全文获取类型
收费全文 | 204篇 |
免费 | 33篇 |
国内免费 | 51篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 13篇 |
地球物理 | 38篇 |
地质学 | 175篇 |
海洋学 | 32篇 |
天文学 | 1篇 |
综合类 | 10篇 |
自然地理 | 10篇 |
出版年
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 11篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 12篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 4篇 |
2013年 | 20篇 |
2012年 | 11篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 15篇 |
2008年 | 13篇 |
2007年 | 18篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有288条查询结果,搜索用时 174 毫秒
61.
62.
加强目标观测,服务防灾减灾 总被引:3,自引:0,他引:3
以深入浅出的方式介绍了目标观测的定义、历史、确定目标观测敏感区的方法,以及实施目标观测与防灾减灾的关系;并以欧洲中期天气预报中心目标观测业务化为例,简明地概括了目标观测的实施过程;结合国内目标观测研究现状,对中国目标观测的未来提出了看法。 相似文献
63.
塔里木河下游不同生活型植被对地表的防护效果 总被引:2,自引:1,他引:1
在干旱区植被生态建设过程中,需要进行决策并经常引起争论的问题是,究竟应该选择哪种生活型植被才能获得最大的防护效果.为比较不同生活型植被对地表防护效果的差异,本文选取塔里木河下游6种常见乔灌草植被,以降低风速百分比的平均值作为植被对地表防护效果的评价指标,对不同生活型植被对地表防护效果进行定量比较.结果表明:上述6种植被防风性能大小次序依次为:花花柴>罗布麻>骆驼刺>柽柳>盐穗木>胡杨.花花柴对地表防护效果最好,降低地表风速百分比的平均值达44.00%,胡杨对地表防护效果最差,降低地表风速百分比平均值13.21%.就乔、灌、草不同生活型植被而言,防护效果大小次序为:多年生草本>灌木>乔木.因此,从生态防护效应角度来说,在干旱区植被生态建设中,应坚持灌、草先行的原则,乔木植被只能在水分条件较优越的地区适度发展.只有这样才能充分利用有限的水资源, 取得最佳的生态防护效应. 相似文献
64.
65.
文中研究在粒状铁化学还原三氯乙烯渗透反应格栅和生物降解苯和甲苯渗透反应格栅的联合格栅技术中,下游生物降解格栅中铁还原环境下微生物对苯和甲苯的生物降解。通过模拟粒状铁渗透反应格栅下游铁还原环境,主要研究微生物以苯、甲苯作为碳源时,对碳源的专一性。通过批实验发现,对于分别用苯和甲苯培养驯化的微生物,互换碳源后,微生物对2 000.00μg/L苯和甲苯的生物降解半衰期分别由之前的1.0和1.5 d减少到0.7和1.0 d,互换碳源后苯和甲苯的去除率分别增加38%和32%。在粒状铁渗透反应格栅下游生物降解渗透反应格栅中,微生物在铁还原环境下以苯、甲苯作为碳源时对碳源没有专一性,苯和甲苯可以同时被生物降解去除。 相似文献
66.
依据渭河上游实测水文资料和水利水保措施统计数据, 分析了流域水文要素和水利水保措施的变化规律。根据双累积曲线、 有序聚类、 Lee-Heghinan、 滑动T检验等方法, 结合流域内水利水保措施的变化, 将研究期分为基准期(1956 - 1981年)和措施期(1982 - 2016年)。采用水量平衡法, 分析还原了河流天然径流量和输沙量, 评价了水利工程取用耗水的减水减沙作用; 分别建立拟合了基准期和措施期年径流量、 年输沙量与年降水量的相关公式, 分析计算了措施期的减水减沙效应。结果表明: 基准期主要为水利工程减水减沙, 分别减水6.8%, 减沙3.9%; 措施期综合减水效应42.9%, 综合减沙效应76.5%, 水保措施减水减沙效应大于水利工程减水减沙效应, 综合减沙效应大于综合减水效应。 相似文献
67.
Polymetalic sulfide is the main product of sea-floor hydrothermal venting, and has become an important sea-floor mineral resources for its rich in many kinds of precious metal elements. Since 2007, a number of investigations have been carried out by the China Ocean Mineral Resources Research and Development Association(COMRA)cruises(CCCs) along the Southwest Indian Ridge(SWIR). In 2011, the COMRA signed an exploration contract of sea-floor polymetallic sulfides of 10 000 km2 on the SWIR with the International Seabed Authority. Based on the multibeam data and shipborne gravity data obtained in 2010 by the R/V Dayang Yihao during the leg 6 of CCCs21, together with the global satellite surveys, the characteristics of gravity anomalies are analyzed in the Duanqiao hydrothermal field(37°39′S, 50°24′E). The "subarea calibration" terrain-correcting method is employed to calculate the Bouguer gravity anomaly, and the ocean bottom seismometer(OBS) profile is used to constrain the two-dimensional gravity anomaly simulation. The absent Moho in a previous seismic model is also calculated.The results show that the crustal thickness varies between 3 and 10 km along the profile, and the maximum crustal thickness reaches up to 10 km in the Duanqiao hydrothermal field with an average of 7.5 km. It is by far the most thicker crust discovered along the SWIR. The calculated crust thickness at the Longqi hydrothermal field is approximately 3 km, 1 km less than that indicated by seismic models, possibly due to the outcome of an oceanic core complex(OCC). 相似文献
68.
Nikolaos Skarpelis 《Resource Geology》2020,70(4):311-335
Massive Zn‐Pb‐Ag sulfide mineralization appears conformable with felsic volcanism, developed in an Upper Jurassic volcanic arc to the Southwest (SW) of the Serbo‐Macedonian continent in Northern Greece. The host volcanic sequence of the mineralization comprises mylonitized rhyolitic to rhyodacitic lavas, pyroclastics, quartz‐feldspar porphyries, and cherty tuffs. A “white mica—quartz—pyrite” mineral assemblage characterizes the volcanic rocks in the footwall and hanging‐wall of massive sulfide ore layers, formed as a result of greenschist‐grade regional metamorphism on “clay‐quartz‐pyrite” hydrothermal alteration haloes. Massive ore lenses are usually underlain by deformed Cu‐pyrite and quartz‐pyrite stockworks. Most of the sulfide ore bodies have proximal‐type features. Ductile deformation and regional metamorphism have transformed many of the stockwork structures. The mineralization is characterized by high Zn, Pb, and Ag contents, while Cu and critical metals are low. Primary depositional textures, for example, layering, clastic pyrite, colloform, and atoll textures were identified. The overall textural features of the mineralization indicate it has undergone mechanical deformation. The most prominent features of the effects of metamorphism, folding and shearing, are modification of the ore body morphology toward flattened and boudinage structures and transformation of the ore textures toward the dominance of planar fabrics. Sulfur isotope analyses of sulfides along with textural observations are consistent with a dual source of sulfide sulfur. Sulfur isotope values for sphalerite, non‐colloform pyrite, galena, and chalcopyrite fall in a limited range from ?1.6 to +4.8‰ (mean δ34S + 2‰), indicating a hydrothermal source derived from the reduction of coeval seawater sulfate in the convective system. Pyrites with colloform and atoll textures are characterized by a 34S depletion, indicating a bacterial reduction of coeval seawater sulfate. The morphology of ore beds, the mineralogy, sulfide textures, and ore chemistry along with the petrology and tectonic setting of the host rocks can be attributed to typical of a bimodal‐felsic metallogenesis. Although similar in many respects to classic Kuroko‐type volcanogenic massive sulfide mineralization, it has some atypical features, like the absence of barite ore, which is possibly a result of significant temporal depletion in sulfate due to bacterial reduction, a conclusion supported by the widespread occurrence of colloidal and atoll textures of pyrite. 相似文献
69.
哈素海区域高砷地下水对当地居民饮用水安全造成严重威胁, 揭示其形成演化机制对科学合理的开发利用水资源、保障居民身体健康具有重要意义。本文在水文地质调查的基础上, 应用Piper三线图、PHREEQC的砷形态计算及相关性分析等方法, 研究高砷地下水化学特征、构建砷形态模型(SM)和砷吸附模型(HSM), 以揭示高砷地下水的成因机制。结果表明, 研究区砷浓度为0.2~231.5 μg/L, 高砷区主要分布在大青山以南的冲湖积平原区; 地下水砷的类型以As(Ⅲ)为主, SM分析显示优势形态为H3AsO3, HSM分析显示存在Hfo_wH2AsO3和H3AsO3两种主要形态。地下水中的砷化物可能来源于山区富砷岩石的风化溶解以及第四系富砷河湖相沉积物; 研究区河湖相沉积环境是高砷水形成的前提, 有机质分解主导的还原环境是导致砷从含水介质释放到地下水中的主要因素, 弱碱性环境和HCO– 3的竞争吸附也会引起砷的释放。 相似文献
70.
《Climate Policy》2013,13(2):216-231
Reducing emissions from deforestation and forest degradation (REDD) in developing countries has been at the centre of negotiations on a renewed international climate regime. Developing countries have made it clear that their ability to engage in REDD activities would depend on obtaining sufficient and stable funding. Two alternative REDD financing options are examined to find possible ways forward: financing through a future compliance market and financing through a non-offset fund. First, global demand for hypothetical REDD credits is estimated. The demand for REDD credits would be highest with a base year of 1990, using gross—net accounting. The key factors determining demand in this scenario are the emission reduction targets and the allowable cap. A proportion of emission reduction targets available for offsets lower than 15% would fail to generate a sufficient demand for REDD. Also examined is the option of financing REDD through a fund. Indirectly linking the replenishment of a REDD fund to the market is a promising mechanism, but its feasibility depends on political will. The example of overseas development assistance for global health indicates the conditions for possible REDD financing. The best financial approach for REDD would be a flexible REDD mechanism with two tracks: a market track serving as a mitigation option for developed countries, and a fund track serving as a mitigation option for developing countries. 相似文献