全文获取类型
收费全文 | 14155篇 |
免费 | 2818篇 |
国内免费 | 3776篇 |
专业分类
测绘学 | 1501篇 |
大气科学 | 2556篇 |
地球物理 | 3452篇 |
地质学 | 7539篇 |
海洋学 | 2227篇 |
天文学 | 570篇 |
综合类 | 1218篇 |
自然地理 | 1686篇 |
出版年
2024年 | 100篇 |
2023年 | 316篇 |
2022年 | 722篇 |
2021年 | 832篇 |
2020年 | 676篇 |
2019年 | 768篇 |
2018年 | 809篇 |
2017年 | 802篇 |
2016年 | 832篇 |
2015年 | 830篇 |
2014年 | 861篇 |
2013年 | 966篇 |
2012年 | 1044篇 |
2011年 | 1038篇 |
2010年 | 1042篇 |
2009年 | 984篇 |
2008年 | 1002篇 |
2007年 | 868篇 |
2006年 | 743篇 |
2005年 | 685篇 |
2004年 | 515篇 |
2003年 | 447篇 |
2002年 | 491篇 |
2001年 | 458篇 |
2000年 | 455篇 |
1999年 | 423篇 |
1998年 | 317篇 |
1997年 | 298篇 |
1996年 | 252篇 |
1995年 | 236篇 |
1994年 | 158篇 |
1993年 | 182篇 |
1992年 | 119篇 |
1991年 | 93篇 |
1990年 | 55篇 |
1989年 | 75篇 |
1988年 | 61篇 |
1987年 | 29篇 |
1986年 | 24篇 |
1985年 | 20篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1958年 | 12篇 |
1957年 | 6篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
鄂尔多斯盆地延安组在全盆地发育,是盆地内最重要的含煤、油、气地层之一,依据大量的钻井、测井资料,运用沉积学的方法,对东胜煤田艾来五库沟-台吉召延安组沉积体系及聚煤特征进行了分析。研究认为延安组为辫状河、曲流河及辫状河三角洲沉积,沉积微相主要发育有辫状河体系的河床滞留沉积及心滩、河漫滩和河漫沼泽沉积;曲流河体系的河床滞留沉积、边滩、天然堤、河漫滩、河漫沼泽和河漫湖泊沉积;辫状河三角洲体系的分支河道、天然堤和河漫沼泽沉积等。辫状河及曲流河垂向上表现为下粗上细的间断性正韵律或正旋回,为典型的河流二元结构特征。聚煤特征分析认为,辫状河和曲流河体系河漫沼泽环境是有利成煤场所,由于河道的冲刷、下切作用,辫状河道和曲流河道形成的煤层厚度较小、侧向连续性差;三角洲体系的三角洲平原是有利的成煤带,其煤层具有厚度较大、结构较为简单、分布范围较广、连续性较好的特征。 相似文献
182.
In the geological evolution of the Tarim Basin, many transgressions and relictions happened. So there have been plentiful sources of salt. Moreover, because of uttermost drought, a lot of salt has been deposited. It is possible to find potash salt in this area. In our fieldwork, we have found salt and brine in western Tarim Basin. Based on a geological survey and the characteristics of sedimentary facies and paleogeography, this paper deals with the geochemical parameters and discusses the possibility of formation of potash salt in terms of the chemical analyses of samples collected from western Tarim Basin. Results of brine analysis lead to some conclusions: most of these salt brines have eluviated from very thick halite beds, mainly chloridetype salt and this kind of halite does not reach the stage of potash deposition in all aspects; WKSL (Wukeshalu) occupies a noticeable place, and we should attach importance to this district because there have been some indicators of the occurrence of potash deposits as viewed from the contents of Br and K. Finally, low Br contents are recognized in the Tarim Basin as a result of salt aggradation, and this point of view has been proved by the results of this experiment and the data available. It cannot depend upon the index of Br to judge the evolution stage of halite. We must look for other facies of potash except marine facies. 相似文献
183.
Xisheng Xu William L. Griffin Xi Ma Suzanne Y. O’Reilly Zhenyu He Chengli Zhang 《Mineralogy and Petrology》2009,97(1-2):43-59
The "Taihua Group" is a collective term for a series of old terranes scattered along the southern margin of the North China Craton. The timing of formation and thermal overprinting of the Taihua Group have long been contentious, and its relationship with the Qinling orogenic belt has been unclear. In this study, new data from integrated in-situ U–Pb dating and Hf isotope analysis of zircons from an amphibolite (from the Xiong’ershan terrane) and a biotite gneiss (from the Lantian-Xiaoqinling terrane) indicate that the Upper Taihua Group formed during the Paleoproterozoic (2.3–2.5 Ga) and thus was originally part of the southern edge of North China Craton, detached during the Mesozoic Qinling orogeny and displaced about 100 km north from its original location. This suggests that the Taihua Group became part of the tectonic terrane associated with the Qinling orogeny and now forms part of the overthrust basement section of the Qinling belt. Before the Qinling orogeny, the Taihua Group was metamorphosed at 2.1 Ga. The initial Hf-isotope compositions of zircons, together with positive εNd(t) values for the whole-rocks, imply that the original magmas were derived from a juvenile source with some assimilation of an Archean crustal component. 相似文献
184.
表生异极矿成因研究及其找矿意义 总被引:2,自引:0,他引:2
云南金顶异极矿产于铅锌矿床氧化带中,基于对该矿床异极矿产出特征、颜色环带、不同颜色环带的成份、显微结构以及其他铅锌氧化物的分析,认为异极矿是由硅酸与锌的重碳酸盐溶液反应生成。镜下异极矿集合体纤维交织结构、环带结构、毛粘状结构等显微结构特征分析表明异极矿是表生环境下形成。扫描电镜获得异极矿清晰的单晶体、集合体和晶体间充填物的图像,晶体大小约为100μm~300μm,晶体间片状充填物约为250μm。同时对云南金顶铅锌矿床和异极矿与其他地区铅锌矿床和异极矿产出特征进行比较认为:异极矿一般产出于铅锌矿床表生氧化带,在风化淋滤作用较强环境下产出,对矿床环境和原生铅锌矿床找矿有一定指示意义。 相似文献
185.
186.
Spatial prediction of soil water content in karst area using prime terrain variables as auxiliary cokriging variable 总被引:1,自引:0,他引:1
In karst areas, accurately measuring and managing the spatial variability of soil water content (SWC) is very critical in settling numerous issues such as karst rocky desertification, ecosystem reconstruction, etc. In these areas, SWC exhibits strong spatial dependence, and it is a time and labor consuming procedure to measure its spatial variability. Therefore, estimation of this kind of soil property at an acceptable level of accuracy is of great significance. This study was conducted to evaluate and compare the spatial estimation of SWC by using ordinary kriging (OK) and cokriging (COK) methods with prime terrain variables, tending to predict SWC using limited available sample data for a 2,363.7 km2 study area in Mashan County, Guangxi Zhuang Autonomous Region, Southwest China. The measured SWC ranged from 3.36 to 26.69 %, with a mean of 17.34 %. The correlation analysis between SWC and prime terrain variables indicated that SWC showed significantly positive correlation with elevation (r is 0.46, P < 0.01), and significantly negative correlation with slope (r is ?0.30, P < 0.01); however, SWC was not significantly correlated with aspect in the study area. Therefore, elevation and slope were used as auxiliary data together for SWC prediction using COK method, and mean error (ME) and root mean square error were adopted to validate the prediction of SWC by these methods. Results indicated that COK with prime terrain variables data was superior to OK with relative improvement of 28.52 % in the case of limited available data, and also revealed that such elevation and slope data have the potential to improve the precision and reliability of SWC prediction as useful auxiliary variables. 相似文献
187.
188.
内蒙古白乃庙铜-金-钼矿床成矿机制——来自流体包裹体和He-Ar同位素的证据 总被引:1,自引:0,他引:1
白乃庙铜-金-钼矿是华北板块北缘中段一个重要矿床,其矿化特征既显示斑岩型蚀变特征,同时又表现出明显的后期造山作用改造的特点。本次研究通过系统的流体包裹体显微测温、激光拉曼和气液相色谱分析揭示其成矿流体为中—低温、中低盐度的CO_2(CO)-H_2O-CH_4(C_2H_2+C_2H_4)-NaCl-CaCl_2体系,流体混合作用和CO_2逃逸为成矿主要因素。富还原性流体的存在可能促使气相流体携带大量的Cu、Au等成矿元素迁移至较远点的白乃庙群地层,沿着片理或裂隙沉淀成矿。对不同成矿阶段矿石中黄铁矿的He-Ar同位素组成测试结果显示白乃庙矿床黄铁矿流体包裹体的~3He/~4He比值在0.06~0.71Ra之间,~(40)Ar/~(36)Ar比值为375.5~1436.3,指示成矿体系由不同性质和组成的两个端元流体混合而成,即混入了类似于MORB型地幔端元的高温高盐度流体和富含地壳放射成因氦但具有空气氩同位素组成特征的低温大气降水。白乃庙矿床属受后期造山作用改造的斑岩型铜-金-钼矿床,形成于古亚洲洋板块持续向南俯冲背景。 相似文献
189.
190.
成矿系统嵌套分形结构和自有序效应 总被引:10,自引:0,他引:10
成矿系统具有嵌套分形结构 ,岩石孔隙结构的传输性质制约着聚矿功能的实现。矿床(脉 )群聚分形分布特征明显 ,数量随时代先后呈幂律增长 ,成矿裂隙系统分维值大 ,高含量矿脉分维值低 ,这为隐伏矿床 (体 )预测提供了依据。裂隙生长是一种自组织临界现象 ,矿脉起源于微裂隙发展而成的张性裂隙 ,并最终形成脉系。超大型矿床的裂隙系统表现为临界分维状态 (5~ 12 5km ,D≈ 1 5;0 5~ 2 0km ,D≈ 1 3;1~ 10 0cm ,D≈ 1 5;0 0 0 36~ 0 18cm ,D =1 2 8~1 39)。成矿元素运移通过扩散和渗流实现 ,扩散速率的差异性导致运移路径的有序性 ,流体流动导致金及金属硫化物在界面处发生反应而沉淀成矿 ,矿床密度分布随矿化中心距离增大而减小的自有序效应保证了成矿系统的组织层次性。输运反应耦合成矿动力学计算机模拟验证了分形脉体演化模式和自有序效应。 相似文献