全文获取类型
收费全文 | 836篇 |
免费 | 164篇 |
国内免费 | 128篇 |
专业分类
测绘学 | 115篇 |
大气科学 | 23篇 |
地球物理 | 206篇 |
地质学 | 465篇 |
海洋学 | 118篇 |
天文学 | 41篇 |
综合类 | 56篇 |
自然地理 | 104篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 22篇 |
2021年 | 44篇 |
2020年 | 48篇 |
2019年 | 32篇 |
2018年 | 29篇 |
2017年 | 41篇 |
2016年 | 42篇 |
2015年 | 40篇 |
2014年 | 69篇 |
2013年 | 65篇 |
2012年 | 58篇 |
2011年 | 47篇 |
2010年 | 60篇 |
2009年 | 45篇 |
2008年 | 59篇 |
2007年 | 53篇 |
2006年 | 58篇 |
2005年 | 60篇 |
2004年 | 40篇 |
2003年 | 24篇 |
2002年 | 21篇 |
2001年 | 26篇 |
2000年 | 26篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1128条查询结果,搜索用时 15 毫秒
521.
?????????????????CEGM02????????LRO_LTM02??????????????α?????????????ο??????棬??????????????棬??????λ??W0??=2 822 327.8±16.2 m2 s-2??????????????????????????????????1 737 462 m??????????1/2 579?????????1/6 863??????????-76.8 ″??????ο???????òο??????????????????????????????????????С?60×10-5ms-2??????????????25×10-5ms-2?????????????-325.9 ??389.1 m?? 相似文献
522.
This study analyses beach morphological change during six consecutive storms acting on the meso‐tidal Faro Beach (south Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub‐aerial beach profile was monitored through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics, and wave run‐up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of steep‐sloping beaches, since sub‐aerial beach volume reductions up to 30 m3/m were followed by intertidal area recovery (–2 < z < 3 m) with rates reaching ~10 m3/m. However, the observed cumulative dune erosion and profile pivoting imply that storms, even of regular intensity, can have a dramatic impact when they occur in groups. Nearshore bars seemed to respond to temporal scales more related to storm sequences than to individual events. The formation of a prominent crescentic offshore bar at ~200 m from the shoreline appeared to reverse the previous offshore migration trend of the inner bar, which was gradually shifted close to the seaward swash zone boundary. The partially understood nearshore bar processes appeared to be critical for storm wave attenuation in the surf zone; and were considered mainly responsible for the poor interpretation of the observed beach behaviour on the grounds of standard, non‐dimensional, morphological parameters. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
523.
524.
月球正面撞击坑的空间分布特征分析 总被引:1,自引:0,他引:1
通过IAU最新公布的撞击坑名录、“嫦娥一号”影像与DEM数据,本文使用数理统计和空间分析的方法研究了月球正面撞击坑分布的空间不均衡性.主要体现在:(1)月球正面直径较大的撞击坑主要分布在月陆区域,且集中趋势明显,而月海区域直径较大的撞击坑分布较少,周围有大量直径较小的撞击坑;(2)直径较大的撞击坑在月表具有一定随机性,... 相似文献
525.
盛强 《CT理论与应用研究》2012,21(2):197-204
近年来,泡沫流体在三次采油中越来越受到学者重视,在提高三次采油采收率机理研究方面,计算机层析(CT)有着自身技术上的优势。本文利用ACTIS微焦点X-rayCT技术对三次采油中泡沫驱油岩心进行研究与分析,直观地描述岩心中泡沫的特征与分布规律。采用可视化新方法研究得出泡沫驱油中的流体饱和度分布,揭示泡沫驱油特征机理。研究结果对于指导矿场试验具有重要意义。 相似文献
526.
Recovery of Plant Nutrients from Dilute Solutions of Human Urine and Preliminary Investigations on Pot Trials 总被引:1,自引:0,他引:1
Within the context of Ecological Sanitation (ECOSAN), human urine has been the subject of research and practice as a potential fertilizer in the recent years. Although quite a lot had been done with original undiluted urine with promising outcomes, not much appears in the literature which concentrates on dilute solutions of urine. This is important because unless waterless toilets are employed, urine will be diluted with flush water in actual use. In this work, dilute solutions of urine are investigated with emphasis on the recovery of plant nutrients. A natural zeolite namely clinoptilolite was loaded with nitrogen, phosphorus, and potassium as an indirect route of processing urine. The results have revealed that hydrolysis is completed in shorter times in dilute samples. Clinoptilolite could successfully remove plant nutrients from all dilute solutions. Nitrogen could be recovered up to 86% with higher efficiencies at higher concentrations in general. Recovery of orthophosphates increases with increasing concentration to reach 96%, however, potassium could not be recovered. The preliminary experiments with grass have revealed that nutrient loaded clinoptilolite was as effective as chemical fertilizers while direct application of original and diluted solutions of urine had shown inferior yields. 相似文献
527.
地震数据重构问题是一个病态的反演问题. 本文基于地震数据在curvelet域的稀疏性, 将地震数据重构变为一个稀疏优化问题, 构造0范数的逼近函数作为目标函数, 提出了一种投影梯度求解算法. 本文还运用最近提出的分段随机采样方式进行采样, 该采样方式能够有效地控制采样间隔并且保持采样的随机性. 地震数值模拟表明, 基于0范数逼近的投影梯度法计算效率有明显的提高; 分段随机采样方式比随机欠采样有更加稳定的重构结果. 相似文献
528.
摩擦摆隔震支座理论分析与数值模拟研究 总被引:5,自引:0,他引:5
介绍了摩擦摆隔震支座的基本构成和隔震原理。利用力学平衡原理,对摩擦摆隔震支座进行了理论分析,推导了摩擦摆隔震支座的刚度和等效粘滞阻尼比,构造了摩擦摆隔震支座的滞回模型,并探讨了该支座的自回复能力,得到了其最大残余位移计算公式。采用有限元软件ABAQUS,对摩擦摆隔震支座进行实体单元建模,模拟低周反复荷载作用下,该支座的滞回特性与回复特性。研究结果表明:①理论分析和数值模拟结果吻合较好,验证了提出的滞回模型和最大残余位移计算公式的正确性;②摩擦摆隔震支座的滞回曲线饱满,具有良好的滞回性能;③摩擦摆隔震支座的刚度与球面半径成反比,可能的最大残余位移为摩擦系数和球面半径的乘积;④该支座的最大应力出现在支座处于设计位移的时刻,且一般位于滑块或支座板球铰面边缘。 相似文献
529.
M. J. Winterbourn 《新西兰海洋与淡水研究杂志》2013,47(3):459-465
The distribution of algae and insects was examined in two hot spring outflow channels at Waimangu in the Rotorua thermal district. The upper temperature limit for algal growth was 68°c, with maximum biomass occurring at 59–62°c. Two species of Diptera were present on the algal mat, Ephydrella thermarum Dumbleton at 34–43°c and Chironomus cylindricus Freeman at 39–41°c. The composition and temperature relations of the community are similar to those found in thermal regions in other parts of the world. 相似文献
530.
CE-1伽马能谱测量中4种月球岩石的能谱特征分析 总被引:1,自引:0,他引:1
从CE-1 γ能谱测量获得的数据出发,对原始数据进行处理,将原始谱线按每5°×5°网格内平均而获得月表上的γ能谱数据。选取了12条不同位置分别代表玄武岩、斜长岩、富镁岩和KREEP岩的能谱曲线进行分析,发现同一岩性的谱线具有相似性。通过对每种岩性选择的一条谱线进行分析可知,不同的岩性能谱曲线有一定的差别,表现为不同岩性在元素特征能谱峰的变化不同,玄武岩的能谱曲线特征峰主要的元素为Th、K、Si、Ca、C、Fe和Ti;斜长岩的能谱曲线特征峰主要元素为U、Ca、C、Mg、Al和Mn。KREEP岩的能谱曲线特征峰主要为K、Th、U、Si、Ca和Fe,而低C和Al;富镁岩能谱曲线表现为低U、Si、Ca和Cl而高K、Mg、Th和Fe含量特征。文中给出了能较好区分不同岩性的元素特征峰能量,可为月表γ能谱的定量分析奠定基础。 相似文献