首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2608篇
  免费   430篇
  国内免费   654篇
测绘学   88篇
大气科学   55篇
地球物理   682篇
地质学   2274篇
海洋学   219篇
天文学   21篇
综合类   134篇
自然地理   219篇
  2024年   12篇
  2023年   40篇
  2022年   93篇
  2021年   91篇
  2020年   86篇
  2019年   136篇
  2018年   103篇
  2017年   95篇
  2016年   91篇
  2015年   102篇
  2014年   121篇
  2013年   164篇
  2012年   167篇
  2011年   150篇
  2010年   159篇
  2009年   202篇
  2008年   187篇
  2007年   174篇
  2006年   169篇
  2005年   159篇
  2004年   157篇
  2003年   143篇
  2002年   104篇
  2001年   100篇
  2000年   97篇
  1999年   101篇
  1998年   97篇
  1997年   74篇
  1996年   72篇
  1995年   52篇
  1994年   36篇
  1993年   40篇
  1992年   29篇
  1991年   14篇
  1990年   19篇
  1989年   9篇
  1988年   7篇
  1987年   13篇
  1986年   7篇
  1985年   7篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1981年   3篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1973年   1篇
  1954年   1篇
排序方式: 共有3692条查询结果,搜索用时 15 毫秒
31.
The Plattengneis shear zone is a 250–600 m thick, flat lying, Cretaceous, eclogite facies, mylonitic shear zone, with north-over-south transport direction, that is exposed over almost 1000 km2 in the Koralpe region along the eastern margin of the Alps. Although the shear zone is one of the largest in the Alps, its role in the Eoalpine metamorphic evolution and the subsequent exhumation of the region, remain enigmatic and its large-scale geometry is not well understood. The outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn- and antiforms with wavelengths of about 10 km. Eclogite bodies occur above, within and below the shear zone and there is no metamorphic grade change across the shear zone. In the south, the fold axes strike east–west and plunge shallowly to the east. In the north, the fold axes are oriented in north–south direction and form a dome shaped structure of the shear zone. Total shortening during this late stage warping event was of the order of 5%. Indirect evidence constrains this folding event to have occurred between 80 and 50 Ma and the fold geometry implies that the final exhumation in the Koralpe occurred somewhat later than further north. Interestingly, the shear zone appears to strike out of the topography in the south and dip into the topography in the north, so that north of the shear zone only hanging-wall rocks are exposed and south of it only foot-wall rocks. Possibilities for the geometric relationship of the Plattengneis shear zone with the surrounding south dipping detachments are discussed.  相似文献   
32.
Dire financial constraints and the threats of forced structural reform have had the unforeseen effect of forcing municipal councils across Australia to reconsider their operational activities and organisational arrangements. With considerable ingenuity, numerous municipalities have proposed and sometimes adopted new structural formations that embody various forms of co-operative service provision. This remarkable development has unfortunately been largely ignored in the scholarly literature on Australian local government. In a modest effort aimed at remedying this neglect, the present paper seeks to outline the small, rural New South Wales Gilgandra Shire Council's (2004) ‘Co-operative/Local Government Service Company’ model, place it in the broader context of alternative models of local governance suitable for Australian conditions, and evaluate its characteristics.  相似文献   
33.
尚洪田 《中国煤田地质》2006,18(4):25-26,52
分析了洪山预测区西部洪山岩体地质特征及其向外围扩散的范围和程度,研究了北掌勘查区和焦窑煤矿两邻区煤层受岩浆岩影响的程度,认为洪山岩体对预测区煤系及煤层赋存的影响较小,岩体外围仍有煤系赋存。为下一步找煤指明了方向。  相似文献   
34.
张钦文 《中国煤田地质》2006,18(5):14-16,37
通过对漳平市吾祠煤矿区的煤层地质构造特征分析,探讨了复杂构造条件下的矿井生产布局,主要是煤矿区段水平划分、煤炭采区的巷道布置、采煤方法及有关地质硐探等问题,对矿山开发有一定的指导意义。  相似文献   
35.
Midstream of the Keelung River Basin in Northern Taiwan has become highly urbanized and densely populated area. Flood inundation along riversides frequently occurred during typhoons or rainstorms. Three protection measures, including constructions of high-level protection levees, a diversion channel, and a detention reservoir, were proposed for flood mitigation. The main purpose of this study is to evaluate the flood mitigation performance of the three proposed structural measures by using combined hydrologic analyses and hydraulic routings. A semi-distributed parallel-type linear reservoirs rainfall-runoff model was used for estimating the surface runoff. Furthermore, a 1-D dynamic channel routing model was coupled with a two-dimensional inundation model to simulate the hydraulic characteristics of river flooding and overland flow. Simulation results of flood stages, runoff peak discharges, and inundation extent under design rainfall scenarios were chosen as the criteria for evaluation. The results showed a diversion channel is superior to the other two measures for flood mitigation of the study area. After the process of environmental impact assessment, a revised diversion channel approach has been approved for construction as the major structural measure.  相似文献   
36.
利用井田勘探和矿井生产的地质资料,对上京井阳的构造特征进行了总结,认为该井田以褶皱为主,尤以翻卷褶曲为特征,并且其复杂的构造格局是在经受了多次构造运动而形成的,其形成过程可概括为四个阶段:含煤盆地形成阶段;Ⅰ级褶皱和辗掩断层形成阶段;Ⅱ、Ⅲ级褶皱和一系列正断层形成阶段;构造体系的叠加、改造和定型阶段。  相似文献   
37.
DMC+4小卫星在国际灾害监测中的应用与评价   总被引:8,自引:0,他引:8  
李伯林  左烨 《遥感学报》2005,9(4):468-474
针对国际灾害监测星座应用技术和中国各种自然灾害的现状,着重研究了DMC(DisasterMonitoringConstellation)星座应用技术和DMC 4小卫星的数据特点,研究了利用小卫星星座对防灾、抗灾救灾的突出作用,研究了小卫星地面系统集成技术和星地一体化运营、管理和控制体系,以便进一步推动国内小卫星技术、遥感应用技术、卫星星座技术、天地一体化运管控技术和机制创新的发展。促进中国灾害监测星座的研制,最终实现对各种自然灾害的实时、动态监测。  相似文献   
38.
班公湖—怒江构造带西段三叠纪—侏罗纪构造—沉积演化   总被引:20,自引:2,他引:20  
王冠民  钟建华 《地质论评》2002,48(3):297-303
班公湖-怒江构造带西段在大地构造位置上处于特提斯构造域东端,横跨班公湖-怒江断裂带。三叠纪-株罗纪期间,其构造-沉积演化经历了大陆初始裂谷(T)、原洋裂谷(J1)、残余弧后盆地(J2-J3)阶段。初始裂谷阶段的拉张是呈南断北超的半地堑式由东向西进行的,逐渐形成地堑式原洋裂谷盆地。中晚侏罗世,南部新特提斯洋壳开始北各俯冲,产生的区域挤压应力使原洋裂谷逐渐封闭,裂谷盆地的小洋壳表现出以南向俯冲为主的双向式腑冲,同时伴生区域热沉降,盆地具残余弧后盆地的性质。该阶段,羌南地区发育碳酸盐岩为主的稳定陆缘沉积,冈度斯-念青唐古拉板片北部则形成广泛南超的近源碎屑沉积。  相似文献   
39.
This work presents a novel neural network‐based approach to detect structural damage. The proposed approach comprises two steps. The first step, system identification, involves using neural system identification networks (NSINs) to identify the undamaged and damaged states of a structural system. The partial derivatives of the outputs with respect to the inputs of the NSIN, which identifies the system in a certain undamaged or damaged state, have a negligible variation with different system errors. This loosely defined unique property enables these partial derivatives to quantitatively indicate system damage from the model parameters. The second step, structural damage detection, involves using the neural damage detection network (NDDN) to detect the location and extent of the structural damage. The input to the NDDN is taken as the aforementioned partial derivatives of NSIN, and the output of the NDDN identifies the damage level for each member in the structure. Moreover, SDOF and MDOF examples are presented to demonstrate the feasibility of using the proposed method for damage detection of linear structures. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
40.
Passive energy dissipation devices (EDDs), such as viscous dampers, viscoelastic dampers, etc., have been used to effectively reduce the dynamic response of civil infrastructures, such as buildings and bridges, subject to earthquakes and strong winds. The design of these passive energy dissipation devices (EDDs) involves the determination of the optimal locations and the corresponding capacities. In this paper, we present two optimal design methodologies for passive EDDs based on active control theories, including H and H2 performances, respectively. The optimal design methodologies presented are capable of determining the optimal locations and the corresponding capacities of EDDs. Emphasis is placed on the application of linear matrix inequality (LMI) for the effective design of passive EDDs using the popular MATLAB toolboxes. One important advantage of the proposed approaches is that the computation of the structural response is not needed in the design process. The proposed optimal design methodologies have been applied to: (i) a 10‐storey building and a 24‐storey building both subject to earthquake excitations, and (ii) a 76‐storey wind‐excited benchmark building, to demonstrate the advantages of the proposed design methodologies over the conventional equal capacity design. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号