全文获取类型
收费全文 | 544篇 |
免费 | 338篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 64篇 |
地球物理 | 459篇 |
地质学 | 208篇 |
海洋学 | 24篇 |
天文学 | 88篇 |
综合类 | 18篇 |
自然地理 | 18篇 |
出版年
2023年 | 24篇 |
2022年 | 57篇 |
2021年 | 60篇 |
2020年 | 50篇 |
2019年 | 65篇 |
2018年 | 250篇 |
2017年 | 99篇 |
2016年 | 26篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 5篇 |
2011年 | 29篇 |
2010年 | 13篇 |
2009年 | 4篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2005年 | 4篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 15篇 |
2001年 | 11篇 |
2000年 | 27篇 |
1999年 | 45篇 |
1998年 | 9篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1985年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
1970年 | 3篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1964年 | 2篇 |
排序方式: 共有892条查询结果,搜索用时 31 毫秒
832.
Braarudosphaera 《Cretaceous Research》1999,20(6):773
Braarudosphaera -rich sediments occur in the Turonian (nannofossil zones CC13 and UC9a) epicontinental marine sediments of the Bohemian Cretaceous Basin. This phenomenon is linked to the input of terrigenous material during deceleration of sea-level rise, or stillstand in sea level, which possibly both triggered the Braarudosphaera bigelowii bloom and reduced the diversity of the nannoplankton assemblages. The occurrence of Marthasterites furcatus and Lithastrinus septenarius probably reflects depositional conditions that were suitable for their preservation. Hence, the resultant limitations to their use as local zonal markers in the Bohemian Cretaceous Basin are discussed. The influence of the Tethyan Bioprovince is documented by the coincident first occurrences of L. septenarius and M. furcatus. The presence of the high-latitude species Thiersteinia ecclesiastica indicates penetration of Boreal biota into this depositional area within the Turonian. 相似文献
833.
辫状河储层建模方法研究 总被引:10,自引:1,他引:9
辫状河储层在我国陆相盆地中广泛分布,而对这类储层的认识却较差。辫状河砂体的非均质性严重,这是影响开发效果的重要原因。本文以张家口地区的露头砂体为例,在密集取样的基础上建立了砂体的地质模型,分析了砂体的非均质性特征,探讨了辫状河储层的建模方法。根据孔隙度和渗透率的变差函数分别建立了孔隙度和渗透率的克里金模型和条件模拟模型;利用频谱分析法和变尺度分析法对渗透率进行了赫斯特指数的求取,得到该砂体的赫斯特指数的平均值在0.8左右,同时利用分形几何的插值理论建立了渗透率的分形几何模型。对各种模型进行的比较显示克里金模型较好地表现了物性参数的整体趋势;条件模拟模型较好地再现了储层非均质性;而分形几何模型既反映了储层宏观物性分布,又反映了其内部非均质性变化。整体上看,分形几何模型是一种相对比较好的模型,可应用于油田开发早期。 相似文献
834.
介绍了地下钢筋混凝土桩的控制爆破方法,以及在钻孔设备及外界约束较特殊的情况下,钻孔、装药及起爆等方面的注意事项。 相似文献
835.
836.
837.
论电离层对GPS定位的影响 总被引:13,自引:2,他引:11
电离层是GPS定位的主要误差源。本文论述电离层的特征和折射系数,以及电离层的下列影响:电离层码群延、电离层载波相位超前、电离层多普勒频移、振幅闪烁、电离层相位闪烁效应、磁暴对GPS定位测量的影响、电离层对差分GPS的影响和GPS接收机的电离层改正。 相似文献
838.
Hiroo Kagami Masaki Yuhara Shigeru Iizumi Yoshiaki Tainosho Masaaki Owada Yasuo Ikeda
Osamu Okano Shuji Ochi Yoshikazu Hayama and Terukazu Nureki 《Island Arc》2000,9(1):3-20
Osamu Okano Shuji Ochi Yoshikazu Hayama and Terukazu Nureki 《Island Arc》2000,9(1):3-20
Abstract The Ryoke Belt is one of the important terranes in the South‐west Japan Arc (SJA). It consists mainly of late Cretaceous granitoid rocks, meta‐sedimentary rocks (Jurassic accretionary complexes) and mafic rocks (gabbros, metadiabases; late Permian–early Jurassic). Initial ?Sr (+ 25– + 59) and ?Nd (? 2.1–?5.9) values of the metadiabases cannot be explained by crustal contamination but reflect the values of the source material. These values coincide with those of island arc basalt (IAB), active continental margin basalt (ACMB) and continental flood basalt (CFB). Spiderdiagrams and trace element chemistries of the metadiabases have CFB‐signature, rather than those of either IAB or ACMB. The Sr–Nd isotope data, trace element and rare earth element chemistries of the metadiabases indicate that they result from partial melting of continental‐type lithospheric mantle. Mafic granulite xenoliths in middle Miocene volcanic rocks distributed throughout the Ryoke Belt were probably derived from relatively deep crust. Their geochemical and Sr–Nd isotopic characteristics are similar to the metadiabases. This suggests that rocks, equivalent geochemically to the metadiabases, must be widely distributed at relatively deep crustal levels beneath a part of the Ryoke Belt. The geochemical and isotopic features of the metadiabases and mafic granulites from the Ryoke Belt are quite different from those of mafic rocks from other terranes in the SJA. These results imply that the Ryoke mafic rocks (metadiabase, mafic granulite) were not transported from other terranes by crustal movement but formed in situ. Sr–Nd isotopic features of late Cretaceous granitoid rocks occurring in the western part of the Japanese Islands are coincident with those of the Ryoke mafic rocks. Such an isotopic relation between these two rocks suggests that a continental‐type lithosphere is widely represented beneath the western part of the Japanese Islands. 相似文献
839.
840.
Chin-Hsiung Loh Fwu-Shing Baw
Yeong-Tein Yeh
《Soil Dynamics and Earthquake Engineering》1992,11(8):497-508The objectives of this paper are (1) to obtain estimates on the effect of uncertainties of the hazard model, and (2) to evaluate the seismic hazard in Taiwan for structural analysis and design purposes. The seismic hazard in the Taiwan area is presented in terms of an iso-acceleration map. Such a map is developed for return periods of peak ground acceleration of 225 years and 475 years. The contour map of b-values and mean occurence rates for this region is also presented. Uncertainty analyses of model parameters in hazard analysis are concentrated on the analysis of dispersion of PGA values and the probabilistic modeling of stationary and nonstationary Poisson models of occurrences. Th e overall results are considered to be conservative since for most uncertainty analyses the more conservative values are used. 相似文献