全文获取类型
收费全文 | 659篇 |
免费 | 103篇 |
国内免费 | 141篇 |
专业分类
测绘学 | 70篇 |
大气科学 | 146篇 |
地球物理 | 170篇 |
地质学 | 267篇 |
海洋学 | 117篇 |
天文学 | 54篇 |
综合类 | 53篇 |
自然地理 | 26篇 |
出版年
2024年 | 10篇 |
2023年 | 29篇 |
2022年 | 64篇 |
2021年 | 54篇 |
2020年 | 30篇 |
2019年 | 38篇 |
2018年 | 9篇 |
2017年 | 16篇 |
2016年 | 47篇 |
2015年 | 22篇 |
2014年 | 31篇 |
2013年 | 18篇 |
2012年 | 26篇 |
2011年 | 39篇 |
2010年 | 35篇 |
2009年 | 39篇 |
2008年 | 61篇 |
2007年 | 36篇 |
2006年 | 42篇 |
2005年 | 38篇 |
2004年 | 24篇 |
2003年 | 31篇 |
2002年 | 24篇 |
2001年 | 25篇 |
2000年 | 23篇 |
1999年 | 25篇 |
1998年 | 13篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有903条查询结果,搜索用时 15 毫秒
101.
含钙铝铁水解聚合产物的矿物学研究Ⅱ:热分解特性 总被引:2,自引:2,他引:0
分别以NaOH和Ca(OH)2作为碱化剂,合成了聚合氯化铝铁(PAFCNa,PAFCCa),比较样聚合氯化铝(PACNa,PACCa)、聚合氯化铁(PFCNa,PFCCa),制成低温干燥样进行热分解检测.热重分析证明,PAFCCa中的含水量高,主要是配位水与结晶水.当n(Al)/n(Fe)>5:5后,PAFCCa的含水量平均为42.3%.按Ca6Al2(SO4)3(OH)12·26H2O分子式计算,钙矾石的结构水(含OH水)含量为43.06%,两者含水量相当接近.TG-DTG热分析结果支持XRD对PAFCCa中存在含Ca3Al2(OH)12柱体的类钙矾石结构体的认定.PAFC-Ca根据其DTG曲线上的125℃和180℃两个脱水速率(肩)峰可以判别其中有无钙矾石结构体,以及相对量的多少. 相似文献
102.
本文介绍了几种纵横断面测设的常用方法及记录方法 ,通过数据传输和数据格式的转换 ,在AutoCADR14环境下 ,利用VB6和AutoLISP语言 ,自动生成断面图 ,形成标准格式的电子文件。 相似文献
103.
104.
R. Morales A. C. Fabian C. S. Reynolds 《Monthly notices of the Royal Astronomical Society》2000,315(1):149-154
The variable warm absorber seen with ASCA in the X-ray spectrum of MCG–6-30-15 shows complex time behaviour in which the optical depth of O viii anticorrelates with the flux whereas that of O vii is unchanging. The explanation in terms of a two-zone absorber has since been challenged by BeppoSAX observations. These present a more complicated behaviour for the O viii edge. We demonstrate here that the presence of a third, intermediate, zone can explain all the observations. In practice, warm absorbers are likely to be extended, multi-zone regions of which only part causes directly observable absorption edges at any given time. 相似文献
105.
Kenneth L. Pierce Daniel R. Muhs Shannon A. Mahan Joseph M. Licciardi 《Quaternary Research》2011,76(1):119-141
Loess accumulated on a Bull Lake outwash terrace of Marine Oxygen Isotope Stage 6 (MIS 6) age in southern Jackson Hole, Wyoming. The 9 m section displays eight intervals of loess deposition (Loess 1 to Loess 8, oldest), each followed by soil development. Our age-depth model is constrained by thermoluminescence, meteoric 10Be accumulation in soils, and cosmogenic 10Be surface exposure ages. We use particle size, geochemical, mineral-magnetic, and clay mineralogical data to interpret loess sources and pedogenesis. Deposition of MIS 6 loess was followed by a tripartite soil/thin loess complex (Soils 8, 7, and 6) apparently reflecting the large climatic oscillations of MIS 5. Soil 8 (MIS 5e) shows the strongest development. Loess 5 accumulated during a glacial interval (~ 76-69 ka; MIS 4) followed by soil development under conditions wetter and probably colder than present. Deposition of thick Loess 3 (~ 43-51 ka, MIS 3) was followed by soil development comparable with that observed in Soil 1. Loess 1 (MIS 2) accumulated during the Pinedale glaciation and was followed by development of Soil 1 under a semiarid climate. This record of alternating loess deposition and soil development is compatible with the history of Yellowstone vegetation and the glacial flour record from the Sierra Nevada. 相似文献
106.
107.
Genetic algorithm for fitting a mixed Bingham distribution to 3D orientations: a tool for the statistical and paleostress analyses of fracture orientations 下载免费PDF全文
Atsushi Yamaji 《Island Arc》2016,25(1):72-83
The clustering of fracture orientations is important for tectonic studies and for geotechnical engineering. In this study, a real‐coded genetic algorithm was adopted to fitting a mixed Bingham distribution to orientation data by maximizing the log‐likelihood function of the distribution. The maximization is a difficult problem, because the function has multimodality and singularity. It was found that the algorithm was effective for this problem. Given the orientations of dilational fractures, the present method determines not only the stress axes and stress ratio of each of the fracture groups but also the maximum non‐dimensionalized fluid pressure at the time of their formation. In addition, the software calculates the 95 % error ellipses of the concentration axes. The present method found that the orientations of ore veins of the Akenobe Mine, SW Japan, should be partitioned into three clusters. It is shown that two of the groups had distinctive Zn and Sn contents, and that the ore fluids had overpressures only slightly greater than the minimum principal stress at the time of the deposition of Zn‐ and Sn‐rich veins. 相似文献
108.
利用第六次国际耦合模式比较计划(CMIP6)提供的5个气候模式,并结合基于地面气象站的CN05.1气象资料,评估了CMIP6模式对黄河上游地区1961—2014年气温变化的模拟能力。基于7个共享社会经济路径及代表性浓度路径(SSP-RCP)组合情景,结合多模式集合平均预估了2015—2100年黄河上游地区年均气温和季平均气温的时空变化规律。结果表明:多模式集合平均能较好地模拟黄河上游地区历史平均气温的空间分布格局与年变化。7个未来情景一致表明,2015—2100年黄河上游地区年平均气温呈现波动上升趋势[0.03~0.82 ℃?(10a)-1]。其中,低辐射强迫情景下(SSP1-1.9、SSP1-2.6及SSP4-3.4)气温先呈现增加趋势,21世纪中期到达增幅峰值,之后增温呈现放缓趋势;而中、高辐射强迫情景下(SSP2-4.5、SSP3-7.0、SSP4-6.0及SSP5-8.5)气温表现为持续上升态势。空间上,未来气温增幅显著的区域位于黄河上游西部地区;时间上,呈现夏季增温快,春季增温慢。四季增温的空间分布呈现出一致特征,表现为西部增温强于东部,北部增温强于南部。研究结果可为黄河流域水资源管理及气候变化的适应性研究提供科学依据。 相似文献
109.
110.
A new Lower Triassic (Induan) Jerus Limestone locality in northwest Pahang,Peninsular Malaysia: Conodont fauna,depositional and tectonic settings 下载免费PDF全文
Ian Metcalfe 《Island Arc》2016,25(2):126-136
Limestones exposed north of Raub, Pahang, Malaysia, and sandwiched between the Bentong‐Raub Suture Zone and the westernmost margin of the Sukhothai Arc terrane, yield a late Dienerian (late Induan) conodont fauna. The co‐occurrence of Neospathodus dieneri Sweet (morphotypes 1, 2 and 3) and Neospathodus pakistanensis Sweet represents the Neospathodus dieneri morphotype 3 sub‐zone of the Neospathodus dieneri Zone. The sampled limestones are interpreted as the northwards extension of the Jerus Limestone which crops out near Cheroh and Jerus villages, significantly extending the known outcrop of the Jerus Limestone northwards. The Jerus Limestone is interpreted as hemipelagic and formed in a foredeep or forearc setting on top of the accretionary complex formed by eastwards subduction of the Palaeo‐Tethys during the Lower to Middle Triassic. 相似文献