全文获取类型
收费全文 | 20838篇 |
免费 | 4013篇 |
国内免费 | 4005篇 |
专业分类
测绘学 | 848篇 |
大气科学 | 1854篇 |
地球物理 | 4686篇 |
地质学 | 12118篇 |
海洋学 | 2866篇 |
天文学 | 2352篇 |
综合类 | 1290篇 |
自然地理 | 2842篇 |
出版年
2024年 | 95篇 |
2023年 | 231篇 |
2022年 | 548篇 |
2021年 | 774篇 |
2020年 | 747篇 |
2019年 | 820篇 |
2018年 | 728篇 |
2017年 | 814篇 |
2016年 | 784篇 |
2015年 | 906篇 |
2014年 | 1158篇 |
2013年 | 1425篇 |
2012年 | 1207篇 |
2011年 | 1290篇 |
2010年 | 1180篇 |
2009年 | 1443篇 |
2008年 | 1373篇 |
2007年 | 1511篇 |
2006年 | 1530篇 |
2005年 | 1336篇 |
2004年 | 1272篇 |
2003年 | 1138篇 |
2002年 | 997篇 |
2001年 | 857篇 |
2000年 | 776篇 |
1999年 | 665篇 |
1998年 | 622篇 |
1997年 | 486篇 |
1996年 | 367篇 |
1995年 | 376篇 |
1994年 | 320篇 |
1993年 | 250篇 |
1992年 | 205篇 |
1991年 | 144篇 |
1990年 | 106篇 |
1989年 | 120篇 |
1988年 | 70篇 |
1987年 | 47篇 |
1986年 | 37篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 9篇 |
1973年 | 1篇 |
1971年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
71.
72.
1 INTRODUCTIONThe South China Sea (SCS) is a semi-enclosedmarginal sea in western North Pacific Ocean withvery complex topography and is the important pas-sage connecting the Pacific and Indian Oceans. Ithas great impact to the global climate and a greatinterest of many oceanography researchers. Twodominant surface hydrographic and circulation fea-tures in the northern SCS are a strong fresh waterexpansion and a warm and high-salinity seawaterintrusion such as the SCS Diluted Water… 相似文献
73.
74.
75.
76.
Yanjun ZHANG Fenglong ZHANG Full QI Fuquan NI 《东北亚地学研究》2006,9(2):199-203
In view of the situation of excavation of open coal mine for the underground water disaster,we should carry out simulation studies for the numerical value of the water lowering project and improve the accuracy and the level of the water lowering project.On the basis of the hydrological geological conditions of certain open mine digging,a more reasonable seepage numerical model was built according to MODFLOW.It was simulated in advance that the process of the confined water level descending with the time,and combining with the actual observations to test the correctness of the model.The calculation showed that the results coincided well with the results of actual measurement.Based on this,different water lowering numerical simulations were built for the open coal mine digging.It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit,and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process,which provide an important basis for the actual water lowering project and the possible project disposal. 相似文献
77.
陈刘组为新建立的岩石地层单位,代表广西早三叠世盆地滨岸相带沉积类型。层型剖面位于贵港市陈刘村附近。层型定义指位于龙潭组与板纳组之间的沉积序列,岩性为灰绿、紫红色泥岩、粉砂细砂岩夹少量火山岩及碳酸盐岩,含菊石、双壳类、牙形石等化石,厚359m。 相似文献
78.
Natural and agricultural wetlands are considered to be the major sources of global atmospheric methane (CH4). A one‐dimensional model was developed to simulate methane emission and used to examine the influence of various physical processes on the rate of methane emission. Three processes involved in the methane emission are implemented in the model: production, reoxidation and transport. Three transport pathways were considered: diffusion across water–air or soil–air interfaces, ebullition and diffusion through plants. These pathways are influenced by soil properties, plant growth, water‐table conditions, temperature and external inputs (e.g. fertilizer). The model was used to examine the seasonal variation of the methane emission at a rice field in Hunan, China, which was observed during a field experiment for consecutive (early and late) rice seasons in 1992. The observed seasonal variations of methane emission, and role of plants in transporting methane to the atmosphere, are captured by the model simulation. Further model applications were conducted to simulate effects of fertilizer and water‐level condition on the methane emission. The results indicate that unfermented organic fertilizer produces a higher methane emission rate than mineral fertilizer. The simulations with treatments of a deep‐water covering and constant moisture reduced the methane emission. The rice field study provides a framework for further development of the model towards simulations based on spatially distributed variables (e.g. water table, soil temperature and vegetation) at a regional scale. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
79.
熊耳群为玄武粗安岩-英安流纹岩组合,大红口组为粗面岩组合,属B类的过渡型拉斑玄武岩浆系列,具以太华群为岩浆房的壳幔混染型成因;秦岭群和宽坪群为变拉斑玄武岩建造,属A类拉斑玄武岩浆系列,具幔源型成因;二郎坪群和丹凤群属细碧岩-石英角斑岩建造,C类石英角斑岩浆系列与A类拉斑玄武岩浆系列共存,具壳幔双层混合型成因。 相似文献
80.