全文获取类型
收费全文 | 1609篇 |
免费 | 496篇 |
国内免费 | 112篇 |
学科分类
地球科学 | 2217篇 |
出版年
2025年 | 15篇 |
2024年 | 32篇 |
2023年 | 45篇 |
2022年 | 72篇 |
2021年 | 73篇 |
2020年 | 67篇 |
2019年 | 89篇 |
2018年 | 82篇 |
2017年 | 72篇 |
2016年 | 80篇 |
2015年 | 71篇 |
2014年 | 76篇 |
2013年 | 68篇 |
2012年 | 71篇 |
2011年 | 100篇 |
2010年 | 87篇 |
2009年 | 90篇 |
2008年 | 71篇 |
2007年 | 73篇 |
2006年 | 71篇 |
2005年 | 51篇 |
2004年 | 45篇 |
2003年 | 33篇 |
2002年 | 41篇 |
2001年 | 43篇 |
2000年 | 59篇 |
1999年 | 86篇 |
1998年 | 63篇 |
1997年 | 64篇 |
1996年 | 50篇 |
1995年 | 56篇 |
1994年 | 46篇 |
1993年 | 47篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 22篇 |
1989年 | 10篇 |
1988年 | 17篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1965年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有2217条查询结果,搜索用时 22 毫秒
991.
Traditional magneto-electric vibration sensors and servo accelerometers have severe shortcomings when used to measure vibration where low frequency components predominate. A low frequency characteristic extension for velocity vibration sensors is presented in this paper. The passive circuit technology, active compensation technology and the closedcycle pole compensation technology are used to extend the measurable range and to improve low frequency characteristics of sensors. Thses three types of low frequency velocity vibration sensors have been developed and widely adopted in China. 相似文献
992.
Hou Jianjun Bai Taixu Liang Haihua Zheng Wentao and Wang ShiminDepartment of Geology Peking University Beijing China 《中国地震研究(英文版)》1995,(3)
Based on field observations and mechanic analysis,the authors think that synthetic faults,antithetic faults,and hangingwall cross-faults are formed on the piedmont alluvial-pluvial plain under the action of hangingwall blocks sliding downward and rotating along concave fault planes of the listric normal fault on the southeastern margin of Weihe Basin.The characteristics of different movements and expressions on the surface of these structures may be taken as the main marks for listric normal fault segmentation. 相似文献
993.
ABSTRACTMiniature submersible linear variable differential transformer (LVDT) is commonly used for small strain stiffness measurement. However, it has not been widely used on cement-treated clays. This paper proposes a method of installing and setting up submersible LVDT to minimize testing problems and errors for cement-treated clays. In soft clay testing, the LVDT mount can be anchored to the specimen by pressed-in anchor pins or rods. However, this cannot be done on cement-treated clay due to the latter’s hardness. Preliminary trials also indicate that direct attachment of the LVDT mounts to the membrane without anchor pins is not feasible owing to the tendency of the LVDT to tilt and detach from the specimen. The system adopted involves pre-casting holes for the insertion of anchor pins during placement of the admixture into the moulds. The diameter of the anchors pins was found to have significant effect on the results; smaller diameter pins give more consistent results with those of resonant column and bender element tests. This can be attributed to the effect of stress concentration around the anchor pins. The results showed that, used appropriately, submersible LVDTs can give small strain measurements which have a high degree of inner consistency with results from resonant column and bender element tests. 相似文献
994.
Huaiwei Feng;Shumei Xu;Hou Xubo;Cui Hongzhuang;Jinduo Wang; 《Geological Journal》2024,59(5):1488-1502
The Dunhuang Basin, situated in western China along the Altyn Tagh Fault (ATF) zone, intersects the Tethys and Paleo-Asian Ocean tectonic domains. Influenced by both the ATF system and the far-field effects of the Qiangtang-Lhasa-Eurasia collision during the Mesozoic, the mechanism of the Jurassic sedimentary migration of the basin in response to tectonic movements is unclear so far. The paper uses a comprehensive approach, including field geological surveys, lithologic and lithofacies discern, stratigraphic relationships analysis and 2D seismic profile interpretation, to examine the distribution of Jurassic residual strata in the basin. The comprehensive results of our study suggest that the Dunhuang Basin exists as an isolated block with unique tectonic and sedimentary evolution characteristics. In the Early Jurassic, the Dunhuang Basin underwent initial rifting, leading to the formation of small segmented intermontane sags. This phase was marked by the coarse particle sedimentary system of alluvial fans and braided rivers, represented the near source rapid deposition in the initial formation period of the basin. Stratigraphic distribution was primarily influenced by pre-Jurassic basement topography and was not significantly constrained by faulting during this period. The formation of these isolated discontinuous small intermontane sags indicates the segmented activities of the ATF in the Early Jurassic period. In the Middle Jurassic period, influenced by the ATF dextral strike-slip faulting, sedimentation extended eastward and the depocenter migrated clockwise compared with the distribution of the Middle Jurassic strata within the Dunhuang Basin. This period witnessed the development of coal measure strata at the basin's margins and lacustrine fine-grained clastic deposition in the centre. The segmented fracture of the ATF gradually initiated a unified dextral strike-slip tectonic movement. In the Late Jurassic period, sedimentary strata were locally present in the Wanyao Sag but absent in other sags. The depocenter migrated counterclockwise compared with the distribution of Middle Jurassic strata within the Dunhuang Basin, due to regional uplift accompanied by the ATF sinistral strike-slip faulting caused by the collision between the Lhasa Block and the Eurasia Plate. The depocenter migration of the Dunhuang Basin constrained within the ATF system from the Early to Middle and Late Jurassic can be attributed to the transition of the ATF strike-slip faulting in context of the stress relaxation and compression between the collision of the Qiangtang and Lhasa blocks to the Eurasia Plate, respectively. 相似文献
995.
海水中铜离子对氨基酸—粘土体系液—固界面作用的影响 总被引:2,自引:0,他引:2
用E(%)-pH曲线法实验研究了海水中三元表面络合物的形成和构型。通过海水中金属铜离子对氨基酸—粘土界面作用的E(%)-pH曲线影响的研究,发现曲线具有“单向上移”的规律,表明甘氨酸、天冬氨酸—铜离子—高岭土三元体系在实验条件下主要形成(Ⅰ)型三元表面络合物即≡S—O—M—L。该系列论文另一部分已研究氨基酸对金属离子—粘土体系的影响,证明可形成(Ⅱ)型三元表面络合物即≡S—O—L—M。据此可以推测(Ⅰ)型和(Ⅱ)型在某一条件下可以转变构型,其中间构型可能即是Leckie等提出的环形三元表面络合物。 相似文献
996.
1 INTRODUCTION The unicellular Dunaliella salina, is one of the well studied microalgae for mass culture and is of commercial importance as a source of natural beta-carotene (Avron and Ben-Amot, 1992). D. sa- lina has desirable properties of halotolerance… 相似文献
997.
数据的组织是建立三维可视化模型的关键,数据组织的好坏对整个可视化系统的性能有着直接的影响,而组织数据的核心问题又是几何模型的表达。介绍了三维模型数据组织方法,应用该方法在Delphi 环境下结合OpenGL 成功开发了三维边坡信息系统,从而验证了该数据组织方法的正确性和可行性。 相似文献
998.
低温冷害是我区东部主要的农业灾害之一,本文统计分析了四十年来VEI≥4级强大山喷发指数与我区东部夏季(6—8月)低温的关系,发现了强火山喷发与本区夏季低温有较好的遥相关系。分析结果表明,强火山爆发后当年或次年引起气温下降。平均下降幅度4.0—7.0℃,致使农业减产,减产率一般为20—25%。 相似文献
999.
1000.
Seismic imaging quality is critical to describing reservoirs. There are many methods that can improve imaging quality; some rely on advanced processing means, whereas others rely on changing the field acquisition methods. However, most of the acquisition methods focus on improving imaging by using infill shots without considering the target-layer illumination energy. Moreover, total infill shooting greatly increases the acquisition cost. In this paper, we present a new method for maximizing the contribution to the target shadow area illumination by automatic local infill shooting. Thus, we designed 2D and 3D models and obtained the depth migration section by forward modeling, infill shots, depth migration, etc. The model results also show that by choosing the most appropriate number of shot points, we can enhance the shadow area energy and improve the target-layer imaging quality at low cost. 相似文献