全文获取类型
收费全文 | 14319篇 |
免费 | 2644篇 |
国内免费 | 3508篇 |
专业分类
测绘学 | 798篇 |
大气科学 | 3054篇 |
地球物理 | 3712篇 |
地质学 | 7524篇 |
海洋学 | 1479篇 |
天文学 | 695篇 |
综合类 | 1385篇 |
自然地理 | 1824篇 |
出版年
2024年 | 79篇 |
2023年 | 268篇 |
2022年 | 670篇 |
2021年 | 757篇 |
2020年 | 637篇 |
2019年 | 770篇 |
2018年 | 906篇 |
2017年 | 784篇 |
2016年 | 863篇 |
2015年 | 716篇 |
2014年 | 900篇 |
2013年 | 779篇 |
2012年 | 769篇 |
2011年 | 887篇 |
2010年 | 853篇 |
2009年 | 761篇 |
2008年 | 669篇 |
2007年 | 707篇 |
2006年 | 574篇 |
2005年 | 481篇 |
2004年 | 404篇 |
2003年 | 402篇 |
2002年 | 442篇 |
2001年 | 386篇 |
2000年 | 462篇 |
1999年 | 616篇 |
1998年 | 491篇 |
1997年 | 514篇 |
1996年 | 437篇 |
1995年 | 396篇 |
1994年 | 415篇 |
1993年 | 376篇 |
1992年 | 260篇 |
1991年 | 202篇 |
1990年 | 156篇 |
1989年 | 124篇 |
1988年 | 137篇 |
1987年 | 81篇 |
1986年 | 64篇 |
1985年 | 54篇 |
1984年 | 43篇 |
1983年 | 40篇 |
1982年 | 46篇 |
1981年 | 30篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1958年 | 21篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
841.
842.
特提斯最初是指欧亚大陆南缘的古海洋,后逐渐引申出从元古宙、古生代到中生代的一系列位于劳亚大陆与冈瓦纳大陆之间的古大洋,如原特提斯洋、古特提斯洋和新特提斯洋,不同大洋在时间上前后交叠。如今横亘在冈瓦纳大陆(南极洲)和欧亚大陆之间的是印度洋,是新特提斯洋的继承者,可以另称为“全新特提斯洋”。这一概念的引申直接体现了印度洋与特提斯构造域一脉相承的关系,有助于将今论古、由此及彼,更直观地了解特提斯构造域的演化过程。本文按时间序列梳理了印度洋的大地构造演化和岩浆作用过程,识别了印度洋在155 Ma、120 Ma、90~84 Ma、76 Ma、65 Ma、52 Ma、45 Ma、38 Ma等关键时期的异常海底扩张记录,这些扩张事件将为标定新特提斯构造域的演化提供参照。其中155 Ma可能指示了新特提斯洋的鼎盛期,90 Ma指示了新特提斯洋的洋中脊俯冲,76~52 Ma是非洲-阿拉伯大陆与欧亚大陆初始碰撞-主碰撞(即新特提斯洋西部关闭)的时期,65~45 Ma是印度次大陆与欧亚大陆初始碰撞-主碰撞(即新特提斯洋中部关闭)的时期,38 Ma是澳大利亚北部大洋开始净俯冲(即新提斯洋东部开始消减)的时间。... 相似文献
843.
Based on four reanalysis datasets including CMA-RA, ERA5, ERA-Interim, and FNL, this paper proposes an improved intelligent method for shear line identification by introducing a second-order zonal-wind shear. Climatic characteristics of shear lines and related rainstorms over the Southern Yangtze River Valley(SYRV) during the summers(June-August) from 2008 to 2018 are then analyzed by using two types of unsupervised machine learning algorithm,namely the t-distributed stochastic neighbor embeddin... 相似文献
844.
845.
A 3D discrete FEM iterative algorithm for solving the water pipe cooling problems of massive concrete structures
下载免费PDF全文
![点击此处可从《国际地质力学数值与分析法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Water pipe cooling has been widely used for the temperature control and crack prevention of massive concrete structures such as high dams. Because both under‐cooling and over‐cooling may reduce the efficiency of crack prevention, or even lead to great harm to structures, we need an accurate and robust numerical tool for the prediction of cooling effect. Here, a 3D discrete FEM Iterative Algorithm is introduced, which can simulate the concrete temperature gradient near the pipes, as well as the water temperature rising along the pipes. On the basis of the heat balance between water and concrete, the whole temperature field of the problem can be computed exactly within a few iteration steps. Providing the pipe meshing tool for building the FE model, this algorithm can take account of the water pipe distribution, the variation of water flow, water temperature, and other factors, while the traditional equivalent algorithm based on semi‐theoretical solutions can only solve problems with constant water flow and water temperature. The validation and convergence are proved by comparing the simulated results and analytical solutions of two standard second‐stage cooling problems. Then, a practical concrete block with different cooling schemes is analyzed and the influences of cooling factors are investigated. In the end, detailed guidance for pipe system optimization is provided. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
846.
The surface energy balance algorithm for land method was used in this study to calculate the evapotranspiration (ET) rate for the middle reaches of the Heihe River Basin, Gansu Province, China, to analyse ET distribution within the oasis and the surrounding desert and, especially, on the edge zone of the oasis. Five profile graphs were created vertical to the river. Because of the inverse humidity phenomenon, the least amount of evapotranspiration occurred on the desert close to the oasis. The average evapotranspiration rate was roughly proportioned from the edge of the oasis to inside and outside its boundary. Two meteorological ground stations located close to the oasis edge showed a notable difference in net radiation flux that led to the difference found in ET. The primary reason for the significant differences observed in net radiation may be largely the result of differences in flux reflectivity and surface temperature. Meteorological data show that water supply also played an important role. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
847.
848.
Integrating downscaled CMIP5 data with a physically based hydrologic model to estimate potential climate change impacts on streamflow processes in a mixed‐use watershed
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Climatic changes have altered surface water regimes worldwide, and climate projections suggest that such alterations will continue. To inform management decisions, climate projections must be paired with hydrologic models to develop quantitative estimates of watershed scale water regime changes. Such modeling approaches often involve downscaling climate model outputs, which are generally presented at coarse spatial scales. In this study, Coupled Model Intercomparison Project Phase 5 climate model projections were analyzed to determine models representing severe and conservative climate scenarios for the study watershed. Based on temperature and precipitation projections, output from GFDL‐ESM2G (representative concentration pathway 2.6) and MIROC‐ESM (representative concentration pathway 8.5) were selected to represent conservative (ΔC) and severe (ΔS) change scenarios, respectively. Climate data were used as forcing for the soil and water assessment tool to analyze the potential effects of climate change on hydrologic processes in a mixed‐use watershed in central Missouri, USA. Results showed annual streamflow decreases ranging from ?5.9% to ?26.8% and evapotranspiration (ET) increases ranging from +7.2% to +19.4%. During the mid‐21st century, sizeable decreases to summer streamflow were observed under both scenarios, along with large increases of fall, spring, and summer ET under ΔS. During the late 21st century period, large decreases of summer streamflow under both scenarios, and large increases to spring (ΔS), fall (ΔS) and summer (ΔC) ET were observed. This study demonstrated the sensitivity of a Midwestern watershed to future climatic changes utilizing projections from Coupled Model Intercomparison Project Phase 5 models and presented an approach that used multiple climate model outputs to characterize potential watershed scale climate impacts. 相似文献
849.
Particle manifold method (PMM) is a new extension of the numerical manifold method (NMM). PMM uses a mathematical cover system to describe the motion and deformation of a particle‐based physical domain. By introducing the concept of particle into NMM, PMM takes the advantages of easy topological and contact operations with particles. In this article, the methodology, formulations and implementation of the method are presented, together with modelling examples for validation. It is found that good solutions for both continuous and discontinuous problems are obtained by the new developed PMM. Due to the underlying coupled continuum‐discontinuum property of PMM, it has great potential for modelling of geomechanical problems. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
850.