全文获取类型
收费全文 | 283篇 |
免费 | 108篇 |
国内免费 | 30篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 50篇 |
地球物理 | 61篇 |
地质学 | 107篇 |
海洋学 | 71篇 |
天文学 | 1篇 |
综合类 | 8篇 |
自然地理 | 104篇 |
出版年
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 11篇 |
2017年 | 18篇 |
2016年 | 14篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 7篇 |
2012年 | 15篇 |
2011年 | 25篇 |
2010年 | 15篇 |
2009年 | 36篇 |
2008年 | 33篇 |
2007年 | 26篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 12篇 |
1996年 | 6篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有421条查询结果,搜索用时 125 毫秒
61.
四川盆地地下卤水自震旦系至白垩系各层系皆有分布。卤水具有分布广泛、资源丰富、品质优异、高承压及气卤同产等优势特点,是四川得天独厚的液态矿产资源。卤水中含有K+、Br-I、-、B3+、Li+、Sr2+、Rb+等多种有用组分,皆为国家紧缺和紧俏物质,其含量多数可达工业开采品位,为优质化工原料水,经济价值极高,综合开发利用前景广阔。 相似文献
62.
Peter Griggs 《The Australian geographer》2002,33(1):43-61
The growing of tobacco was one of the most tightly regulated industries in Australia, until deregulation in 1995. Commonwealth regulations controlled the area cultivated with tobacco, the number of growers (i.e. quota holders) and marketing arrangements for tobacco leaf. This paper begins by outlining the nature and historical development of controls in the tobacco-growing industry, and discusses how the Commonwealth government removed the industry's regulatory and protective framework in 1995. The third part of the paper examines how deregulation has impacted upon the Mareeba-Dimbulah Irrigation Area, Far North Queensland, where small farmers produced 60 per cent of Australia's tobacco in 1995. The discussion will show that the agricultural landscape once dominated by tobacco has been transformed, as local farmers abandoned growing tobacco in favour of sugar cane, avocadoes, mangoes, macadamia nuts and other small vegetable crops (e.g. navy beans, pumpkins). Tobacco, once promoted by the Queensland government as a crop to facilitate closer settlement in the Mareeba-Dimbulah Irrigation Area, will have almost vanished from the landscape by 2002. 相似文献
63.
A comprehensive analytical solution is developed to examine the torsional vibration of an elastic foundation on a semi-infinite saturated elastic medium for the first time. First, the governing equations of saturated media are solved by use of Hankel transform techniques. Then, based on the assumption that the contact between the foundation and the half-space is perfectly bonded, this dynamic mixed boundary-value problem can lead to dual integral equations, which are further reduced to the standard Fredholm integral equations of the second kind and solved by numerical procedures. Numerical examples are given at the end of the paper. The numerical results indicate that the response of the elastic foundation strongly depends on the material and geometrical properties of both the saturated soil-foundation system and the load acting on the foundation. In most of the cases, the dynamic behavior of an elastic foundation on saturated media significantly differs from that of a rigid plate bearing on the elastic half-space. 相似文献
64.
为了研究东台吉乃尔盐湖卤水蒸发时的相化学,确定钾、镁和锂盐的结晶特性,在实验室内25℃等温蒸发实验基础上和自然条件下进行了冬夏季日晒蒸发试验.东台吉乃尔盐湖卤水是由氯化钠饱和的多组分复杂体系构成的.卤水中存在的离子是Na+、K+、Mg2+、Li+、Ca2+、B3+、SO42-和Cl-.试验数据与Na+、K+、Mg2+Cl-、SO42-KH2O五元体系介稳平衡数据进行了讨论和比较.Autenrieth相图被用来表示各数据间的关系和证明冬夏季蒸发时结晶行为的差别. 相似文献
65.
对柴达木盆地察尔汗盐湖区外围沙下盐湖的卤水及沉积进行了综合研究。沙下盐湖卤水化学组成与地表径流和开放性盐湖卤水之间存在明显的差异性,具有高Na++Cl-、低Mg2++Ca2++SO42-、贫K++CO32-+HCO3-等特征。沙下盐湖析盐层位含有新生矿物并夹带碎屑矿物,其盐类矿物组合为:石盐+羟氯镁铝石+光卤石。25℃等温蒸发相图表明,其卤水演化方向往光卤石析出区迁移,在穿越上覆盖层通道中卤水发生的物理化学反应与独特的沉积特征,可以作为继续寻找沙下盐湖的指导。 相似文献
66.
67.
鄱阳湖地区土壤,植被光谱混合模型的研究 总被引:12,自引:1,他引:12
本文针对鄱阳湖地区的土壤、植被的特点设计了一套非线性混合光谱模型、较好了地预测了实际的混合光谱,从预测精度上看,要优于传统的线性混合光谱模型。 相似文献
68.
The heights of the daytime convective boundary layer (CBL), computed by a one-dimensional model for a bare soil surface at a semi-arid station,Anand, during the dry and hot summer month of May 1997, are presented. As input, the model requires surface heat flux, friction velocity and air temperature as functions of time. Temperature data at the one-metre level from a tower and sonic anemometer data at 9.5 m collected during the period 13–17 May 1997 in the Land Surface Processes Experiment (LASPEX-97) are used to compute hourly values of surface heat flux, friction velocity and Obukhov length following the operational method suggested by Holtslag and Van Ulden [J. Climate Appl. Meteorol.
22,517–529 (1983)]. The model has been tested with different values for the potential temperature gradient ( ) above the inversion. The model-estimated CBL heights comparefavourably with observed heights obtained from radiosonde ascents. 相似文献
69.
70.
Zbigniew Sorbjan 《Boundary-Layer Meteorology》2001,101(2):183-207
Local similarity, referred to as type II similarity,in the interfacial, stably-stratified layer at thetop of the atmospheric (or oceanic) mixed layer isdiscussed. Type II scales for scalars are based onthe local values of scalar gradients. Similaritypredictions are derived from the second-orderclosure model of Yamada and Mellor, and also fromsimilarity arguments. The obtainedformulation is verified for active and passive scalarsbased on the large-eddy simulation model. 相似文献