全文获取类型
收费全文 | 96篇 |
免费 | 8篇 |
国内免费 | 18篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 19篇 |
地球物理 | 23篇 |
地质学 | 39篇 |
海洋学 | 12篇 |
天文学 | 4篇 |
综合类 | 6篇 |
自然地理 | 7篇 |
出版年
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 5篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2010年 | 2篇 |
2009年 | 7篇 |
2008年 | 6篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有122条查询结果,搜索用时 15 毫秒
41.
复杂地形低风速气象特征分析 总被引:2,自引:0,他引:2
利用13个地面站和1个100 m气象塔的全年实测资料分析湖南中北部丘陵地区中尺度范围的低风速气象特征。结果表明:(1)该区域低风速出现频率高,小于15 m/s的风速出现频率年均达416%;(2)低风速与地形情况密切相关,区域内西部山地的低风速出现频率明显高于东部平原地区;(3)低风速的出现具有日变化特点,典型出现时间段是夜间至次日上午;(4)低风速条件下10 min平均风向多出现大角度变化的情况,60°以上的风向变化频率可达20%~30%。(5)水平风向标准差在低风速情况下明显增大,但观测仪器性能会对小风结果产生影响。 相似文献
42.
王柏钧 《成都信息工程学院学报》1987,(1)
本文提出了一种使尽可能多的因子载荷变为0(或接近于0)的新的因子变换方法。它不同于常用的因子旋转方法。主要步骤是于中的行向量单独考虑,使其有尽可能多的0(或近于0)。从有关地球科学的举例证明,这个方法比一般斜交因子解的方法更符合实际,解释更令人满意。 相似文献
43.
Pieter Vermeesch 《地学前缘(英文版)》2021,12(2):843-850
In a recent review published in this journal,Coutts et al.(2019)compared nine different ways to estimate the maximum depositional age(MDA)of siliclastic rocks by means of detrital geochronology.Their results show that among these methods three are positively and six negatively biased.This paper investigates the cause of these biases and proposes a solution to it.A simple toy example shows that it is theoretically impossible for the reviewed methods to find the correct depositional age in even a best case scenario:the MDA estimates drift to ever smaller values with increasing sample size.The issue can be solved using a maximum likelihood model that was originally developed for fission track thermochronology by Galbraith and Laslett(1993).This approach parameterises the MDA estimation problem with a binary mixture of discrete and continuous distributions.The‘Maximum Likelihood Age’(MLA)algorithm converges to a unique MDA value,unlike the ad hoc methods reviewed by Coutts et al.(2019).It successfully recovers the depositional age for the toy example,and produces sensible results for realistic distributions.This is illustrated with an application to a published dataset of 13 sandstone samples that were analysed by both LA-ICPMS and CA-TIMS U–Pb geochronology.The ad hoc algorithms produce unrealistic MDA estimates that are systematically younger for the LA-ICPMS data than for the CA-TIMS data.The MLA algorithm does not suffer from this negative bias.The MLA method is a purely statistical approach to MDA estimation.Like the ad hoc methods,it does not readily accommodate geological complications such as post-depositional Pb-loss,or analytical issues causing erroneously young outliers.The best approach in such complex cases is to re-analyse the youngest grains using more accurate dating techniques.The results of the MLA method are best visualised on radial plots.Both the model and the plots have applications outside detrital geochronology,for example to determine volcanic eruption ages. 相似文献
44.
Isoplot R: A free and open toolbox for geochronology 总被引:1,自引:0,他引:1
Pieter Vermeesch 《地学前缘(英文版)》2018,9(5):1479-1493
45.
强调了统计域的正确选择对区域地球化学数据分析的重要性。本文以南岭研究区的W元素原始异常作为统计域,分析得出了研究区内不同成矿类型钨矿一种量化的简单元素组合特征。以此量化的元素组合特征,并结合相似度分析方法,统计了研究区内样点与各典型钨矿元素组合特征的相似性系数,其成图结果非常准确地圈定了已知的各类型钨矿,相比W元素原始异常其准确率得到了明显提升。该方法亦可认为是对地球化学场的一种成因分解,能够准确提取其中与成矿有关的异常信息。该研究可作为区域异常结构模式研究的重要补充,也可以为扩大南岭地区钨矿找矿远景提供线索。 相似文献
46.
2013年,受世界经济复苏乏力、国内经济下行压力加大等不利因素影响,国内非开挖市场在经历了黄金十年后增速明显回落,市场需求萎缩,行业竞争更为激烈,企业之间的分化也进一步加剧。本文回顾了2013年对我国非开挖行业发展具有较大影响的十大重要事件,详细介绍和分析了中关两国非开挖行业的统计情况。 相似文献
47.
48.
Venkata Swamy Yerramsetti Nikhil Gauravarapu Navlur Venkanna Rapolu N. S. K. Chitanya Dhulipala Puna Ram Sinha Shailaja Srinavasan Gangagni Rao Anupoju 《洁净——土壤、空气、水》2013,41(3):215-225
In this study, temporal variations of surface ozone (O3) were investigated at tropical urban site of Hyderabad during the year 2009. O3, oxides of nitrogen (NOx = NO + NO2), black carbon (BC), and meteorological parameters were continuously monitored at the established air monitoring station. Results revealed the production of surface O3 from NO2 through photochemical oxidation. Averaged datasets illustrated the variations in ground‐level concentrations of these air pollutants along different time scales. Maximum mean concentrations of O3 (56.75 ppbv) and NOx (8.9 ppbv) were observed in summer. Diurnal‐seasonal changes in surface O3 and NOx concentrations were explicated with complex atmospheric chemistry, boundary layer dynamics, and local meteorology. In addition, nocturnal chemistry of NOx played a decisive role in the formation of O3 during day time. Mean BC mass concentration in winter (10.92 µg m?3) was high during morning hours. Heterogeneous chemistry of BC on O3 destruction and NOx formation was elucidated. Apart from these local observations, long‐range transport of trace gases and BC aerosols were evidenced from air mass back trajectories. Further, statistical modeling was performed to predict O3 using multi‐linear regression method, which resulted in 91% of the overall variance. 相似文献
49.
50.
Errors of isotope ratios acquired by double interpolation 总被引:1,自引:0,他引:1
Measurement of isotope ratios via double interpolation of cyclic peak jumping produces error correlations between time-adjacent ratios which, if ignored, result in underestimated errors of their means. Equations that incorporate the error correlations are derived, and an example given for a typical U–Pb/zircon analysis via ion microprobe showing that isotope-ratio uncertainties for a single spot are usually underestimated by factors of 1.2–1.3. 相似文献