全文获取类型
收费全文 | 1296篇 |
免费 | 168篇 |
国内免费 | 97篇 |
专业分类
测绘学 | 247篇 |
大气科学 | 186篇 |
地球物理 | 528篇 |
地质学 | 205篇 |
海洋学 | 123篇 |
天文学 | 30篇 |
综合类 | 77篇 |
自然地理 | 165篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 31篇 |
2021年 | 31篇 |
2020年 | 41篇 |
2019年 | 55篇 |
2018年 | 41篇 |
2017年 | 41篇 |
2016年 | 27篇 |
2015年 | 44篇 |
2014年 | 57篇 |
2013年 | 86篇 |
2012年 | 55篇 |
2011年 | 84篇 |
2010年 | 50篇 |
2009年 | 85篇 |
2008年 | 95篇 |
2007年 | 79篇 |
2006年 | 70篇 |
2005年 | 61篇 |
2004年 | 54篇 |
2003年 | 68篇 |
2002年 | 40篇 |
2001年 | 48篇 |
2000年 | 43篇 |
1999年 | 36篇 |
1998年 | 32篇 |
1997年 | 19篇 |
1996年 | 24篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 29篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 5篇 |
排序方式: 共有1561条查询结果,搜索用时 31 毫秒
71.
72.
于2006年5-11月对东海泉州湾赤潮监控区四个监测站位开展赤潮常规监测。根据监测结果,分别以各站位23项水质理化生物环境因子指标为自变量,相应赤潮藻类优势种的细胞密度为因变量,进行多元逐步回归分析,建立了各站位优势种中肋骨条藻(Skeletonema costatum)、太平洋海链藻(Thalassiosira pacifica)、微小原甲藻(Prorocentrum minimum)、尖刺拟菱形藻(Pseudo-nitzschia pungens)、丹麦细柱藻(Leptocylindrus danicus)和旋链角毛藻(Chaetoceros curvisetus)等的细胞密度多参量回归方程。结果表明,所有回归方程的复相关系数都接近于1,方差分析的结果均为回归极显著,表明所建立的回归方程可作为相应赤潮优势种细胞密度预报方程的高度有效性,将对今后泉州湾的赤潮预报提供良好的指导作用。 相似文献
73.
Marek Szczotka 《Ocean Engineering》2010,37(7):539-548
Dynamic and quasi-static models for analysis of a pipe lay spread are presented in the paper. Depending on the type of a pipe, spooling it on a big drum (reel) may cause plastic deformations. When the pipe is reeled out at sea, again it undergoes plastic deformations. In order to model such a nonlinear behaviour, a model, which includes both elasto-plastic material characteristics and large deformations, is required. Discretisation of the pipe is performed by means of the Rigid Finite Element Method (RFEM), which allows us to study static and dynamic problems, taking into account required properties of the model. Different sea conditions are simulated and analysed. It is shown how operational conditions can limit the ability of laying operation by a dedicated vessel, due to an unstable system response. The second part of the paper presents an upgrade of a passive reel drive by application of an active drive. In the model used for control applications, the pipe is modelled by a neural network. This allows us to perform a real-time calculations. In this fast-response calculation model, nonlinear aspects of the system are taken into account. The improvements in a pipe laying vessel performance are presented by some results of numerical simulations. The conclusions are also formulated. 相似文献
74.
Automated threshold selection methods for extreme wave analysis 总被引:2,自引:0,他引:2
The study of the extreme values of a variable such as wave height is very important in flood risk assessment and coastal design. Often values above a sufficiently large threshold can be modelled using the Generalized Pareto Distribution, the parameters of which are estimated using maximum likelihood. There are several popular empirical techniques for choosing a suitable threshold, but these require the subjective interpretation of plots by the user.In this paper we present a pragmatic automated, simple and computationally inexpensive threshold selection method based on the distribution of the difference of parameter estimates when the threshold is changed, and apply it to a published rainfall and a new wave height data set. We assess the effect of the uncertainty associated with our threshold selection technique on return level estimation by using the bootstrap procedure. We illustrate the effectiveness of our methodology by a simulation study and compare it with the approach used in the JOINSEA software. In addition, we present an extension that allows the threshold selected to depend on the value of a covariate such as the cosine of wave direction. 相似文献
75.
It is well known that high-leverage observations significantly affect the estimation of parameters. In geodetic literature,
mainly redundancy numbers are used for the detection of single high-leverage observations or of single redundant observations. In this paper a further objective method for the detection of groups of important and less important (and thus redundant) observations is developed. In addition, the parameters which are predominantly
affected by these groups of observations are identified. This method thus complements other diagnostics tools, such as, e.g.,
multiple row diagnostics methods as described in statistical literature (see, e.g., Belsley et al. in Regression diagnostics:
identifying influential data and sources of collinearity. Wiley, New York, 1980). The method proposed in this paper is based
on geometric aspects of adjustment theory and uses the singular value decomposition of the design matrix of an adjustment
problem together with cluster analysis methods for regression diagnostics. It can be applied to any geodetic adjustment problem
and can be used for the detection of (groups of) observations that significantly affect the estimated parameters or that are
of negligible impact. One of the advantages of the proposed method is the improvement of the reliability of observation plans
and thus the reduction of the impact of individual observations (and outliers) on the estimated parameters. This is of particular importance for the very long baseline interferometry
technique which serves as an application example of the regression diagnostics tool. 相似文献
76.
针对使用传统的编程方式进行空间回归分析过于繁杂的问题,本文提出将Python函数式编程引入空间回归分析方法,分析和探讨脚本语言+函数式编程方式在GIS数据分析中的推广应用前景。编程实践证明,采用Python函数式编程,结合既有的开源软件包,可以有效提高编程效率,减少代码量,将实践人员的注意力集中在问题本身。 相似文献
77.
Separate space- or time-lags have been considered regularly in data analyses; as space–time models are more recently being
studied extensively in data analytic fashion, joint estimation of both lags has to be considered explicitly. This paper addresses
this issue, taking into special consideration parametric parsimony together with specification richness; use of the bivariate
Poisson frequency distribution is advocated and applied to an empirical case. The relation of this approach to random effects
specifications is investigated. Data for Belgian regional products constitute the empirical case study.
相似文献
Daniel A. GriffithEmail: |
78.
提出了一个基于3层PB神经网络的云南5月雨量的短期气候预测模型。由于神经网络本身是一个非线性动态系统,将其应用到短期气候变化预测这一非线性系统中,更能反映出气候系统状态量之间的物理关系和动力行为特性。并用该预测模型对云南5个区域1991~1998年的5月雨量距平趋势进行了共40次的预测试验和检验,其预测的距平符号相关准确率可达到77.5%。 相似文献
79.
80.