全文获取类型
收费全文 | 1161篇 |
免费 | 203篇 |
国内免费 | 350篇 |
专业分类
测绘学 | 226篇 |
大气科学 | 103篇 |
地球物理 | 190篇 |
地质学 | 823篇 |
海洋学 | 194篇 |
天文学 | 12篇 |
综合类 | 84篇 |
自然地理 | 82篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 26篇 |
2021年 | 38篇 |
2020年 | 47篇 |
2019年 | 59篇 |
2018年 | 43篇 |
2017年 | 41篇 |
2016年 | 53篇 |
2015年 | 71篇 |
2014年 | 82篇 |
2013年 | 71篇 |
2012年 | 92篇 |
2011年 | 90篇 |
2010年 | 74篇 |
2009年 | 87篇 |
2008年 | 65篇 |
2007年 | 93篇 |
2006年 | 85篇 |
2005年 | 70篇 |
2004年 | 61篇 |
2003年 | 54篇 |
2002年 | 51篇 |
2001年 | 42篇 |
2000年 | 28篇 |
1999年 | 43篇 |
1998年 | 19篇 |
1997年 | 49篇 |
1996年 | 34篇 |
1995年 | 23篇 |
1994年 | 26篇 |
1993年 | 15篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1979年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有1714条查询结果,搜索用时 0 毫秒
451.
Using geographic information system to study flooded area and damage evaluation has been a hotspot in environmental disaster research for years. In this paper, a model for flooded area calculation and damage evaluation is presented. Flooding is divided into two types: ‘source flood’ and ‘non-source flood’. The source-flood area calculation is based on seed spread algorithm. The flood damage evaluation is calculated by overlaying the flooded area range with thematic maps and relating the result to other social and economic data. To raise the operational efficiency of the model, a skipping approach is used to speed seed spread algorithm and all thematic maps are converted to raster format before overlay analysis. The accuracy of flooded area calculation and damage evaluation is mainly dependent upon the resolution and precision of the digital elevation model (DEM) data, upon the accuracy of registering all raster layers, and upon the quality of economic information. This model has been successfully used in the Zhejiang Province Comprehensive Water Management Information System developed by the authors. The applications show that this model is especially useful for most counties of China and other developing countries. 相似文献
452.
454.
There are many chemical products where product conformity is decided upon by qualitative humanjudgements of overall product quality.Nowadays,quantitative instrumentally determined qualityparameters become available which are intended to replace such qualitative judgements by means ofautomatic decision rules using multivariate specification limits.Six classification methods to derive suchlimits are compared in terms of their power to predict corresponding human judgements on overall colorconformity of 17 dyestuffs based on historical quality data.Standard statistical classification methodsturned out to be unacceptable for the routine generation of decision rules because of the frequent distinctsuboptimality of their predictive power.Instead,a simple non-statistical classification method utilizinga priori knowledge about the underlying data structure yielded uniformly satisfactory decision rules. 相似文献
455.
456.
中国土壤热通量的气候计算及其分布特征 总被引:6,自引:0,他引:6
根据北京等6个热平衡站的资料,通过5种方案计算比较得出土壤热通量Qs动的气候计算方法Qs=2.826·△θs-20+0.486·△T-0.777这里△θs-20、△T分别为土中5与20厘米温差和地一气温差.该式相关比为0.897,平均拟合误差1.4wm-2。据此计算全国215站的土中热交换量,并分析其时空变化,得出一些有意义的结果。 相似文献
457.
James P. Reger 《地球表面变化过程与地形》1979,4(3):267-273
As part of an investigation of mass movement on outslopes of contour surface-mines in West Virginia, discriminant analysis was used to determine whether selected spoil properties could statistically distinguish failed and unfailed embankments. The analysis utilized the variables degree of saturation, liquid limit, and shrinkage limit, and the a priori assignment of samples into either actively failing, unfailed, or regraded categories. Results were encouraging, with seventy-four percent of the samples being correctly classified. All misclassifications involved samples from active or regraded landslides, suggesting the method was conservative. Performance of discriminant analysis could probably be improved by modifying the sampling plan. 相似文献
458.
内燃机性能指标的简化计算 总被引:1,自引:0,他引:1
邱伟光 《广东海洋大学学报》2004,24(3):52-55
循环热效率和指示热效率是两个不同的热效率概念 ,本文推导出了两种热效率之间相互换算的因子———“热效率修正因子”的计算式 ,应用该因子可以计算或预测内燃机实际循环的性能指标 ,计算结果与热计算结果吻合 ,该方法比热计算简单 ,适用于所有四冲程内燃机。 相似文献
459.
460.