全文获取类型
收费全文 | 1041篇 |
免费 | 58篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 76篇 |
地球物理 | 279篇 |
地质学 | 352篇 |
海洋学 | 106篇 |
天文学 | 136篇 |
综合类 | 1篇 |
自然地理 | 132篇 |
出版年
2022年 | 6篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 21篇 |
2018年 | 30篇 |
2017年 | 33篇 |
2016年 | 39篇 |
2015年 | 32篇 |
2014年 | 43篇 |
2013年 | 72篇 |
2012年 | 49篇 |
2011年 | 57篇 |
2010年 | 46篇 |
2009年 | 42篇 |
2008年 | 42篇 |
2007年 | 41篇 |
2006年 | 39篇 |
2005年 | 31篇 |
2004年 | 34篇 |
2003年 | 36篇 |
2002年 | 25篇 |
2001年 | 21篇 |
2000年 | 29篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 21篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1968年 | 6篇 |
1948年 | 3篇 |
排序方式: 共有1111条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
Rachel E. Adams Ayumi Hyodo Toby SantaMaria Cynthia L. Wright Thomas W. Boutton Jason B. West 《水文研究》2020,34(4):991-1003
Questions persist about interpreting isotope ratios of bound and mobile soil water pools, particularly relative to clay content and extraction conditions. Interactions between pools and resulting extracted water isotope composition are presumably related to soil texture, yet few studies have manipulated the bound pool to understand its influence on soil water processes. Using a series of drying and spiking experiments, we effectively labelled bound and mobile water pools in soils with varying clay content. Soils were first vacuum dried to remove residual water, which was then replaced with heavy isotope-enriched water prior to oven drying and spiking with heavy isotope-depleted water. Water was extracted via centrifugation or cryogenic vacuum distillation (at four temperatures) and analysed for oxygen and hydrogen isotope ratios via isotope ratio mass spectrometry. Water from centrifuged samples fell along a mixing line between the two added waters but was more enriched in heavy isotopes than the depleted label, demonstrating that despite oven drying, a residual pool remains and mixes with the mobile water. Soils with higher clay + silt content appeared to have a larger bound pool. Water from vacuum distillation samples have a significant temperature effect, with high temperature extractions yielding progressively more heavy isotope-enriched values, suggesting that Rayleigh fractionation occurred at low temperatures in the vacuum line. By distinctly labelling bound and mobile soil water pools, we detected interactions between the two that were dependent on soil texture. Although neither extraction method appeared to completely extract the combined bound and mobile (total water) pool, centrifugation and high temperature cryogenic vacuum distillations were comparable for both δ2H and δ18O of soil water isotope ratios. 相似文献
46.
Erodibility of low‐compaction steep‐sloped reclaimed surface mine lands in the southern Appalachian region,USA 下载免费PDF全文
The use of loose spoils on steep slopes for surface coal mining reclamation sites has been promoted by the US Department of Interior, Office of Surface Mining for the establishment of native forest, as prescribed by the Forest Reclamation Approach (FRA). Although low‐compaction spoils improve tree survival and growth, erodibility on steep slopes was suspected to increase. This study quantified a combined KC factor (combining the effects of the soil erodibility K factor and cover management C) for low compaction, steep‐sloped (>20°) reclaimed mine lands in the Appalachian region, USA. The combined KC factor was used because standard Unit Plot conditions required to separate these factors, per Revised Universal Soil Loss Equation (RUSLE) experimental protocols, were not followed explicitly. Three active coal mining sites in the Appalachian region of East Tennessee, each containing four replicate field plots, were monitored for rainfall and sediment yields during a 14‐month period beginning June 2009. Average cumulative erosivity for the study sites during the monitoring period was measured as 5248.9 MJ·mm·ha?1·h?1. The KC ranged between 0.001 and 0.05 t·ha·h·ha?1·MJ?1·mm?1, with the highest values occurring immediately following reclamation site construction as rills developed (June – August 2009). The KC for two study sites with about an 18–20 mm spoil D84 were above 0.01 t·ha·h·ha?1·MJ?1·mm?1 during rill development, and below 0.003 t·ha·h·ha?1·MJ?1·mm?1 after August 2009 for the post‐rill development period. The KC values for one site with a 40 mm spoil D84 were never above 0.008 t·ha·h·ha?1·MJ?1·mm?1 and also on average were lower, being more similar to the other two sites after the rill development period. Based on an initial KC factor (Ke) measured during the first few storm events, the average C factor (Ce) was estimated as 0.58 for the rill development period and 0.13 for the post‐rill development period. It appears that larger size fractions of spoils influence KC and Ce factors on low‐compaction steep slopes reclamation sites. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
47.
Alice Schaffhauser Serge Payette Michelle Garneau Élisabeth C. Robert 《Boreas: An International Journal of Quaternary Research》2017,46(3):428-441
The initiation and growth of boreal peatlands developed on well‐drained, sandy landforms are closely associated with podzolic soil paludification processes. The origin of Sphagnum bogs extending on large deltaic plains was examined to test the hypothesis of the dual impact of indurated (ortstein) podzols and fire on forest soil paludification and concurrent peatland initiation and expansion. Mineral soil, basal organic matter and peat monoliths were sampled for soil and macrofossil analyses along an 800‐m toposequence starting from a mixed‐wood boreal forest to a Sphagnum bog (Lebel bog, eastern Quebec, Canada), and ending at a peat dome in the thickest section of the peatland. Mineral soils along the toposequence are ortstein humo‐ferric podzols distributed in the forest environment and beneath Sphagnum peat in the bog, except at the peat dome. Initial peatland growth occurred c. 6000 cal. a BP. Soil paludification coincided with the cessation of fire occurrence as recorded in the organic and mineral layers preceding Sphagnum expansion. Unlike most temperate and boreal raised bogs, the Sphagnum bog developed directly from a forest environment without passing through a transitional fen stage. Conifer forests regenerated successively after several fires between 4200 and 1600 cal. a BP before bog expansion. Pre‐bog forests were composed of fire‐prone black spruce (Picea mariana) and jack pine (Pinus banksiana) trees, and ericaceous species. Given the distribution and thickness of ortstein horizons progressively decreasing and disappearing towards the peatland dome, growth and expansion of the Sphagnum bog was not caused by soil induration processes, which could have potentially impeded vertical and horizontal drainage. The development of indurated podzols outside and several hundred metres inside the peatland preceded the initiation and expansion of the Sphagnum bog. Cessation of fire activity appears to be a key factor facilitating the lateral expansion of the Sphagnum bog under wet soil conditions. 相似文献
48.
49.
50.
Kathleen M. Baker Andrew C. Johnson Caitlin N. Callahan Heather L. Petcovic 《制图学和地理信息科学》2016,43(2):176-187
Topographic maps and aerial photographs are particularly useful when geoscientists are faced with fieldwork tasks such as selecting paths for observation, establishing sampling schemes, or defining field regions. These types of images are crucial in bedrock geologic mapping, a cognitively complex field-based problem-solving task. Geologic mapping requires the geologist to correctly identify rock types and three-dimensional bedrock structures from often partial or poor-quality outcrop data while navigating through unfamiliar terrain. This paper compares the walked routes of novice to expert geologists working in the field (n = 66) with the results of a route planning and navigation survey of a similar population of geologists (n = 77). Results show clearly that those geologists with previous mapping experience make quick and decisive determinations about field areas from available imagery and maps, regardless of whether they are or not physically present in the field area. Recognition of geologic features enabled experts to form and verbalize a specific plan for travel through a landscape based on those features. Novices were less likely to develop specific travel route plans and were less likely to identify critical landscape cues from aerial photographs. 相似文献