全文获取类型
收费全文 | 2586篇 |
免费 | 543篇 |
国内免费 | 723篇 |
专业分类
测绘学 | 254篇 |
大气科学 | 436篇 |
地球物理 | 647篇 |
地质学 | 1506篇 |
海洋学 | 417篇 |
天文学 | 82篇 |
综合类 | 264篇 |
自然地理 | 246篇 |
出版年
2024年 | 25篇 |
2023年 | 78篇 |
2022年 | 216篇 |
2021年 | 242篇 |
2020年 | 173篇 |
2019年 | 233篇 |
2018年 | 219篇 |
2017年 | 194篇 |
2016年 | 212篇 |
2015年 | 220篇 |
2014年 | 165篇 |
2013年 | 165篇 |
2012年 | 187篇 |
2011年 | 159篇 |
2010年 | 153篇 |
2009年 | 121篇 |
2008年 | 125篇 |
2007年 | 111篇 |
2006年 | 77篇 |
2005年 | 74篇 |
2004年 | 67篇 |
2003年 | 58篇 |
2002年 | 71篇 |
2001年 | 48篇 |
2000年 | 46篇 |
1999年 | 62篇 |
1998年 | 66篇 |
1997年 | 53篇 |
1996年 | 46篇 |
1995年 | 34篇 |
1994年 | 23篇 |
1993年 | 33篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1958年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有3852条查询结果,搜索用时 15 毫秒
41.
贵州三都早奥陶世同高组下燕高页岩段的生物标志化合物 总被引:8,自引:1,他引:8
本文着重报道了贵州三都早奥陶世同高组下燕高页岩段生物标志化合物特征,首次在采自该层位的样品中检出丰富的正烷烃、链状类异戊二烯烷烃、萜类化合物及甾类化合物。测试结果显示:正烷烃图谱呈双驼峰形,碳数分布为nC15~nC35,以nC18为主峰碳,nC29为次主峰碳,C-21/C+22为0.77~1.02,OEP为0.94~1.04;植烷占优势,Pr/Ph为0.40~0.46;藿烷碳数为C27~C35,以C30占优势,C27+C29<C+31;仅见碳数分布为C20~C29的长链三环二萜烷,以C28为主峰碳;甾烷丰度顺序为C29甾烷>C27甾烷>C28甾烷,同时检出了孕甾烷和4-甲基甾烷。生物标志化合物显示出还原环境特点,且可能主要来自藻类。 相似文献
42.
Liangyi Meng 《中国科学D辑(英文版)》1997,40(3):225-231
The copper deposits in the mid-lower reaches of the Changjiang River consist mainly of porphyry, skarn and massive sulphide
deposits. According to the geological background, the types of ore deposits and the mineralization, the metallogenic model
of the copper deposits is discussed. It is pointed out that the ore-forming hydrothermal fluids came mainly from magmatic
water and were related to the intermediate-acid intrusions, and that the formation of skarn arid massive sulphide deposits
coincided with the mineralization of porphyry deposits.
Project supported by Doctorate Foundation of the State Education Commission of China. 相似文献
43.
44.
Biomarkers in the Molar Tooth (MT)-Bearing Limestones in the Jilin-Liaoning Area of China 总被引:2,自引:1,他引:2
The origin of Molar Tooth (MT) carbonates has been argued for more than 100 years, which are a kind of Proterozoic carbonates especially composed of microsparite with ptygmatically folded and sheet-like structures. Biomarkers detected in the microcalcsparite from the Wanlong and Xingmincun formations in the Jilin-Liaoning area showed there are abundant normal alkanes, isoprenoids, hopanes, steranes, alkylmethylcyclohexanes, and alkyleyclohexanes, indicating a diversity of biological source: long-chain isoprenoids, the major components of chlorophyll, such as C19, C20, a kind of major biomarkers synthesized early by isoprenoid monomers; hopanes a type of characteristic biomarkers from prokaryote, such as archaebacteria and cyanobacteria; sterane a biomarker for eukaryote; and two kinds of alkanes with C17, C18 as the main peaks representing aquatic bacteria and with C23, C24 as the main peaks representing fungi, respectively. Biomarker analysis showed that MT is the result of bacterial and algal activities, which is a kind of organisms between aerobic and anaerobic bacteria, reproducing well in normal or slightly saline sea water under weak oxidation-reduction conditions, resulting in rapid deposition of calcite as microsparite clue to some mechanisms. 相似文献
45.
46.
安徽铜陵矿集区海底喷流沉积体系的流体包裹体微量元素对比 总被引:7,自引:3,他引:7
铜陵矿集区与铜-金(多金属)矿床有关的热液活动主要有两大体系。即与海西期海底喷流沉积有关的热液体系和与矽卡岩矿化有关的燕山期岩浆热液体系。查明这两类热液体系的流体包裹体特征对区域找矿和矿床成因研究都有实际意义。在包裹体岩相学研究基础上,应用ICP-MS技术和热爆提取方法,研究了新桥、冬瓜山、峙门口、铜官山、朝山等矿床具代表性的热液石英中流体包裹体的微量元素、稀土元素特征。结果表明,两类热液体系在流体包裹体特征上有较大的区别,在流体的微量元素和稀土元素特征方面也很不相同。海底喷流沉积体系的热液石英中流体包裹体与岩浆热液体系的相比。稀土总量较高,LREE/HREE比值较大,δEu不明显。且Mo/(W Sn)比值较高,反映流体中成矿物质的深源特征;Ga/T1、Rb/Cs大。Zr/Hf低,也不同于岩浆热液体系。 相似文献
47.
基于XML的WebGIS体系结构 总被引:5,自引:1,他引:5
针对WebGIS中存在的地理空间数据语义共享问题,在分析XML和GML特点的基础上,论述了基于XML构架WebGIS系统的方案和应用方式,并详析了实现构架的相关技术。 相似文献
48.
Including spatial distribution in a data‐driven rainfall‐runoff model to improve reservoir inflow forecasting in Taiwan 下载免费PDF全文
Multi‐step ahead inflow forecasting has a critical role to play in reservoir operation and management in Taiwan during typhoons as statutory legislation requires a minimum of 3‐h warning to be issued before any reservoir releases are made. However, the complex spatial and temporal heterogeneity of typhoon rainfall, coupled with a remote and mountainous physiographic context, makes the development of real‐time rainfall‐runoff models that can accurately predict reservoir inflow several hours ahead of time challenging. Consequently, there is an urgent, operational requirement for models that can enhance reservoir inflow prediction at forecast horizons of more than 3 h. In this paper, we develop a novel semi‐distributed, data‐driven, rainfall‐runoff model for the Shihmen catchment, north Taiwan. A suite of Adaptive Network‐based Fuzzy Inference System solutions is created using various combinations of autoregressive, spatially lumped radar and point‐based rain gauge predictors. Different levels of spatially aggregated radar‐derived rainfall data are used to generate 4, 8 and 12 sub‐catchment input drivers. In general, the semi‐distributed radar rainfall models outperform their less complex counterparts in predictions of reservoir inflow at lead times greater than 3 h. Performance is found to be optimal when spatial aggregation is restricted to four sub‐catchments, with up to 30% improvements in the performance over lumped and point‐based models being evident at 5‐h lead times. The potential benefits of applying semi‐distributed, data‐driven models in reservoir inflow modelling specifically, and hydrological modelling more generally, are thus demonstrated. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
49.
WANG Fang HE Yongtao FU Gang NIU Ben ZHANG Haorui LI Meng WANG Zhipeng WANG Xiangtao ZHANG Xianzhou 《资源与生态学报(英文版)》2020,11(3):290-297
Enclosure is one of the most widely used management tools for degraded alpine grassland on the northern Tibetan Plateau, but the responses of different types of grassland to enclosure may vary, and research on these responses can provide a scientific basis for improving ecological conservation. This study took one site for each of three grassland types (alpine meadow, alpine steppe and alpine desert) on the northern Tibetan Plateau as examples, and explored the effects of enclosure on plant and soil nutrients by comparing differences in plant community biomass, leaf-soil nutrient content and their stoichiometry between samples from inside and outside the fence. The results showed that enclosure can significantly increase all aboveground biomass in these three grassland types, but it only increased the 10-20 cm underground biomass in the alpine desert. Enclosure also significantly increased the leaf nutrient content of the dominant plants and contents of total nitrogen (N), total potassium (K), and organic carbon (C) in 10-20 cm soil in alpine desert, thus changing the stoichiometry between C, N and P (phosphorus). However, enclosure significantly increased only the N content of dominant plant leaves in alpine steppe, while other nutrients and stoichiometries of both plant leaves and soil did not show significant differences in alpine meadow and alpine steppe. These results suggested that enclosure has differential effects on these three types of alpine grasslands on the northern Tibetan Plateau, and the alpine desert showed the most active ecological conservation in the responses of its soil and plant nutrients. 相似文献
50.