匀度方法,分别提取滇西北、滇中北、滇西南、滇东南和滇东北地区水氡观测资料的地震前兆群体异常。结果表明,该方法能满足水氡观测点所在地区成组中强地震的中、短临预报要求;且该方法能自动识别异常,排除人为主观影响,便于在其他震区进行预报效能检验。 相似文献
995.
996.
997.
《Marine Geodesy》2012,35(1):63-85
AbstractWe introduce an iterative inversion method to address the problems in high-order seafloor topography inversion using gravity data (gravity anomaly and vertical gravity gradient anomaly), such as the difficulty in computing the equation and the uniqueness of the calculation results. A part of the South China Sea is selected as the experimental area. Considering the coherence and admittance function of gravity topography and vertical gravity gradient topography, the inversion band of the gravity anomaly and vertical gravity gradient anomaly in the study area is 30?km–120?km. Seafloor topography models of different orders are constructed using an iterative method, and the performance of each seafloor topography model is analyzed against ETOPO1 and other seafloor topography models. The experimental results show that as the inversion order increases, the clarity and richness of seafloor topographic expression continuously improve. However, the accuracy of seafloor topography inversion does not improve significantly when the inversion order exceeds a certain value, which is related to the contribution of high-order seafloor topography to gravity information. The results show that the accuracy of BGT4 (inversion model constructed by the gravity anomaly) is slightly poorer than that of BVGGT4 (inversion model constructed by the vertical gravity gradient anomaly) in areas with complex topography, such as multi-seamounts and trenches, and the results are generally better in areas with flat seafloor topography. 相似文献
998.
Santanu Banerjee Shovan Lal ChattorajP.K. Saraswati Somnath DasguptaUrbashi Sarkar 《Marine and Petroleum Geology》2012,30(1):144-160
Formation and maturation of glauconites within the early Middle Eocene Harudi Formation, built up in a lagoon to shelf transition in western Kutch, India is addressed taking recourse to a combined sedimentological, micropalaeontological and mineralogical investigation. The glauconite is authigenic and its occurrence coincides with maximum flooding. The glauconite is more matured within the fecal pellets and is less matured within the intra-particle pores of bioclasts namely, foraminifera, ostracoda, gastropoda and bryozoa. SEM-EDS, XRD and geochemical studies clearly document that the infilling within the intra-particle pores of bioclasts belong to nascent to slightly evolved glauconite (<5 wt% K2O), while the pellet belongs to slightly evolved to evolved glauconite (5-7 wt% K2O). Based on chemical characteristics and SEM investigations the glauconitization process can be best explained by the ‘verdissement theory’. The glauconite possibly formed as initial authigenic glauconitic smectite precipitates; while the pellet matured subsequently by addition of K, the process was hindered in case of infillings. The maturation process also involved addition of Si and release of Al, with or without release of Mg. The glauconite maturation was facilitated in case of fecal pellets because of higher porosity, inter-granular nature of pores and availability of necessary elements in semi-confined micro-environments. In contrast, the maturation was aborted at an early stage in case of infillings because of the minute, closed nature of the pores and prevalent alkaline conditions not allowing dissolution of calcitic tests. A low negative cerium anomaly suggests glauconite formation in sub-oxic micro-environments, created by decay of organic matters within the fecal pellets and bioclasts. A clear case of substratum control on glauconitization becomes apparent. 相似文献
999.
利用NCEP/NCAA再分析资料,国家气候中心74项环流指数及云南省122个观测站资料,结合诊断、合成和相关分析等方法,探讨2011年初云南东部极端低温冰冻灾害天气气候特征及成因,并与2008年初低温冰冻灾害进行对比分析。旨在寻找云南低温冰冻天气的预报着眼点,为提前做好防灾减灾工作提供决策依据。研究表明:500hPa高度场欧亚中高纬呈两槽一脊,西西伯利亚高压脊异常强大,贝巴之间为东西向横槽,东亚中高纬呈"+-+"的高度场距平分布,西太平洋副热带高压异常偏东偏弱,南海副高异常偏南偏弱是2011年1月云南东部频遭冷空气影响的大尺度大气环流背景。另外,相关分析发现NINO4区海温持续异常偏冷对应云南东部气温异常偏低。较2008年初持续近2个月的低温雨雪冰冻灾害相比,虽然2011年灾害影响时间较短,范围较小,但冷空气过程频发,昆明准静止锋长时间控制云南东部,最终造成近50年来的极端低温冰冻灾害。 相似文献
1000.
????IGS????120??E???1999??2009??IONEX?????????????????????TEC?????????????С?????鷽??????????????????????????????????????TEC?????????????2009???TEC?????????????顣????????????????????????????????????TEC??仯?????????????????????Ч?????????????????????????????TEC?????????????????4.441 0??2.915 1 TECU??????????????23.26%??10.78%????????????????????????0.712 2??0.785 9?? 相似文献