全文获取类型
收费全文 | 8489篇 |
免费 | 1276篇 |
国内免费 | 2504篇 |
专业分类
测绘学 | 1337篇 |
大气科学 | 3089篇 |
地球物理 | 1668篇 |
地质学 | 3205篇 |
海洋学 | 1047篇 |
天文学 | 389篇 |
综合类 | 603篇 |
自然地理 | 931篇 |
出版年
2024年 | 44篇 |
2023年 | 157篇 |
2022年 | 232篇 |
2021年 | 309篇 |
2020年 | 308篇 |
2019年 | 418篇 |
2018年 | 291篇 |
2017年 | 389篇 |
2016年 | 395篇 |
2015年 | 461篇 |
2014年 | 535篇 |
2013年 | 621篇 |
2012年 | 544篇 |
2011年 | 537篇 |
2010年 | 481篇 |
2009年 | 609篇 |
2008年 | 657篇 |
2007年 | 688篇 |
2006年 | 688篇 |
2005年 | 533篇 |
2004年 | 529篇 |
2003年 | 435篇 |
2002年 | 362篇 |
2001年 | 307篇 |
2000年 | 310篇 |
1999年 | 248篇 |
1998年 | 206篇 |
1997年 | 199篇 |
1996年 | 134篇 |
1995年 | 130篇 |
1994年 | 118篇 |
1993年 | 99篇 |
1992年 | 66篇 |
1991年 | 48篇 |
1990年 | 42篇 |
1989年 | 27篇 |
1988年 | 30篇 |
1987年 | 14篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
2-D crustal velocity structure and vp/vs are obtained by processing and interpretation of S-wave data from Maqen-Jingbian deep seismic sounding(DSS)profile.The result shows that there exist obvious differences in 2-D S-wave velocity structure and vp/vs ratio structure along the profile.The S-wave velocities are low and vp/vs ration is high for the westem section of the profile and Haiyuan region,while they are normal for the middle and eastern sections.The changes in lithologic characters of two major anomalous zones are discussed according to lateral variation of S-wave velocity structure and vp/vs ratio structure.It is concluded that the development and occurrence of the Haiyuan strong earthquake is not only related to tectonic activities,but also to lithologic characters of the region. 相似文献
23.
通过分析、比较1996--2003年喀什地震台站记录到的新疆伽师及附近地区发生的多次6级地震的地磁前兆异常特征,发现在这几组地震活动过程中喀什地震台的地磁表现出不同的异常特征,说明与地震破裂特征有更深层次的相关性,且地磁响应比异常和总强度差值异常在一定程度上反映了台站周围小范围的震源区介质电性结构的变化。巴楚-伽师6.8级地震前地磁异常特征并不十分突出,有别于1996—1998年伽师强震群震前地磁异常量较丰富的特点。 相似文献
24.
Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the boundary between Sinian/Cambrian at Tianmenshan of Western Hunan, which may possibly demonstrate that an extraterrestrial impact event has ever occurred there on the S/C boundary. 相似文献
25.
26.
27.
Sequential aerial photography, sonar bathymetry, ground-penetrating radar (GPR), and sediment sampling and analysis provide the basis for calculating the volumetric and mass rate of progradation of the delta of Fitzsimmons Creek, a steep, high-energy, debris-flow-dominated channel draining about 100 km2 of the southern Coast Mountains of British Columbia. Fitzsimmons Creek is typical of small mountain rivers in the region. GPR imaging is used to define the pre-depositional morphology of the receiving basin, a technique that improves the accuracy of the volumetric survey. The 52-year record (1947–1999) of progradation yielded an average annual volumetric transport rate of 1.00±0.16×104 m3 year−1 for bed load, corresponding to a mass transport rate of 1.60±0.28×104 Mg year−1. Bed load yields are consistent with those obtained in hydrogeomorphically similar basins in the region and elsewhere. Decade-based annual rates, which vary from 0.64±0.11×104 to 2.85±0.38×104 Mg year−1, provide poor estimates of the 52-year average. Indeed, the 52-year record may also not be long enough to fully integrate the significant fluctuations in the sediment efflux from Fitzsimmons Creek. The methodology proposed in this paper can be transferred to other comparable mountain environments worldwide. 相似文献
28.
The role of moisture cycling in the weathering of a quartz chlorite schist in a tropical environment: findings of a laboratory simulation 总被引:1,自引:0,他引:1
Long‐term weathering of a quartz chlorite schist via wetting and drying was studied under a simulated tropical climate. Cubic rock samples (15 mm × 15 mm × 15 mm) were cut from larger rocks and subjected to time‐compressed climatic conditions simulating the tropical wet season climate at the Ranger Uranium Mine in the Northern Territory, Australia. Fragmentation, moisture content and moisture uptake rate were monitored over 5000 cycles of wetting and drying. To determine the impact of climatic variables, five climatic regimes were simulated, varying water application, temperature and drying. One of the climatic regimes reproduced observed temperature and moisture variability at the Ranger Uranium Mine, but over a compressed time scale. It is shown that wetting and drying is capable of weathering quartz chlorite schist with changes expected over a real time period of decades. While wetting and drying alone does produce changes to rock morphology, the incorporation of temperature variation further enhances weathering rates. Although little fragmentation occurred in experiments, significant changes to internal pore structure were observed, which could potentially enhance other weathering mechanisms. Moisture variability is shown to lead to higher weathering rates than are observed when samples are subjected only to leaching. Finally, experiments were conducted on two rock samples from the same source having only subtle differences in mineralogy. The samples exhibited quite different weathering rates leading to the conclusion that our knowledge of the role of rock type and composition in weathering is insufficient for the accurate determination of weathering rates. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
29.
A remarkable invariance in the ratio of 1,3-dimethylcarbazole (DMC) to 1,6-DMC was discovered in crude oils from the Pearl River Mouth Basin, South China Sea. The remarkably invariant ratio is kept at a constant of about unity regardless of their concentrations, sources or maturities for the sampies. In combination with the molecular structures of 1,3- and 1,6-DMCs, the invariance might indicate that the nitrogen compounds share a common precursor with a skeleton of 1-methylcarbazole and are formed through methylation at C3 and C6 with an essentially identical rate. 相似文献
30.
Roger Guérin 《Hydrogeology Journal》2005,13(1):251-254