全文获取类型
收费全文 | 21677篇 |
免费 | 4844篇 |
国内免费 | 4826篇 |
专业分类
测绘学 | 1006篇 |
大气科学 | 3092篇 |
地球物理 | 5332篇 |
地质学 | 14123篇 |
海洋学 | 3311篇 |
天文学 | 103篇 |
综合类 | 1507篇 |
自然地理 | 2873篇 |
出版年
2024年 | 68篇 |
2023年 | 280篇 |
2022年 | 710篇 |
2021年 | 926篇 |
2020年 | 903篇 |
2019年 | 996篇 |
2018年 | 803篇 |
2017年 | 898篇 |
2016年 | 887篇 |
2015年 | 1002篇 |
2014年 | 1366篇 |
2013年 | 1554篇 |
2012年 | 1358篇 |
2011年 | 1495篇 |
2010年 | 1308篇 |
2009年 | 1428篇 |
2008年 | 1446篇 |
2007年 | 1587篇 |
2006年 | 1533篇 |
2005年 | 1350篇 |
2004年 | 1288篇 |
2003年 | 1078篇 |
2002年 | 1025篇 |
2001年 | 878篇 |
2000年 | 811篇 |
1999年 | 704篇 |
1998年 | 639篇 |
1997年 | 573篇 |
1996年 | 429篇 |
1995年 | 381篇 |
1994年 | 377篇 |
1993年 | 293篇 |
1992年 | 238篇 |
1991年 | 190篇 |
1990年 | 115篇 |
1989年 | 121篇 |
1988年 | 82篇 |
1987年 | 55篇 |
1986年 | 33篇 |
1985年 | 41篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 4篇 |
1978年 | 16篇 |
1977年 | 6篇 |
1972年 | 2篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
53.
通过对蓄水前后三峡库首区构造应力场进行三维数值模拟发现,相对于蓄水前,蓄水至135 m水位时,官渡口断裂-马鹿池断裂-牛口断裂围限区、秭归地理中心和九湾溪断裂带,出现了4个主应力下降区和共轭的主应力增长区,形成了差应力场;175 m水位与135 m水位相比,局部差应力场呈现逆向变化,即形成了加载效应与卸载效应的交替过程。这一过程,可能是水库诱发地震的诱震(或触震)因素。 相似文献
54.
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
55.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
56.
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
57.
1995年7月11日—12日,广西地矿厅和河池地区行署首次联合举办矿产资源勘查成果展销会,会址设在河池市,与会代表130余人。展销会提交大会展销的矿产资源勘查成果38项,引资勘查项目38项。经买卖双方三天的洽谈,涉及到的项目25项,会议期间签订矿产资源勘查成果合同协议4项,愈千万元,取得较好的社会经济效益。为地勘资金多渠道来源开辟了新路子,对促进地勘单位地质找矿工作及勘查成果有偿使用发挥了重要作用 相似文献
58.
59.
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
60.
通过对美国地下空间开发利用的考察,认为有如下特点,第一,结合城市建设,构筑地下铁道,第二立足于战略,建立水下通路,第三,地下空间的开发利用平战结合.这些方法对我国的地下空间开发利用值得借鉴. 相似文献