全文获取类型
收费全文 | 1156篇 |
免费 | 170篇 |
国内免费 | 443篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 5篇 |
地球物理 | 94篇 |
地质学 | 1276篇 |
海洋学 | 130篇 |
天文学 | 1篇 |
综合类 | 71篇 |
自然地理 | 171篇 |
出版年
2024年 | 13篇 |
2023年 | 34篇 |
2022年 | 51篇 |
2021年 | 74篇 |
2020年 | 56篇 |
2019年 | 70篇 |
2018年 | 47篇 |
2017年 | 36篇 |
2016年 | 44篇 |
2015年 | 39篇 |
2014年 | 83篇 |
2013年 | 76篇 |
2012年 | 49篇 |
2011年 | 65篇 |
2010年 | 51篇 |
2009年 | 72篇 |
2008年 | 72篇 |
2007年 | 86篇 |
2006年 | 83篇 |
2005年 | 64篇 |
2004年 | 62篇 |
2003年 | 56篇 |
2002年 | 43篇 |
2001年 | 49篇 |
2000年 | 57篇 |
1999年 | 61篇 |
1998年 | 34篇 |
1997年 | 40篇 |
1996年 | 23篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 23篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 21篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有1769条查询结果,搜索用时 437 毫秒
981.
从可持续发展的内涵出发,分析了可持续发展的机制,阐述了中国可持续发展过程中应注意的重大战略问题,最后提出了相应的对策。 相似文献
982.
通过中国东部红土剖面的环境磁学参数(磁化率、频率磁化率、非磁滞剩磁、饱和等温剩磁等)测量,获得了红土剖面磁性矿物浓度、粒度和类型等特性随深度的变化曲线以及红土经连二亚硫酸钠一柠檬酸钠一重碳酸钠溶液(DCB)处理后的磁性参数变化.根据红土剖面环境磁学参数及其磁参数比值的变化可将红土分为3个层段,各层段的磁性矿物特征存在明显的差异.证实了红土剖面中的磁性载体主要是磁赤铁矿、赤铁矿和针铁矿,并分离出了球粒状磁颗粒.认为红土磁性矿物的数量、粒度、类型等的变异指示了其形成时的环境特征,其频率磁化率和DCB处理的磁化率损失量指示了红土成壤化作用的强弱,可作为在红壤区研究过去全球变化的一种新途径. 相似文献
983.
Nine Namurian clay bands retrieved from boreholes in the northern part of the Pennine Basin are, on the basis of their petrography, mineralogy and geochemistry, shown to be volcanic in origin and are therefore bentonites. The bentonites, which have a fragmental texture, are normally graded and show rare preservation of shard textures, representing vitric tuff deposits that have been altered subsequently to clay-dominated horizons. Crystals are a minor component of the bentonites, but biotite, in particular, is concentrated at the base of the beds. A clay mineral assemblage of mixed-layer illite–smectite with subordinate kaolinite identifies most of the samples as K-bentonites, but kaolinite dominates two samples that can be classed as tonsteins. Temporal variation of salinity within the depositional basin is suggested to explain these different clay assemblages. The major element geochemistry of the bentonites reflects their clay mineralogy and the compositions of diagenetic minerals present, the latter including pyrite, carbonates and hydroxyapatite. Enrichment of the bentonites in some trace elements (including Ba, Sr, Pb, Cu and Ni) can be related to the presence of the diagenetic minerals, but the extent to which the elements are added from external sources as opposed to being redistributed within the ash is unclear. Immobile trace element systematics suggest a rhyodacite/dacite composition for the original ash and derivation from the collision of plates, this being supported by evidence provided by the rare earth elements (REE) in one group of samples. However, in another group of samples, variations in REE concentrations may be caused by mobility of these elements during alteration. The chemistry of the Namurian bentonites contrasts markedly with that of the local Carboniferous volcanics but is comparable, in some respects, with one group of Westphalian tonsteins, although the latter are more rhyolitic in character. It is suggested that the Namurian bentonites and the Westphalian tonsteins of acid affinities originated from volcanic activity associated with a destructive plate margin in the Variscan externides and that the observed compositional trend may reflect magma evolution possibly related to the progressive east–west closure. 相似文献
984.
淡—咸水界面切换中矿物表面吸附性变化研究 总被引:7,自引:3,他引:4
实验研究表明,当电解质离子浓度从有低上升到极高时,矿物吸附金属离子的普遍下降,例外的仅有石英、水云母、CaCO3和三水铝矿对Pb^3+、Zn^3+离子的吸 云母对Cu^2+的吸附和石英对Cr^3+的吸附。理论研究表明,一方面,电解质NaCl的加入,使矿物表面Sten的层电位发生变化,△ψ(ψ0-ψβ)的绝对值增大,提高了矿物表面吸附离子的能力;另一方面,由于Na离子的竞争吸附和Cl离子与深液中金 相似文献
985.
吉林省夹皮沟黄金矿业公司是为国家作出较大贡献的国有黄金大型企业,现资源危机,企业陷入困境.但夹皮沟金矿区经专家论证,金矿成矿地质条件优越,找矿前景较好,只要采取措施,加强地质探矿工作,增加储量,摆脱困境,以保老矿的稳定和可持续发展仍然是大有希望的. 相似文献
986.
陨石矿物种类的研究进展和矿物表 总被引:3,自引:0,他引:3
早在约 2 0 0年前 ,科学家就在铁陨石中鉴定出了两种陨石矿物——陨硫铁和金属铁—镍。到了 1 9世纪 80年代 ,陨石矿物的数量增加到 1 6种。 2 0世纪 60年代以来 ,随着显微镜的广泛应用 ,以及许多新的测试技术如 X射线衍射、电子探针、扫描电镜和透射电镜的应用 ,使更多的陨石矿物能被发现。1 967年 ( Mason列出 60种陨石矿物 )至 1 987年( Yudin和 Kolomenskiy列出了 2 0 0种陨石矿物 )的2 0年间陨石矿物种数增加到原来的 3倍多。1 991年Ulyanov完成了陨石、星际尘粒和玻璃陨石共 350种矿物的列表。Rubin〔1〕在前人工作的基础上 ,去掉… 相似文献
987.
In this paper the authors introduce their past years' study results about the exploitation and application of three sorts of nontraditional nonmetal minerals. In this research, the main aspects and techniques of basic study for the exploitation and application are summarized, and some key science and technological problems are proposed as the objects of their future research. 相似文献
988.
Li Zhen Shen Shangyue Chi bo Zhang De Yang Mei Faculty of Material Sciences Chemistry Engineering China University of Geosciences Wuhan 《中国地质大学学报(英文版)》2000,(2)
RESEARCH RESULTS IN THREE SORTS OF NONTRADI-TIONAL NONMETAL MINERALSMicro-Scale Metagenetic SericitesWith international development of industrial mineral androck,a great amount of sheet muscovite and phlogopite havebeen used in pastdecades,butthe micro-scale sericites are notmined and used in a normal way.As substitution of expensivewhite carbon are used in rubber production,the micro-scalesericites which are superfinely smashed and modified in theirsurface properties … 相似文献
989.
W. C. Mahaney M. W. Milner J. Voros V. Kalm G. Hütt M. Bezada R. G. V. Hancock S. Aufreiter 《Journal of South American Earth Sciences》2000,13(8):761
The Mérida Glaciation (cf. Wisconsinan, Weichselian) as proposed by Schubert (1974b) culminated at about 18 ka during the last glacial maximum (LGM) and ended at about 13 ka as indicated by 14C dating and correlation with the Cordillera Oriental of Colombia. Moraines of an early stade of Mérida Glaciation reached to 2800 m a.s.l. and were largely overrun or eradicated by the maximum Wisconsinan advance (LGM); where they outcrop, the older moraines are characterized by eroded, weathered glacial diamictons and outwash fans.At Pueblo Llano in the central Mérida Andes (Cordillera de Trujillo), older to younger beds of contorted glacitectonized diamict, overlying beds of bouldery till and indurated outwash, all belong to the early Mérida stade. Overlying the early Mérida stade, deposits of rhythmically bedded glaciolacustrine sediments are in turn overlain with contorted sand and silt beds capped with outwash. Above the outwash terrace a loop moraine of LGM age completely encircles the margins of the basin. A stream cut exposed by catastrophic (tectonic or surge?) release of meltwater displays a lithostratigraphic succession that is bereft of organic material for radiocarbon dating. Five optically-stimulated luminescence (OSL) dates place the maximum age of the lowest till at 81 ka.Particle size distributions allow clear distinctions between major lithic units. Heavy mineral analysis of the middle and lower coarse units in the section provide information on sediment sourcing and on major lithostratigraphic divisions. Trace element concentrations provide information on the relative homogeneity of the deposits. The HREE (heavy rare earth element) concentrations allow discrimination of the lower till from the rest of the section; the LREE (light rare earth element) concentrations highlight differences between the lower till, LGM till, and the rest of the section. 相似文献
990.
青金石结构有无序和有序之别。无序青金石为光性均质体,但它的有序化及由此引起的结构调制,则有可能使青金石产生光性异常。使结构仍保持立方对称的有序化并不改变它光性上的均质性,而其他形式的有序化以及结构调制,如果它们是多方向的 且在空间取向上具有立方对称的特征,则晶体仍是光性均质体,否则便转变为光性非均质体 。此外,还提出了根据选区电子衍射花样对结构调制方向进行三维判识的可能性;报道了在所研究青金石中发现的沿[110]方向n=4的有公度调制的有序结构,以及所观察到的其他有序结构和无公度调制结构。 相似文献