全文获取类型
收费全文 | 1556篇 |
免费 | 308篇 |
国内免费 | 476篇 |
专业分类
测绘学 | 137篇 |
大气科学 | 463篇 |
地球物理 | 358篇 |
地质学 | 782篇 |
海洋学 | 192篇 |
天文学 | 39篇 |
综合类 | 183篇 |
自然地理 | 186篇 |
出版年
2024年 | 18篇 |
2023年 | 36篇 |
2022年 | 123篇 |
2021年 | 122篇 |
2020年 | 110篇 |
2019年 | 115篇 |
2018年 | 118篇 |
2017年 | 134篇 |
2016年 | 130篇 |
2015年 | 98篇 |
2014年 | 113篇 |
2013年 | 86篇 |
2012年 | 94篇 |
2011年 | 93篇 |
2010年 | 86篇 |
2009年 | 92篇 |
2008年 | 69篇 |
2007年 | 76篇 |
2006年 | 62篇 |
2005年 | 64篇 |
2004年 | 45篇 |
2003年 | 32篇 |
2002年 | 31篇 |
2001年 | 30篇 |
2000年 | 35篇 |
1999年 | 77篇 |
1998年 | 49篇 |
1997年 | 38篇 |
1996年 | 32篇 |
1995年 | 25篇 |
1994年 | 22篇 |
1993年 | 21篇 |
1992年 | 18篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有2340条查询结果,搜索用时 15 毫秒
61.
High resolution UAV image acquisition method and modeling practice for geological outcrop with a large slope 下载免费PDF全文
The observation on the outcrop in the field is one of the most direct and efficient methods to obtain the underground formation information, which provides the most direct first-hand geological data for geological science research. However, the traditional outcrop investigation, especially for the outcrop with a large slope and unreachable area, mainly relies on the inspection, measurement of the slope bottom, and photos to record outcrop information, making it difficult to accurately characterize the whole geological body. Consumer unmanned aerial vehicle (UAVs) with the advantages of good mobility, strong adaptability and low cost, can obtain outcrop images from a short distance, multiple perspectives and varying heights. In this paper, the image acquisition method and model construction accuracy without control points available for the geological outcrop with a large slope are discussed. Consumer UAVs is used to capture images through vertical route and then the geological model is set up. The results show that oblique photogrammetry technology combined with consumer UAVs can effectively build a large slope geological outcrop model with millimeter resolution. The model has the characteristics of high resolution, uniform resolution and high measurement accuracy up to millimeter, which can effectively reduce the difficulty of field investigation and the personnel safety risk, thus it accurately reproduces the outcrop situation with large slope in the field, providing a real and reliable data basis for the section interpretation, analysis and measurement of large slope outcrop. 相似文献
62.
Using NCEP/NCAR reanalysis geopotential height (GHT) and wind at 850 hPa, GHT at 500 hPa, precipitation rate, sea level pressure
(SLP) and precipitation observations from more than 600 stations nationwide in June–August from 1951 to 2006, and focusing
on the East Asia-West Pacific region (10°–80°N, 70°–180°E), interannual variation of East Asian summer monsoon (EASM) and
its correlations with general circulation and precipitation patterns are studied by using statistical diagnostic methods such
as 9-point high pass filtering, empirical orthogonal function (EOF) analysis, composite analysis and other statistical diagnosis,
etc. It is concluded as follows: (1) EOF analysis of SLP in the East Asia-West Pacific region shows the existence of the zonal
dipole oscillation mode (APD) between the Mongolia depression and the West Pacific high, and APD index can be used as an intensity
index of EASM. (2) EOF analysis of GHT anomalies at 500 hPa in the East Asia-West Pacific region shows that the first EOF
mode is characterized with an obvious meridional East Asian pattern (EAP), and EAP index can also be used as an EASM intensity
index. (3) The composite analysis of high/low APD index years reveals the close correlation of APD index with EAP at 500 hPa
(or 850 hPa). The study shows an obvious opposite correlation exists between APD index and EAP index with a correlation coefficient
of −0.23, which passes the confidence test at 0.10 level. (4) Both APD and EAP indexes are closely correlated with precipitation
during flood-prone season in China and precipitation rate over the East Asia-West Pacific region. The significant correlation
area at 5% confidence level is mainly located from the southern area of the Yangtze River valley to the ocean around southern
Japan, and the former is a positive correlation and the latter is a negative one.
Foundation: Cooperative Project funded by the Ministry of Science and Technology of the People’s Republic of China, No.2007DFB20210;
National Natural Science Foundation of China, No.90502003; JICA China-Japan Technical Cooperative Project “China-Japanese
Cooperative Research Center on Meteorological Disasters”.
Author: Yu Shuqiu, Associate Professor, specialized in climate and climate change. 相似文献
63.
64.
胶州湾沉积物重金属形态不同浸取方法的比较与污染讯息指示作用初探 总被引:1,自引:0,他引:1
海洋沉积物中重金属的活性形态对于指示沉积物污染状况具有重要作用;为探寻简洁且能够有效提取重金属活性形态的浸提方法;实验研究了0.1 mol/L和1 mol/L盐酸的单级提取和欧共体标准局(European Community Bureau of Reference)提出的BCR分级提取法对胶州湾表层沉积物中重金属(Cr、Cu、Ni、Pb、Zn)和Al、Fe、Mn的浸取效果。结果显示;3种提取方法提取的金属含量呈显著正相关关系;两种浓度的稀盐酸对BCR方法中的酸可提取态和可还原态金属均具有较好浸提效果;但对可氧化态金属浸提能力相对较弱。不同提取方法的人为信号指数(ASI)计算结果表明;BCR浸取法提取结果的金属ASI值最大;表明其对沉积物中金属活性形态提取效率较高;1 mol/L HCl提取结果的金属ASI值最低;可能是较高浓度强酸使沉积物较大颗粒内层中“惰性”金属被浸取出来;“增加”了金属活性组分的污染讯息信号;对沉积物中Cu、Pb和Zn而言;0.1 mol/L HCl提取结果的ASI值与BCR方法接近。经过Al归一化后;0.1 mol/L HCl浸提的重金属含量的空间分布与胶州湾的实际污染状况相吻合;表明0.1 mol/L的HCl在一定程度上能够代替复杂的BCR浸取法;此方法可简化重金属活性形态的提取步骤;适合大范围沉积物重金属污染评价。 相似文献
65.
晚更新世以来的活动构造与现代地质灾害密切相关,目前针对陆域活动构造的定量研究成果卓著,而在海域方面研究薄弱。本文综述了国内外有关海域活动构造的研究进展,提出了目前国内海域活动构造定量研究存在的主要问题。在研究实践的基础上,阐述了海域活动构造的主要研究方法、其定量研究的关键问题及解决方案,重点总结了海域活动构造区地震危险性定量评价的研究方案,并进一步探讨了海域活动构造自身因素的危险性定量评价的研究思路。 相似文献
66.
海上固定平台的冰激振动响应计算与分析 总被引:6,自引:0,他引:6
本文用强迫振动理论计算了辽东湾常见冰情挤压冰作用下JZ20—2—1采油平台和测冰平台的自振特性、位移、速度和加速度响应以及平台的应力响应,取得了一些有意义的结果,供平台设计和使用时参考。 相似文献
67.
Duan Lin XiuQin LiHongDa Fang YanHong DongZhuoXuan Huang JiaHui Chen 《Estuarine, Coastal and Shelf Science》2011
To study the relationships between species distribution and environmental variables, calanoid copepods were classified and enumerated, and environmental variables were analyzed along 91 sites of the Pearl River Estuary (China) and adjacent waters. The 91 sites were divided into 3 groups based on surface salinity: the Inner area had salinity level below 10‰ and was mostly located in the Pearl River Estuary, the Coastal area had salinity between 10‰ and 32‰ and was almost located along the coastline, while the Offshore area had salinity level higher than 32‰ and was mainly located in the open area. Indicator Species Analysis was conducted to identify the indicator species within each group from among all calanoid copepods taxa. We found that the Inner area was characterized by Acartiella sinensis, Pseudodiaptomus poplesia and Pseudodiaptomus inopinus, the coastal area was characterized by Temora turbinata and Subeucalanus subcrassus, and the Offshore area was characterized by Paracandacia truncata, Subeucalanus subtenuis, Euchaeta rimana, Pareucalanus attenuatus, Rhincalanus cornutus, Cosmocalanus darwini, Centropages gracilis, Undinula vulgaris, Nannocalanus minor and Paraeuchaeta russelli. Canonical Correspondence Analysis (CCA) was used to identify relevant biotic and abiotic parameters that can best explain the distribution of calanoid copepods. CCA showed that during the summer of 2006, salinity, nutrient variables, especially SiO3–Si, NO3–N and DTN, Depth and Chl a were the environmental variables that strongly impacted the distribution and community structure of calanoid copepods. 相似文献
68.
69.
提出利用国际参考电离层附加虚拟观测值对总电子含量值为负数的地区、赤道异常区域和南半球区域电离层进行约束,在日固地磁参考系下采用15阶次的球谐展开建立全球电离层模型,解算得单位权中误差约为1. 6TECU,残差绝对值小于3TECU的比例达90%以上,且全球电离层图与IGS电离层工作组的电离层产品精度相当,偏差RMS约为3. 7 TECU,卫星差分码偏差与欧洲定轨中心相比优于0. 1 ns,与 IGS相比优于0. 2 ns,接收机差分码偏差与欧洲定轨中心相比优于1 ns(大部分优于0. 5 ns),与lGS相比优于1. 5 ns.实验结果表明,附有国际参考电离层约束的全球电离层模型确保了全球各个地区的电离层总电子含量为正值,且有效提高了全球电离层模型在赤道异常区域、海洋地区和南半球的精度。 相似文献
70.