全文获取类型
收费全文 | 9083篇 |
免费 | 1917篇 |
国内免费 | 2699篇 |
专业分类
测绘学 | 1213篇 |
大气科学 | 1477篇 |
地球物理 | 2140篇 |
地质学 | 5003篇 |
海洋学 | 1533篇 |
天文学 | 397篇 |
综合类 | 793篇 |
自然地理 | 1143篇 |
出版年
2024年 | 93篇 |
2023年 | 303篇 |
2022年 | 596篇 |
2021年 | 716篇 |
2020年 | 632篇 |
2019年 | 691篇 |
2018年 | 636篇 |
2017年 | 591篇 |
2016年 | 626篇 |
2015年 | 622篇 |
2014年 | 640篇 |
2013年 | 702篇 |
2012年 | 740篇 |
2011年 | 668篇 |
2010年 | 620篇 |
2009年 | 613篇 |
2008年 | 606篇 |
2007年 | 487篇 |
2006年 | 440篇 |
2005年 | 320篇 |
2004年 | 250篇 |
2003年 | 193篇 |
2002年 | 217篇 |
2001年 | 189篇 |
2000年 | 180篇 |
1999年 | 207篇 |
1998年 | 177篇 |
1997年 | 152篇 |
1996年 | 156篇 |
1995年 | 106篇 |
1994年 | 86篇 |
1993年 | 89篇 |
1992年 | 84篇 |
1991年 | 59篇 |
1990年 | 40篇 |
1989年 | 26篇 |
1988年 | 30篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 3篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1979年 | 8篇 |
1977年 | 3篇 |
1958年 | 10篇 |
1957年 | 5篇 |
1954年 | 2篇 |
1933年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
复杂断块构造具有断层复杂,小断层广泛发育,断层识别难度大,储层分布及连通性复杂,地震成像不清、资料品质较差等特征。对于此类问题,常规地震资料无法满足断层解释精度要求。提出了一种新的断层EDF解释性处理技术,将地震资料处理与解释融为一体,以提高资料的信噪比和断层的识别能力。断层EDF解释性处理技术是利用扩散滤波和中值倾角滤波相结合的断层增强滤波方法来提高资料的信噪比,突出断层和地层的接触关系,再在滤波后的地震资料数据体上进行分频处理,选择最佳成像频带,突出识别不同规模的断层。通过在涠洲A油田的应用,取得了良好的效果。 相似文献
52.
53.
54.
Based on the analyses of mineralogical compositions by X-ray diffraction and microstructure by optical microscopy, the Young’ modulus and hardness of a claystone were characterized by the nano-indentation technique and homogenization method. Three distinct microstructural zones are identified in the claystone: clay matrix, a composite matrix of clay and small mineral grains and imbedded quartz grains. The elastic modulus and hardness of different zones were determined by nano-indentation testing. Based on the statistical analysis of nano-indentation results, the spatial mappings and frequency distributions of elastic modulus and hardness of the different zones were obtained. The elastic moduli of main constituent phases of the claystone are then estimated from the nano-indentation tests. These values were further used for the determination of the macroscopic elastic modulus of the claystone using two different homogenization schemes: the dilute scheme and Mori–Tanaka scheme. The predicted values by the homogenization schemes are compared with experimental data obtained from conventional uniaxial compression tests. 相似文献
55.
The aim of this paper is to propose a location model of earthquake emergency service depot on the basis of hybrid multi-attribute decision-making method. The advantage of the proposed method is that practical mixed uncertainty of location decision information is considered, and the corresponding factors that affect the location of transfer stations are contained. To solve the location problem, a hybrid multi-attribute decision procedure without information transformation is developed. Besides, a novel weighting method and aggregation process is given. Finally, a numerical example is provided to show the feasibility and validity of the proposed method. 相似文献
56.
在165℃、175℃、185℃和195℃的温度条件下,对水热处理前和处理后的粗晶三水铝石样品分别进行了XRD分析和SEM表征,研究了粗晶三水铝石在水蒸气和热水中转变成勃姆石的相变过程。结果表明,水热条件下粗晶三水铝石转化成勃姆石的过程受控于溶解-再沉淀机制,而并非是通常认为的固体状态下的转变;相对于在热水中,水蒸气环境可以加速三水铝石向勃姆石的转化;所形成的勃姆石的粒径(4~7 μm)明显比前驱体三水铝石的粒径(120~200 μm)要小得多,表明可以利用粗晶三水铝石生产微晶勃姆石。在转化过程中,勃姆石微晶首先生长在三水铝石的晶体表面上,通过控制反应温度和反应时间,可形成壳层为勃姆石、壳下为三水铝石的具有双层结构的铝的氢氧化物颗粒,也有可能形成具有中空结构的勃姆石集合体颗粒。 相似文献
57.
The Early Cretaceous deposits are composed of important source rocks in Boli Basin. The types of the source rocks include black mudstones and coal (with carbonaceous mudstone). By the organic geochemical analysis methods, the authors discussed the organic petrological characters, abundance of organic matter, degree of maturity and the type of source rocks. The main micro-component of black mudstone is exinite or vitrinite, and the content of vitrinite is high in coal. The weathering of the outcrop is very serious. The abundance of organic matter in source rock reaches the poor to better rank. The major kerogens in mudstone are type-Ⅲ, type-Ⅱ2 and some type-Ⅱ1; the organic type of coal is type-Ⅲ. The thermal evolution of the source rocks in every structural unit is very different, from low-maturity to over-maturity. The depositional environment is reductive, which is good for the preservation of organic matter. The organic matter in source rocks is mainly from aquatic organisms and terrigenous input. 相似文献
58.
红层软岩边坡生态防护技术探讨 总被引:1,自引:0,他引:1
红层软岩边坡,土质贫瘠,浅层稳定性差,生态防护失效的现象比较突出。为提高西部红层软岩边坡生态防护的可靠性,在对西部红层软岩地区铁路、公路边坡生态防护状况进行调研和分析的基础上,总结红层软岩边坡生态防护失败的原因,吸取经验教训,提出适于红层软岩边坡的生态防护方法和适合该区栽植的草木品种及配置方法。 相似文献
59.
The conformity effect,indicating the evolution of galaxies is related to its surrounding neighbor galaxies as far as a few Mpc,is an interesting phenomenon in the modeling of galaxy and evolution.Here we study the conformity effect of HI galaxies in a matched galaxy sample between SDSS DR7 and ALFALFA surveys.By checking the probability difference for the detected H i galaxies as a function of distance around a normal or an H i galaxy,we find that this effect is significant out to 5 Mpc.It also shows a dependence on the stellar mass of galaxies,with the strength the strongest in the stellar mass range of 1010*/M⊙<1010.5.However,when the sample is confined to central galaxies in groups with virial radii smaller than 1 Mpc,the 1-halo conformity signal is still evident,while the 2-halo conformity signal is reduced to a very weak amplitude.Our results confirm the previous study in the optical band that the 2-halo term is possibly caused by the bias effect in the sample selection.Furthermore,we confirm the existence of the 1-halo conformity discovered in the optical and radio band in previous investigations.Our results provide another viewpoint on the conformity effect and hope to shed light on the co-evolution of the galaxies and their neighbors in the current galaxy formation models. 相似文献
60.
波浪在斜坡地形上破碎,破波后稳定波高多采用物理模型试验方法进行研究,利用近岸波浪传播变形的抛物型缓坡方程和波能流平衡方程,导出了适用于斜坡上波浪破碎的数值模拟方法。首先根据波能流平衡方程和缓坡方程基本型式分析波浪在破波带内的波能变化和衰减率,推导了波浪传播模型中波能衰减因子和破波能量流衰减因子之间的关系;其次,利用陡坡地形上的高阶抛物型缓坡方程建立了波浪传播和波浪破碎数学模型;最后,根据物理模型试验实测数据对数值模拟的效果进行验证。数值计算与试验资料比较表明,该模型可以较好地模拟斜坡地形的波浪传播波高变化。 相似文献