全文获取类型
收费全文 | 1136篇 |
免费 | 233篇 |
国内免费 | 216篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 222篇 |
地球物理 | 300篇 |
地质学 | 564篇 |
海洋学 | 282篇 |
天文学 | 9篇 |
综合类 | 31篇 |
自然地理 | 171篇 |
出版年
2024年 | 4篇 |
2023年 | 14篇 |
2022年 | 27篇 |
2021年 | 56篇 |
2020年 | 32篇 |
2019年 | 38篇 |
2018年 | 38篇 |
2017年 | 41篇 |
2016年 | 41篇 |
2015年 | 50篇 |
2014年 | 63篇 |
2013年 | 59篇 |
2012年 | 50篇 |
2011年 | 69篇 |
2010年 | 78篇 |
2009年 | 90篇 |
2008年 | 77篇 |
2007年 | 81篇 |
2006年 | 75篇 |
2005年 | 51篇 |
2004年 | 63篇 |
2003年 | 66篇 |
2002年 | 43篇 |
2001年 | 42篇 |
2000年 | 37篇 |
1999年 | 44篇 |
1998年 | 35篇 |
1997年 | 37篇 |
1996年 | 30篇 |
1995年 | 20篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 3篇 |
排序方式: 共有1585条查询结果,搜索用时 15 毫秒
21.
Anjali Bahuguna Shailesh Nayak Dam Roy 《International Journal of Applied Earth Observation and Geoinformation》2008,10(2):229-1
Tsunami waves struck the Indian coast on 26th December 2004 affecting the Andaman and Nicobar group of islands. A quick assessment of the status of the vital coastal ecosystems has been made using pre- and post-tsunami Advance Wide Field Sensor (AWiFS) data of Indian satellite RESOURCESAT with an accuracy of 87–90% and the Kappa ranging from 0.8696 to 0.9053. Among the coastal ecosystems the coral reefs have suffered the maximum with the Nicobar reefs (69% eroded and 29% degraded) bearing the brunt more than the Andaman reefs (54% eroded and 22% degraded). Significant improvement to the condition of the reef damaged due to backwash has been noted. About 41% of the Sentinel reef area has undergone significant improvement. The continuance of the erosion of the southwestern Andaman reefs is due to the impact of recurring earthquakes. The impact on mangroves of both the groups of islands has been due to uprooting as well as inundation of seawater and resulting stagnation. Changes are expected in community structure of mangroves as a result of tsunami. 相似文献
22.
23.
Results from numerical investigations regarding the exchange of HNO3, NH3, and NH4NO3 between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with group concentrationsc
1=[HNO3]+[NH4NO3] (total nitrate),c
2=[NH3]+[NH4NO3] (total ammonia), andc
3=[HNO3]-[NH3] as well as the fluxes of the individual nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified inferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO3, NH3, and NH4NO3) measured at a reference height by stations of a monitoring network. 相似文献
24.
丰台—野鸡坨断裂为唐山地区主要断裂之一,西侧为鸦鸿桥凹陷,东侧为唐山凸起,断裂两侧第四系厚度之差巨大。本文依据该断层两侧钻孔对其第四纪以来活动性进行初步的探讨。通过对丰台—野鸡坨断裂上下两盘PZK14和PZK20孔磁性地层学研究,并结合钻孔岩石地层,及浅部光释光和14C测年结果,建立第四纪地层格架。结果表明:两孔底部“泥包砾”为新近纪沉积;PZK14孔下更新统底界埋深为387 m,中更新统底界埋深为114 m,上更新统底界埋深为71 m,全新统底界埋深为6 m;PZK20孔下更新统底界埋深为155 m,中更新统底界埋深为73 m,上更新统底界为36 m,无全新世地层。丰台—野鸡坨断裂活动在早更新世时表现为逐渐增强的特点,活动速率由早期的5.4 cm/ka增加到13.9 cm/ka。中更新世断裂活动基本处于停滞状态,活动速率为1.0 cm/ka。晚更新世以后,断裂重新活动,且更加剧烈,活动速率达到了54.5 cm/ka。 相似文献
25.
Heikki Simola 《Journal of Paleolimnology》1991,6(3):257-260
The utility of classifying chrysophyte stomatocysts by their characteristic honeycomb and ridge patterns is questioned, because a strikingly similar expanding pattern appears on the surface of ionized polymer gels during osmotical swelling as a result of simple physical forces. The rapid accumulation of silicate into a spherical cyst inside a chrysophyte cell appears to be as a physical process sufficiently similar to result in an analogous pattern in microscopic scale. Chrysophyte stomatocysts that possess honeycomb or ridge patterns could be regarded as frozen moments of the pattern evolution during the silicate gel phase. As a consequence, such structures should have little taxonomical value. 相似文献
26.
Houyi ZHENG Congqiang LIU Zhongliang WANG 《中国地球化学学报》2006,25(B08):174-174
Bedrock weathering and atmospheric deposition are the two primary sources of base cations (K^+, Na^+, Ca^2+ and Mg^2+) to forest ecosystems. Therefore, the key problem is to understand the relative inputs from these two sources and the cycling in the ecosystem. This study focuses on the effects of acid deposition on cation cycling in a small-forested karstic catchment in Guizhou Province. Sr isotope ratios were used as a tracer for understanding the transport process between the different cation pools: rock, soil, surface water, atmospheric deposition and plant. The samples of wet deposition, total deposition, throughfall, surface and ground waters, vegetation, and soil were monthly collected. The exchangeable Sr^2+ and Ca^2+ in soil samples were extracted by using 1 M ammonium acetate. The leaf-tissue samples were ashed at 550℃, and the residue was digested in ultrapure HClO4 and HNO3. All water samples were filtrated through 0.45 μm aperture filter paper. Base cation concentrations and Sr isotopic composition were analyzed for all the samples. The results show that acid deposition (average pH 4.9) frequently occurred in the studied region. Cation abundance follows an increasing manner from rainwater, throughfall, to surface water or ground water samples, suggesting that acid deposition at first eiuviates Ca^2+ , Mg^2+ and Sr^2+ from leaf, then the exchangeable cations from soil, and at last cations accumulate in surface water or ground water. 相似文献
27.
从地上、地下有机物质生产对湿地碳输入的贡献,湿地土壤碳库以及土地利用变化对湿地土壤碳库和碳排放的影响,甲烷排放和可溶性有机碳输出以及影响因子,湿地生态系统碳循环动态模型4个方面对湿地生态系统碳循环国内外研究进展和研究成果进行综述、分析,提出了我国亚热带区域天然湿地碳循环研究的主要热点和方向:⑴沿海湿地碳库估算及土地利用转化对土壤碳库和温室气体排放的影响;⑵酸沉降对于我国东南沿海低纬度地区湿地甲烷排放的影响;⑶沿海湿地生态系统碳循环动态模型的应用与开发;⑷湿地系统可溶性有机碳的输出机理探讨. 相似文献
28.
M. Catherine Eimers Andrew M. Paterson Peter J. Dillon Sherry L. Schiff Brian F. Cumming Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109
Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in
the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~
20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ 34S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment
were relatively low (1.9–5 mg S g−1 dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in
δ 34S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally
reciprocal depth pattern between total S concentration and δ 34S ratios. While initial shifts in total S and δ 34S were likely due to enhanced SO4 reduction of newly available anthropogenic SO4, both the magnitude and pattern of up-core S enrichment and shifts in δ 34S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and
δ 34S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake
characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S
deposition in this region, likely due to redox-related mobility of S in upper sediment. 相似文献
29.
岩石、土壤样品中210Po测定方法的研究 总被引:1,自引:0,他引:1
研究了以铜箔为镀片时,自沉积总α计数法定量测定岩石、土壤样品中210Po的最佳制源环境、同位素的干扰和去除、共存元素的允许量以及适宜的溶(熔)矿方法,同时研究了银、铜两种镀片的区别。试验发现,当盐酸浓度为2.0mol/L,恒温80℃,振荡频率为180次/min、振程20mm时,制源2.0h,210Po自镀回收率在99.6%~100.4%之间,210Po加入量与α净计数率线性相关系数为0.9999。放置衰变法可以消除212Bi和218Po等短半衰期核素对210Po测量产生的影响,Vc存在时其它共存元素不干扰测定。方法配合HNO3HFHClO4溶矿(对复杂试样酸溶后的不溶渣,再进行碱熔),全程回收率为99.5%~100.4%。 相似文献
30.
Mass size distribution of the crustal elements (Al, Ca, Fe, Mg, Si, Ti), anthropogenic elements (Zn, Mn, Cr, Cu, K, P, Pb) and sea elements (Na, Cl) were obtained from measurements carried out with an inertial cascade impactor in Sfax. A fitting procedure by data inversion was applied to those data. This procedure yields accurate size distributions of aerosols in the diameter range 0.1–25 μm in two different sites. In a coastal industrial site, the mass distribution of the aerosol showed a bimodal structure; and in urban area, the lower particle mode cannot be observed. The elemental dry deposition flux was calculated as a function of particle size. The element flux size distribution increased rapidly with particle size. The modelling results indicate that the majority of the crustal and anthropogenic elements flux (>90%) was due to particles larger than 3 μm in diameter. 相似文献