全文获取类型
收费全文 | 56621篇 |
免费 | 14273篇 |
国内免费 | 20968篇 |
专业分类
测绘学 | 10405篇 |
大气科学 | 8016篇 |
地球物理 | 10344篇 |
地质学 | 37738篇 |
海洋学 | 11027篇 |
天文学 | 802篇 |
综合类 | 5052篇 |
自然地理 | 8478篇 |
出版年
2024年 | 482篇 |
2023年 | 1298篇 |
2022年 | 3422篇 |
2021年 | 4183篇 |
2020年 | 3409篇 |
2019年 | 4105篇 |
2018年 | 3636篇 |
2017年 | 3453篇 |
2016年 | 3365篇 |
2015年 | 4039篇 |
2014年 | 4003篇 |
2013年 | 4847篇 |
2012年 | 5289篇 |
2011年 | 5318篇 |
2010年 | 5298篇 |
2009年 | 4884篇 |
2008年 | 4982篇 |
2007年 | 4719篇 |
2006年 | 4474篇 |
2005年 | 3825篇 |
2004年 | 2906篇 |
2003年 | 1990篇 |
2002年 | 1967篇 |
2001年 | 1824篇 |
2000年 | 1541篇 |
1999年 | 777篇 |
1998年 | 313篇 |
1997年 | 220篇 |
1996年 | 182篇 |
1995年 | 139篇 |
1994年 | 139篇 |
1993年 | 114篇 |
1992年 | 109篇 |
1991年 | 68篇 |
1990年 | 78篇 |
1989年 | 30篇 |
1988年 | 30篇 |
1987年 | 36篇 |
1986年 | 46篇 |
1985年 | 36篇 |
1984年 | 35篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1979年 | 30篇 |
1978年 | 11篇 |
1976年 | 12篇 |
1957年 | 19篇 |
1954年 | 30篇 |
1933年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
Dissolved and particulate trace metals and their partitioning in a hypoxic estuary: The Tanshui Estuary in Northern Taiwan 总被引:1,自引:0,他引:1
The distribution and partitioning of trace metals (Co, Cu, Fe, Mn, Ni, and Zn) between dissolved and particulate phases were studied in the Tanshui Estuary. The upper reach of the estuary is hypoxic and heavily polluted due to domestic and industrial discharges. The concentration ranges of dissolved and leachable particulate trace metals in the Tanshui Estuary were: Co: 0.3–6.1 nM, 1.8–18.6 mg kg−1; Cu: 5–53 nM, 22–500 mg kg−1; Fe: 388–3,364 nM, 1.08–6.67%; Mn: 57–2,914 nM, 209–1,169 mg kg−1; Ni: 7–310 nM, 6–108 mg kg−1; and Zn: 12–176 nM, 62–1,316 mg kg−1; respectively. The dissolved concentrations of the metals were 2–35 times higher than the average values of the world river water. The distributions of dissolved and particulate studied metals, except Mn, in the estuary showed scattering, which could be attributed to the discharges from many industrial wastewater disposal works located in the upper tributaries. The daily input of dissolved metals from the disposal works to the Tanshui Estuary ranged from 0.1–0.4 tons. Dissolved Mn was nearly conservative in the region with salinity higher than 10 psu, while particulate Mn decreased in the region with salinity of 10–15 psu. The concentration increased significantly seawards, corresponding with the distribution of dissolved oxygen. The distribution coefficient (KD) for Mn in the lower estuary was nearly three orders of magnitude higher than in the upper estuary. This phenomenon may be attributed to the diffusion of Mn from the anoxic sediment in the upper estuary and gradual oxidation into particulate Mn in the middle and lower estuary as the estuarine water became more oxygenated. The distribution coefficient for Cu decreased with increasing salinity. The percentages of trace metals bound by suspended particulate matter decreased in the following order: Fe>Zn, Cu>Co>Mn>Ni. 相似文献
822.
823.
Geochronology of Gold Deposits and Its Implication for Metallogenesis in the Fengxian-Lixian Area, Qinling Orogenic Belt, China 总被引:2,自引:0,他引:2
Abstract: A series of super large‐scale and large‐scale Pb and Zn, and Au deposits are distributed in the Qinling orogenic belt, China. Gold deposits were generally ascribed to Carlin‐type originated from circular meteoric water. Visible and coarse‐grained gold (up to over 3mm in grain size) was recently identified in some gold deposits in the Fengxian‐Lixian area, Qinling. Au‐bearing quartz lodes related to magmatism were discovered in the Xiaogouli gold deposit. Two types of Au‐bearing quartz veins, i.e., NW‐trending quartz veins and NE‐trending quartz veins cutting strata are widely present in the Baguamiao gold deposit. Both are spatially associated with each other. The former is generally snake–like, S‐shape or zigzag, which was resulted from plastic deformation by ductile shearing, being generally cut by the latter. The latter is generally linear with widely developed bleaching alteration zones in its adjacent wall rocks, which symbolizes the superimposition of brittle deformation and filling and metasomatism of magmatic hydrothermal solution in ductile shear zones after uplifting of the shear zones near the surface. The NW‐trending quartz veins contain Au of lower than 3ppm. The NE‐trending quartz veins contain Au of more than 3 ppm, so that NE‐trending quartz veins and the adjoining altered rocks are important ores. The NW‐trending Au–bearing quartz vein was dated as 210.61.26 to 232.581.59 Ma by 40Ar–39Ar method, i.e., late Indosinian epoch (Triassic). The NE‐trending Au–bearing quartz vein was dated as 131.910.89 to 197.451.13 Ma by 40Ar–39Ar method, i.e., Yanshanian epoch (Jurassic). The 40Ar–39Ar age of the NW‐trending Au–bearing quartz veins represents the age of the ductile shear formation. The isotope data of the NE‐trending quartz veins indicate that gold mineralization was closely related to Indosinian and Yanshanian granite intrusives not only in time and space, but also in origin. 相似文献
824.
825.
826.
827.
828.
简要介绍了土钉挡墙技术的发展历史及其国内外的发展现状,分析了常用深基坑土钉挡墙的计算方法和使用条件,提出了当前土钉技术应用中亟待解决的问题,探讨了土钉技术今后的发展方向. 相似文献
829.
830.