全文获取类型
收费全文 | 29655篇 |
免费 | 5330篇 |
国内免费 | 7091篇 |
专业分类
测绘学 | 1287篇 |
大气科学 | 6693篇 |
地球物理 | 7620篇 |
地质学 | 14938篇 |
海洋学 | 3466篇 |
天文学 | 1456篇 |
综合类 | 3284篇 |
自然地理 | 3332篇 |
出版年
2024年 | 120篇 |
2023年 | 537篇 |
2022年 | 1229篇 |
2021年 | 1476篇 |
2020年 | 1270篇 |
2019年 | 1319篇 |
2018年 | 1609篇 |
2017年 | 1470篇 |
2016年 | 1708篇 |
2015年 | 1300篇 |
2014年 | 1805篇 |
2013年 | 1560篇 |
2012年 | 1499篇 |
2011年 | 1552篇 |
2010年 | 1693篇 |
2009年 | 1694篇 |
2008年 | 1441篇 |
2007年 | 1403篇 |
2006年 | 1175篇 |
2005年 | 1067篇 |
2004年 | 859篇 |
2003年 | 859篇 |
2002年 | 856篇 |
2001年 | 811篇 |
2000年 | 1012篇 |
1999年 | 1452篇 |
1998年 | 1223篇 |
1997年 | 1303篇 |
1996年 | 1085篇 |
1995年 | 1000篇 |
1994年 | 897篇 |
1993年 | 782篇 |
1992年 | 638篇 |
1991年 | 464篇 |
1990年 | 317篇 |
1989年 | 348篇 |
1988年 | 291篇 |
1987年 | 199篇 |
1986年 | 165篇 |
1985年 | 121篇 |
1984年 | 101篇 |
1983年 | 78篇 |
1982年 | 76篇 |
1981年 | 54篇 |
1980年 | 50篇 |
1979年 | 31篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1958年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
本文主要分析南京地区7-8月发生午后雷阵雨天气,气候与其相关的革些参数的特征,以及大尺度的天气形势条件,用南京单站资料分析位热不稳定度和不稳定能量,从物理场判定南京是否处于产生雷阵雨的潜在不稳定区内,从相关资料中建立南京地区7 ̄8月午后雷阵雨天气的概率预报方程。e 相似文献
132.
Weak ENSO Asymmetry Due to Weak Nonlinear Air–Sea Interaction in CMIP5 Climate Models 总被引:1,自引:0,他引:1
State-of-the-art climate models have long-standing intrinsic biases that limit their simulation and projection capabilities.Significantly weak ENSO asymmetry and weakly nonlinear air–sea interaction over the tropical Pacific was found in CMIP5(Coupled Model Intercomparison Project, Phase 5) climate models compared with observation. The results suggest that a weak nonlinear air–sea interaction may play a role in the weak ENSO asymmetry. Moreover, a weak nonlinearity in air–sea interaction in the models may be associated with the biases in the mean climate—the cold biases in the equatorial central Pacific. The excessive cold tongue bias pushes the deep convection far west to the western Pacific warm pool region and suppresses its development in the central equatorial Pacific. The deep convection has difficulties in further moving to the eastern equatorial Pacific, especially during extreme El Ni o events, which confines the westerly wind anomaly to the western Pacific. This weakens the eastern Pacific El Ni o events, especially the extreme El Ni o events, and thus leads to the weakened ENSO asymmetry in climate models. An accurate mean state structure(especially a realistic cold tongue and deep convection) is critical to reproducing ENSO events in climate models. Our evaluation also revealed that ENSO statistics in CMIP5 climate models are slightly improved compared with those of CMIP3. The weak ENSO asymmetry in CMIP5 is closer to the observation. It is more evident in CMIP5 that strong ENSO activities are usually accompanied by strong ENSO asymmetry, and the diversity of ENSO amplitude is reduced. 相似文献
133.
134.
135.
136.
Mass and energy fluxes between the atmosphere and vegetation are driven by meteorological variables, and controlled by plant
water status, which may change more markedly diurnally than soil water. We tested the hypothesis that integration of dynamic
changes in leaf water potential may improve the simulation of CO2 and water fluxes over a wheat canopy. Simulation of leaf water potential was integrated into a comprehensive model (the ChinaAgrosys)
of heat, water and CO2 fluxes and crop growth. Photosynthesis from individual leaves was integrated to the canopy by taking into consideration the
attenuation of radiation when penetrating the canopy. Transpiration was calculated with the Shuttleworth-Wallace model in
which canopy resistance was taken as a link between energy balance and physiological regulation. A revised version of the
Ball-Woodrow-Berry stomatal model was applied to produce a new canopy resistance model, which was validated against measured
CO2 and water vapour fluxes over winter wheat fields in Yucheng (36°57′ N, 116°36′ E, 28 m above sea level) in the North China
Plain during 1997, 2001 and 2004. Leaf water potential played an important role in causing stomatal conductance to fall at
midday, which caused diurnal changes in photosynthesis and transpiration. Changes in soil water potential were less important.
Inclusion of the dynamics of leaf water potential can improve the precision of the simulation of CO2 and water vapour fluxes, especially in the afternoon under water stress conditions. 相似文献
137.
138.
Comparison of manual and automatic methods for measurement of methane emission from rice paddy fields 总被引:29,自引:0,他引:29
Zheng Xunhu Wang Mingxing Wang Yuesi Shen Renxing Li Jing J. Heyer M. Kogge Li Laotu Jin Jisheng 《大气科学进展》1998,15(4):569-579
The methane emission flux from rice paddies was simultaneously measured with automatic and manual methods in the suburban of Suzhou. Both methods were based on the static chamber/ GC-FID techniques. Detail analysis of the experimental results indicates: a) The data of methane emission measured with the automatic method is reliable. b) About 11 or 19 o’clock of local time is recommended as the optimum sampling time for the manual spot measurement of methane emission from rice paddies. The methane emission fluxes measured by manual sampling at local time other than the optimum time have to be corrected. The correction coefficient may be determined by automatic and continuous measurement. c) In order to get a more accurate result, an empirical correction factor, such as 18%, is recommended to correct the seasonally total amount of measured methane emission by enlarging the au-tomatically measured data or reducing the manually measured ones. 相似文献
139.
140.
内蒙武川后石花金矿床辉钼矿Re-Os同位素年龄及其地质意义 总被引:4,自引:0,他引:4
后石花金矿是华北克拉通北缘一小型石英脉型金矿床。对矿体5件辉钼矿样品的ReOs同位素分析,获得了介于280.3±3.8~283.0±3.9Ma,加权平均为282.0±1.8Ma(MSWD=0.28)的同位素模式年龄,以及一个相关性很好的等时线年龄281.9±1.8Ma(MSWD=0.57),表明矿床形成于早二叠世,推测是海西晚期古亚洲洋俯冲体制下陆缘弧背景中构造-热液成矿事件产物。综合区域资料认为,华北北缘中段在海西晚期曾发生过重要成矿作用,但多在后期被剥蚀破坏。华北北缘中段大陆弧范围内,叠加在前寒武纪结晶基底韧性剪切带之上的脆性断裂构造带,以及华北北缘早古生代增生带内部,是形成海西晚期金、钼矿床的有利部位。 相似文献