全文获取类型
收费全文 | 48174篇 |
免费 | 8556篇 |
国内免费 | 11285篇 |
专业分类
测绘学 | 3384篇 |
大气科学 | 9967篇 |
地球物理 | 11887篇 |
地质学 | 23408篇 |
海洋学 | 5637篇 |
天文学 | 2113篇 |
综合类 | 5407篇 |
自然地理 | 6212篇 |
出版年
2024年 | 133篇 |
2023年 | 634篇 |
2022年 | 1957篇 |
2021年 | 2283篇 |
2020年 | 1895篇 |
2019年 | 2252篇 |
2018年 | 2585篇 |
2017年 | 2353篇 |
2016年 | 2735篇 |
2015年 | 2277篇 |
2014年 | 2816篇 |
2013年 | 2820篇 |
2012年 | 2692篇 |
2011年 | 2818篇 |
2010年 | 2849篇 |
2009年 | 2787篇 |
2008年 | 2565篇 |
2007年 | 2447篇 |
2006年 | 1935篇 |
2005年 | 1925篇 |
2004年 | 1391篇 |
2003年 | 1417篇 |
2002年 | 1370篇 |
2001年 | 1410篇 |
2000年 | 1614篇 |
1999年 | 2305篇 |
1998年 | 1872篇 |
1997年 | 1864篇 |
1996年 | 1728篇 |
1995年 | 1500篇 |
1994年 | 1253篇 |
1993年 | 1145篇 |
1992年 | 904篇 |
1991年 | 706篇 |
1990年 | 536篇 |
1989年 | 471篇 |
1988年 | 425篇 |
1987年 | 264篇 |
1986年 | 233篇 |
1985年 | 153篇 |
1984年 | 139篇 |
1983年 | 111篇 |
1982年 | 97篇 |
1981年 | 78篇 |
1980年 | 65篇 |
1979年 | 55篇 |
1978年 | 24篇 |
1977年 | 22篇 |
1975年 | 16篇 |
1958年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 57 毫秒
121.
APPLICATION OF GEOGRAPHICAL PARAMETER DATABASE TO ESTABLISHMENT OF UNIT POPULATION DATABASE 总被引:1,自引:1,他引:0
Now GIS is turning into a good tool in handling geographical, economical, and population data, so we can obtain more and more information from these data. On the other hand, in some cases, for a calamity, such as hurricane, earthquake, flood, drought etc., or a decision-making, such as setting up a broadcasting transmitter, building a chemical plant etc., we have to evaluate the total population in the region influenced by a calamity or a project. In this paper, a method is put forward to evaluate the population in such special region. Through exploring the correlation of geographical parameters and the distribution of people in the same region by means of quantitative analysis and qualitative analysis, unit population database (1km× 1km) is established. In this way, estimating the number of people in a special region is capable by adding up the population in every grid involved in this region boundary. The geographical parameters are obtained from topographic database and DEM database on the scale of 相似文献
122.
LIUXin-wei CHENBai-ming ZHANGDing-xiang 《中国地理科学(英文版)》2004,14(3):209-214
Efficiency and sustainability of grain production are now important in China. In this study, the grain production systems of Jiangsu and Shaanxi Provinces were compared, to analyze their efficiency and sustainability in terms of utilization of natural resources, inputs of purchased energy and materials, and outputs. Flows of energy and materials between environment and human society were identified, and the natural and human work involved in generating inputs as materials or energy were valued in terms of equivalent amount of solar energy required for their production using emergy method. The results showed environmental resources were continually playing a less important role in the systems, when inorganic subsidiary emergy inputs increased drastically while organic ones decreased or increased little. Deterioration of input emergy structure affected the systems‘ efficiency and sustainability, resulting in emergy investment ratios and environmental loading ratios increasing while yield ratios and sustainability indices decreasing. In general, efficiency and sustainability of grain production in Jiangsu are worse than those in Shaanxi. This analysis also suggested that inorganic subsidiary emergy should be introduced properly, and peasants in Jiangsu should utilize natural conditions wisely while those in Shaanxi pay enough attention to soil and surface water conservation. 相似文献
123.
LIU Na CHEN Hongxia 《中国海洋大学学报(英文版)》2006,5(2):99-105
Using the monthly wind and sea surface temperature (SST) data, southern meridional atmospheric circulation cells associated with the Indian Ocean Dipole Mode (IOD) events in the Indian Ocean are for the first time described and examineS. The divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells. During the four different phases of the positive IOD events, the anomalous meridional Hadley circulation over the western Indian Ocean shows that the air rises in the tropics, flows poleward in the upper troposphere, sinks in the subtropics, and returns back to the tropics in the lower troposphere. The anomalous Hadley circulation over the eastern Indian Ocean is opposite to that over the western Indian Ocean. During positive IOD events, the meridional Hadley circulation over the eastern Indian Ocean is weakened while it is strengthened over the western Indian Ocean. Correlation analysis between the IOD index and the indices of the Hadley cells also proves that, the atmospheric circulation patterns are evident in every IOD event over the period of record. 相似文献
124.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
125.
A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ)SCALE ATMOSPHERIC MODEL——PARTI:MODEL DESCRIPTION
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A three-dimensional elastic nonhydrostatic mesoscale(β-γ)model with nested-grid is presented.It uses a set of fullequations in terrain-following coordinates as its basic dynamic frame,which is solved with a time-splitting algorithmfor acoustic and gravity waves.The model physical parameterization includes a K-theory subgrid eddy mixing for cloudand free atmosphere,a bulk planetary boundary layer parameterization,and three types of sofisticated cloudmicrophysics schemes with double-parameters for hail-bearing clouds,warm clouds and snowing clouds respectively.The model is designed to be used flexibly for simulations of a variety of meso-and small-scale atmospheric processes,and can be improved as a regional and local operational NWP system in future. 相似文献
126.
网络经济是相对于大工业经济而言的,其网络企业经济效益的评价,可以从网络企业成本及收益两个方面讨论,然后以投入产出比等五个方面来建立其评价指标体系。 相似文献
127.
This study on the distribution features of petroleum hydrocarbon in water and sedi-ment off the Fujian shore using data obtained from the baseline research on oceanic contamination in Fujian showed that:during the research preiod,petroleum hydrocarbon concentrations in water varied from 5.77μg/L to 37.28μg/L,averaged 14.48 μg/L;was lower in the wet seasson than in the dry season;and was highest in the Minjiang Estuary and Jiulong Estuary in both seasons ,The petorleum hydrocarbon concentrations in shore sediment varied from 14.48 mg/kg to 784.36 mg/kg,averaged 133.3 mg/kg ,and was closely related to sediment types (granularity). 相似文献
128.
本文对徐州地震台JB—72水平摆倾斜仪1988年11月至1989年5月间所记录到的24次同震阶变进行了深入分析,认为:a.造成同震阶变的原因是多方面的,而反应了地球应变场准静态调整的同震阶变才是有价值的价变异常;b.多观测手段的地震台站,同震阶变应该在不止一台仪器上得到响应。 相似文献
129.
130.