全文获取类型
收费全文 | 19155篇 |
免费 | 4962篇 |
国内免费 | 3911篇 |
专业分类
测绘学 | 1707篇 |
大气科学 | 2418篇 |
地球物理 | 3607篇 |
地质学 | 10482篇 |
海洋学 | 3535篇 |
天文学 | 248篇 |
综合类 | 1436篇 |
自然地理 | 4595篇 |
出版年
2024年 | 270篇 |
2023年 | 395篇 |
2022年 | 734篇 |
2021年 | 876篇 |
2020年 | 842篇 |
2019年 | 932篇 |
2018年 | 819篇 |
2017年 | 916篇 |
2016年 | 918篇 |
2015年 | 969篇 |
2014年 | 1206篇 |
2013年 | 1141篇 |
2012年 | 1288篇 |
2011年 | 1209篇 |
2010年 | 1066篇 |
2009年 | 1259篇 |
2008年 | 1153篇 |
2007年 | 1392篇 |
2006年 | 1367篇 |
2005年 | 1217篇 |
2004年 | 1126篇 |
2003年 | 1070篇 |
2002年 | 937篇 |
2001年 | 730篇 |
2000年 | 597篇 |
1999年 | 553篇 |
1998年 | 465篇 |
1997年 | 432篇 |
1996年 | 382篇 |
1995年 | 338篇 |
1994年 | 291篇 |
1993年 | 235篇 |
1992年 | 221篇 |
1991年 | 177篇 |
1990年 | 109篇 |
1989年 | 162篇 |
1988年 | 73篇 |
1987年 | 52篇 |
1986年 | 31篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1954年 | 3篇 |
1877年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
房产测量中面积测算问题探讨 总被引:3,自引:1,他引:3
房产测量成果是为产权产籍管理、开发管理、交易管理和拆迁管理服务,是为城市规划和城市建设等提供基础数据和资料的重要基础性工作,得到全社会的关注。本文对房产测量中房屋面积测算过程经常遇到的问题进行了探讨,并提出了一些解决的建议。 相似文献
112.
113.
《水文科学杂志》2012,57(15):1909-1917
ABSTRACTThis study was conducted to characterize the hysteresis of suspended sediment concentration (SSC) at different timescales for the Educational and Research Forest Watershed of Tarbiat Modares University, Iran. Hysteresis loops were developed between flow discharge and SSC using data for (i) the whole period, (ii) seasonal, (iii) monthly and (iv) storm-event timescales. The data were collected on an hourly basis at daily and storm-event scales from October 2007 to July 2008. The SSC hysteresis for all the events in the whole study period showed a clockwise pattern, with a flushing behaviour pointing to sudden changes in sediment sources. The results further reveal that the study watershed behaves differently from the viewpoint of hysteresis patterns, with different conditions of dilution and flushing between SSC and flow discharge at different timescales. These result from the complex varying effect of governing conditions on the watershed. 相似文献
114.
太平洋海温异常对大理雨季开始期的影响 总被引:1,自引:0,他引:1
采用大理州雨季开始期资料、1961年6月~2008年5月太平洋5°×5°共286个格点的逐月平均海温资料及NCEP/NCAR的SSTA资料,通过相关分析发现,太平洋海温与大理雨季开始期的关系密切,春季和上年秋季太平洋海温对大理雨季开始的影响较大。雨季开始前若发生厄尔尼诺事件,大理雨季开始期偏晚,反之,若发生拉尼娜事件,大理雨季开始期偏早。N ino3区的海温异常对大理雨季开始期的影响相当明显,当5月N ino3区的海温异常偏高时,大理雨季开始期偏晚;反之,当5月N ino3区的海温异常偏低时,大理雨季开始期偏早,N ino3区海温异常可以作为大理雨季开始期预测的一个强信号因子。 相似文献
115.
神经网络模型是近年来在需水预测方面应用较为广泛的一种方法,在陕西省的需水预测中根据实际情况采用遗传模拟退火算法对其进行优化,预测的结果和其他预测方法进行对比,证明该方法预测的结果较为合理,能够在类似的预测中加以推广应用. 相似文献
116.
117.
Baptiste Marteau Damià Vericat Chris Gibbins Ramon J. Batalla David R. Green 《地球表面变化过程与地形》2017,42(3):503-515
Structure‐from‐Motion (SfM) photogrammetry is now used widely to study a range of earth surface processes and landforms, and is fast becoming a core tool in fluvial geomorphology. SfM photogrammetry allows extraction of topographic information and orthophotos from aerial imagery. However, one field where it is not yet widely used is that of river restoration. The characterisation of physical habitat conditions pre‐ and post‐restoration is critical for assessing project success, and SfM can be used easily and effectively for this purpose. In this paper we outline a workflow model for the application of SfM photogrammetry to collect topographic data, develop surface models and assess geomorphic change resulting from river restoration actions. We illustrate the application of the model to a river restoration project in the NW of England, to show how SfM techniques have been used to assess whether the project is achieving its geomorphic objectives. We outline the details of each stage of the workflow, which extend from preliminary decision‐making related to the establishment of a ground control network, through fish‐eye lens camera testing and calibration, to final image analysis for the creation of facies maps, the extraction of point clouds, and the development of digital elevation models (DEMs) and channel roughness maps. The workflow enabled us to confidently identify geomorphic changes occurring in the river channel over time, as well as assess spatial variation in erosion and aggradation. Critical to the assessment of change was the high number of ground control points and the application of a minimum level of detection threshold used to assess uncertainties in the topographic models. We suggest that these two things are especially important for river restoration applications. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
118.
韩国“新北方政策”与“一带一路”倡议的对接合作为中韩两国带来了重要发展机遇。文章主要探讨韩国“新北方政策”的内涵及其与“一带一路”倡议对接的进展、机遇与挑战,得出双方对接的合作机遇主要在政策沟通、设施联通、贸易投资和资金融通4个方面,同时也存在着制度性风险、地缘风险和投资合作风险的三大挑战。在具体对接过程中,产业、金融、物流3个领域可能成为突破口。 相似文献
119.
关联度分析法在确定土地定级因素权重中的应用 总被引:5,自引:0,他引:5
从关联度分析法的基本原理入手,介绍了应用关联度分析法确定土地定级因素权重的具体方法,探讨了关联度分析法运用于土地定级因素权重确定的可行性。 相似文献
120.
Hydrogen and oxygen isotope studies were carried out on mineral separates from high to ultrahigh pressure metamorphic rocks
at Huangzhen and Shuanghe in the eastern Dabie Mountains, East China. The δ18O values of eclogites cover a wide range of −5‰ to+9‰, but the δD values of micas fall within a narrow range of −85% to −70‰.
Both equilibrium and disequilibrium oxygen isotope fractionations were observed between quartz and the other minerals, with
reversed fractionations between omphacite and garnet in some eclogite samples. The δ18 O values of −5‰ to −1‰ for some of the eclogites represent the oxygen isotope compositions of their protoliths which underwent
meteoric water-rock interaction prior to plate subduction. The preservation of oxygen isotope heterogeneity in the eclogites
implies a channelized flow of fluids during progressive metamorphism caused by rapid subduction. Retrograde metamorphism has
caused oxygen and hydrogen isotope disequilibria between some of the minerals, but the fluid for retrograde reactions was
internally buffered in the stable isotope compositions.
Project supported by the Chinese Ministry of Science and Technology (Grant No. 95-Pre-39), the National Natural Science Foundation
of China (Grant Nos. 49794042, 49473173 and 49453003) and the Chinese Academy of Sciences (Grant No. KZ951-A1-401-5) 相似文献