全文获取类型
收费全文 | 476篇 |
免费 | 83篇 |
国内免费 | 176篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 1篇 |
地球物理 | 59篇 |
地质学 | 584篇 |
海洋学 | 29篇 |
天文学 | 1篇 |
综合类 | 22篇 |
自然地理 | 34篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 25篇 |
2019年 | 27篇 |
2018年 | 18篇 |
2017年 | 27篇 |
2016年 | 39篇 |
2015年 | 20篇 |
2014年 | 33篇 |
2013年 | 37篇 |
2012年 | 22篇 |
2011年 | 39篇 |
2010年 | 27篇 |
2009年 | 42篇 |
2008年 | 32篇 |
2007年 | 21篇 |
2006年 | 34篇 |
2005年 | 22篇 |
2004年 | 20篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 18篇 |
2000年 | 22篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有735条查询结果,搜索用时 15 毫秒
51.
The Task Group on Global Geochemical Baselines,operating under the auspices of both the International Union of Geological Sciences(IUGS) and the International Association of Geochemistry(IAGC),has the long-term goal of establishing a global geochemical database to document the concentration and distribution of chemical elements in the Earth's surface or near-surface environment.The database and accompanying element distribution maps represent a geochemical baseline against which future human-induced or natural changes to the chemistry of the land surface may be recognized and quantified.In order to accomplish this long-term goal,the activities of the Task Group include:(1) developing partnerships with countries conducting broad-scale geochemical mapping studies;(2) providing consultation and training in the form of workshops and short courses;(3) organizing periodic international symposia to foster communication among the geochemical mapping community;(4) developing criteria for certifying those projects whose data are acceptable in a global geochemical database;(5) acting as a repository for data collected by those projects meeting the criteria for standardization;(6) preparing complete metadata for the certified projects;and(7) preparing,ultimately,a global geochemical database.This paper summarizes the history and accomplishments of the Task Group since its first predecessor project was established in 1988. 相似文献
52.
A geochemical baseline provides the means to distinguish between the pedogenic origin and the anthropogenic origin of the
trace element in the environmental compartments. We collected 271 soil samples representative of different parent rocks and
soil types from the whole territory of Hong Kong and analyzed the composition of clay mineralogy and the contents of 15 chemical
elements (Fe, Cd, As, etc.) for these samples. The baseline was predicted with the method of the normalization procedure combined
with the relative cumulative frequency curve. The result indicated that Fe was the best reference element for the normalization
procedure among the five potential reference elements (Fe, Al, Sc, Ti, and Mn), followed by Sc and Ti. A poor correlation
was found between Sc, Ti, and Cu. The predicted baseline was much lower than the A-value of the Dutch List used usually in screening the polluted soil of Hong Kong, implying that the extent of heavy metal
pollution might have been underestimated with respect to local lands. We also applied the cluster analysis to distinguish
the geochemical associations of the trace elements due to its importance to the baseline. Approximately three major associations
including the Fe–Mn-oxides related, Al oxides or Al-bearing-clay-mineralogy related and sulfide- related associations were
observed from the dendrogram. 相似文献
53.
The Sample Catchment Basin (SCB) mapping technique extends the representativeness of the geochemical features of stream sediments to the surface of the whole upstream drainage basin. SCB boundaries clash with the water divides traced from each sampling point and are limited upstream by the presence of further SCBs. They are also assumed to represent the elementary map unit. The rank of SCBs can be defined counting the number of upstream SCBs along the branches of a fluvial network. The presence of low rank SCBs minimizes the statistical redundancy of measures. The SCB technique is particularly suitable for the geochemical mapping of mountainous or hilly areas and to correctly display the information into a morphological context. This approach can be also valuable in the case of low sampling density, inhomogeneous sampling schemes, and especially when very accurate evaluations of the spatial distribution of chemicals (with natural or anthropogenic origin) are required. 相似文献
54.
山东省沂源县金星头地处沂源-沂南金及多金属成矿带北部,该成矿带位于中国东部矽卡岩金多金属矿带中北部,属于环太平洋带组成部分。通过对该区的地质、地球化学特征等分析,运用1∶1万土壤地球化学测量方法,发现了一批以Au为主的化探异常,对部分异常运用岩石地球化学测量和探槽进行查证,发现具有工业品位的金铜矿(化)体5处,提出下一步找矿的工作重点地段,即在中生代燕山晚期中偏碱性或中酸性侵入杂岩体与寒武纪朱砂洞组、馒头组白云岩、灰岩等接触部位及两侧寻找接触交代型(矽卡岩)金铜矿床。 相似文献
55.
对XD银矿床外围水系沉积物地球化学异常特征研究表明,区内具有极好的寻找银(金)多金属矿前景,认为Ag,Pb是近程指标元素,Zn,As,Sb为远程指标元素,拆离断层及隐伏拆离断层上盘,次火山岩与长城系碎屑岩接触带的Ag多金属异常分布区是今后找矿的重要靶区。 相似文献
56.
As, Be, Cd, Co, Cr, Cu, Hg, Ni, Pb, V, Se and Zn concentrations were determined and compared in lake and overbank sediments
from 33 catchments without local pollution sources in southern Norway. There were no significant differences in concentrations
of Be, Co, Cr, Cu, Ni, and V in overbank and pre-industrial lake sediments. In areas with shallow overburden, and significant
influence from long-range atmospheric pollution, concentrations of As, Cd, Hg, Pb, Se, and Zn in overbank sediments were probably
modified by vertical percolating water. In such areas, we suggest using lake sediments as a better sampling medium for mapping
pre-industrial concentrations. Pre-industrial lake sediments yield natural concentrations of Hg and Se, which consist of both
geogenic and natural atmospheric deposition. Important covariables like organic carbon content, Fe oxides, and fine mineral
fraction were generally higher in pre-industrial lake sediments as compared to overbank sediments. By adjusting for such differences
overbank sediments could be used as an alternative in mapping background concentrations of trace metals in regions with few
lakes.
Received: 19 February 1999 · Accepted: 17 April 1999 相似文献
57.
《International Geology Review》2012,54(3):296-313
ABSTRACTSeveral alkaline massifs on inland southeastern Brazil extend offshore, roughly parallel to ~20° S, through a seamount chain of the Vitoria-Trindade ridge. This paper presents the first extensive work on the Martin Vaz volcano through whole-rock and Sr and Nd isotopic composition of volcanic and subvolcanic lithotypes from the Martin Vaz Island, located at the easternmost of this volcanic chain. These alkaline rocks were generated during the Plio-Pleistocene (~0.47 My, 40Ar/39Ar dating in whole-rock) and represent the crystallization of sodic magmas of nephelinitic composition that evolved through fractional crystallization towards phonolites. Calculations from P–TLiquidus using PELE software show temperatures of 1045°C and 818°C, viscosity of 2.47 log Poise and 5.02 log Poise, and densities of 2.57 g/cm3 and 2.26 g/cm3 for nephelinite and phonolite, respectively. Like in Trindade Island, the nephelinitic volcanism in Martin Vaz may represent a Strombolian and/or Hawaii-type eruption due to low viscosity magma according to its physical properties whereas phonolitic intrusions present higher viscosity characteristics forming lava domes. The 87Sr/86Sr (~ 0.703800) and 143Nd/144Nd (~ 0.512750) ratios of lavas from the seamounts and Martin Vaz do not vary significantly, pointing to partial melting process from a homogeneous mantle source showing isotope signature close to HIMU. Beside the restrict variation on these isotopic ratios, a conspicuous enrichment in incompatible trace elements, mainly LREE, indicates that metasomatism is a recent process and not a long-term source characteristic. Non-modal partial melting models (fractional melting and batch melting) suggest that the source of the Martin Vaz magmatism is consistent with the garnet-lherzolite mantle stability field (>90 km depth; Tb/Yb >0.7), generated about 3.0 GPa by very small degree of partial melting of an enriched wet mantle source (F = 0.03–0.04) with 2.5 wt. % of CO2. 相似文献
58.
Kang-kang Xu Hong-wei Sun Wei Xie Fu-qing He Xiao-yang Liu Kai Sun Sheng-fei He Xing-yuan Wu Peng-hui Gong Godfrey Machumu 《China Geology》2023,37(1):1-14
Tanzania is located in eastern Africa with a predominantly agricultural ecomomy, the potential for developing and utilizing cultivated land are promising, but scientific guidance is required. B, Zn and Se are essential micronutrients for plants and human body with crucial biological functions, in particular, Se is significant for human health and considered as “the king of anti-cancer”. As these elements required by human or plants are mainly absorbed from soil directly or indirectly, therefore,... 相似文献
59.
个旧—文山区可分为五个地球化学区,以此为基础分析各区成矿地质条件及水系沉积物元素含量特征,找出元素异常分布信息,进行科学有效评价。 相似文献
60.