全文获取类型
收费全文 | 259篇 |
免费 | 44篇 |
国内免费 | 125篇 |
专业分类
大气科学 | 64篇 |
地球物理 | 33篇 |
地质学 | 211篇 |
海洋学 | 62篇 |
天文学 | 1篇 |
综合类 | 17篇 |
自然地理 | 40篇 |
出版年
2024年 | 3篇 |
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 17篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 14篇 |
2015年 | 17篇 |
2014年 | 30篇 |
2013年 | 16篇 |
2012年 | 8篇 |
2011年 | 19篇 |
2010年 | 16篇 |
2009年 | 24篇 |
2008年 | 20篇 |
2007年 | 18篇 |
2006年 | 21篇 |
2005年 | 20篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有428条查询结果,搜索用时 546 毫秒
71.
72.
73.
The barium deposits in Ankang and Xunyang counties,Shaanxi Province,China,occur in the northernmost part of the world-class barium metallogenic belt in south Qinling.The deposits are hosted by the Lower Silurian carbonaceous siliceous rocks,with a unique combination of barite and witherite.The homogenization temperatures of fluid inclusions in the barite are mainly concentrated between 135 and 155 ℃,whereas those from the witherite have two peaks of 165-175 ℃,and 215-225℃,respectively.Laser Raman analysis of fluid inclusions indicates that the vapor phase of fluid inclusions in barite is dominated by H_2O,although some contains N_2,H_2S,and CH_4.The compositions of the vapor and liquid phases of fluid inclusions in witherite can be divided into two end-members,one dominated by H_2O without other volatiles,and the other containing CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6 in addition to H_2O.CO_2,H_2S,and some CH_4 are interpreted as products of chemical reactions during mineralization.Organic gases(CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6) in the fluids were critical in the formation of barium sulfate versus carbonate.The δ~(34)S values of barite range from 38.26‰ to54.23‰(CDT),the δ~(34)S values of sulfides coexisting with barium minerals vary from 22.44‰ to25.11‰(CDT),and those in the wall rock from 11.60‰ to 19.06‰(CDT).We propose that the SO_4~(2-)generally experienced bacterial sulfate reduction in seawater before mineralization,and some SO_4~(2-)also experienced thermochemical sulfate reduction in hydrothermal system during mineralization.The δ~(13)C values of witherite range from-27.30‰ to-11.80‰(PDB),suggesting that carbon was sourced from organic substances(like CH_4,C_2H_4,and C_2H_6).The formation of witherite was possibly associated with thermochemical sulfate reduction,which caused the consumption of the organic gases and SO_4~(2-) in the hydrothermal solutions,consequently inhibiting barite formation.The important conditions for forming witherite include high fluid temperatures,high Ba~(2+) concentrations,CO_2 in the fluids,low HS~- concentrations,and the subsequent rapid diffusion of H_2S during thermochemical sulfate reduction of the fluids. 相似文献
74.
The Jinshachang lead–zinc deposit is mainly hosted in the Upper Neoproterozoic carbonate rocks of the Dengying Group and located in the Sichuan–Yunnan–Guizhou(SYG) Pb–Zn–Ag multimetal mineralization area in China.Sulfides minerals including sphalerite,galena and pyrite postdate or coprecipitate with gangue mainly consisting of fluorite,quartz,and barite,making this deposit distinct from most lead–zinc deposits in the SYG.This deposit is controlled by tectonic structures,and most mineralization is located along or near faults zones.Emeishan basalts near the ore district might have contributed to the formation of orebodies.The δ34S values of sphalerite,galena,pyrite and barite were estimated to be 3.6‰–13.4‰,3.7‰–9.0‰,6.4‰ to 29.2‰ and 32.1‰–34.7‰,respectively.In view of the similar δ34S values of barite and sulfates being from the Cambrian strata,the sulfur of barite was likely derived from the Cambrian strata.The homogenization temperatures(T ≈ 134–383°C) of fluid inclusions were not suitable for reducing bacteria,therefore,the bacterial sulfate reduction could not have been an efficient path to generate reduced sulfur in this district.Although thermochemical sulfate reduction process had contributed to the production of reduced sulfur,it was not the main mechanism.Considering other aspects,it can be suggested that sulfur of sulfides should have been derived from magmatic activities.The δ34S values of sphalerite were found to be higher than those of coexisting galena.The equilibrium temperatures calculated by using the sulfur isotopic composition of mineral pairs matched well with the homogenization temperature of fluid inclusions,suggesting that the sulfur isotopic composition in ore-forming fluids had reached a partial equilibrium. 相似文献
75.
对盐胀和冻胀规律的研究有助于深入认识硫酸(亚硫酸)盐渍土的工程性质。通过对天山北麓水磨河流域细土平原区硫酸(亚硫酸)盐渍土盐胀和冻胀试验研究发现:(1)随着温度的降低,试样盐胀和冻胀率逐渐增大。试样冻结前土体产生的膨胀是盐胀,试样冻结后产生的膨胀是盐胀和冻胀,当土体达到-15℃以后,土体盐胀和冻胀趋于稳定。(2)硫酸钠含量不变的情况下,随着含水量的增大,其起胀温度降低。土体起胀温度取决于土体中硫酸钠析水结晶温度、硫酸钠结晶含量的多少、土体结构、内摩阻力、粘聚力、土颗粒间的引力、土体孔隙间和孔隙接触间吸收结晶硫酸钠的程度。(3)硫酸钠含量增加,其单次盐胀和冻胀率变化区间增大。 相似文献
76.
以钛白副产绿矾和氯化钾为原料 ,采取硫酸铁钾转化法制备硫酸钾。该工艺既具有反应时间短、操作控制方便、产品质量符合国标要求等优点 ,又治理了钛白粉厂环境污染 ;既具有一定的经济效益 ,又有一定的社会效益。 相似文献
77.
78.
79.
氯离子和硫酸根离子是海水中重要的无机阴离子,在研究海洋生态变化、海洋循环作用过程与海洋全球气候变化等领域具有重要的指示意义。其测定方法较多,但缺少相应的测试方法。本文对测定海水中Cl-,SO42-的离子色谱方法进行了优化,选用IonPacAS14碳酸盐选择性离子色谱柱,以3.5 mmol/L Na2CO3+1 mmol/L NaHCO3为流动相,可消除海水样品中碳酸盐及其他阴离子的干扰。该方法对Cl-检出限为0.29 mg/L,线性相关系数r2=0.999 2,对SO42-检出限为0.42 mg/L,线性相关系数r2=0.997 9。样品的加标回收率在95%~102%,Cl-和SO42-的相对标准偏差分别为1.92%和4.18%。该方法简便、迅速、灵敏、准确度高,可满足批量海水样品中Cl-与SO42-的准确测试。 相似文献
80.
新型珊瑚海水混凝土力学性能试验研究 总被引:2,自引:1,他引:1
为了解决全珊瑚海水混凝土(coral aggregate seawater concrete,简称CASC)的脆性问题,采用碱式硫酸镁水泥(basic magnesium sulfate cement,简称BMSC)为胶凝材料和剑麻纤维为增韧材料制备了一种新型全珊瑚海水混凝土(NCASC),系统测定了基本力学性能,并与普通硅酸盐水泥制备的CASC、碱式硫酸镁水泥砂石混凝土(basic magnesium sulfate cement concrete,简称BMSCC)、普通砂石混凝土(ordinary portland cement concrete,简称OPC)以及普通轻骨料混凝土(lightweight aggregate concrete,简称LAC)的力学性能进行对比。结果表明:立方体抗压强度(f_(cu),m)在15~35 MPa范围内的NCASC的轴心抗压强度(f_c,m)、劈裂抗拉强度(f_(sp),m)与f_(cu),m之间具有较显著的线性关系;对于f_(cu),m为15~35 MPa的混凝土,相同强度NCASC的f_c,m高于OPC、LAC及BMSCC,其f_c,m与f_(cu),m比值最大,大致在0.85~0.96之间,NCASC的f_(sp),m比OPC和LAC高,但比BMSCC低,且随着强度的提高,OPC与NCASC的f_(sp),m间的差距在增大,而LAC和BMSCC与NCASC的f_(sp),m间的差距在缩小;在强度等级C15~C55的范围中,NCASC和CASC的f_(sp),m、f_c,m与f_(cu),m之间的关系基本可以采用相同的线性回归方程来描述,利用这两个回归线性方程得到对应于标准强度等级的CASC和NCASC的f_(sp),m和f_c,m数据,为CASC力学性能研究与结构设计提供参考依据。 相似文献