全文获取类型
收费全文 | 275篇 |
免费 | 12篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 39篇 |
地球物理 | 53篇 |
地质学 | 86篇 |
海洋学 | 35篇 |
天文学 | 48篇 |
综合类 | 2篇 |
自然地理 | 19篇 |
出版年
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 14篇 |
2014年 | 6篇 |
2013年 | 4篇 |
2012年 | 8篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 30篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 13篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1953年 | 1篇 |
1952年 | 1篇 |
1951年 | 1篇 |
1949年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有297条查询结果,搜索用时 484 毫秒
291.
292.
Hun-Bok Jung Seong-Taek Yun Bernhard Mayer Soon-Oh Kim Seong-Sook Park Pyeong-Koo Lee 《Environmental Geology》2005,48(4-5):437-449
Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied
in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid
(0.1 N HCl) extraction, strong acid (HF–HNO3–HClO4) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher
in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump
upstream of Chonam-ri creek. The sediment–water distribution coefficients (K
d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd.
K
d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among
non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation
of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved
trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean
Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three
weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure.
This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable
forms of trace metals in natural stream sediments. 相似文献
293.
侧扫声呐是海洋科学调查中常用的仪器设备,针对此类声学探测设备出台相关检测、检定等计量化的标准势在必行。本文介绍了侧扫声呐的工作原理和技术参数,针对侧扫声呐分辨能力和扫宽能力这两个性能指标,提出了一种评价方法。最后通过海上试验,对比分析了3种常用的侧扫声呐仪器的分辨能力和扫宽能力,为侧扫声呐系统的选用和引进提供参考。 相似文献
294.
Anthropogenic S emissions in the Athabasca oil sands region (AOSR) in Alberta, Canada, affect SO4 deposition in close vicinity of industrial emitters. Between May 2008 and May 2009, SO4-S deposition was monitored using open field bulk collectors at 15 sites and throughfall collectors at 14 sites at distances between 3 and 113 km from one of the major emission stacks in the AOSR. At forested plots >90 km from the operations, SO4 deposition was ∼1.4 kg SO4-S ha−1 yr−1 for bulk deposition and ∼3.3 kg SO4-S ha−1 yr−1 for throughfall deposition. Throughfall SO4 deposition rates in the AOSR exceeded bulk deposition rates at all sites by a factor of 2–3, indicating significant inputs of dry deposition especially under forest canopies. Both bulk and throughfall SO4 deposition rates were elevated within 29 km distance of the industrial operations with deposition rates as high as 11.7 kg SO4-S ha−1 yr−1 for bulk deposition and 39.2 kg SO4-S ha−1 yr−1 for throughfall at industrial sites. Sulfur isotope ratio measurements of atmospheric SO4 deposited in the AOSR revealed that at a few selected locations 34S-depleted SO4, likely derived from H2S emissions from tailing ponds contributes to local atmospheric SO4 deposition. In general, however, δ34S values of SO4 deposition at distant forested plots (>74 km) with low deposition rates were not isotopically different from δ34S values at sites with high deposition rates in the AOSR and are, therefore, not suitable to determine industrial S contributions. However, O isotope ratios of atmospheric SO4 in bulk and throughfall deposition in the AOSR showed a distinct trend of decreasing δ18O-SO4 values with increasing SO4 deposition rates allowing quantification of industrial contributions to atmospheric SO4 deposition. Two-end-member mixing calculations revealed that open field bulk SO4 deposition especially at industrial sites in close proximity (<29 km) to the operations is significantly (17–59%) affected by industrial S emissions and that throughfall generally contained 49–100% SO4 of industrial origin. Hence, it is suggested that δ18O values of SO4 may constitute a suitable tracer for quantifying industrial contributions to atmospheric SO4 deposition in the AOSR. 相似文献
295.
Jérôme Carrayrou Joachim Hoffmann Peter Knabner Serge Kräutle Caroline de Dieuleveult Jocelyne Erhel Jan Van der Lee V. Lagneau K. Ulrich Mayer Kerry T. B. MacQuarrie 《Computational Geosciences》2010,14(3):483-502
Although multicomponent reactive transport modeling is gaining wider application in various geoscience fields, it continues
to present significant mathematical and computational challenges. There is a need to solve and compare the solutions to complex
benchmark problems, using a variety of codes, because such intercomparisons can reveal promising numerical solution approaches
and increase confidence in the application of reactive transport codes. In this contribution, the results and performance
of five current reactive transport codes are compared for the 1D and 2D subproblems of the so-called easy test case of the
MoMaS benchmark (Carrayrou et al., Comput Geosci, 2009, this issue). This benchmark presents a simple fictitious reactive transport problem that highlights the main numerical difficulties
encountered in real reactive transport problems. As a group, the codes include iterative and noniterative operator splitting
and global implicit solution approaches. The 1D easy advective and 1D easy diffusive scenarios were solved using all codes,
and, in general, there was a good agreement, with solution discrepancies limited to regions with rapid concentration changes.
Computational demands were typically consistent with what was expected for the various solution approaches. The differences
between solutions given by the three codes solving the 2D problem are more important. The very high computing effort required
by the 2D problem illustrates the importance of parallel computations. The most important outcome of the benchmark exercise
is that all codes are able to generate comparable results for problems of significant complexity and computational difficulty. 相似文献
296.
Geoarchaeological investigations in western Middle Park provide important information for understanding the soil‐stratigraphic context of Paleoindian components, as well as the latest Quaternary environmental change and landscape evolution in a Southern Rocky Mountain intermontane basin. Paleoindian components are associated with the oldest two of four latest Quaternary stratigraphic units (1–4) recognized in co‐alluvial mantles (combined slopewash and colluvium) in uplands and in alluvial valley fills. Limited data suggest accumulation of unit 1 as early as ∼12,500 14C yr B.P. in alluvial valleys and by at least ∼11,000 14C yr B.P. in uplands was followed by brief stability and soil formation. A relatively widespread disconformity marks earliest Holocene erosion and substantial removal of latest Pleistocene deposits in upland and alluvial settings followed by unit 2 deposition ∼10,000–9000 14C yr B.P., perhaps signaling the abrupt onset of an intensified summer monsoon. In situ Paleoindian components in uplands are found in a moderately developed buried soil (the Kremmling soil) formed in units 1 and 2 in thin (≤1m) hillslope co‐alluvial mantles. The Kremmling soil reflects geomorphic stability in upland and alluvial settings ∼9000–4500 14C yr BP, and represents a buried landscape with the potential to contain additional Paleoindian components, although elsewhere in western Middle Park Early Archaic components are documented in morphologically similar soils. Kremmling soil morphology, the relative abundance of charcoal in unit 2 relative to younger units, and charcoal morphology indicate the expansion of forest cover, including Pinus, and grass cover during the early and middle Holocene, suggesting conditions moister than present. © 2010 Wiley Periodicals, Inc. 相似文献
297.