全文获取类型
收费全文 | 4391篇 |
免费 | 877篇 |
国内免费 | 1151篇 |
专业分类
测绘学 | 348篇 |
大气科学 | 704篇 |
地球物理 | 1228篇 |
地质学 | 2489篇 |
海洋学 | 625篇 |
天文学 | 99篇 |
综合类 | 474篇 |
自然地理 | 452篇 |
出版年
2024年 | 16篇 |
2023年 | 81篇 |
2022年 | 203篇 |
2021年 | 240篇 |
2020年 | 231篇 |
2019年 | 269篇 |
2018年 | 280篇 |
2017年 | 247篇 |
2016年 | 247篇 |
2015年 | 251篇 |
2014年 | 276篇 |
2013年 | 268篇 |
2012年 | 239篇 |
2011年 | 249篇 |
2010年 | 281篇 |
2009年 | 305篇 |
2008年 | 257篇 |
2007年 | 248篇 |
2006年 | 181篇 |
2005年 | 171篇 |
2004年 | 137篇 |
2003年 | 141篇 |
2002年 | 162篇 |
2001年 | 135篇 |
2000年 | 132篇 |
1999年 | 170篇 |
1998年 | 134篇 |
1997年 | 133篇 |
1996年 | 99篇 |
1995年 | 94篇 |
1994年 | 88篇 |
1993年 | 91篇 |
1992年 | 80篇 |
1991年 | 57篇 |
1990年 | 51篇 |
1989年 | 39篇 |
1988年 | 30篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1958年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有6419条查询结果,搜索用时 390 毫秒
991.
八道壕含煤盆地位于辽西的黑山一彰武地区,与阜新一义县盆地相邻,是阜新外围的一个重要含煤盆地。本文从生物地层和沉积学角度说明八道壕矿区的煤层属于早白垩世,可与阜新盆地的沙海组对比,在此基础上对八道壕矿区的地层层序及煤炭资源赋存的规律进行了研究,认为八道壕盆地的煤层可分为上下两个煤层组,下煤组形成于水下扇边缘.上煤组形成于扇三角洲覆水合适的地区。早期冲积扇自盆地西南注入湖盆,煤层发育在盆地北部,自西侧盆缘断裂前向东超覆,向南碎屑岩增多,煤层变薄尖灭。 相似文献
992.
Rongke Xu Xiongfei Cai Yulian Zhang Liang Shan Yaoyu Chen Jianhong Qi Gang Wang 《Frontiers of Earth Science》2009,3(4):402-410
Three fluvial terraces in Porougong River in the middle reach of Shiquan River were identified, and the palynological records
were investigated to decipher the paleoenvironmental changes in the west inland of the Tibetan Plateau. Three phases of uplift
in the west inland of the Tibetan Plateau are suggested to be associated with the third, second, and first fluvial terraces
(T3, T2, and T1) being formed at ca.126-25.1 ka B.P., 25.1-4.5 ka B.P., and 4.5-1.3 ka B.P., respectively. The differentiated uplift rate
infers that the inland Tibetan Plateau shows an earlier uplift than the surroundings. Coincident with the phased uplift, three
episodes of the changes in paleovegetation and paleoclimate since late Middle Pleistocene could be identified by the spore-pollen
records, including the forests under the warm-wet climate featured by the assemblage of Picea + Pinus-Betula-Ulmus-Chenopodiaceae-Epheara in the third terrace, the forest-grassy vegetation under the semi-arid and semi-wet climate as shown by the Picea + Pinus-Chenopodiaceae-Epheara assemblage in the second terrace, and the grassland under the cold-dry climate indicated by the Chenopodiaceae-Artemisia-Ephedra assemblage in the first terrace. The association of the paleovegetation and paleoclimate changes with the phased uplift of
the fluvial terraces has revealed the important impact of the Plateau uplift. 相似文献
993.
Dan Zhang Hui Liu Ying Liang Cheng Wang Hecheng Liang Hesheng Cai 《Frontiers of Earth Science》2009,3(1):73-79
Samples of groundwater were collected from 17 sites in the Jianghan plain in July 2007. Sixteen phthalate esters (PAEs) were
detected in samples collected by using solid-phase extraction (SPE)-gas chromatography (GC). The results show that there were
one or several PAEs in all the samples, and the concentrations of total PAEs ranged from 80.12 to 1882.18 ng/L. Four PAEs,
i.e. di-isobutyl phthalate (DIBP), di-n-butyl phthalate (DBP), bis (2-ethoxyethyl) phthalate (BEEP) and di (2-ethylhexyl)
phthalate DEHP) were the dominant species. Among these, DIBP, DBP and DEHP concentrations were closely related to the water
supply from the Yangtze River, Hanjiang River and Honghu Lake. However, the distribution of BEEP was irregular, which may
be due to the application of some kind of products containing BEEP in the related areas. PAE distribution was irrelevant to
the electrical conductivity and sample depth. 相似文献
994.
Comparison of linear and nonlinear shallow wave water equations applied to tsunami waves over the China Sea 总被引:4,自引:0,他引:4
Yingchun Liu Yaolin Shi David A. Yuen Erik O. D. Sevre Xiaoru Yuan Hui Lin Xing 《Acta Geotechnica》2009,4(2):129-137
This paper discusses the applications of linear and nonlinear shallow water wave equations in practical tsunami simulations.
We verify which hydrodynamic theory would be most appropriate for different ocean depths. The linear and nonlinear shallow
water wave equations in describing tsunami wave propagation are compared for the China Sea. There is a critical zone between
400 and 500 m depth for employing linear and nonlinear models. Furthermore, the bottom frictional term exerts a noticeable
influence on the propagation of the nonlinear waves in shallow water. We also apply different models based on these characteristics
for forecasting potential seismogenic tsunamis along the Chinese coast. Our results indicate that tsunami waves can be modeled
with linear theory with enough accuracy in South China Sea, but the nonlinear terms should not be neglected in the eastern
China Sea region. 相似文献
995.
Finite element modelling of non-linear deformation of rate-dependent materials using a R-minimum strategy 总被引:1,自引:0,他引:1
A R-minimum strategy, which was proposed and successfully applied to analyse the non-linear rate-independent finite deformation
(including the thermal–mechanical coupling and frictional contact) of elasto-plastic materials, is extended and applied here
to simulate the deformation of rate-dependent materials. It involves no iterations, thus belongs to the static-explicit algorithm
and avoids the convergence problem resulting from nonlinearities. The R-minimum strategy-based adaptive control scheme of
the time step size is proposed and applied to the related analysis of the rate-dependent materials with both the time-dependent
and the time-independent viscosity. Both the simple benchmark test and the practical application in evaluation of the effect
of the Earth materials on its response to the centrifugal force are carried out to demonstrate the stability, efficiency and
usefulness of this algorithm. 相似文献
996.
997.
中国东北地区地震空间分布与主要断裂带、深部构造及应力场关系 总被引:5,自引:1,他引:4
中国东北地区在北东东向应力场控制下, 地震有其特殊性。地震空间分布和深度统计结果表明, 东北地区地震主要受岩石圈断裂(开原-赤峰断裂带) 控制, 以44°N为界, 南北具有明显差异。北部地震发生的数量少于南部, 震源深度主要集中在4~6 km和8~12 km两个深度范围内; 而南部主要集中在8~12 km和28~30 km两个深度范围内。发震深度分析显示, 开原-赤峰、郯庐断裂带、大兴安岭断裂带下可能存在地温较低的区域, 使地震可以在深部孕育。地震分布的Vp和Vs剖面资料的研究暗示, 断裂与速度变化带、断裂与断裂的相交区域是地震易发生区域。 相似文献
998.
文中对地震体波走时层析成像技术近30年的发展进行回顾和评述,并对该方法所存在的问题进行了分析和探讨以及给出应对策略。在壳幔速度结构的横向不均匀性、强震发生的深部构造环境、活火山区的深部结构和起源,以及造山带、板块碰撞带区域深部结构等4个方面对应用地震层析成像技术所取得的主要成果做了分类总结和探讨。研究证明,利用地震层析成像技术所获得的高分辨率地球内部结构为探索岩石圈的演化和板块运动规律及地震、火山活动发生的深部构造环境等提供了十分重要的科学依据。 相似文献
999.
1000.
赛里木地块北缘古元古界变质杂岩地质特征及构造意义 总被引:2,自引:0,他引:2
六十年代前,前人对新疆赛里木地块北缘地区构造单元划分侧重对地层、矿产等方面的考察及研究,地质构造涉及较少:六十年代后,随着对本区地质构造研究不断深入,大都以槽台学观点划分,并有较大区别.本次工作在研究前人成果基础上,运用板块学观点,以构造事件时空演化为主线,在区内初步划分出变质核部杂岩.该变质核部杂岩位于伊犁-伊赛克湖微板块的赛里木地块中,由古元古界温泉岩群及博河片麻岩套组成,受挤压作用推覆于长城系特克斯岩群上,其推覆方向由北向南,古生界汗吉尕组、托斯库尔他乌组及阿克沙克组、科古琴山组以盖层叠覆于古元古界上.温泉岩群原岩为亚杂砂岩、杂砂岩,该套地层Sm-Nd模式年龄为2 081~1 884 Ma;博河片麻岩套原岩为一套中酸性侵入岩(花岗岩、英云闪长岩、花岗闪长岩、奥长花岗岩),Sm-Nd模式年龄为2 10~1 086 Ma.长城系特克斯岩群与古元古界温泉岩群为逆冲推覆韧性断层接触,为一套浅海相碎屑岩、碳酸盐岩. 相似文献