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   1344篇
  免费   282篇
  国内免费   342篇
测绘学   104篇
大气科学   325篇
地球物理   458篇
地质学   621篇
海洋学   149篇
天文学   44篇
综合类   118篇
自然地理   149篇
  2024年   5篇
  2023年   21篇
  2022年   49篇
  2021年   86篇
  2020年   59篇
  2019年   70篇
  2018年   88篇
  2017年   81篇
  2016年   67篇
  2015年   97篇
  2014年   91篇
  2013年   98篇
  2012年   87篇
  2011年   97篇
  2010年   78篇
  2009年   71篇
  2008年   77篇
  2007年   58篇
  2006年   51篇
  2005年   41篇
  2004年   50篇
  2003年   42篇
  2002年   62篇
  2001年   59篇
  2000年   51篇
  1999年   51篇
  1998年   40篇
  1997年   31篇
  1996年   29篇
  1995年   15篇
  1994年   35篇
  1993年   28篇
  1992年   21篇
  1991年   13篇
  1990年   14篇
  1989年   9篇
  1988年   9篇
  1987年   8篇
  1986年   2篇
  1985年   3篇
  1984年   6篇
  1983年   1篇
  1982年   7篇
  1981年   1篇
  1980年   4篇
  1977年   1篇
  1974年   1篇
  1964年   1篇
  1958年   1篇
  1949年   1篇
排序方式: 共有1968条查询结果,搜索用时 62 毫秒
951.
The Qaidam Basin,located in the northern margin of the Qinghai-Tibet Plateau,is a large Mesozoic-Cenozoic basin,and bears huge thick Cenozoic strata.The geologic events of the Indian-Eurasian plate-plate collision since~55 Ma have been well recorded.Based on the latest progress in high-resolution stratigraphy,a technique of balanced section was applied to six pieces of northeast-southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deform...  相似文献   
952.
The Hohxil region in the northern Qinghai-Tibet Plateau is occupied by numerous plateau lakes,which have long been inferred as being tectonic products.However,so far little evidence has been found to support this tentative inference.Field survey and morphotectonic analysis of TM satellite images in the eastern segment of the Hohxil region revealed that Kusai Lake and Yelusu Lake are S- shaped pull-apart basins,which were dominated by left strike-slip master faults trending WNW-ESE. The pull-apart distanc...  相似文献   
953.
The Qaidam Basin, located in the northern margin of the Qinghai–Tibet Plateau, is a large Mesozoic–Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian-Eurasian plate–plate collision since ~55 Ma have been well recorded. Based on the latest progress in high-resolution stratigraphy, a technique of balanced section was applied to six pieces of northeast–southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deformation history during the Cenozoic collision. The results show that the Qaidam Basin began to shorten deformation nearly synchronous to the early collision, manifesting as a weak compression, the deformation increased significantly during the Middle and Late Eocene, and then weakened slightly and began to accelerate rapidly since the Late Miocene, especially since the Quaternary, reflecting this powerful compressional deformation and rapid uplift of the northern Tibetan Plateau around the Qaidam Basin.  相似文献   
954.
2008年5月12日四川省汶川发生MS 8.0级地震,造成龙门山断裂带映秀-北川断裂长达240km和灌县-江油断裂72km的地表破裂。同时在龙门山山前的成都平原内出现了地表弯曲变形、地裂缝、河流跌水以及具有条带状分布的喷砂冒水点和建筑物破坏加剧的现象。为此,对这一地区进行了进一步的调查工作。调查采取以寻访形式为主,结合使用高精度3D扫描仪进行地形测量和探槽开挖。通过调查,发现平原区的隐伏断裂在汶川MS8.0地震中发生了错动,断层破裂面在地表未见有出露,而是在近地表形成弯曲变形。什邡市师古镇和隐丰镇之间存在两条地震灾害异常带,北北东向灾害异常带长约7km; 北北西向灾害异常带长约5km。通过探槽开挖和地形测量得到的汶川MS8.0级地震在平原区形成的垂直位移为20cm。  相似文献   
955.
湖北宜昌地区寒武系水井沱组探获页岩气   总被引:4,自引:1,他引:3       下载免费PDF全文
<正>1研究目的(Objective)中扬子中部黄陵隆起东南缘宜昌斜坡带在太古宙结晶基底之上,发育有元古宙至第四纪各时代地层,保存有埃迪卡拉系陡山沱组、寒武系水井沱组,奥陶系五峰组—志留系龙马溪组等多套黑色富有机质泥岩。区域构造稳定,地层产状平缓,页岩气地质条件优越,但页岩气的勘探一直未获突破。本文的目的旨在查明宜昌斜坡带寒武系水井沱组页岩的分布和含气性,确定页岩气储层特点,为区域页岩气的勘探开发提供基础资料。  相似文献   
956.
抗滑桩与桥梁桩和普通侧向受荷桩结构设计的区别在于,抗滑桩容许"大位移"和"超配筋"。荷载结构计算法采用10mm为位移容许值,导致抗滑桩工程设计中不能充分发挥"大位移"的抗滑性能。本文结合钢筋混凝土受弯构件力学原理,引入抗滑桩裂缝控制准则,在荷载结构计算法的基础上,用裂纹控制准则替代桩顶水平位移容许值进行抗滑桩设计验算,可最大限度地挖掘抗滑桩的抗滑潜力;推导基于K法的抗滑桩设计验算方法的计算公式,阐述裂纹控制荷载结构法的原理、计算和设计流程;以十堰天水国家高速公路K593+850-K594+070滑坡治理工程为案列,分析了抗滑桩桩顶的水平位移组成和影响因素,并比较了传统设计法与本文阐述方法的优缺点。结果表明:桩顶水平位移主要由锚固段岩土体变形引起,位移由岩土体刚度决定,与桩体设计参数无关,优化桩体设计参数仅能限制由桩身弹塑性变形引起的桩顶水平位移。  相似文献   
957.
对印支地块思茅地区始新世陆相红层进行古地磁研究,获得勐伴剖面特征剩磁方向为Ds=118.2°,Is=22.1°,k=31.6,α95=10.9°;勐腊剖面特征剩磁方向为Ds=47.6°,Is=22.8°,k=20.2,α95=5.9°。其特征剩磁方向与前人研究结果基本一致。利用Hodych等的磁倾角校正方法得到校正磁倾角为28.4°±4.3°,对前人的数据重新进行E/I统计得到的校正磁倾角值为30.7°,置信区间为[25.4°,35.9°],两种不同方法得到了较一致的结果,思茅地区的古近纪磁倾角显示了一定程度的偏低。E/I磁倾角偏低检验方法在应用时存在一定的局限性,变形微弱地层的古地磁学数据适合进行E/I磁倾角偏低校正,以避免倾伏褶皱或差异性旋转变形作用对E/I磁倾角偏低校正的影响。Hodych等提出的磁倾角校正方法是现今比较可靠的磁倾角校正方法。结合前人印支地块的古地磁研究成果,本次研究结果表明印支地块思茅地区自始新世以来相对于华南板块向南滑移量约500km。  相似文献   
958.
Growing demand for point-of-use water treatment including greywater recycling as well as appropriate disinfection without formation of harmful disinfection byproducts (DBPs) calls for new methods of efficient microbial control. In recent years, antimicrobial nanomaterials (NMs) have been widely studied as a potential alternative to traditional chlorine disinfection, yet concerns over their releases to environments and subsequent impacts have limited their use on a large scale. In this work, recycled concrete aggregate (RCA) was proposed as a sustainable and environmentally friendly disinfecting substrate for water disinfection by coating with a composite of silica-quaternary ammonium compound (Fixed-Quat). Two different types (gel and particle) of Fixed-Quat were applied to RCA, and their adherence and antimicrobial activities were compared each other. When using E. Coli as a model bacterial pathogen, the Fixed-Quat gel and particle coated RCA materials showed similar and effective microbial inactivation performance with a rate of 2.0 × 10?3 (gel) and 1.82 × 10?3 (particle) log reduction cm?2 min?1. By potentially eliminating regulated DBPs formation and minimizing release of NMs into the environment, the antimicrobial coated RCA would be a promising and sustainable alternative to conventional disinfection methods in engineered aquatic systems.  相似文献   
959.
The decomposition of plant litter is a key process in the flows of energy and nutrients in ecosystems. However, the response of litter decomposition to global climate warming in plateau wetlands remains largely unknown. In this study, we conducted a one-year litter decomposition experiment along an elevation gradient from 1891 m to 3260 m on the Yunnan Plateau of Southwest China, using different litter types to determine the influences of climate change, litter quality and microenvironment on the decomposition rate. The results showed that the average decomposition rate(K) increased from 0.608 to 1.152, and the temperature sensitivity of litter mass losses was approximately 4.98%/℃ along the declining elevation gradient. Based on a correlation analysis, N concentrations and C︰N ratios in the litter were the best predictors of the decomposition rate, with significantly positive and negative correlations, respectively. Additionally, the cumulative effects of decomposition were clearly observed in the mixtures of Scirpus tabernaemontani and Zizania caduciflora. Moreover, the litter decomposition rate in the water was higher than that in the sediment, especially in high-elevation areas where the microenvironment was significantly affected by temperature. These results suggest that future climate warming will have significant impacts on plateau wetlands, which have important functions in biogeochemical cycling in cold highland ecosystems.  相似文献   
960.
The research on typhoon wave spectrum in northwestern South China Sea   总被引:1,自引:0,他引:1  
Based upon the one-year wind wave measurement data, collected from the South China Sea (SCS) at coordinates 20° 36.298′N, 110°45.433′E. by Acoustic Wave And Current (AWAC), we analyzed the wave characteristics and concluded that the most common wave direction was E and the second most common direction was ENE, the mean and the maximum values of significant height was 1.2 m and 4.36 m, respectively. The mean period was 4.0 s. We also evaluated the wave spectrums under conditions existing in three typhoons: Rumbi, Jeti and Utor. We found that unimodal spectrums occurred more often than others, and the maximum spectrum peak was 30.7911 m2 s. The minimum peak frequency was 0.0625 Hz, and the mean peak frequency was 0.126 Hz. The wave period is important for the design of marine structures, especially the position of peak frequency had a great influence on the stress calculation. Spectral analysis showed that the values of peak frequency distributed between 0.063 Hz and 0.217 Hz, with the mean value 0.114 Hz. We fit the normalized spectrum with 6 theoretical spectral models, out of which, the Wen spectrum, JONSWAP spectrum and Wallops spectrum were proved to give the best fit. What distinguished the Wen Spectrum from the rest was that it does not rely on the measured spectrum for parameter estimation. Hence, we recommend that the Wen spectrum should be widely used in marine construction.  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