全文获取类型
收费全文 | 5029篇 |
免费 | 1215篇 |
国内免费 | 2435篇 |
专业分类
测绘学 | 250篇 |
大气科学 | 485篇 |
地球物理 | 1511篇 |
地质学 | 4770篇 |
海洋学 | 548篇 |
天文学 | 225篇 |
综合类 | 663篇 |
自然地理 | 227篇 |
出版年
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 12篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 16篇 |
2016年 | 20篇 |
2015年 | 62篇 |
2014年 | 16篇 |
2013年 | 77篇 |
2012年 | 36篇 |
2011年 | 511篇 |
2010年 | 311篇 |
2009年 | 462篇 |
2008年 | 156篇 |
2007年 | 306篇 |
2006年 | 541篇 |
2005年 | 596篇 |
2004年 | 1174篇 |
2003年 | 760篇 |
2002年 | 513篇 |
2001年 | 406篇 |
2000年 | 267篇 |
1999年 | 250篇 |
1998年 | 299篇 |
1997年 | 276篇 |
1996年 | 177篇 |
1995年 | 142篇 |
1994年 | 119篇 |
1993年 | 318篇 |
1992年 | 284篇 |
1991年 | 134篇 |
1990年 | 41篇 |
1989年 | 70篇 |
1988年 | 20篇 |
1987年 | 53篇 |
1986年 | 29篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 18篇 |
1976年 | 12篇 |
1950年 | 8篇 |
1943年 | 7篇 |
1940年 | 9篇 |
1937年 | 15篇 |
1934年 | 9篇 |
1933年 | 13篇 |
1928年 | 7篇 |
1924年 | 6篇 |
排序方式: 共有8679条查询结果,搜索用时 15 毫秒
1.
中国地质学会2020年度“十大地质科技进展” 总被引:1,自引:0,他引:1
大庆油田等:松辽盆地北部古龙页岩油勘探取得重大发现大庆油田在松辽盆地北部古龙凹陷青一段地层的纯页岩内实现水平井产量重大战略突破,试油获高产工业油气流,定产试采表现出稳定的高产能力,平面上15口直井试油证实古龙页岩油平面分布范围广,规模立体含油,轻质油带具有较好的产油能力,轻质油带页岩油气资源量达到几十亿吨。通过岩心精细描述及实验分析化验数据,建立了以古沉积环境控制原始优质烃源岩发育、适中的热演化程度控制油气富集。 相似文献
2.
<正>由《中国学术期刊(光盘版)》电子杂志社有限公司、中国科学文献计量评价研究中心和清华大学图书馆出版的《中国学术期刊影响因子年报(自然科学与工程技术)(2022年版)》(简称《年报》)已发布。根据《年报》的统计结果,在105种地质类期刊中,《地球学报》2022年影响力指数为377.707,排名第21,复合影响因子是2.578,分区为Q1(表1)。《年报》采用的统计分析方法体现了如下8个特点: 相似文献
3.
Torgeir O. Rthe Jostein Bakke Eivind Wilhelm Nagel Stren 《Boreas: An International Journal of Quaternary Research》2019,48(3):616-634
A sudden release of large volumes of water during a glacier outburst flood (GLOF) is a major hazard worldwide. Here, we identify the sedimentary signature of glacial and non‐glacial processes, including GLOFs, based on lacustrine sediments from the distal glacier‐fed Lake Buarvatnet in western Norway. Historically documented GLOFs in 2002 CE and during the 1980s CE are identified in the 210Pb‐ and 14C‐dated sediments. These events have the same sedimentary signature as 12 earlier events throughout the Holocene interpreted to represent previous GLOFs in the catchment. The GLOFs are interpreted to have occurred during periods when the glacier extent was similar to the modern positions, and the events are thus used to pinpoint past positions of the glacier terminus and, hence, the equilibrium line altitudes (ELAs). The results indicate that the glacier Svartenutbreen, located at the eastern part of Folgefonna, had a similar size in 2002 CE as c. 8200–8300 cal. a BP, corresponding to the 8.2 ka event in the North Atlantic region. The regrowth of Sørfonna after the Holocene Thermal Optimum occurred at c. 6900 cal. a BP and Svartenutbreen was at modern size and extent in the periods c. 6400, c. 5450, c. 4850, c. 3850, c. 3550 and c. 1650 cal. a BP. Since 1650 cal. a BP, we infer that the glacier was larger than the 2002 CE glacier extent until 1910 CE when a GLOF occurred. Svartenutbreen has been retreating since 1910 CE, which led to the ice damming of the two historical GLOFs in the 1980s and 2002 CE separated by a glacier advance in the 1990s CE. The findings are discussed and compared to other regional glacier reconstructions in Norway, and emphasize the value of identifying and utilizing GLOFs as an indicator of past ELA variability. 相似文献
5.
Xiandong Liu Xiancai Lu Evert Jan Meijer for the Collab 《Geochimica et cosmochimica acta》2011,75(17):4978-4986
The acid chemistry of confined waters in smectite interlayers have been investigated with first principles molecular dynamics (FPMD) simulations. Aiming at a systematic picture, we establish the model systems to take account of the three possible controlling factors: layer charge densities (0 e, 0.5 e and 1.0 e per cell), layer charge locations (tetrahedral and octahedral) and interlayer counterions (Na+ and Mg2+). For all models, the interlayer structures are characterized in detail. Na+ and Mg2+ show significantly different hydration characteristics: Mg2+ forms a rigid octahedral hydration shell and resides around the midplane, whereas Na+ binds to a basal oxygen atom and forms a very flexible hydration shell, which consists of five waters on average and shows very fast water exchanges. The method of constraint is employed to enforce the water dissociation reactions and the thermodynamic integration approach is used to derive the free-energy values and the acidity constants. Based on the simulations, the following points have been gained. (1) The layer charge is found to be the direct origin of water acidity enhancement in smectites because the neutral pore almost does not have influences on water dissociations but all charged pores do. (2) With a moderate charge density of 0.5 e per cell, the interlayer water shows a pKa value around 11.5. While increasing layer charge density to 1.0 e, no obvious difference is found for the free water molecules. Since 1.0 e is at the upper limit of smectites’ layer charge, it is proposed that the calculated acidity of free water in octahedrally substituted Mg2+-smectite, 11.3, can be taken as the lower limit of acidities of free waters. (3) In octahedrally and tetrahedrally substituted models, the bound waters of Mg2+ show very low pKa values: 10.1 vs 10.4. This evidences that smectites can also promote the dissociations of the coordinated waters of metal cations. The comparison between the two Mg2+-smectites reveals that different layer charge locations do not lead to obvious differences for bound and free water acidities. 相似文献
6.
7.
8.
9.
10.