全文获取类型
收费全文 | 27118篇 |
免费 | 5166篇 |
国内免费 | 7683篇 |
专业分类
测绘学 | 1435篇 |
大气科学 | 4957篇 |
地球物理 | 7074篇 |
地质学 | 16054篇 |
海洋学 | 3196篇 |
天文学 | 1162篇 |
综合类 | 3126篇 |
自然地理 | 2963篇 |
出版年
2024年 | 124篇 |
2023年 | 456篇 |
2022年 | 1054篇 |
2021年 | 1228篇 |
2020年 | 1027篇 |
2019年 | 1098篇 |
2018年 | 1301篇 |
2017年 | 1173篇 |
2016年 | 1371篇 |
2015年 | 1060篇 |
2014年 | 1379篇 |
2013年 | 1342篇 |
2012年 | 1225篇 |
2011年 | 1758篇 |
2010年 | 1510篇 |
2009年 | 1662篇 |
2008年 | 1223篇 |
2007年 | 1351篇 |
2006年 | 1344篇 |
2005年 | 1469篇 |
2004年 | 1747篇 |
2003年 | 1356篇 |
2002年 | 1132篇 |
2001年 | 995篇 |
2000年 | 952篇 |
1999年 | 1285篇 |
1998年 | 1112篇 |
1997年 | 1159篇 |
1996年 | 999篇 |
1995年 | 846篇 |
1994年 | 695篇 |
1993年 | 818篇 |
1992年 | 670篇 |
1991年 | 422篇 |
1990年 | 291篇 |
1989年 | 251篇 |
1988年 | 198篇 |
1987年 | 179篇 |
1986年 | 133篇 |
1985年 | 85篇 |
1984年 | 60篇 |
1983年 | 50篇 |
1982年 | 45篇 |
1981年 | 32篇 |
1980年 | 42篇 |
1979年 | 38篇 |
1978年 | 22篇 |
1977年 | 25篇 |
1976年 | 21篇 |
1958年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
Xiaoping Liu Xingjian Liu He Jin Jinpei Ou Limin Jiao 《International journal of geographical information science》2018,32(4):738-756
To-date few research has successfully integrated big data from multiple sources to characterize urban mixed-use buildings. In this paper, we introduce a probabilistic model to integrate multi-source and geospatial big data (social network data, taxi trajectories, Points of Interest and remote sensing images) to characterize urban mixed-use buildings. The usefulness of our model is demonstrated with a case study of the Tianhe District in megacity Guangzhou, China. The model predicted building functions at 85% accuracy based on ground truth data from field surveys. We further explored the spatial patterns of the identified building functions. Most mixed-use buildings are located along major streets. Our proposed model can identify mixed-use buildings in a city; information is useful for planning evaluation and urban policymaking. 相似文献
292.
利用ECHOG海气耦合气候模式模拟的中国东部过去近1000年的降水资料,通过经验正交函数分解方法得到了中国东部夏季降水分布的主要空间型态: 华北和华南地区与长江中下游地区反位相,即华北和华南地区降水多(少)时长江中下游地区降水少(多)。对31年滑动平均后3种空间分布型的时间系数进行Morlet小波分析和功率谱分析发现,3个地区均存在准60年的年代际振荡周期,长江中下游和华南地区均存在准200年的百年际振荡周期,华南地区还存在120年和80年的变化周期。全球海温场与3个地区夏季降水31年滑动平均后的相关分析表明,在40°~70°S,170°~60°W海域海温与华北和长江中下游地区夏季降水负相关,与华南地区夏季降水正相关除该区外的南北半球(30°~60°)中高纬海域海温与华北和长江中下游地区夏季降水正相关、与华南地区夏季降水负相关,说明在年代际和百年际时间尺度上,中高纬海域海温是影响长江中下游地区和华南地区夏季降水反相的主要因子之一。最后通过对太阳常数、火山活动等外强迫因子与中国东部夏季降水的功率谱分析发现: 中国东部夏季降水的年代际与百年际变化周期大都与外强迫因子的变化周期一致,说明外强迫因子,尤其是太阳常数和火山活动的变化是影响中国东部夏季降水年代际和百年际振荡的主要原因。 相似文献
293.
294.
鲁东南岚山头含柯石英榴辉岩主要产于花岗质片麻岩内,是苏鲁超高压变质带主要榴辉岩体密集分布区之一。流体包裹体研究表明,榴辉岩矿物及细脉石英中捕获有四种类型包裹体:在超高压-高压榴辉岩相条件下捕获的 N_2±CO_2包裹体;在高压榴辉宕重结晶阶段被捕获的 CO_2-H_2O 包裹体和含子矿物高盐度 H_2O 溶液包裹体:在超高压岩石折返过程中的最晚(角闪岩相退变质甚至更晚)阶段捕获的低盐度 H_2O 溶液包裹体。利用榴辉岩矿物及脉体石英中捕获的流体包裹体相互期次关系,可以对本区超高压变质作用板片折返过程中的流体演化史进行重建。 相似文献
295.
296.
The inverted charge structure formation of a hailstorm was investigated using the Advanced Weather Research and Forecasting(WRF-ARW) model coupled with electrification and discharge schemes. Different processes may be responsible for inverted charge structure in different storms and regions. A dynamical-derived mechanism of inverted charge structure formation was confirmed by the numerical model: the inverted structure was formed by strong updraft and downdraft under normal-polarity charging conditions such that the graupel charged negatively in the main charging region in the middle-upper level of the cloud. The simulation results showed the storm presented a normal charge structure before and after hail-fall; while during the hail-fall stage, it showed an inverted charge structure—negative charge region in the upper level of the cloud and a positive charge region in the middle level of the cloud—appearing at the front edge near the strong updraft in the hailstorm. The charging processes between the two particles mainly occurred at the top of the cloud, where the graupel charged negatively and ice crystals positively due to the strong updraft. When the updraft air reached the top of the storm, it would spread to the rear and front. The light ice crystals were transported backward and forward more easily. Meanwhile, the positively charged ice crystals were transported downward by the frontal subsidence, and then a positive charge region formed between the ?10 and ?25°C levels. Subsequently, a negative charge region materialized in the upper level of the cloud, and the inverted charge structure formed. 相似文献
297.
Yue-Ping Xu Martijn J. Booij Yang-Bin Tong 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(5):567-578
With the increase of both magnitude and frequency of hydrological extreme events such as drought and flooding, the significance
of adequately modeling hydrological extreme events is fully recognized. Estimation of extreme rainfall/flood for various return
periods is of prime importance for hydrological design or risk assessment. However, due to knowledge and data limitation,
uncertainty involved in extrapolating beyond available data is huge. In this paper, different sources of uncertainty in statistical
modeling of extreme hydrological events are studied in a systematic way. This is done by focusing on several key uncertainty
sources using three different case studies. The chosen case studies highlight a number of projects where there have been questions
regarding the uncertainty in extreme rainfall/flood estimation. The results show that the uncertainty originated from the
methodology is the largest and could be >40% for a return period of 200 years, while the uncertainty caused by ignoring the
dependence among multiple hydrological variables seems the smallest. In the end, it is highly recommended that uncertainty
in modeling extreme hydrological events be fully recognized and incorporated into a formal hydrological extreme analysis. 相似文献
298.
The mean value concept in mono-linear regression of multi-variables and its application to trace studies in geosciences 总被引:3,自引:1,他引:3
A J T JULL 《中国科学D辑(英文版)》2007,50(12):1828-1834
The "mean value concept" in a mono-linear regression of multi-variables is clarified.Its applications to reconstruction of the past 90-year salinity of the sea surface water in Xisha Islands and to tracing the past 80 ka paleo-geomagnetic events from the Luochuan loess 10Be record are introduced in detail,which show the significance and the potential of the "mean value concept" in geoscience research. 相似文献
299.
300.
Earthquake probabilities and magnitude distribution (M ≥ 6.7) along the Haiyuan fault, northwestern China 总被引:2,自引:0,他引:2
冉洪流 《地震学报(英文版)》2004,17(6)
Introduction Haiyuan fault is a major seismogenic fault in north-central China. One of the most devastat-ing great earthquake in the 20th century occurred near Haiyuan in northwestern China on Decem-ber 16, 1920. More than 220 000 people were killed and thousands of towns and villages weredestroyed during the devastating earthquake. A 230 km long left-lateral surface rupture zone wasformed along the Haiyuan fault during the earthquake with maximum left-lateral displacement of10 m. Pale… 相似文献