全文获取类型
收费全文 | 1179篇 |
免费 | 266篇 |
国内免费 | 384篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 97篇 |
地球物理 | 443篇 |
地质学 | 1091篇 |
海洋学 | 80篇 |
天文学 | 6篇 |
综合类 | 30篇 |
自然地理 | 63篇 |
出版年
2024年 | 7篇 |
2023年 | 20篇 |
2022年 | 29篇 |
2021年 | 50篇 |
2020年 | 63篇 |
2019年 | 51篇 |
2018年 | 36篇 |
2017年 | 61篇 |
2016年 | 62篇 |
2015年 | 64篇 |
2014年 | 67篇 |
2013年 | 57篇 |
2012年 | 82篇 |
2011年 | 88篇 |
2010年 | 45篇 |
2009年 | 106篇 |
2008年 | 95篇 |
2007年 | 87篇 |
2006年 | 79篇 |
2005年 | 88篇 |
2004年 | 69篇 |
2003年 | 38篇 |
2002年 | 55篇 |
2001年 | 30篇 |
2000年 | 45篇 |
1999年 | 41篇 |
1998年 | 36篇 |
1997年 | 43篇 |
1996年 | 38篇 |
1995年 | 30篇 |
1994年 | 25篇 |
1993年 | 28篇 |
1992年 | 27篇 |
1991年 | 21篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有1829条查询结果,搜索用时 31 毫秒
31.
32.
通过对向斜洼地含水层水文地质特征的勘探及研究,对研究区的水文地质边界条件进行了概化,并用水均衡法估算了地下水资源量,对拟建一级电站引水渠沿线提取地下水进行融冰的可行性进行了研究,并提出了取水方案. 相似文献
33.
胶北晚中生代煌斑岩的岩石地球化学特征及其成因研究 总被引:16,自引:5,他引:16
胶北煌斑岩分别采自龙口、烟台和威海地区,包括拉辉煌斑岩、斜闪正煌岩和角闪煌斑岩,煌斑岩K—Ar全岩年龄变化于89.3~169.5Ma,为晚中生代岩浆活动的产物。在岩石化学组成上,SiO2=42.02%~54.95%,以钙碱性系列为主.岩石以富集大离子亲石元素(LILE)(Ba,U,K,Th)和LREE,亏损高场强元素(HFSE)(Nb,Ta和Ti)为特征,Mg^#=33.9~53.9,Eu/Eu^*=0.71~0.89,^87Sr/^86Sr初始比值0.707642~0.709791,εNd(t)为-17.6~-10.4,^206Pb/^204Pb=37.588~38.431,^207Pb/^204Pb=15.423~15.531,^206Pb/^204Pb=17.204~18.179。表明煌斑岩源自俯冲陆壳(扬子下地壳)在地幔源区发生交代作用时形成的富集型地幔的部分熔融体.考虑到煌斑岩具有大陆边缘弧玄武岩的特征,我们认为煌斑岩在成因上同样与古大洋板块的俯冲作用有关,为碰撞后弧岩浆作用形成的脉岩。 相似文献
34.
35.
Melt loss and the preservation of granulite facies mineral assemblages 总被引:29,自引:3,他引:29
The loss of a metamorphic fluid via the partitioning of H2O into silicate melt at higher metamorphic grade implies that, in the absence of open system behaviour of melt, the amount of H2O contained within rocks remains constant at temperatures above the solidus. Thus, granulite facies rocks, composed of predominantly anhydrous minerals and a hydrous silicate melt should undergo considerable retrogression to hydrous upper amphibolite facies assemblages on cooling as the melt crystallizes and releases its H2O. The common occurrence of weakly retrogressed granulite facies assemblages is consistent with substantial melt loss from the majority of granulite facies rocks. Phase diagram modelling of the effects of melt loss in hypothetical aluminous and subaluminous metapelitic compositions shows that the amount of melt that has to be removed from a rock to preserve a granulite facies assemblage varies markedly with rock composition, the number of partial melt loss events and the P–T conditions at which melt loss occurs. In an aluminous metapelite, the removal of nearly all of the melt at temperatures above the breakdown of biotite is required for the preservation of the peak mineral assemblage. In contrast, the proportion of melt loss required to preserve peak assemblages in a subaluminous metapelite is close to half that required for the aluminous metapelite. Thus, if a given proportion of melt is removed from a sequence of metapelitic granulites of varying composition, the degree of preservation of the peak metamorphic assemblage may vary widely. 相似文献
36.
Abstract The initial volcanic phase of Cretaceous island arc strata in central Puerto Rico, at the eastern end of the extinct Greater Antilles Arc, comprises a 6‐km thick pile of lava and volcanic breccia (Río Majada Group). Preserved within the sequence is a conspicuous shift in absolute abundances of the more incompatible elements, including Th, Nb, and the light rare earth elements (LREE: La, Ce, Pr and Nd). The compositional shift is marked by a decrease in La/Sm from averages of 2.11 in the lowest third of the pile (Formation A) to 1.48 at the top (Formation C), and by a distinctive flattening of LREE segments of chondrite‐normalized REE patterns. i87Sr/86Sr and ?Nd average about 0.7035 and 8.2, respectively, in early Formation A basalts. These ranges normally overlap samples from later Formations B and C. Isotope compositions of the latter group are more variable, however, and several samples are considerably more radiogenic than Formation A basalts, such that i87Sr/86Sr averages almost 0.7042 while ?Nd‐values decrease to 7.5 in Formation B and C basalts. Theoretical models of non‐modal melting processes in both amphibole peridotite and spinel lherzolite sources provide insight into the origin of depleted Th, Nb, and LREE abundances in Puerto Rican basalts. Low Nb concentrations less than normal mid‐oceanic ridge basalts in Formation A basalts indicate the wedge was slightly depleted by low‐volume decompression fusion due to induced convection in the back‐arc region prior to entry of the source into the arc melting zone. However, depleted patterns in Formation C basalts cannot be generated by relatively greater degrees of decompression fusion in the back‐arc, because addition of the La‐enriched slab‐derived component to more depleted source material invariably produces elevated rather than decreased La/Sm. Refluxing of Formation A harzburgitic residua is similarly precluded. In contrast, the observed patterns are readily reproduced by multistage melting models involving hybridized sources containing normal Formation A lherzolite source material blended with recycled, unrefluxed harzburgite residua. Successful models require hybrid sources containing large volumes of recycled harzburgite (up to 50%) during generation of Formation C basalts. Slightly elevated radiometric Sr and Nd isotopes in a few flows from Formation C are attributed to partial refluxing of the hybrid sources within the wedge. 相似文献
37.
38.
对新疆北天山l931年以来6级以上、l970年以来5级以上地震前的地震活动空间图像进行了分析,发现震前多有不同程度的地震空区或条带出现,其孕育时间一般为8-14年;震源深度呈现由浅而深、通常超过25km的变化,孕育时间一般为3—4年。同时对上述地震活动空间图像前兆特征的机理进行了定性分析,并对所选资料的精度等问题进研了讨论。 相似文献
39.
青藏高原土壤水热分布特征及冻融过程在季节转换中的作用 总被引:21,自引:0,他引:21
利用GAME-Tibet期间所取得的高分辩率土壤温度和含水量资料,对青藏高原(主要是藏北高原)土壤水热分布特征及冻融过程在季节转换中的作用进行了分析。指出藏北高原4cm学深处土壤在10月份开始冻结,次年4-5月份开始消融,冻结持续时间长达5-7个月。冻结过程有利于土壤维持其水分,因此,在刚刚开始消融时土壤含水量仍然很高。从而为夏季风爆发前土壤通过蒸发向大气提供水分打下了基础。指出土壤冻融过程可能在高原季节转换中起着重要作用。 相似文献
40.