全文获取类型
收费全文 | 1220篇 |
免费 | 235篇 |
国内免费 | 405篇 |
专业分类
测绘学 | 212篇 |
大气科学 | 182篇 |
地球物理 | 179篇 |
地质学 | 894篇 |
海洋学 | 210篇 |
天文学 | 12篇 |
综合类 | 91篇 |
自然地理 | 80篇 |
出版年
2024年 | 2篇 |
2023年 | 12篇 |
2022年 | 27篇 |
2021年 | 40篇 |
2020年 | 45篇 |
2019年 | 64篇 |
2018年 | 46篇 |
2017年 | 47篇 |
2016年 | 51篇 |
2015年 | 60篇 |
2014年 | 96篇 |
2013年 | 81篇 |
2012年 | 92篇 |
2011年 | 106篇 |
2010年 | 89篇 |
2009年 | 91篇 |
2008年 | 75篇 |
2007年 | 104篇 |
2006年 | 95篇 |
2005年 | 80篇 |
2004年 | 69篇 |
2003年 | 61篇 |
2002年 | 55篇 |
2001年 | 44篇 |
2000年 | 31篇 |
1999年 | 49篇 |
1998年 | 26篇 |
1997年 | 48篇 |
1996年 | 38篇 |
1995年 | 26篇 |
1994年 | 31篇 |
1993年 | 17篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1860条查询结果,搜索用时 15 毫秒
991.
992.
晴天太阳总辐射的参数化及气候计算 总被引:6,自引:0,他引:6
在文献[1]基础上,根据北京、拉萨等站1735次实测资料,进一步讨论了应用别尔梁德理论式Qo=Iosinh/1+fm作晴天总辐射参数化的可能性。提出了f 的新参数化方案。与原方案相比,保持较高拟合精度外,新方案的普适性更好。按本方案计算的各地晴天总辐射廓线形式,与国内外地面和飞艇探测结果一致。对青藏高原6站所作晴天总辐射气候计算也与实例值相符。 相似文献
993.
In the context of measurements from all the thermal balance stations over China,two methodsof calculating surface latent heat for its climatic features are proposed through experiments with arange of schemes,one being the empirical type based on the relationship between ground latent heatand vapor pressure,and the other upon the Bowen ratio parameterization.Either of them has itsunique merits so that they can be considered in specific case to have higher accuracy.On this basis.investigation is done of the feature of geographic distribution and annual variability of the heatacross the country. 相似文献
994.
流域冰川平均物质平衡的计算方法及其应用 总被引:2,自引:7,他引:2
应用统计力学方法和最大熵原理,论证了高山流域内降水、径流和径流系数与其所占面积之间呈负指数关系。流域内的冰川分布区是各参数的最大分布区,从而给出了高山流域冰川平均物质平衡的计算公式。 相似文献
995.
The assemblage diaspore+quartz in metamorphic rocks: a petrological, experimental and thermodynamic study 总被引:1,自引:0,他引:1
The upper pressure limit of pyrophyllite is given by the equilibria (i) pyrophyllite=diaspore+quartz and (ii) pyrophyllite=diaspore+coesite. High- P experimental investigations carried out to locate equilibrium (i) yield brackets between 497 °C/24.8 kbar and 535 °C/25.1 kbar, and between 500 °C/23 kbar and 540 °C/23 kbar. Equilibrium (ii) was bracketed at 550 °C between 26.0 and 28.3 kbar. In the experimental P–T range, equilibria (i) and (ii) are metastable with respect to kyanite. A stable P–T grid is calculated using thermodynamic data derived under consideration of the present experimental results. According to these data, the lower pressure limit of the assemblage diaspore+quartz according to equilibrium (i) range from about 12 kbar/300 °C to 20 kbar/430 °C (in the presence of pure water). The upper stability of diaspore+quartz is limited by the reaction diaspore+quartz=kyanite+H2 O at about 450 °C (nearly independent of pressure) and, to higher pressure, by the quartz=coesite transition. Equilibrium (ii) is metastable over the whole P–T range.
Natural occurrences600.S of the diaspore–quartz assemblage in metamorphic rocks in Sulawesi, New Caledonia, Amorgos and the Vanoise are characterized by minerals indicative of high- P such as ferro-magnesiocarpholite, glaucophane, sodic pyroxene and lawsonite. The metamorphic P–T conditions of these rocks are estimated to be in the range 300–400 °C, >8 kbar. These data are compatible with the derived P–T stability field of the diaspore+quartz assemblage. We conclude that, in metamorphic rocks, diaspore+quartz is, as ferrocarpholite, an indicator for unusual low- T /very high- P settings. 相似文献
Natural occurrences600.S of the diaspore–quartz assemblage in metamorphic rocks in Sulawesi, New Caledonia, Amorgos and the Vanoise are characterized by minerals indicative of high- P such as ferro-magnesiocarpholite, glaucophane, sodic pyroxene and lawsonite. The metamorphic P–T conditions of these rocks are estimated to be in the range 300–400 °C, >8 kbar. These data are compatible with the derived P–T stability field of the diaspore+quartz assemblage. We conclude that, in metamorphic rocks, diaspore+quartz is, as ferrocarpholite, an indicator for unusual low- T /very high- P settings. 相似文献
996.
碳酸盐矿物氧同位素分馏的理论研究 总被引:13,自引:2,他引:13
应用增量方法系统地计算了碳酸盐矿物的同位素分馏系数,得到不同结构和成分的碳酸盐矿物的18O富集顺序为:菱铁矿〉铁白云石〉菱镁矿≥白云石≥方解石〉文石〉菱锶矿〉白铅矿〉碳钡矿。在0℃~1200℃范围内获得了一组内部一致的碳酸盐-水体系的理论分馏系数,这些计算结果与已知的实验和/或经验数据之间存在良好的一致性,因此本文对碳酸盐矿物氧同位素分馏系数的理论校准不仅可应用于共生矿物组合形成温度的确定,而且能够应用于其形成机理的示踪。 计算结果表明,白云石的氧同位素分馏行为与方解石相似,在25℃下白云石与方解石之间的平衡分馏为0.56‰ 。理论预测文石相对于方解石显著地亏损 δ18O,在25℃时方解石与文石之问的平衡分馏为4.47‰ 。文石向方解石的同质多相转变可能是通过一种没有同位素再造的惰性氧结构单元[CO3]2- 进行的,即只涉及Ca2+ 与[C03]2- 基团之间键的断裂和再组台而未出现[CO3]2- 基团内部C-O键的断裂和再组合。结果在自然界和实验室实验中,文石中氧同位索配分的温度关系能够传递副方解石中来。这种在同质多相转变形成方解石过程中的氧同位素继承性对于了解白云石-方解石-水体系分馏的难题至关重要。理论预测也能够用来解释对方解石分馏的经验估算与实验测定之间的分歧。 相似文献
997.
为保证在盐矿中进行核废料存放的安全性,人们使用了许多办法堵漏,不使盐矿被淹。用CaCl2或MgCl2溶液注入盐帽的悬浮溶液中使盐析出,自上而下堵漏,可保证盐矿的安全。 相似文献
998.
论铀成矿过程中的气还原作用 总被引:17,自引:4,他引:17
热力学计算及成矿实验结果表明H2,CH4,CO和H2S等气体能作为还原剂使UO还原成UO2(晶质铀矿)。尽管在许多铀矿床中存在的黄铁矿能作为还原剂,但上述还原性气体是比黄铁矿更有效的还原剂。一些矿床的钻探资料及流体包裹体中气体含量测定结果证实了上述气体的存在。文中提出了气还原作用这一概念,它被认为是澳大利亚、加拿大和中国等地不整合脉型铀矿床及其他一些脉型铀矿床成矿富集的重要机制。 相似文献
999.
杨天笑 《华东地质学院学报》1995,18(1):40-42
本文讨论了地下水化学分类的现状,归纳了现有地下水化学分类的优、缺点,并根据水分析、水化学、水文地球化学和实践中出现的一些问题,对地下水化学分类提出一些新的认识,为提出新的地下水化学分类提供依据。 相似文献
1000.
Abstract Petrogenetic grids for ultrahigh-pressure (UHP) metamorphism were calculated at different Xco2 conditions in the model system CaO-MgO-SiO2-CO2-H2O involving coesite (Co), diopside (Di), dolomite (Do), enstatite (En), forsterite (Fo), magnesite (Ms), quartz (Qz), talc (Tc), tremolite (Tr) using a published internally consistent thermodynamic data set. Two P-T grids at Xco2= 0.01 and 0.5 are described. In the calculated P-T grid at Xco2= 0.01, four out of 10 stable invariant points, Co-En-Ms-Tc, Co-Di-En-Tc-Tr, Co-Di-Ms-Tc-Tr and Di-En-Ms-Tc-Tr lie within the stability field of coesite. If the fluid phase has Xco2= 0.5, no invariant point is stable under UHP conditions. Some magnesite-bearing assemblages are stabilized by the following three reactions: Di + Ms = Do + Fo + CO2, Ms + Tr = Do + Fo + CO2+ H2O and Ms + Tc = Fo+ CO2+ H2O at Xco2= 0.01 and by reaction Ms + Tc = Fo + CO2+ H2O together with these three at Xco2= 0.5. Ten possible UHP assemblages for mafic and ultramafic compositions at very low Xco2 conditions include the following: Co-Do-Ms, Co-Di-Ms, Co-Di-Tc, Di-Ms-Tc, Di-En-Tc-, Di-En-Ms, Co-Di-En, Di-En-Fo, Di-Fo-Ms, Di-Do-Fo. Among them, talc-bearing assemblages are restricted to Xco2 < 0.02 and their high-P limit is 31.7 kb (749°C) at Xco2= 0.01. Dolomite-magnesite-silica assemblages have large P-T stability fields even if Xco2 is as low as 0.1, and could occur in cold subduction zones with very low geothermal gradients. Reported UHP coesite-dolomite assemblage is restricted only to a calc-silicate rock interlayered with marble where Xco2 is relatively higher; no such assemblage appears for mafic and ultramafic rocks with low Xco2 evidenced by the occurrence of diopside (or omphacite) at the expense of dolomite + coesite. The effect of Xco2 on the stability of coesite-dolomite-magnesite, diopside-enstatite-magnesite, diopside-talc assemblages is examined and the occurrence of coesite-dolomite, magnesite-bearing and talc-bearing assemblages in the Dabie UHP rocks are interpreted by employing the calculated P-T grids. 相似文献