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111.
In this study,to further promote the application of the stable carbon isotope natural abundance(SCINA)method to the study of CH4in paddy fields in China,field experiments were carried out to investigate carbon isotope fractionation during CH4transport in both rice-and non-rice-growing seasons.More importantly,two new methods for the measurement of the CH4transport fractionation factor(εtransport)in paddy fields were introduced.The results indicated that the closed chamber+syringe method was much better for the determination ofεtransport during the non-rice-growing season.Presently,εtransport was calculated using theδ13C value of the CH4emitted from a rice field minus that of the CH4in the floodwater(–6.7‰to–3.0‰).In addition,there were three methods available for estimatingεtransport during the rice-growing season:deduction of theδ13C value of the CH4in the floodwater from that of the CH4emitted from the field(–16.6‰to–15.2‰);deduction of theδ13C value of the CH4in the soil pore water from that of the CH4emitted from the field(–13.2‰to–1.1‰);and deduction of theδ13C value of the CH4in the aerenchyma of plants from that of the CH4emitted from plants(–16.3‰to–10.9‰).Unfortunately,the first two methods showed relatively large uncertainties.Only the last one,the dividing+cutting method,was not only scientific and reliable but also provided accurate measurements. 相似文献
112.
气候变暖背景下,块石路基及通风管-封闭块石基底复合路基成为多年冻土区高等级公路冷却路基的主要结构形式. 为探明不同直径块石层的渗流特征和规律,开展了立方排列球体室内风洞试验,一方面获得了渗透率和惯性阻力系数及其与球体直径间的统计关系;另一方面得到了球体层内部压力梯度与渗流速度呈二次非线性关系. 基于该试验得到的参数和关系,采用多孔介质中流固耦合传热模型,通过有限体积法模拟了柴木铁路块石路基的降温效果,并利用实测数据验证了模型及参数的可靠性. 在此基础之上,以青藏高等级公路特殊路基为原型,使用该传热模型开展了封闭块石基底路基和通风管-块石复合路基长期冷却降温效果的数值模拟研究. 结果表明:封闭块石基底路基和通风管-封闭块石复合路基在研究期内均有降温效果,可以提高路基下人为上限,而块石夹层路基在一定时期内可以提高冻土上限,但下部土体温度升高,长期降温效果较差. 相似文献
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114.
《African Journal of Marine Science》2013,35(3):313-322
Spartina alterniflora Loisel., widely recognised as an aggressive invader of estuaries and salt marshes around the world, was discovered growing in the temporarily open/closed Great Brak Estuary on the southern Cape coast of South Africa in 2004. This is the first record of this invasive plant in Africa as well as its first occurrence in an estuary that closes to the sea. Plant traits and sediment characteristics were measured in 2009 and 2011 and found to be comparable to those reported elsewhere. Prior to the 2011 sampling, S. alterniflora stands had been flooded for almost eight months. As a result, sediment redox potential (?268 + 4 mV) was significantly lower in 2011. Sediments were mostly clay in 2009 (71 ± 0.01%) compared to a predominance of sand in 2011 (40 ± 0.02%). These differences were related to the artificial breaching of the estuary one month prior to sampling in March 2011. The grass currently occupies 1.1 ha in the salt marsh, sandflat and mudflat habitats of the estuary where its cover is expanding at a rate of 0.162 ha y?1. Individual stands numbered about 12 in 2006, but have increased to 24 in 2011. These stands are expanding laterally at 0.9 m y?1 although the long period of inundation during 2010 reduced this to 0.6 m y?1. Expansion is due to vegetative spread as an analysis of the sediment seed bank showed no S. alterniflora seeds and very few salt marsh seeds (1 132 seeds m?2). If left unchecked, S. alterniflora has the potential to replace 42.9 ha or 41% of the total estuary habitat in the Great Brak Estuary, but also has the potential to invade other estuaries in South Africa, especially those with extensive intertidal habitat and containing S. maritima (19 estuaries in total). This study illustrates the adaptive potential of this invasive marsh plant and indicates the possibility of invasion in seasonally closed estuaries in other locations around the world. 相似文献
115.
《African Journal of Marine Science》2013,35(4):465-477
Structure and variability of water temperature gradients and potential influence on distribution of two tropical zooplankters (the mysid Mesopodopsis africana and the copepod Acartia natalensis) and their temperate congenerics (M. wooldridgei and A. longipatella) was investigated over a 10-year period in the Mgazi Estuary, South Africa. Intra- and inter-monthly water temperatures were highly variable, driven primarily by the interactive effects of river runoff, tidal exchange and mouth state. Variability was greatest in summer, temperatures ranging between <13 °C (linked to nearshore upwelling and a wide open mouth) and >30 °C when the mouth was near-closed. A strong horizontal temperature gradient characterised the estuary, the upper reaches remaining consistently warmer compared to the lower estuary. In winter, abundance of the tropical zooplankters showed a positive and significant correlation with increasing distance upstream. No pattern was evident in summer. The temperate species reflected a negative trend in abundance moving upstream during both seasons, but correlations were not significant. In terms of climate change, future population responses remain uncertain. This uncertainty is primarily linked to ongoing changes in the relative dominance of key drivers influencing estuarine water temperatures. Estuary mouth state will also respond to changes in nearshore wind regimes and morphodynamics of the adjacent beach. 相似文献
116.
澄(江)—阳(宗)二级公路K5+120~280边坡受断层构造的影响,受雨季因素和上边坡坡度大以及不良地质现象影响,有发生蠕动滑移的可能。针对工程地质水文地质情况,采取了抗滑桩、喷锚护坡以及排水措施等进行综合治理,取得了良好的治理效果。介绍了该边坡的工程治理方案及施工技术。 相似文献
117.
118.
大气环境质量的预测和评价是一个典型的多变量和非线性问题。根据大气环境系统的性质,运用灰色系统理论和模糊数学理论建立大气环境质量预测和评价 的数学模型,通过对江西省抚州市环保局提供的实测数据进行科学计算,得到令人满意的结果,有较好的实用价值。 相似文献
119.
Li Qinghua School of Computer Science Huazhong University of Science Technology Wuhan Dai Guangming School of Computer Science Huazhong University of Science Technology Wuhan Department of Computer Science & Technology China University of Geosciences Wuhan Wang Maocai Department of Computer Science & Technology China University of Geosciences Wuhan 《中国地质大学学报(英文版)》2003,14(4)
Encasingboxisoneofthebasicproblemsincom putinggeometry .ItiswidelyusedinmanyengineeringapplicationssuchasimageprocessingpatternrecognitionandCAD .Theproblemofcomputingthemin arearect angleencasingboxforclosedcontourisaspecialcaseofencasingboxproblem .Thisproblemisinvestigatedforpracticalapplication ,especiallyindesigningpath ,colli siondetectionandreal timeroaming (Day ,1988;PreprataandShamos ,1985 ) .ThecommonapproachisAABB (axis alignedboundingboxes)whenfindingrectangleencasingboxnow ,wh… 相似文献
120.
Low magnetic susceptibility, low Sr content and hence high Rb/Sr ratio in the lake sediment sequence indicate a weak chemical
weathering process under arid and cold climate of the Little Ice Age in a single closed lake watershed. According to different
geochemical behavior between rubidium and strontium in earth surface processes, variation of Rb/Sr ratios in the lake sediment
sequence can be used as an effective geochemical proxy with definite climatic significance of chemical weathering in watershed.
Unlike chemical weathering process in tropic zone and modern temperate-humid climate, concordant changes in both Sr content
and magnetic susceptibility with δ18O values of Dunde ice core suggest that the weak chemical weathering was controlled by air temperature during the Little Ice
Age maximum. After the Little Ice Age, chemical weathering intensity was controlled also gradually by precipitation with increasing
in temperature. 相似文献