全文获取类型
收费全文 | 725篇 |
免费 | 203篇 |
国内免费 | 334篇 |
专业分类
测绘学 | 86篇 |
大气科学 | 710篇 |
地球物理 | 89篇 |
地质学 | 130篇 |
海洋学 | 90篇 |
天文学 | 6篇 |
综合类 | 27篇 |
自然地理 | 124篇 |
出版年
2024年 | 6篇 |
2023年 | 10篇 |
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 25篇 |
2019年 | 19篇 |
2018年 | 37篇 |
2017年 | 31篇 |
2016年 | 46篇 |
2015年 | 42篇 |
2014年 | 59篇 |
2013年 | 67篇 |
2012年 | 56篇 |
2011年 | 65篇 |
2010年 | 52篇 |
2009年 | 74篇 |
2008年 | 54篇 |
2007年 | 42篇 |
2006年 | 73篇 |
2005年 | 63篇 |
2004年 | 49篇 |
2003年 | 52篇 |
2002年 | 36篇 |
2001年 | 24篇 |
2000年 | 37篇 |
1999年 | 18篇 |
1998年 | 28篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 16篇 |
1994年 | 18篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1262条查询结果,搜索用时 31 毫秒
1.
To determine if Cu mediated reactions on atmospheric particles are important to HO2 chemistry in the ambient atmosphere, Cu molalities were calculated from measured Cu aerosol particle concentrations, mass and number size distribution data from a site in central Sweden. A comparison of characteristic times indicates that at low relative humidities the reaction is limited by the mass transport of gas phase HO2 to the particle surface and not by the chemical kinetics of the aqueous reaction. Comparison of half-lives for particle reactions and the gas phase destruction of HO2 to form H2O2 indicate that heterogeneous reactions on aerosol particles may have important consequences on the chemistry of HO2 and H2O2 in the troposphere. 相似文献
2.
The time evolution of a two-dimensional line thermal-a turbulent flow produced by an initial element with signifi-cant buoyancy released in a large water body, is numerically studied with the two-equation k - e model for turbulence closure. The numerical results show that the thermal is characterized by a vortex pair flow and a kidney shaped concentra-tion structure with double peak maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless time around 10. There are two regions in the flow field of a line thermal: a mixing region where the concentration of tracer fluid is high and the flow is turbulent and rotational with a pair of vortex eyes, and an ambient region where the concentration is zero and the flow is potential and well-described by a model of doublet with strength very close to those given by early experimental and analytical studies. The added virtual mass coeffi-cient of the thermal motion is found to be approximat 相似文献
3.
气溶胶的光学厚度与反射率比的处理方法 总被引:2,自引:0,他引:2
气溶胶光学厚度与气溶胶反射率比都是大气校正所需的重要大气参数,同时也是海洋水色卫星主要的数据产品,它们的测量精度将直接到卫星数据产品正演的精度和卫星数据产品的应用。文章在简述气溶胶光学厚度与气溶胶反射率比的基本测量原理和处理方法的基础上,结合多次试验数据结果进行简要的评价。 相似文献
4.
Qian Fenlan Yu Hongjian Lan Youchang Chen Zhi Zhou Mingyu Farn Parungo Wu Peiming 《海洋学报(英文版)》1996,15(1):69-84
AtmosphericinputoftraceelementstothewesternPacificOceanandtheKuroshiooceanarea¥QianFenlan;YuHongjian;LanYouchang;ChenZhi;Zhou... 相似文献
5.
Atmospherically-promoted photosynthetic activity in a well-mixed ecosystem: Significance of wet deposition events of nitrogen compounds 总被引:1,自引:0,他引:1
C. Boulart P. Flament V. Gentilhomme K. Deboudt C. Migon F. Lizon M. Schapira A. Lefebvre 《Estuarine, Coastal and Shelf Science》2006,69(3-4):449
Wet atmospheric deposition of dissolved N, P and Si species is studied in well-mixed coastal ecosystem to evaluate its potential to stimulate photosynthetic activities in nutrient-depleted conditions. Our results show that, during spring, seawater is greatly depleted in major nutrients: Dissolved Inorganic Nitrogen (DIN), Dissolved Inorganic Phosphorus (DIP) and Silicic acid (Si), in parallel with an increase of phytoplanktonic biomass. In spring (March–May) and summer (June–September), wet atmospheric deposition is the predominant source (>60%, relative to riverine contribution) for nitrates and ammonium inputs to this N-limited coastal ecosystem. During winter (October–February), riverine inputs of DIN predominate (>80%) and are annually the most important source of DIP (>90%). This situation allows us to calculate the possibility for a significant contribution to primary production in May 2003, from atmospheric deposition (total input for DIN ≈300 kg km−2 month−1). Based on usual Redfield ratios and assuming that all of the atmospheric-derived N (AD-N) in rainwater is bioavailable for phytoplankton growth, we can estimate new production due to AD-N of 950 mg C m−2 month−1, during this period of depletion in the water column. During the same episode (May 2003), photosynthetic activity rate, considered as gross primary production, was estimated to approximately 30 300 mg C m−2 month−1. Calculation indicates that new photosynthetic activity due to wet atmospheric inputs of nitrogen could be up to 3%. 相似文献
6.
离子色谱分析在黄土和粉尘研究中的应用 总被引:1,自引:0,他引:1
黄土中存在着大量的碱金属及碱土金属,以往的测试方法多为原子吸收和ICP—MS,离子色谱法在测试黄土样品的碱金属和碱土金属元素含量中应用不多。将黄土地质标准样品进行消解后用离子色谱进行测试,测试效果良好,重复测试的相对标准偏差小于5%,与推荐值的相对误差小于5%,准确度和精密度符舍相关的质量控制要求。本实验方法测试的离子含量都在仪器响应呈线性的最佳测试范围之内,标准曲线经回归后相关系数均达到0.9999。黄土样品的分析结果与粉尘气溶胶样品的离子分析结果对比表明,此方法对于探讨粉尘起源以及沙尘暴天气的研究具有重要意义。 相似文献
7.
8.
9.
Southeast South Australia has large reserves of potable groundwater, generally close to the surface. European settlement has had a major impact on groundwater quality due to the presence of extensive karst in the unconfined aquifer. Historically, industries such as cheese factories were often sited close to karst features (e.g. caves and sinkholes) because they provided a convenient means of waste disposal. Although most have long since closed, they have left a legacy of pollution plumes of varying sizes. In Mount Gambier, the main regional centre, the presence of both exposed and subterranean karst features provided a perfect system for the disposal of stormwater. Prior to the provision of a sewerage system within Mount Gambier, all toilet and household wastewaters were disposed to ground. These activities and the subsequent problems that began emerging in the 1960s have led to a concerted effort over the last 20 years to change the philosophy of waste disposal and to generate an understanding and responsibility by those who live in the region and depend on groundwater for the major part of their water supply. Mount Gambier's water supply comes from the Blue Lake. Groundwater inflow from a highly karstic Tertiary limestone aquifer provides 90% of the recharge to the Blue Lake. The lake is a high-value resource in a high-risk environment and in order to minimize this risk, a water-quality management plan for the lake is currently being developed. 相似文献
10.
本文通过环境背景值、风化壳地球化学、对流层(大气气溶胶)地球化学和人为地球化学异常,初步探讨了南极长城站地区的现代环境地球化学特征。分析表明:环境要素固有的地球化学性质、区域环境条件和自然环境演变之间具有深刻的内在联系。 相似文献