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   1530篇
  免费   265篇
  国内免费   357篇
测绘学   267篇
大气科学   143篇
地球物理   306篇
地质学   827篇
海洋学   223篇
天文学   44篇
综合类   158篇
自然地理   184篇
  2024年   8篇
  2023年   30篇
  2022年   45篇
  2021年   74篇
  2020年   82篇
  2019年   78篇
  2018年   61篇
  2017年   81篇
  2016年   83篇
  2015年   72篇
  2014年   103篇
  2013年   114篇
  2012年   97篇
  2011年   101篇
  2010年   91篇
  2009年   96篇
  2008年   97篇
  2007年   108篇
  2006年   121篇
  2005年   84篇
  2004年   76篇
  2003年   74篇
  2002年   59篇
  2001年   51篇
  2000年   42篇
  1999年   35篇
  1998年   29篇
  1997年   45篇
  1996年   21篇
  1995年   15篇
  1994年   12篇
  1993年   20篇
  1992年   14篇
  1991年   9篇
  1990年   8篇
  1989年   6篇
  1988年   6篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1978年   1篇
排序方式: 共有2152条查询结果,搜索用时 15 毫秒
71.
王烨 《岩矿测试》2011,30(3):281-284
应用6σ质量管理方法评价X射线荧光光谱法测定多目标地球化学样品分析中4个日常监控土壤标准物质中Cl、S、总碳、N、Na2O、MgO、Al2O3、SiO2、P、K2O、CaO、Ba、Ti、V、Cr、Mn、TFe2O3、Zn、Ga、Br、Pb、Th、Rb、Sr、Y、Zr、Nb等27个项目检测质量水平。研究结果显示,随着高精度、自动化仪器的应用,多目标样品分析多个项目的精密度、准确度都得到大幅度的提高,部分检测项目的性能已经达到6σ质量水平;但有少数项目如N、总碳、Cr 等低于3σ质量水平,其精密度准确度均需改进,分析性能有待进一步提高,建议更换检测方法。用6σ质量管理方法评价地质实验分析测试质量水平与地质实验室传统质量控制方法得出的结果具有一致性,其评价方法简便、量化、直观、具有一定的应用价值。  相似文献   
72.
Geochemical and isotopic analyses of the Cretaceous–Paleogene (K/Pg) boundary deposits were conducted at the Caravaca section (External Subbetic, southeast of Spain) in order to evaluate the recovery of the macrobenthic tracemaker community and the bioturbational disturbance. Samples from the infilling material of several lower Danian dark-colored trace fossils (Chondrites, Planolites, Thalassinoides and Zoophycos) located in the uppermost 8-cm of the light upper Maastrichtian strata, as well as samples from the host sedimentary rock of these trace fossils, were analyzed and compared with data from the lower Danian deposits. The values of element ratios indicative of extraterrestrial contamination (Cr/Al, Co/Al and Ni/Al) are higher in the infilling trace fossil material than in the upper Maastrichtian and lower Danian deposits, which suggests a contribution of the ejecta layer. Regarding the isotope composition, the δ13C values are lower in the infilling material than in the Maastrichtian host sedimentary rocks surrounding the traces, while the δ18O are higher in the infilling material. The geochemical and isotopic compositions of the infilling material evidence the unconsolidated character of the sediment, including the red boundary layer. Softground conditions confirm a relatively rapid recovery by the macrobenthic tracemaker community, starting a few millimeters above the K/Pg boundary layer. The mixture of the infilling material of the trace fossils moreover reveals a significant macrobenthic tracemaker activity affecting K–Pg boundary transition sediments that may have significantly altered original signatures.  相似文献   
73.
The use of multiple partially penetrating wells (MPPW) during aquifer storage and recovery (ASR) in brackish aquifers can significantly improve the recovery efficiency (RE) of unmixed injected water. The water quality changes by reactive transport processes in a field MPPW-ASR system and their impact on RE were analyzed. The oxic freshwater injected in the deepest of four wells was continuously enriched with sodium (Na+) and other dominant cations from the brackish groundwater due to cation exchange by repeating cycles of ‘freshening’. During recovery periods, the breakthrough of Na+ was retarded in the deeper and central parts of the aquifer by ‘salinization’. Cation exchange can therefore either increase or decrease the RE of MPPW-ASR compared to the RE based on conservative Cl, depending on the maximum limits set for Na+, the aquifer’s cation exchange capacity, and the native groundwater and injected water composition. Dissolution of Fe and Mn-containing carbonates was stimulated by acidifying oxidation reactions, involving adsorbed Fe2+ and Mn2+ and pyrite in the pyrite-rich deeper aquifer sections. Fe2+ and Mn2+ remained mobile in anoxic water upon approaching the recovery proximal zone, where Fe2+ precipitated via MnO2 reduction, resulting in a dominating Mn2+ contamination. Recovery of Mn2+ and Fe2+ was counteracted by frequent injections of oxygen-rich water via the recovering well to form Fe and Mn-precipitates and increase sorption. The MPPW-ASR strategy exposes a much larger part of the injected water to the deeper geochemical units first, which may therefore control the mobilization of undesired elements during MPPW-ASR, rather than the average geochemical composition of the target aquifer.  相似文献   
74.
反渗透膜技术于20世纪60年代取得突破性进展,促使反渗透海水淡化在近50年间高速发展,淡化产能自20世纪90年代起激增.海水反渗透(SWRO)淡化已成为目前投资最省、成本最低的利用海水制备饮用水的过程.文中主要对海水反渗透淡化的发展状况进行了介绍,如膜和组件的改进,关键设备高压泵和能量回收装置效率的提高,多种工艺过程的不断发展,包括预处理和后处理的新工艺,以及对环境的影响和相应对策等.反渗透技术的发展也推动了其他膜分离技术的进步,并扩展其应用领域.预计在不久的将来,膜技术在海水淡化和水再利用、扩大和保护水资源、循环经济、清洁生产、改造传统产业、节能减排及提高人民生活水平等方面发挥的作用会越来越显著.  相似文献   
75.
The variation of the Asian winter monsoonal strength has seriously affected the climate and environmental conditions in the Asian monsoonal region, and even in marginal islands and the ocean in the East Asian region. However, relevant understanding remains unclear due to the lack of suitable geological materials and effective proxies in the key study areas. Here, we present a grain-size record derived from the palaeo-aeolian sand dune in the southeastern Mu Us Desert, together with other proxies and OSL dating, which reflect a relatively detailed history of the winter monsoon and abrupt environmental events during the past 4.2 ka. Our grain-size standard deviation model indicated that >224 μm content can be considered as an indicator of the intensity of Asian winter monsoon, and it shows declined around 4.2-2.1 ka, enhanced but unstable in 2.1-0.9 ka, and obviously stronger since then. In addition, several typical climate events were also documented, forced by the periodic variation of winter monsoonal intensity. These include the cold intervals of 4.2, 2.8, 1.4 ka, and the Little Ice Age (LIA), and relatively warm sub-phases around 3.0, 2.1, 1.8 ka, and the Medieval Warm Period (MWP), which were roughly accordant with the records of the aeolian materials, peat, stalagmites, ice cores, and sea sediments in various latitudes of the Northern Hemisphere. Combined with the previous progresses of the Asian summer monsoon, we preliminarily confirmed a millennial-scale anti-correlation of Asian winter and summer monsoons in the Late Holocene epoch. This study suggests that the evolution of the palaeo-aeolian sand dune has the potential for comprehending the history of Asian monsoon across the desert regions of the modern Asian monsoonal margin in northern China.  相似文献   
76.
专题地质填图及有关问题讨论   总被引:2,自引:1,他引:1  
面积性地质调查及填图是今后地质调查的主要工作,如何做好这个工作,并实现地质调查和科研一体化,特别是在已有填图基础上,如何部署和开展新的填图工作,是一个亟待回答的新问题。专题地质填图是针对存在的重要地质或资源、环境问题,或是针对特定目标地质体等,以解决特定问题或满足社会特定需求为主要目的、填图与研究融为一体的地质填图,填图的范围和比例尺依据解决问题和目标地质体而定。专题地质填图是以问题和需求为驱动,是对已有的综合地质填图的补充和提高,是高效实现地调科研一体化的一种方式。论述了专题填图的内涵、必要性,以及开展专题填图的方式和方法。  相似文献   
77.
Lineament analysis is applied to map the pattern of the Obruchev fault system in the Buguldeika Village area, where several fault zones (Olkhon, Primorsky, Prikhrebtovyi, Buguldeika, and Kurtun) make up a junction. As inferred from the predominant directions of genetically related lineaments, the Olkhon, Primorsky, and Prikhrebtovyi faults originated under NW-SE extension and compression. The extension and compression settings within these zones are reconstructed by analysis of lineaments that have prominent and poor geomorphic expression, respectively. However, the pattern of lineaments well expressed in the surface topography within a weakly deformed block corresponds to reverse slip, while that of poorly pronounced lineaments corresponds to left-lateral strike slip. The study confirms the idea that the latest extension (rifting) stage in the Baikal region reactivated fault zones but did not deform blocks. The blocks store record of residual deformation produced by previous settings of regional compression and shear. The obtained results agree with earlier tectonophysical analysis of faults and fractures in the area and prove the applicability of the suggested approach to map the fault patterns and reconstruct their respective stress settings in areas that underwent multiple deformation events of different ages.  相似文献   
78.
微观驱油试验表明,交联聚合物驱后剩余油进一步减少,主要以斑块状、小油滴状等形态分布于微孔隙中;数值模拟显示,下二门油田H2Ⅲ油组交联聚合物驱后80.8%的面积已为中强水淹,纵向上79.7%的剩余油分布于主力油层.受构造、储层物性及井网因素控制,未淹、弱水淹剩余油平面上主要分布在断层附近、断层破碎带、微构造高点和砂体上倾尖灭区等部位;纵向上主要分布于低渗透层段.针对剩余油分布特征,通过完善注采关系、优化注采结构,单元含水量的上升速度和产量递减幅度得到控制,采收率在交联聚合物驱的基础上进一步提高了2.01%.  相似文献   
79.
早三叠世时期频繁的火山事件是导致全球性气候和海洋环境异常的主要原因,前人对早三叠世重要界线时期的火山事件地层开展了大量研究,但对典型界线时期以外的其他火山事件地层却鲜有报道.本文以上扬子西南普宜地区嘉陵江组两件沉凝灰岩为研究对象开展了岩石学、岩相学、锆石年代学及微量元素组合特征等方面的研究.沉凝灰岩样品具有典型岩浆锆石...  相似文献   
80.
利用1961—2017年中国各省市701个完整时间序列逐日气象资料的台站数据,以《民用建筑供暖通风与空气调节设计规范》(GB50736—2012)中的供暖标准为指标,采用滑动5 d平均方法,从气温和体感温度两种角度,分析了中国南方地区省市供暖的必要性.结果表明:从气温计算的采暖期看,江苏省、安徽省北部、四川省西部、贵州...  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