全文获取类型
收费全文 | 587篇 |
免费 | 75篇 |
国内免费 | 188篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 42篇 |
地球物理 | 233篇 |
地质学 | 392篇 |
海洋学 | 90篇 |
天文学 | 2篇 |
综合类 | 34篇 |
自然地理 | 50篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 22篇 |
2021年 | 26篇 |
2020年 | 29篇 |
2019年 | 33篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 23篇 |
2015年 | 29篇 |
2014年 | 31篇 |
2013年 | 41篇 |
2012年 | 26篇 |
2011年 | 42篇 |
2010年 | 41篇 |
2009年 | 27篇 |
2008年 | 49篇 |
2007年 | 34篇 |
2006年 | 72篇 |
2005年 | 24篇 |
2004年 | 35篇 |
2003年 | 29篇 |
2002年 | 22篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 19篇 |
1998年 | 32篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 17篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有850条查询结果,搜索用时 15 毫秒
841.
将剪切型危岩主控结构面按受力机理归纳为压剪和拉剪两种形式,其本质是Ⅰ-Ⅱ复合型裂纹的断裂扩展问题。应用最大应变能释放准则,建立危岩主控结构面开裂角θ0和断裂韧度GIC的计算方法。选取重庆万州首立山典型危岩进行计算,结果表明,其断裂角与基于最大周向应力准则的断裂角计算结果一致,主控结构面的开裂方向均是指向临空面方向,初步验证了方法的可行性。 相似文献
842.
根据济南市历下区TM遥感影像获取了历下区植被归一化指数(NDVI),利用单窗算法提取了地表温度;通过对比NDVI分布与温度分布分析了植被对城市热岛效应的缓解作用。采用改进的CASA模型提取了植被第一性净生产力(NPP),进而获得了植被的固碳释氧能力,分析了城市植被的固碳释氧价值。采用影子替代法对植被生态价值进行定量化,从而可对济南市历下区植被分布进行科学规划,以提高城市整体的人居适宜性。结果显示,城市植被生态价值非常可观,热岛缓解价值最大可达249021元/hm^2,植被固碳和释氧价值最大分别为15818.2元/hm^2和18645.2元/hm^2。 相似文献
843.
Lactic acid bacteria (LAB) were encapsulated with alginate, gelatin and trehalose additives by the extrusion method and dried at 4 ℃. The microcapsules were generally spherical and had a wrinkled surface with a size of 1.7 mm ± 0.2 mm. Trehalose as a carbohydrate source in the culture medium could reduce acid production and performed no function in the positive proliferation of LAB. Using trehalose as a carbohydrate source and protective medium simultaneously had a benefit in the protection of LAB cells dur... 相似文献
844.
M.-J. Messias A.J. Watson K.I.C. Oliver E. Fogelqvist S. Bacon N. Bergman M. Danielsen E. Jeansson S.R. Olafsdottir T. Tanhua J.R. Ledwell 《Progress in Oceanography》2008,78(1):85-105
In summer 1996, a tracer release experiment using sulphur hexafluoride (SF6) was launched in the intermediate-depth waters of the central Greenland Sea (GS), to study the mixing and ventilation processes in the region and its role in the northern limb of the Atlantic overturning circulation. Here we describe the hydrographic context of the experiment, the methods adopted and the results from the monitoring of the horizontal tracer spread for the 1996-2002 period documented by ∼10 shipboard surveys. The tracer marked “Greenland Sea Arctic Intermediate Water” (GSAIW). This was redistributed in the gyre by variable winter convection penetrating only to mid-depths, reaching at most 1800 m depth during the strongest event observed in 2002.For the first 18 months, the tracer remained mainly in the Greenland Sea. Vigorous horizontal mixing within the Greenland Sea gyre and a tight circulation of the gyre interacting slowly with the other basins under strong topographic influences were identified. We use the tracer distributions to derive the horizontal shear at the scale of the Greenland Sea gyre, and rates of horizontal mixing at ∼10 and ∼300 km scales. Mixing rates at small scale are high, several times those observed at comparable depths at lower latitudes. Horizontal stirring at the sub-gyre scale is mediated by numerous and vigorous eddies. Evidence obtained during the tracer release suggests that these play an important role in mixing water masses to form the intermediate waters of the central Greenland Sea.By year two, the tracer had entered the surrounding current systems at intermediate depths and small concentrations were in proximity to the overflows into the North Atlantic. After 3 years, the tracer had spread over the Nordic Seas basins. Finally by year six, an intensive large survey provided an overall synoptic documentation of the spreading of the tagged GSAIW in the Nordic Seas. A circulation scheme of the tagged water originating from the centre of the GS is deduced from the horizontal spread of the tracer. We present this circulation and evaluate the transport budgets of the tracer between the GS and the surroundings basins. The overall residence time for the tagged GSAIW in the Greenland Sea was about 2.5 years. We infer an export of intermediate water of GSAIW from the GS of 1 to 1.85 Sv (1 Sv = 106 m3 s−1) for the period from September 1998 to June 2002 based on the evolution of the amount of tracer leaving the GS gyre. There is strong exchange between the Greenland Sea and Arctic Ocean via Fram Strait, but the contribution of the Greenland Sea to the Denmark Strait and Iceland Scotland overflows is modest, probably not exceeding 6% during the period under study. 相似文献
845.
The concentrations of rare earth elements in the dissolved, acid-soluble and residual phases in surface waters of the Changjiang
Estuary were determined using ICP-MS. The main purposes of the study are to understand the estuarine geochemistry of rare
earth elements and to explore water-particle interactions in the Changjiang estuarine mixing zone. The results show that there
are two distinct processes operating on dissolved rare earth elements in the estuary: large scale removal at low salinities
due to salt-induced coagulation and remarkable release at mid to high salinities. These processes result in modification of
the effective river water flux and the systematical fractionation of the dissolved rare earth elements toward the East China
Sea. The increase in concentration of dissolved rare earth elements in the mid to high salinity waters of the Changjiang Estuary
suggests a sediment source in the mixing zone of the estuary, which is located over a shallow, broad shelf where there is
extensive physical contact between bottom sediment and estuarine waters. Acid-soluble rare earth elements, the concentrations
of which also dropped sharply in the low salinity region, appear to be controlled by salt-induced coagulation process and
intense deposition of suspended particulate matter in the low salinity region. In the mid to high salinities, all acid-soluble
rare earth element concentrations increase slightly with increasing salinity, suggesting that resuspension of sediments occurred.
In contrast, the residual rare earth element concentrations are relatively constant with salinity variation in the Changjiang
estuarine surface waters. 相似文献
846.
卡林型金矿床中自然砷的特征与成矿物理化学条件示踪 总被引:5,自引:1,他引:4
在"滇黔桂"、"川甘陕"两个金三角密集区内的某些卡林型金矿床中,自然砷矿物的存在并非个别现象。自然砷呈致密块状、致密凝胶体状(肾状)、脉状或微细脉状产出。自然砷呈他形粒状,颗粒大小变化较大,一般为0.05~0.50mm,最大可达2mm。反光显微镜下为白色,显微硬度为114.21~150.60kg/mm2,相当于摩氏硬度3.27~3.59。矿物主要化学成分As的质量分数为92.74%~99.74%,并含有S0.18%~5.25%,Sb0.04%~3.65%。矿物为三方晶系,晶胞参数值a=0.3759nm,c=1.0527nm。利用矿床中含砷矿物的共生组合特点及热力学资料,探讨了卡林型金矿床形成的温度、成矿流体的f(O2)、f(S2)变化范围及金以金砷络合物形式迁移的可能性。 相似文献
847.
增压微波消解-氢化物-原子荧光光谱法测定铁矿石中的砷 总被引:4,自引:0,他引:4
用微波消解方法处理样品,采用抗坏血酸-硫脲-磷酸作为掩蔽剂,以原子荧光光谱法实现了铁矿石中砷的测定。方法检出限0.35μg/L-1,加标回收率97.5%~106.5%。经标样分析验证,结果与标准值相符,测定的RSD为4.24%。采用该方法分离铁矿石中的砷,结果满意。 相似文献
848.
849.
Bin LIU Zhenghui XIE Peihua QIN Shuang LIU Ruichao LI Longhuan WANG Yan WANG Binghao JIA Si CHEN Jinbo XIE Chunxiang SHI 《大气科学进展》2021,38(3):430-445
With economic development and rapid urbanization,increases in Gross Domestic Product and population in fastgrowing cities since the turn of the 21st Century have led to increases in energy consumption.Anthropogenic heat flux released to the near-surface atmosphere has led to changes in urban thermal environments and severe extreme temperature events.To investigate the effects of energy consumption on urban extreme temperature events,including extreme heat and cold events,a dynamic representation scheme of anthropogenic heat release(AHR)was implemented in the Advanced Research version of the Weather Research and Forecasting(WRF)model,and AHR data were developed based on energy consumption and population density in a case study of Beijing,China.Two simulations during 1999?2017 were then conducted using the developed WRF model with 3-km resolution with and without the AHR scheme.It was shown that the mean temperature increased with the increase in AHR,and more frequent extreme heat events were produced,with an annual increase of 0.02?0.19 days,as well as less frequent extreme cold events,with an annual decrease of 0.26?0.56 days,based on seven extreme temperature indices in the city center.AHR increased the sensible heat flux and led to surface energy budget changes,strengthening the dynamic processes in the atmospheric boundary layer that reduce AHR heating efficiency more in summer than in winter.In addition,it was concluded that suitable energy management might help to mitigate the impact of extreme temperature events in different seasons. 相似文献
850.