全文获取类型
收费全文 | 8886篇 |
免费 | 1746篇 |
国内免费 | 3134篇 |
专业分类
测绘学 | 783篇 |
大气科学 | 1264篇 |
地球物理 | 2039篇 |
地质学 | 7479篇 |
海洋学 | 540篇 |
天文学 | 516篇 |
综合类 | 379篇 |
自然地理 | 766篇 |
出版年
2024年 | 76篇 |
2023年 | 202篇 |
2022年 | 289篇 |
2021年 | 415篇 |
2020年 | 387篇 |
2019年 | 463篇 |
2018年 | 367篇 |
2017年 | 390篇 |
2016年 | 442篇 |
2015年 | 455篇 |
2014年 | 628篇 |
2013年 | 619篇 |
2012年 | 710篇 |
2011年 | 670篇 |
2010年 | 637篇 |
2009年 | 624篇 |
2008年 | 576篇 |
2007年 | 679篇 |
2006年 | 637篇 |
2005年 | 492篇 |
2004年 | 473篇 |
2003年 | 432篇 |
2002年 | 378篇 |
2001年 | 344篇 |
2000年 | 338篇 |
1999年 | 300篇 |
1998年 | 259篇 |
1997年 | 268篇 |
1996年 | 235篇 |
1995年 | 204篇 |
1994年 | 163篇 |
1993年 | 147篇 |
1992年 | 110篇 |
1991年 | 83篇 |
1990年 | 81篇 |
1989年 | 59篇 |
1988年 | 48篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
During the Early-Middle Proterozoic era, three major lithostratigraphic unit associations, namely Hekou-Dahongshan, Dongchuan, and Kunyang-Huili Groups, were established for the metamorphosed volcanic-sedimentary rocks exposed in the southwestern Yangtze Block (SWYB). The integration of petrology, geochemistry and geochronology constrains tectonic framework and evolution of the SWYB, in which four sets of SHRIMP U-Pb zircon ages were obtained from the volcanic rocks interbedded within the Middle Proterozoic successions: 1800–1600 Ma, 1600–1300 Ma, 1300–1100 Ma, and 1100–1000 Ma. Major and trace elemental analysis indicate that four key tectonic evolutionary stages, each coinciding with the above radiometric age set, of the SWYB during the Early-Middle Mesoproterozoic. The SWYB was characterized by an east-westerly trending rift in the Hekou, Dongshan, and Dongchuan areas, and separate basin-forming events during 1800–1600 Ma and 1600–1300 Ma, respectively. In the SWYB, an intracontinental rift basin and a rift basin occurred in the Caiziyuan-Matang and Laowushan areas, respectively in 1300–1100 Ma ago. During 1100–1000 Ma, the SWYB was characterized by the closure of the Caiziyuan-Matang rift-ocean basin, collision between the Huili Blocks and Kunyang Blocks, and presence of volcanic arcs in the Tianbaoshan and Fulingpen areas. Accordingly, the SWYB represents a new basin that records the relatively complete assembly process of the Rodina during the Early-Middle Mesoproterozoic era. 相似文献
112.
113.
114.
115.
116.
117.
118.
珠江口伶仃洋锋的类别及其对沉积的影响 总被引:1,自引:0,他引:1
根据近年在珠江口伶仃洋的观测资料,对比国外有关河口锋的定义,归纳了伶仃洋内几种锋的现象,计有潮侵锋、岬角锋及湖水退急时的浅滩锋等。解释了锋生的原因与潮汐进退,特别与随潮入侵的咸水关系。文中也探讨了这些锋对沉积环境的影响,认为它是陆架水入侵河口地区的一种不容忽视的沉积动力过程。 相似文献
119.
Prediction of threshold conditions and incipient motion is the essential issue for the study of sediment transport. This work compares existing empirical threshold curves proposed for Shields diagram, a method based on the concept of probability of sediment movement, and an empirical method based on movability number. These methods are used to predict the incipient motion conditions for experimental runs taken from various studies. Most of the experimental data, used in this work, have not been used before in derivation of alternative formulations for Shields diagram and other methods. The empirical threshold curves based on the Shields entrainment function was the least successful at predicting the measured incipient motion conditions, while the use of the movability number gives good predictions of critical shear velocity compared with experimental data. 相似文献
120.
SONG Zhiyao XUE Hongchao YAN Yixin
Doctor Senior Engineer College of Harbor Waterway Coastal Engineering Hohai University 《中国海洋工程》1999,(4)
To deal with the problems concerning the shore boundary,moving boundary and engineeringboundary which are encountered frequently in 2D tidal current simulation by the finite difference method,theconcept of line boundary is introduced and studied here,and then the line boundary technique in common useis proposed in this paper.Analysis of some calculation cases shows that this technique is practical,effective,and simple in 2D tidal current simulation involving different boundaries. 相似文献