全文获取类型
收费全文 | 19150篇 |
免费 | 3077篇 |
国内免费 | 6098篇 |
专业分类
测绘学 | 329篇 |
大气科学 | 3426篇 |
地球物理 | 3192篇 |
地质学 | 9211篇 |
海洋学 | 6368篇 |
天文学 | 63篇 |
综合类 | 1222篇 |
自然地理 | 4514篇 |
出版年
2024年 | 78篇 |
2023年 | 229篇 |
2022年 | 719篇 |
2021年 | 731篇 |
2020年 | 805篇 |
2019年 | 1009篇 |
2018年 | 839篇 |
2017年 | 872篇 |
2016年 | 871篇 |
2015年 | 904篇 |
2014年 | 1262篇 |
2013年 | 1312篇 |
2012年 | 1156篇 |
2011年 | 1268篇 |
2010年 | 967篇 |
2009年 | 1374篇 |
2008年 | 1300篇 |
2007年 | 1398篇 |
2006年 | 1301篇 |
2005年 | 1194篇 |
2004年 | 1131篇 |
2003年 | 1020篇 |
2002年 | 959篇 |
2001年 | 755篇 |
2000年 | 751篇 |
1999年 | 689篇 |
1998年 | 539篇 |
1997年 | 546篇 |
1996年 | 460篇 |
1995年 | 361篇 |
1994年 | 349篇 |
1993年 | 275篇 |
1992年 | 213篇 |
1991年 | 171篇 |
1990年 | 106篇 |
1989年 | 117篇 |
1988年 | 77篇 |
1987年 | 51篇 |
1986年 | 26篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
The pollen analysis of DGKS9617 core in the East China Sea (covering about the last 6800 years) shows five obvious pollen assemblages and seven sub-assemblages. Combined with the sediment and the result of diatom analysis, the climate changes are reconstructed during the Middle and Late Holocene. Corresponding to the pollen assemblages, the climate shifts just as follows: Assemblage Ⅰ-Warm and Dry Stage, Assemblage Ⅱ-Cool and Humid Stage, Assemblage Ⅲ-Hot and Dry Stage (the mean annual temperature is 2~3 ℃ higher than that today ), Assemblage Ⅳ-Cool and Humid Stage, Assemblage Ⅴ-Wann and Dry Stage. The third stage is divided into three substages i.e. a slight colder and dry one, a slight wanner and humid one and a slight warmer and dry one. During the fifth stage, the climate becomes similar to that today with three warm substages and two cool substages. 相似文献
223.
Abstract. A component analysis of the sugar and lipid fraction in foam layers around kelp beds on the South African west coast showed the following trends: In the residue of foam drainage of both 12 h and 120 h old foam the sugar fraction is represented by mannose (33–41 %), galactose (4–30%), fucose (3–29%) and glucose (19–26%). With the exception of fucose, the same components could be found in foam filtration. In the lipid fraction the main fatty acids are palmitic (23.3–27.3%), oleic (14.0–5.5%) and timnodonic acid (11.2–9.1%). Selacholeinic acid was only found in 12 h old foam while lignoceric acid could not be located in foam filtration. Against expectation mannitol was not identified in quantifiable amounts in foam samples although it is the dominant component of kelp mucilage, whose presence is of major importance for foam formation. Hypotheses explaining the lack of mannitol are forwarded. Component sugar and lipid content for 11 of foam was calculated and estimation of sugar and lipid content in an average foam patch (volume of 30001) is given. The importance of foam formation as a mechanism for binding and transfer of energy in the marine environment is emphasized. 相似文献
224.
225.
226.
东海温度锋的分布特征及其季节变异 总被引:8,自引:4,他引:8
根据1934-1988年东海水文观测资料,重点分析东海温度锋的分布特征及其季节变异,并结合近期中日黑潮合作调查研究成果,初步探讨温度锋季节变异和水团演变的关系,所得主要结论是:(1)东海不仅常年存在浙闽沿岸锋,东海北部陆架锋和黑潮锋,而且、春、夏两季,在东海南部还出现一条东海中部出架锋。(2)江海温度锋季节变化的特点是:冬季,锋的宽度和强度皆是表层最强,夏季,表层温度锋仅出现在浙江近岸小范围海域。 相似文献
227.
228.
229.
Size distribution of colloidal trace metals and organic carbon during a coastal bloom in the Baltic Sea 总被引:1,自引:0,他引:1
Johan Ingri Susanna Nordling Jenny Larsson Jenny Rnnegrd Nina Nilsson Ilia Rodushkin Ralf Dahlqvist Per Andersson
rjan Gustafsson 《Marine Chemistry》2004,91(1-4):117-130
The physico-chemical speciation of organic carbon and selected metals was measured during a coastal bloom in Ekhagen Bay, Baltic Sea, using ultrafiltration.One important objective with the study was to see if any depletion of trace metals could be measured in the directly bioavailable fraction (<1000 Da, the soluble low molecular weight fraction, LMW) during a plankton bloom. Filters with five different cut-offs were used (1 kD (1000 Da), 5 kD, 10 kD, 100 kD and 0.22 μm) in order to delineate the size distribution of colloidal organic carbon (COC) and trace metals.During the bloom in May, LMW Al, Co, Cu, Mn and Ni concentrations decreased although the colloidal and particulate concentrations were relatively high. Data show that desorption of colloidal and particulate bound trace metals to the LMW fraction was slower than the process depleting the LMW fraction.Estimates of the maximum active uptake of Cu, Ni and Mn by the phytoplankton, and the loss of non-bioactive Al from the LMW fraction, indicate that processes other than active uptake by phytoplankton must contribute to the observed depletion of trace metals in the LMW fraction. Hence, in order to estimate the bioavailable pool of trace metals for plankton during bloom conditions, these other processes must be understood and quantified.Transparent Exopolymeric Particles (TEP, reflecting sugar-rich phytoplankton exudates) increased around eight times during the plankton bloom. We hypothesize that the formation of TEP is a process that might be important for the transfer of trace metals from the LMW to the particulate fraction during the phytoplankton bloom, but the significance of TEP for this depletion in Baltic Sea surface water remains to be shown. 相似文献
230.