全文获取类型
收费全文 | 14581篇 |
免费 | 3474篇 |
国内免费 | 5087篇 |
专业分类
测绘学 | 2399篇 |
大气科学 | 2097篇 |
地球物理 | 2968篇 |
地质学 | 9522篇 |
海洋学 | 2435篇 |
天文学 | 436篇 |
综合类 | 1331篇 |
自然地理 | 1954篇 |
出版年
2024年 | 142篇 |
2023年 | 342篇 |
2022年 | 958篇 |
2021年 | 1101篇 |
2020年 | 934篇 |
2019年 | 1040篇 |
2018年 | 1011篇 |
2017年 | 895篇 |
2016年 | 991篇 |
2015年 | 993篇 |
2014年 | 1052篇 |
2013年 | 1244篇 |
2012年 | 1285篇 |
2011年 | 1211篇 |
2010年 | 1234篇 |
2009年 | 1171篇 |
2008年 | 1198篇 |
2007年 | 1031篇 |
2006年 | 970篇 |
2005年 | 805篇 |
2004年 | 603篇 |
2003年 | 437篇 |
2002年 | 442篇 |
2001年 | 433篇 |
2000年 | 337篇 |
1999年 | 260篇 |
1998年 | 136篇 |
1997年 | 143篇 |
1996年 | 109篇 |
1995年 | 104篇 |
1994年 | 94篇 |
1993年 | 79篇 |
1992年 | 62篇 |
1991年 | 42篇 |
1990年 | 38篇 |
1989年 | 42篇 |
1988年 | 19篇 |
1987年 | 19篇 |
1986年 | 32篇 |
1985年 | 26篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1965年 | 4篇 |
1958年 | 3篇 |
1957年 | 5篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
951.
952.
南襄盆地泌阳断陷下第三系陆相层序地层 总被引:3,自引:0,他引:3
泌阳断陷历经中生代小型拉分盆地、早第三纪断陷盆地和晚第三纪坳陷盆地等3个盆地原型的演化、叠合过程,形成了3个盆地充填序列及其所包含的3个构造层序。泌阳断陷下第三系(即构造层序Ⅱ)为湖盆沉积充填主体,其可划分为7个层序组,各层序组具特定的沉积体系配置关系。作为泌阳断陷油气勘探主要目的层段的下第三系核桃园组可进一步划分为12个层序。其中,核三上段包括跨时分别为1.08、1.40、1.02Ma的3个陆相层序,由南往北呈现冲积扇—扇三角洲—湖泊—三角洲的沉积体系空间配置。泌阳断陷下第三系层序地层年代框架模式清晰地显示了断陷湖盆成盆演化史、沉积充填史及其陆相层序时空展布特征。 相似文献
953.
利用2009~2015年的GPS水平运动速度场数据,解算云南地区的地壳应变场,在红河断裂与曲江断裂选取两个GPS剖面,计算并分析两个断裂的应变积累特征。结果显示:1)红河、曲江、小江等多个主要断裂应变场存在张、压交替的时空演化特征,近期曲江断裂南段表现为东西向拉张,红河断裂北段东西向拉张量值较大,约12.0×10-8/a,云南南部主要表现为NNE向的压性变化;2)从GPS剖面看,红河、曲江断裂在两个方向上均显示右旋走滑与拉张的变化特征,从量值上看,红河断裂北段运动速率较大,约8.90 mm/a。 相似文献
954.
基于1980年、2005年和2015年3期区域精密水准网观测资料,利用线性动态平差模型计算获取大别山地区水准网长期垂直运动速度场图像。研究发现,淮河平原地表下沉较为严重,大别山呈现弱隆升趋势运动,长江谷地边缘地区较大别山区呈现明显的隆升运动。跨郯庐断裂带水准剖面结果显示,垂直运动与地形呈负相关和弱相关。 相似文献
955.
在利用国际地磁参考场模型计算主磁场时,往往采用海拔高而非大地高,并且忽略了大地水准面起伏的间接影响。通过全球的实际计算表明,若忽略大地水准面起伏,可引起地表主磁场的北向、东向、垂向与水平分量以及总模量的误差范围分别为-2.37~1.59 nT、-0.51~0.33 nT、-1.95~2.09 nT、-2.37~1.59 nT与-2.39~1.82 nT。 相似文献
956.
Humans and livestock have always dwelling together, especially in rural areas. Based on a multi-method approach of ethnographic fieldwork, grounded theory and one-way multivariate analysis of variance, this paper explores human and livestock dwelling. The findings show that human and livestock dwelling form a special type of human dwelling place, with forms defined as co-, mix- and dis-dwelling. Then, from co-, mix- to dis-dwelling constructed a story line to the evolution of human and livestock dwelling forms, which further explains the entire dwelling situation of humans and livestock, including the dimensions of human dweller, livestock dweller, the rural environment and special events. Among co-, mix- and dis-dwelling significant differences existed between human and livestock individuals, the nature of rural environment, vernacularity and rural tourism development. Between co- and dis-dwelling, significant differences existed in seventeen aspects; between mix- and dis-dwelling, significant differences existed in eleven aspects; meanwhile, no significant differences existed between co- and mix-dwelling. Accordingly, this suggested that human and livestock dwelling forms can be divided into mix- and dis-dwelling. This study on humans and livestock dwelling relationship offer a new perspective on rural and animal geography. This paper is an exploratory foray into rural dwelling geography as part of the Anthrozoology study and broadens the scope of extant scholarship on human dwelling morphology, as well as analyses the spatial relationships between human and livestock dwelling. 相似文献
957.
Journal of Oceanology and Limnology - Microcystins (MCs) are cyclic hepatotoxic peptides produced by the bloom-forming cyanobacterium Microcystis and present a public health hazard to humans and... 相似文献
958.
Journal of Oceanology and Limnology - Genes encoding Wnt ligands, which have important roles in cell communication and organ development, are restricted to multicellular animals. We systematically... 相似文献
959.
自然邻近关系在空间数据库管理系统中具有十分重要的地位。为了克服Voronoi图受空间目标位置的影响,本文采用约束Delaunay三角网,针对在二维欧式空间中离散面目标的自然邻近关系查询问题。首先对离散面进行三角剖分,然后将代表相同邻近关系的三角形合并成一个union,进而建立面目标自然邻近关系表达结构-Unions Delaunay。通过与Unions Delaunay相结合建立空间索引结构-R-tree Gridfile来实现对空间目标自然邻居完备的候选集提取以及索引结构的更新。对比实验结果表明R-tree Gridfile索引结构能够有效支持空间目标的自然邻近关系查询。 相似文献
960.
Understanding streamflow changes in terms of trends and periodicities and relevant causes is the first step into scientific management of water resources in a changing environment. In this study, monthly streamflow variations were analyzed using Modified Mann-Kendall(MM-K) trend test and Continuous Wavelet Transform(CWT) methods at 9 hydrological stations in the Huaihe River Basin. It was found that: 1) streamflow mainly occurs during May to September, accounting for 70.4% of the annual total streamflowamount with Cv values between 0.16–0.85 and extremum ratio values between 1.70–23.90; 2) decreased streamflow can be observed in the Huaihe River Basin and significant decreased streamflow can be detected during April and May, which should be the results of precipitation change and increased irrigation demand; 3) significant periods of 2–4 yr were detected during the 1960 s, the 1980 s and the 2000 s. Different periods were found at stations concentrated within certain regions implying periods of streamflow were caused by different influencing factors for specific regions; 4) Pacific Decadal Oscillation(PDO) has the most significant impacts on monthly streamflow mainly during June. Besides, Southern Oscillation Index(SOI), North Atlantic Oscillation(NAO) and the Ni?o3.4 Sea Surface Temperature(Ni?o3.4) have impacts on monthly streamflow with three months lags, and was less significant in time lag of six months. Identification of critical climatic factors having impacts on streamflow changes can help to predict monthly streamflow changes using climatic factors as explanatory variables. These findings were well corroborated by results concerning impacts of El Nino-Southern Oscillation(ENSO) regimes on precipitation events across the Huaihe River Basin. The results of this study can provide theoretical background for basin-scale management of water resources and agricultural irrigation. 相似文献