全文获取类型
收费全文 | 1764篇 |
免费 | 184篇 |
国内免费 | 175篇 |
专业分类
测绘学 | 234篇 |
大气科学 | 169篇 |
地球物理 | 449篇 |
地质学 | 503篇 |
海洋学 | 161篇 |
天文学 | 307篇 |
综合类 | 79篇 |
自然地理 | 221篇 |
出版年
2023年 | 21篇 |
2022年 | 43篇 |
2021年 | 51篇 |
2020年 | 57篇 |
2019年 | 73篇 |
2018年 | 66篇 |
2017年 | 67篇 |
2016年 | 64篇 |
2015年 | 64篇 |
2014年 | 94篇 |
2013年 | 106篇 |
2012年 | 61篇 |
2011年 | 78篇 |
2010年 | 55篇 |
2009年 | 105篇 |
2008年 | 97篇 |
2007年 | 126篇 |
2006年 | 102篇 |
2005年 | 91篇 |
2004年 | 84篇 |
2003年 | 77篇 |
2002年 | 62篇 |
2001年 | 60篇 |
2000年 | 62篇 |
1999年 | 45篇 |
1998年 | 44篇 |
1997年 | 31篇 |
1996年 | 27篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 18篇 |
1988年 | 8篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 10篇 |
1971年 | 7篇 |
排序方式: 共有2123条查询结果,搜索用时 31 毫秒
131.
132.
尹春芳 《华东地质学院学报》1988,(3)
本文用数理统计方法,快速估算和预报矿山淹井中水住、最高水位,矿井水涌量、涌入矿区的总水量和需要排出水量。用简单易行的反推法确定淹井的涌水量,并推导出计算式,以供使用。该方法在某矿淹井中使用,效果良好。 相似文献
133.
134.
135.
136.
137.
周世健 《武汉大学学报(信息科学版)》1993,(2)
测量平差问题中,方差估计理论是复杂的。本文基于概括模型,组成自由项f(极大似然估计 MLE)的密度函数和改正数向量 V的线性函数(边缘极大似然估计 MMLE)的密度函数,详细推导了函数模型与随机模型中,未知参数 X与σ_0~2 的似然估计公式,分析了基于两种密度函数所得σ_0~2的似然估计存在差异的真正原因,并对两种方法所得的σ_0~2和X 的统计性质进行了讨论。指出边缘极大似然估计,σ_0~2 的具有良好的统计性质,可改善极大似然估计σ_0~2 的不定性(有偏);并且对任一平差模型的边缘极大似然估计,σ_0~2 无偏、有效的统计性质是一致的。 相似文献
138.
Conventional design practice aims at obtaining optimal estimates of floods with specified exceedance probabilities. Such estimates are, however, known on the average to be exceeded more frequently than expected. Alternatively, methods focusing on the expected exceedance probability can be used. Two different methods are considered here; the first is based on the sample distribution of true exceedance probabilities. The second is a Bayesian analogue using the likelihood function and a noninformative prior to describe the variability of exceedance probabilities. Appropriate analytical solutions are presented in both cases using the partial duration series approach. 相似文献
139.
D. -J. Seo J. A. Smith 《Stochastic Environmental Research and Risk Assessment (SERRA)》1991,5(1):17-29
Procedures for estimating rainfall from radar and raingage observations are constructed in a Bayesian framework. Given that the number of raingage measurements is typically very small, mean and variance of gage rainfall are treated as uncertain parameters. Under the assumption that log gage rainfall and log radar rainfall are jointly multivariate normal, the estimation problem is equivalent to lognormal co-kriging with uncertain mean and variance of the gage rainfall field.The posterior distribution is obtained under the assumption that the prior for the mean and inverse of the variance of log gage rainfall is normal-gamma 2. Estimate and estimation variance do not have closed-form expressions, but can be easily evaluated by numerically integrating two single integrals. To reduce computational burden associated with evaluating sufficient statistics for the likelihood function, an approximate form of parameter updating is given. Also, as a further approximation, the parameters are updated using raingage measurements only, yielding closed-form expressions for estimate and estimation variance in the Gaussian domain.With a reduction in the number of radar rainfall data in constructing covariance matrices, computational requirements for the estimation procedures are not significantly greater than those for simple co-kriging. Given their generality, the estimation procedures constructed in this work are considered to be applicable in various estimation problems involving an undersampled main variable and a densely sampled auxiliary variable. 相似文献
140.
Thomas J. East 《地球表面变化过程与地形》1985,10(5):441-463
Q-mode factor analysis of soil particle size data is used to identify the three dominant geomorphic processes responsible for the spatial variability of particle size in a catchment on the basaltic Darling Downs landsurface. Three factors are shown to account for 95 per cent of the textural variability of a suite of transported and sedentary materials. The spatial characteristics of groups of samples associated with the three factors suggests that the three factors are associated with suspended sediment transport and deposition, weathering, and bedload transport and deposition respectively. These interpretations are supported by the detailed graphical analysis of the cumulative particle size curves. The spatially variable influence of the three factors and related processes is given by their respective factor loadings which are mappable for the surface layer materials. 相似文献