全文获取类型
收费全文 | 4272篇 |
免费 | 814篇 |
国内免费 | 948篇 |
专业分类
测绘学 | 431篇 |
大气科学 | 908篇 |
地球物理 | 1222篇 |
地质学 | 1367篇 |
海洋学 | 727篇 |
天文学 | 644篇 |
综合类 | 279篇 |
自然地理 | 456篇 |
出版年
2024年 | 10篇 |
2023年 | 43篇 |
2022年 | 85篇 |
2021年 | 107篇 |
2020年 | 129篇 |
2019年 | 160篇 |
2018年 | 119篇 |
2017年 | 132篇 |
2016年 | 155篇 |
2015年 | 168篇 |
2014年 | 217篇 |
2013年 | 289篇 |
2012年 | 217篇 |
2011年 | 298篇 |
2010年 | 268篇 |
2009年 | 323篇 |
2008年 | 281篇 |
2007年 | 363篇 |
2006年 | 319篇 |
2005年 | 290篇 |
2004年 | 255篇 |
2003年 | 212篇 |
2002年 | 195篇 |
2001年 | 175篇 |
2000年 | 167篇 |
1999年 | 151篇 |
1998年 | 145篇 |
1997年 | 131篇 |
1996年 | 115篇 |
1995年 | 84篇 |
1994年 | 99篇 |
1993年 | 65篇 |
1992年 | 68篇 |
1991年 | 56篇 |
1990年 | 26篇 |
1989年 | 34篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有6034条查询结果,搜索用时 15 毫秒
991.
992.
993.
M5 model tree based modelling of reference evapotranspiration 总被引:1,自引:0,他引:1
This paper investigates the potential of M5 model tree based regression approach to model daily reference evapotranspiration using climatic data of Davis station maintained by California irrigation Management Information System (CIMIS). Four inputs including solar radiation, average air temperature, average relative humidity, and average wind speed whereas reference evapotranspiration calculated using a relation provided by the CIMIS was used as output. To compare the performance of M5 model tree in predicting the reference evapotranspiration, FAO–56 Penman–Monteith equation and calibrated Hargreaves–Samani relation was used. A comparison of results suggests that M5 model tree approach works well in comparison to both FAO–56 and calibrated Hargreaves–Samani relations. To judge the generalization capability of M5 model tree approach, model created by using the Davis data set was tested with the datasets of four different sites. Results from this part of the study suggest that M5 model tree could successfully be employed in modeling the reference evapotranspiration. Further, sensitivity analysis with M5 model tree approach suggests the suitability of solar radiation, average air temperature, average relative humidity, and average wind speed as input parameters to model the reference evapotranspiration Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
994.
曲率模态小波法用于网壳结构损伤的识别和定位 总被引:1,自引:0,他引:1
工程结构损伤的识别与定位研究以往主要针对梁、框架等结构形式,根据大跨度空间结构杆件和节点繁多等特点,提出用曲率模态和小波混合方法对空间结构的损伤进行识别和定位.以跨度100 m的Schwedler网壳结构损伤前、后的曲率模态作为标识量,分别通过离散和连续小波变换,判断网壳结构有无损伤和损伤位置,统计了小波系数差与结构损伤的图形关系,计算了各种损伤工况下该方法判断损伤的准确程度.结果发现基于曲率模态和小波方法的大跨度网壳结构损伤定位精度很高,充分证明该方法对此类结构损伤定位具有有效性和实用性. 相似文献
995.
将Newmark-β法中常平均加速度法的基本假定与精细指数算法结合,根据指数矩阵的Taylor级数展开式,提出了动力方程的显式级数解,并设计了相应的时程积分算法.该算法的精度可根据Taylor级数展开式的项数进行灵活控制.算例的结果表明:在满足稳定性条件的前提下,随着时间步长的增加,其精度优于传统的时程积分法.通过稳定性的分析,指出其稳定性条件是显然满足的. 相似文献
996.
997.
998.
Simulations of flow for a discrete-fracture model in fractured porous rocks have gradually become more practical, as a consequence of increased computer power and improved simulation and characterization techniques. Discrete-fracture models can be formulated in a lower-dimensional framework, where the fractures are modeled in a lower dimension than the matrix, or in an equi-dimensional form, where the fractures and the matrix have the same dimension. 相似文献
999.
Mass and heat transfer occurring across phase-interfaces in multi-phase flow in porous media are mostly approximated using equilibrium relationships or empirical kinetic models. However, when the characteristic time of flow is smaller than that of mass or heat transfer, non-equilibrium situations may arise. Commonly, empirical approaches are used in such cases. There are only few works in the literature that use physically-based models for these transfer terms. In fact, one would expect physical approaches to modeling kinetic interphase mass and heat transfer to contain the interfacial area between the phases as a variable. Recently, a two-phase flow and solute transport model was developed that included interfacial area as a state variable [36]. In that model, interphase mass transfer was modeled as a kinetic process. 相似文献
1000.
This paper concerns efficient uncertainty quantification techniques in inverse problems for Richards’ equation which use coarse-scale simulation models. We consider the problem of determining saturated hydraulic conductivity fields conditioned to some integrated response. We use a stochastic parameterization of the saturated hydraulic conductivity and sample using Markov chain Monte Carlo methods (MCMC). The main advantage of the method presented in this paper is the use of multiscale methods within an MCMC method based on Langevin diffusion. Additionally, we discuss techniques to combine multiscale methods with stochastic solution techniques, specifically sparse grid collocation methods. We show that the proposed algorithms dramatically reduce the computational cost associated with traditional Langevin MCMC methods while providing similar sampling performance. 相似文献