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   340篇
  免费   34篇
  国内免费   81篇
测绘学   2篇
大气科学   8篇
地球物理   97篇
地质学   293篇
海洋学   28篇
综合类   7篇
自然地理   20篇
  2023年   1篇
  2022年   3篇
  2021年   6篇
  2020年   14篇
  2019年   8篇
  2018年   5篇
  2017年   11篇
  2016年   12篇
  2015年   13篇
  2014年   24篇
  2013年   16篇
  2012年   14篇
  2011年   14篇
  2010年   18篇
  2009年   32篇
  2008年   37篇
  2007年   29篇
  2006年   37篇
  2005年   22篇
  2004年   16篇
  2003年   23篇
  2002年   13篇
  2001年   20篇
  2000年   12篇
  1999年   16篇
  1998年   8篇
  1997年   2篇
  1996年   5篇
  1995年   6篇
  1994年   6篇
  1993年   2篇
  1992年   1篇
  1991年   2篇
  1990年   4篇
  1988年   1篇
  1987年   1篇
  1985年   1篇
排序方式: 共有455条查询结果,搜索用时 15 毫秒
91.
水热条件下利用微波加热从粉煤灰合成沸石研究   总被引:14,自引:0,他引:14  
着重选用NaOH水溶液为反应前驱物, 通过改变反应温度、NaOH浓度与合成时间等参数, 在水热条件下利用微波加热直接对粉煤灰进行晶化, 合成得到了浊沸石、菱沸石、NaP1沸石3种沸石.粉煤灰转化为沸石率约15%~40%.研究表明: (1) 反应体系在15min左右即有合成沸石产生, 30min左右合成沸石转化率达到最佳; (2) 为保证沸石晶核生成和晶体的生长, 反应体系的溶液/粉煤灰比不应低于2.5; (3) 在溶液/粉煤灰比为2.5时, 应控制加热时间在30min左右.   相似文献   
92.
粉煤灰与生石灰加固软土的室内试验研究   总被引:20,自引:5,他引:15  
林彤  刘祖德 《岩土力学》2003,24(6):1049-1052
粉煤灰是一种工业废弃物,与生石灰一样均可用来加固软土地基。笔者进行了粉煤灰与生石灰加固土的室内配方试验,分别将水泥或生石灰与粉煤灰按照不同的比例干拌均匀后,再与不同含水量的软土人工拌和均匀,测定了不同龄期的无侧限抗压强度;分析了石灰加固土强度与生石灰掺入比和龄期的关系及其压缩系数、压缩模量等的变化。并进一步分析了粉煤灰的加固机理,旨在为其进一步的研究和工程应用提供参考。  相似文献   
93.
94.
Measurements of anhysteretic (ARM) and isothermal (IRM) remanences in cores 6 and 8 from Big Moose Lake reveal evidence for changes in magnetic mineralogy and grain size within and between the two cores. It is proposed that changes in the strength and demagnetization characterizations of the IRM reflect the accumulation of atmospherically deposited magnetic minerals resulting from industrial processes. The record of magnetite deposition especially in Core 6 parallels that for coal soot at the site. In both cores, the record of haematite deposition parallels that for several anthropogenic indicators.This is the fourth of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series.  相似文献   
95.
Fly ashes from two stoker boilers burning Pennsylvanian Eastern Kentucky high volatile A bituminous coal blends were examined for their petrology and chemistry. The source coals have similar trace element contents. One of the ash collection systems was retrofitted with a baghouse (fabric filter) system, collecting a finer fly ash at a cooler flue gas temperature than the plant that has not been reconfigured. The baghouse ash has a markedly higher trace element content than the coarser fly ash from the other plant. The enhanced trace element content is most notable in the As concentration, reaching nearly 9000 ppm (ash basis) for one of the collection units. Differences in the ash chemistry are not due to any substantial differences in the coal source, even though the coal sources were from different counties and from different coal beds, but rather to the improved pollution control system in the steam plant with the higher trace element contents.  相似文献   
96.
Sulfur occurs in multiple mineral forms in coals, and its fate in coal combustion is still not well understood. The sulfur isotopic composition of coal from two coal mines in Indiana and fly ash from two power plants that use these coals were studied using geological and geochemical methods. The two coal beds are Middle Pennsylvanian in age; one seam is the low-sulfur (< 1%) Danville Coal Member of the Dugger Formation and the other is the high-sulfur (> 5%) Springfield Coal Member of the Petersburg Formation. Both seams have ash contents of approximately 11%. Fly-ash samples were collected at various points in the ash-collection system in the two plants. The results show notable difference in δ34S for sulfur species within and between the low-sulfur and high-sulfur coal. The δ34S values for all sulfur species are exclusively positive in the low-sulfur Danville coal, whereas the δ34S values for sulfate, pyritic, and organic sulfur are both positive and negative in the high-sulfur Springfield coal. Each coal exhibits a distinct pattern of stratigraphic variation in sulfur isotopic composition. Overall, the δ34S for sulfur species values increase up the section in the low-sulfur Danville coal, whereas they show a decrease up the vertical section in the high-sulfur Springfield coal. Based on the evolution of δ34S for sulfur species, it is suggested that there was influence of seawater on peat swamp, with two marine incursions occurring during peat accumulation of the high-sulfur Springfield coal. Therefore, bacterial sulfate reduction played a key role in converting sulfate into hydrogen sulfide, sulfide minerals, and elemental sulfur. The differences in δ34S between sulfate sulfur and pyritic sulfur is very small between individual benches of both coals, implying that some oxidation occurred during deposition or postdeposition.The δ34S values for fly ash from the high-sulfur Springfield coal (averaging 9.7‰) are greatly enriched in 34S relative to those in the parent coal (averaging 2.2‰). This indicates a fractionation of sulfur isotopes during high-sulfur coal combustion. By contrast, the δ34S values for fly-ash samples from the low-sulfur Danville coal average 10.2‰, only slightly enriched in 34S relative to those from the parent coal (average 7.5‰). The δ34S values for bulk S determined directly from the fly-ash samples show close correspondence with the δ34S values for SO4− 2 leached from the fly ash in the low-sulfur coal, suggesting that the transition from pyrite to sulfate occurred via high-temperature oxidation during coal combustion.  相似文献   
97.
对服役12年的华南某跨海大桥典型构件开展碳化性能、氯离子扩散性能等指标的耐久性检测,评估了海水环境下掺粉煤灰的高性能混凝土长期耐久性。研究表明:随高程的增加混凝土碳化深度逐渐增大,其中大气区浪溅区水位变动区,碳化作用对粉煤灰混凝土结构耐久性的影响较小;粉煤灰可显著提升实体结构混凝土抗氯离子侵蚀性能,粉煤灰高性能混凝土的氯离子扩散系数不大于0.40×10-12m2/s,比普通混凝土氯离子扩散系数降低了约6倍;利用规范计算了引桥承台混凝土中氯离子含量计算值,其计算值与实测值吻合较好,可用于实体工程混凝土结构的耐久性评估,评估结果显示采用粉煤灰高性能的桥梁典型构件满足100年设计使用寿命的要求。  相似文献   
98.
增加硅酸盐供给可缓解海域硅酸盐相对缺乏现象,稻壳灰中含有大量无定形态SiO2,是一种理想的海水硅酸盐肥料。为验证稻壳灰的硅酸盐释放性能以及在环境中应用时的安全性,我们在实验室内将稻壳灰添加到海水中测定了Si、P、N营养盐的释放能力及释放周期,并将稻壳灰放于自然海域浸泡一段时间后测定其4种重金属及Mg元素含量的变化。实验结果表明,稻壳灰在海水中可持续缓慢地释放硅酸盐,释放周期可达3个月以上,同时释放少量磷酸盐,不会增加水体中无机氮营养盐含量;稻壳灰向海水中释放极少量的Cd,但不易造成重金属污染,而对海水中的Cu、Pb、Hg有一定地吸附效果,吸附量远小于Mg离子。  相似文献   
99.
100.
测定了中国团扇鳐和林氏团扇鳐肌肉中的水分含量、灰分含量及能值.中国团扇鳐肌肉水分含量为75.86%,灰分含量为5.15%,能值为21.49MJ/kg;林氏团扇鳐肌肉水分含量为76.66%,灰分含量为5.04%,能值为21.29MJ/kg.中国团扇鳐、林氏团扇鳐的体重与体长有显著的正相关关系;中国团扇鳐、林氏团扇鳐的水分含量随体重的增加而减小,能值随体重的增加而升高;中国团扇鳐肌肉的能值与水分含量之间具有一定的相关递减的趋势,林氏团扇鳐水分含量与灰分含量之间具有一定的相关递增的趋势.此外,中国团扇鳐、林氏团扇水分含量、灰分含量及能值随季节的变化而变化.这与鱼体自身的生物学特性有关。也受到环境因子变化的影响.  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