全文获取类型
收费全文 | 543篇 |
免费 | 82篇 |
国内免费 | 148篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 141篇 |
地球物理 | 105篇 |
地质学 | 265篇 |
海洋学 | 98篇 |
天文学 | 59篇 |
综合类 | 48篇 |
自然地理 | 41篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 26篇 |
2021年 | 35篇 |
2020年 | 23篇 |
2019年 | 23篇 |
2018年 | 37篇 |
2017年 | 26篇 |
2016年 | 44篇 |
2015年 | 29篇 |
2014年 | 32篇 |
2013年 | 34篇 |
2012年 | 25篇 |
2011年 | 40篇 |
2010年 | 25篇 |
2009年 | 20篇 |
2008年 | 27篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 15篇 |
2003年 | 15篇 |
2002年 | 11篇 |
2001年 | 18篇 |
2000年 | 22篇 |
1999年 | 24篇 |
1998年 | 22篇 |
1997年 | 27篇 |
1996年 | 24篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有773条查询结果,搜索用时 15 毫秒
741.
742.
743.
皖西白大山群的发现及其地质意义 总被引:7,自引:0,他引:7
皖、豫交界的白大山-茶庵一带,出露一套碎屑岩夹碳酸盐岩地层,以往被置于青白口系八公山群。近期笔者等赴该地再次进行了调查和研究,结果发现该群地层组合内含有大量球藻类和植物碎片化石,这些微古植物分子在国内外多见于下古生代。并从岩石组合特征对比分析,认为该套地层属志留-泥盆系的可能性最大。对这套地层及微古植物的发现,具有两方面重要的地质意义:1.过去对华北地台南缘从未见有这个时代地层的报导,这就为该区地层填补了一个空白;2.从已采获的微古植物组合及岩性组合特征等分析,这有可能对华北地台南缘的岩相古地理图及地史发展等问题,进行一些必要的改写与补充。 相似文献
744.
Weiwei Chao Ken‐ichiro Hayashi Huishou Ye Jingwen Mao Yanguang Geng Minfeng Bi Peng Wang Qiuming Pei 《Resource Geology》2019,69(4):333-350
The Luanling gold telluride deposit in the Xiong'ershan region is located in the southern margin of the North China Craton. The deposit formed in four stages, that is, an early pyrite‐quartz stage (I), a pyrite‐molybdenite stage (II), a sulfide‐telluride‐gold stage (III), and a late carbonate stage (IV). Six species of telluride in stage (III) are recognized, including hessite, altaite, petzite, unidentified Au‐Ag‐Te mineral, empressite, and unidentified Ag‐Te‐S mineral. Gold occurs mostly as native gold and electrum along the microfractures of sulfides or the contact between sulfide and telluride. The mineralization temperature of stage I and stage III ranges from 296 to 377°C and 241 to 324°C, respectively. Tellurides in stage III precipitate at the log?S2 from ?14.3 to ?7.3 and log?Te2 from ?17.4 to ?9.4. The ores were formed in an oxidizing environment. The Re‐Os model ages of molybdenite are 162–164 Ma, which indicate that the main ore formation stage was in the Late Jurassic. The Re contents of five molybdenite samples from the Luanling deposit have a range of 36.32–81.95 ppm, except for one large value of 220 ppm, which indicates that the ore‐forming materials are mainly derived from a crustal‐dominated source. The δ34S values of sulfides range from ?17.6 to ?6.2‰, whereas those of sulfates are from 6.8 to 11.5‰. The δ34S∑S value of the ore‐forming system is 0.0–3.7‰, indicating that the sulfur of the Luanling deposit derived from a deep igneous source. Mineral association and isotope data of the Luanling deposit, together with its geodynamic setting, imply that this deposit belongs to a part of the metallogenic system of the Nannihu‐Sandaozhuang, Shangfangou porphyry molybdenum deposits, and the Late Jurassic granitic intrusions. 相似文献
745.
Noble Gas and Stable Isotopic Constraints on the Origin of the Ag–Cu Polymetallic Ore Deposits in the Baiyangping Area,Yunnan Province,SW China 下载免费PDF全文
Zhichao Zou Ruizhong Hu Xianwu Bi Liyan Wu Jinrang Zhang Yongyong Tang Na Li 《Resource Geology》2016,66(2):183-198
The Lanping basin, Yunnan province, SW China, is located at the juncture of the Eurasian and Indian Plates in the eastern part of the Tibetan Plateau. The Lanping basin, in the Sanjiang Tethyan metallogenic province, is a significant Cu–Ag–Zn–Pb mineralized belt in China that includes the largest sandstone‐hosted Zn–Pb deposit in the world, the Jinding deposit, as well as several Ag–Cu deposits (the Baiyangping and Jinman deposits). These deposits, with total reserves of over 16.0 Mt Pb + Zn, 0.6 Mt Cu, and 7,000 t Ag, are mainly hosted in Meso‐Cenozoic clastic rocks and are dominantly controlled by two Cenozoic thrust systems developed in the western and eastern segments of the basin. The Baiyangping, Babaoshan, and Hetaoqing ore deposits are representative of the epithermal base metal deposits in the Lanping basin. The microthermometric data show that the ore‐forming fluids for these deposits were low temperature (110–180 °C) and had bimodal distribution of salinity at moderate and mid to high salinities (approximately 2–8 wt.% and 18–26 wt.% NaCl equivalent). The C and O isotope data indicate that the ore‐forming fluids were related to hot basin brines. We present new He and Ar isotope data on volatiles released from fluid inclusions contained in sulfides and in barite in these three deposits. 3He/4He ratios of the ore‐forming fluids are 0.01 to 0.14 R/Ra with a mean of 0.07 Ra (where R is the 3He/4He ratio and Ra is the ratio for atmospheric helium). This mean value is intermediate to typical 3He/4He ratios for the crust (R/Ra = 0.01 to 0.05) and the ratio for air‐saturated water (R/Ra = 1). The mean ratio is also significantly lower than the ratios found for mantle‐derived fluids (R/Ra = 6 to 9). The 40Ar/36Ar ratios of the ore‐forming fluids range from 298 to 382 with a mean of 323. This value is slightly higher than that for the air‐saturated water (295.5). The 3He/4He ratios of fluids from the fluid inclusions imply that the ore‐forming fluid for the Baiyangping, Babaoshan, and Hetaoqing deposits was derived from the crust and that any mantle‐derived He was negligible. The content of the radiogenic Ar ranges between 0.2 to 20.4%, and the proportion of air‐derived 40Ar averages 94.1%. This indicates that atmospheric Ar was important in the formation of these deposits but that some radiogenic 40Ar was derived from crustal rocks. Based on these observations coupled with other geochemical evidence, we suggest that the ore‐forming fluids responsible for the formation of the Ag–Cu–Pb–Zn polymetallic ore deposits in the Baiyangping area of the Lanping basin were mainly derived from crustal fluids. The fluids may have mixed with some amount of air‐saturated water, but there was no significant involvement of mantle‐derived fluids. 相似文献
746.
土地档案是国土资源管理机关在土地资源管理、开发、使用过程中形成的,具有保存、利用价值的文件、图表、声像等资料,它记载着土地利用的全部过程,是一种重要的具有长期查考、利用价值的信息资源。如何科学合理地利用土地档案资源,充分发挥其在国土资源管理和地方经济建设中的作用,是土地档案管理部门应该认真研究的问题。 相似文献
747.
Geology of gold-bearing skarn deposits in the middle and lower Yangtze River Valley and adjacent regions 总被引:5,自引:0,他引:5
The middle and lower Yangtze River Valley and adjacent regions are the most important metallogenic belt of gold (and copper)-bearing skarn deposits in China. The total gold reserves in this belt have been estimated at more than 600 t. The gold-bearing skarns are mainly distributed in the southeastern Hubei, Tongling and northern Anhui regions. Favorable tectonic settings are depressions and fold zones of the platforms, i.e., mobile belts. These skarns are hosted by platformal limestone, dolomitic limestone and dolomite of the Triassic, Carboniferous-Permian and Middle to Lower Cambrian formations. The related intrusions are Yenshanian (180 to 113 Ma) calc-alkaline quartz monzodiorite, granodiorite, quartz monzonite, monzogabbro, and their hybabyssal facies. The intrusions have high Fe2O3/FeO (>0.5) and intermediate initial 87Sr/86Sr ratios (0.7046 to 0.7087). Their REE distribution patterns are LREE-enriched and exhibit smooth, right-dipping curves. These suggest that the source materials mainly came from upper mantle, with contamination by sialic crustal components. The auriferous skarns are both calcic and magnesian, but calcic skarns are most common. The constituent minerals of the calcic skarns are diopside, garnet, wollastonite, vesuvianite and scapolite, whereas magnesian skarns are dominated by forsterite, spinel, diopside, phlogopite, chondrodite and clinohumite, with abundant superimposed serpentine, clinochlore and brucite. The compositions of coexisting pyroxenes and garnets are diopside and andradite, indicating the high oxygen fugacity and low acidity conditions. Gold is closely associated with Cu (Pb, Zn) sulfides and exists mainly in the form of native gold and electrum. Arsenides, tellurides, bismuthides and selenides are present in many ore deposits. Therefore, Cu, As, Bi, Te, Ag, Pb, Zn, Se and Co are the major metals present in the deposits and are important geochemical ore-searching indicators. In some Au (Fe, Cu) magnesian skarns, magnesiomagnetite, magnesioferrite and ludwigite are locally abundant. The metasomatic zoning in many gold skarn deposits is very distinct consisting of an outward sequence of: Fe (Cu)→Cu (Mo)→Cu (Au)→Au (Cu)→Au (Pb, Zn). The geologic characteristics of Au (Cu) skarn deposits that formed in the mobile platformal setting of China have distinct differences compared to Au skarns formed in orogenic belts at convergent plate margins in British Columbia and the western USA. 相似文献
748.
749.
750.