全文获取类型
收费全文 | 18882篇 |
免费 | 2777篇 |
国内免费 | 4002篇 |
专业分类
测绘学 | 4555篇 |
大气科学 | 3069篇 |
地球物理 | 2922篇 |
地质学 | 5319篇 |
海洋学 | 5128篇 |
天文学 | 416篇 |
综合类 | 1553篇 |
自然地理 | 2699篇 |
出版年
2024年 | 77篇 |
2023年 | 203篇 |
2022年 | 702篇 |
2021年 | 836篇 |
2020年 | 867篇 |
2019年 | 1035篇 |
2018年 | 773篇 |
2017年 | 939篇 |
2016年 | 909篇 |
2015年 | 1022篇 |
2014年 | 1101篇 |
2013年 | 1424篇 |
2012年 | 1102篇 |
2011年 | 1130篇 |
2010年 | 964篇 |
2009年 | 1245篇 |
2008年 | 1217篇 |
2007年 | 1300篇 |
2006年 | 1134篇 |
2005年 | 1018篇 |
2004年 | 957篇 |
2003年 | 786篇 |
2002年 | 734篇 |
2001年 | 623篇 |
2000年 | 514篇 |
1999年 | 471篇 |
1998年 | 461篇 |
1997年 | 406篇 |
1996年 | 331篇 |
1995年 | 248篇 |
1994年 | 227篇 |
1993年 | 204篇 |
1992年 | 174篇 |
1991年 | 114篇 |
1990年 | 103篇 |
1989年 | 61篇 |
1988年 | 52篇 |
1987年 | 37篇 |
1986年 | 23篇 |
1985年 | 35篇 |
1984年 | 17篇 |
1983年 | 21篇 |
1982年 | 22篇 |
1981年 | 15篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
982.
泥质砂岩复电阻率的频散特性实验 总被引:5,自引:0,他引:5
不同孔隙流体特性的岩石复电阻率频散实验,是复电阻率测井资料评价水淹层和低阻油层的岩石物理基础。通过水驱水、水驱油、油驱水的岩石复电阻率频散特性的实验研究,发现泥质砂岩的复电阻率频散特性受含油饱和度的影响较大,受地层水矿化度的影响较小,尤其是异相电阻率,受地层水矿化度的影响更小;与含水泥质砂岩相比,含油泥质砂岩的相角相对较大,且随着含油饱和度的增加而增大;含水岩石和含油岩行在频散特性上存在着较大差异。实验研究结果表明,利用基于岩石频散特性发展起来的复电阻率测井技术,可以有效地识别油水层。 相似文献
983.
984.
结合青岛市四方区围海造地工程的实例,分析了在厚度较大的软弱地基层上水下铺设大型编织布袋作为围堰的主体结构的优点和结构特点,重点介绍了施工工艺以及在施工过程中需注意的问题。 相似文献
985.
辽宁省城市人居环境系统耦合协调度时空格局演变及驱动力研究 总被引:2,自引:0,他引:2
人居环境系统内部的耦合协调是保证人居环境均衡发展的基础。基于“人类-居住-支撑-自然-社会”5个子系统,构建人居环境系统耦合协调发展评价指标体系,将2个系统间的容量耦合模型扩展运用到人居环境5个子系统中,综合熵值法、GIS空间分析以及地理探测器对辽宁省2005~2016年人居环境系统耦合协调度的时空演化特征与驱动力进行探讨,阐述人居环境系统内部协调性。研究表明:①2005~2016年辽宁省人居环境系统内部的耦合度与耦合协调度整体呈缓慢浮动上升趋势;②辽宁省人居环境耦合协调度呈分散格局,并且呈现从中间向两侧递减的“屋脊”式格局和“双核结构”;东西方向上,空间演变趋势由倒U型逐渐向一字型演变,南北方向上由斜线型向“L”型演变。③全省出现了中耦合低协调区、中耦合过渡协调区、高耦合低协调区、高耦合过渡协调区、高耦合高协调区5种类型区。④空间分异驱动力主要包括人的需求、经济发展、住房、互联网发展等。 相似文献
986.
近20年京津唐主体城区地表热场空间特征变化分析 总被引:3,自引:1,他引:2
基于Landsat遥感影像获取京津唐主体城区1995~2015年地表温度(Land Surface Temperature, LST)和不透水地表盖度(Impervious Surface Percentage, ISP)数据。采用热点聚集和阈值分割法,依据地表的温度和不透水盖度属性将京津唐主体城区划分成9种地表热场类型,分析并探讨地表热场的发展规律、年际变化状况和区域贡献作用。研究发现,京津唐主体城区地表温度与不透水地表盖度间存在显著的正向相关关系,两者分别呈现“阶梯降”和“两端高、中间低”的变化特征。京津唐主体城区地表热场的发展主轴保持在西北-东南方向,且随时间推移沿主轴呈聚集态势。 京津唐主体城区地表热场的影响范围在空间上持续扩张,对于不同的主体城区,其在整体区域的热场贡献中有差异化表现。 相似文献
987.
MIN Jianxiong LI Guangxue DING Dong QIAO Lulu MA Yanyan YANG Gang ZHANG Yaqi ZHANG Lei LI Shuhao 《中国海洋大学学报(英文版)》2019,(1):9-19
Based on the observed surface suspended matter in the East China Sea in February 2007 and June 2015, an empirical model was established using L1 b's band 4 data to retrieve surface suspended matter from the Moderate Resolution Imagine Spectroradiometer Terra imagery. The squared correlation coefficient is 0.8358, and the root mean square error is 0.4285 mg L-1. The model reflects the distribution characteristics of surface suspended matter in the inner shelf of the East China Sea. In this paper, the satellite images of the study area were retrieved in January from 2001 to 2015, and the monthly distribution of surface suspended matter were obtained. The inter-annual distribution of the study area is similar, and the concentration of surface suspended matter is higher near the shore than offshore. A large amount of surface suspended matter is transported southeast under the influence of Zhejiang and Fujian coastal current and Taiwan warm current. Only a small amount of surface suspension can reach the Kuroshio area. The surface suspended matter concentration changes obviously near the estuary because of the effect of differences in the flux of the Yangtze River. Meanwhile, winter monsoon, temperature front, El Ni?o events, and other factors affect the distribution of surface suspended matter in 100 m isobath to coastal water but minimally influence the distribution in 100 m isobath to deep sea. 相似文献
988.
In this study, we used Landsat images and meteorological data to examine the spatiotemporal distribution and variability of sea ice in Jiaozhou Bay(JZB) between 1986 and 2016. The results show that JZB is not always covered by sea ice in winter, but in some extreme cases, sea ice has covered more than one-third of the sea area of the bay. Sea ice in JZB has generally formed between January 1 and February 5, primarily along the coast, and gradually expanding to the central area of the bay. Both meteorological and artificial factors have played important roles in modulating the sea ice distribution. We found sea ice coverage to have been strongly correlated with the accumulated freezing-degree days nine days before the occurrence of sea ice(R2 = 0.767). North-northwest surface winds have dominated the freezing period of sea water in the JZB, and wind speed has exerted a more significant influence on the formation of sea ice when the sea ice coverage has been generally small. Additionally, artificial factors began to affect the expansion of sea ice in JZB since 2007. The construction of the Jiao-Zhou-Bay Bridge(JZBB) is believed to have retarded water flow and reduced the tidal prism, thereby leading to the formation of an ice bridge along the JZBB, which effectively prevents the southward expansion of sea ice. 相似文献
989.
990.
This study used the synthetic running correlation coefficient calculation method to calculate the running correlation coefficients between the daily sea ice concentration(SIC) and sea surface air temperature(SSAT) in the Beaufort-Chukchi-East Siberian-Laptev Sea(BCEL Sea), Kara Sea and southern Chukchi Sea, with an aim to understand and measure the seasonally occurring changes in the Arctic climate system. The similarities and differences among these three regions were also discussed. There are periods in spring and autumn when the changes in SIC and SSAT are not synchronized, which is a result of the seasonally occurring variation in the climate system. These periods are referred to as transition periods. Spring transition periods can be found in all three regions, and the start and end dates of these periods have advancing trends. The multiyear average duration of the spring transition periods in the BCEL Sea, Kara Sea and southern Chukchi Sea is 74 days, 57 days and 34 days, respectively. In autumn, transition periods exist in only the southern Chukchi Sea, with a multiyear average duration of only 16 days. Moreover, in the Kara Sea, positive correlation events can be found in some years, which are caused by weather time scale processes. 相似文献