全文获取类型
收费全文 | 22957篇 |
免费 | 3621篇 |
国内免费 | 3923篇 |
专业分类
测绘学 | 7896篇 |
大气科学 | 2044篇 |
地球物理 | 3981篇 |
地质学 | 8403篇 |
海洋学 | 2406篇 |
天文学 | 433篇 |
综合类 | 1898篇 |
自然地理 | 3440篇 |
出版年
2024年 | 338篇 |
2023年 | 1105篇 |
2022年 | 1310篇 |
2021年 | 1419篇 |
2020年 | 1074篇 |
2019年 | 1347篇 |
2018年 | 1048篇 |
2017年 | 1037篇 |
2016年 | 1079篇 |
2015年 | 1172篇 |
2014年 | 1519篇 |
2013年 | 1218篇 |
2012年 | 1356篇 |
2011年 | 1341篇 |
2010年 | 1243篇 |
2009年 | 1302篇 |
2008年 | 1256篇 |
2007年 | 1066篇 |
2006年 | 993篇 |
2005年 | 925篇 |
2004年 | 870篇 |
2003年 | 852篇 |
2002年 | 774篇 |
2001年 | 714篇 |
2000年 | 567篇 |
1999年 | 448篇 |
1998年 | 424篇 |
1997年 | 361篇 |
1996年 | 370篇 |
1995年 | 391篇 |
1994年 | 294篇 |
1993年 | 251篇 |
1992年 | 210篇 |
1991年 | 211篇 |
1990年 | 190篇 |
1989年 | 164篇 |
1988年 | 43篇 |
1987年 | 39篇 |
1986年 | 20篇 |
1985年 | 33篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 20篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1964年 | 17篇 |
1963年 | 4篇 |
1962年 | 4篇 |
1957年 | 10篇 |
1954年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Cheng-Wu CHEN Hsien-Chueh Peter YANG Chen-Yuan CHEN Alex Kung-Hsiung CHANG Tsung-Hao CHEN 《中国海洋工程》2008,22(1):43-56
Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ridge height and potential energy during wave-ridge interaction with a binary and cumulative logistic regression model. In testing the Global Null Hypothesis, all values are p 〈0.001, with three statistical methods, such as Likelihood Ratio, Score, and Wald. While comparing with two kinds of models, tests values obtained by cumulative logistic regression models are better than those by binary logistic regression models. Although this study employed cumulative logistic regression model, three probability functions p^1, p^2 and p^3, are utilized for investigating the weighted influence of factors on wave reflection. Deviance and Pearson tests are applied to cheek the goodness-of-fit of the proposed model. The analytical results demonstrated that both ridge height (X1 ) and potential energy (X2 ) significantly impact (p 〈 0. 0001 ) the amplitude-based refleeted rate; the P-values for the deviance and Pearson are all 〉 0.05 (0.2839, 0.3438, respectively). That is, the goodness-of-fit between ridge height ( X1 ) and potential energy (X2) can further predict parameters under the scenario of the best parsimonious model. Investigation of 6 predictive powers ( R2, Max-rescaled R^2, Sorners' D, Gamma, Tau-a, and c, respectively) indicate that these predictive estimates of the proposed model have better predictive ability than ridge height alone, and are very similar to the interaction of ridge height and potential energy. It can be concluded that the goodness-of-fit and prediction ability of the cumulative logistic regression model are better than that of the binary logistic regression model. 相似文献
912.
Evaluation of Inference Adequacy in Cumulative Logistic Regression Models: An Empirical Validation of ISW-Ridge Relationships 总被引:3,自引:0,他引:3
Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ridge height and potential energy during wave-ridge interaction with a binary and cumulative logistic regression model. In testing the Global Null Hypothesis, all values are p<0.001, with three statistical methods, such as Likelihood Ratio, Score, and Wald. While comparing with two kinds of models, tests values obtained by cumulative logistic regression models are better than those by binary logistic regression models. Although this study employed cumulative logistic regression model, three probability functions p^1, p^2 and p^3, are utilized for investigating the weighted influence of factors on wave reflection. Deviance and Pearson tests are applied to check the goodness-of-fit of the proposed model. The analytical results demonstrated that both ridge height (X1) and potential energy (X2) significantly impact (p<0.0001) the amplitude-based reflected rate; the P-values for the deviance and Pearson are all >0.05 (0.2839, 0.3438, respectively). That is, the goodness-of-fit between ridge height (X1) and potential energy (X2) can further predict parameters under the scenario of the best parsimonious model.Investigation of 6 predictive powers (R2, Max-rescaled R2, Somers'D, Gamma, Tau-a, and c, respectively) indicate that these predictive estimates of the proposed model have better predictive ability than ridge height alone, and are very similar to the interaction of ridge height and potential energy. It can be concluded that the goodness-of-fit and prediction ability of the cumulative logistic regression model are better than that of the binary logistic regression model. 相似文献
913.
为了检测动态导航观测异常和动力学模型异常,采用预测残差构造观测误差和动力学模型误差整体检验法,对观测异常可分别采用以模型为准的观测异常检验、以当前历元可靠观测为基准的异常检验或以Kalman滤波估值为基础的异常检验的方法;对于动力学模型异常检验,可以分别采用状态不符值检验法、以状态参数Kalman滤波估值为基础的动力学模型异常检验或以可靠观测为基础的动力学模型误差整体检验的方法.分析了以上几种检验方法的特点,并用实测数据进行了检验.结果表明:在观测异常或动力学模型异常处,异常检验对导航数据精度有一定程度地提高. 相似文献
914.
变形观测数据时间序列建模中的几个问题 总被引:1,自引:0,他引:1
针对在变形观测数据时间序列建模中所遇到的问题,对变形观测数据时间序列建模中的数据预处理、模型选择、模型定阶与系统稳定性检验等问题进行了研究,提出了分析数据趋势项提取的AR模型方法,编写了C语言计算程序,实现了样条函数插值方法、周期项提取的差值法,建立ARMA分析模型,对变形预测数据与实际观测数据进行了比较.结果表明:该方法的正确性以及时间序列分析方法在变形数据处理与分析中的适用性与可行性. 相似文献
915.
916.
建立宽浅河道与管道水流的二、三维嵌套的数学模型,对基本的控制方程、方程的数值离散格式和求解方法、嵌套连接和初始边界条件等问题进行研究.利用上述方法对某工程实例进行计算,在宽广水域上给出了水力要素的平面分布,在复杂边界强三维流动的计算区域得到其三维运动特性.计算结果与实验资料进行了比较,两者吻合较好,说明嵌套连接的二、三维数学模型是解决某些实际工程问题的一种可靠的和有效的工具. 相似文献
917.
Over the past 20 years, significant progress has been made in virtual plant modeling corresponding to the rapid advances in information technology. Virtual plant research has broad applications in agronomy, forestry, ecology and remote sensing. As many biological processes are driven by light, it is the key for virtual plant to estimate the light absorbed by each organ. This paper presents the radiance equation suitable for calculating sun and sky light intercepted by plant organs based on the principles of the interaction between light and plant canopy firstly; analyzes the process principles of plant canopy primary lighting based on ray casting and projection secondly; describes the multiple scattering of plant lighting based on Monte Carlo ray tracing method and on the radiosity method thirdly; and confirms the research with 3D visualization based on Virtual Reality Modeling Language (VRML) finally. The research is the primary work of digital agriculture, and important for monitoring and estimating corn growth in Northeast China. 相似文献
918.
Jianjun NIU Xiaopei ZHANG Lizhi DU College of Construction Engineering Jilin University Changchun China 《东北亚地学研究》2008,11(4):232-236
Multi-electrodes Resistivity Imaging Survey (MRIS) is an array method of electrical survey. In practice how to choose a reasonable array is the key to get reliable survey results. Based on four methods of MRIS such as Wenner, Schlumberger, Pole-pole and Dipole-dipole the authors established the model, by studying the result of the forward numerical simulation modeling and inverse modeling, and analyzed the differences among the different forms of detection devices. 相似文献
919.
本文介绍了确定GPS正常高的常用方法--GPS水准高程,通过工程实例,得出各种常用拟合方法的适用范围及精度情况,通过对各种拟合模型进行详尽的对比分析,选择有助于高程拟合时选择适宜的拟合函数,获得满意的精度和结果. 相似文献
920.