全文获取类型
收费全文 | 358篇 |
免费 | 62篇 |
国内免费 | 94篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 6篇 |
地球物理 | 66篇 |
地质学 | 350篇 |
海洋学 | 36篇 |
综合类 | 18篇 |
自然地理 | 37篇 |
出版年
2024年 | 4篇 |
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 8篇 |
2017年 | 16篇 |
2016年 | 23篇 |
2015年 | 22篇 |
2014年 | 26篇 |
2013年 | 39篇 |
2012年 | 24篇 |
2011年 | 35篇 |
2010年 | 24篇 |
2009年 | 22篇 |
2008年 | 30篇 |
2007年 | 12篇 |
2006年 | 27篇 |
2005年 | 14篇 |
2004年 | 20篇 |
2003年 | 23篇 |
2002年 | 28篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 2篇 |
排序方式: 共有514条查询结果,搜索用时 15 毫秒
101.
Root properties of vegetation communities and their impact on the erosion resistance of river dikes 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《地球表面变化过程与地形》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wouter Vannoppen Jean Poesen Patrik Peeters Sarah De Baets Bart Vandevoorde 《地球表面变化过程与地形》2016,41(14):2038-2046
Predicted climate change and the associated sea level rise poses an increased threat of flooding due to wave overtopping events at sea and river dikes. To safeguard the land from flooding it is important to keep the soil erosion resistance at the dikes high. As plant roots can be very effective in reducing soil erosion rates by concentrated flow, the main goal of this study is to explore the variability in root system characteristics of five dike vegetation communities along the Scheldt River (Belgium) and to assess their effectiveness in controlling soil erosion rates during concentrated flow. This study is the first one to investigate systematically the erosion‐reducing potential of the root properties of representative dike vegetation communities in a temperate humid climate. Results show that the presence of Urtica dioica resulted in large differences in root length density (RLD) among dike vegetation communities. Observed RLD values in the topsoil ranged from 129 to 235 km m‐3 for dike vegetation communities without U. dioica, while smaller values ranging from 22 to 58 km m?3 were found for vegetation communities with U. dioica. The erosion‐reducing effect of the dike vegetation communities was estimated based on a global Hill curve model, linking the RLD to the soil detachment ratio (SDR; i.e. the ratio of the soil detachment rate for root‐permeated topsoils to the soil detachment rate for root‐free topsoils). Concentrated flow erosion rates are likely to be reduced to 13–16% of the erosion rates for root‐free topsoils if U. dioica is absent compared to 22–30% for vegetation communities with U. dioica. Hence, to maintain a high resistance of the soil against concentrated flow erosion it is important to avoid the overgrowth of grassland by U. dioica through an effective vegetation management. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
102.
103.
针对在钻探实践中高能射流式冲击器的活塞杆频繁出现尾部塑性变形严重影响冲击器工作性能和整体寿命的现象,拟对活塞杆进行优化改进。利用非线性动力学仿真软件Ls-Dyna对活塞杆的回程撞击缸体进行数值模拟和优化分析,并进行了室内试验,结果表明:冲击末速度为4 m/s,活塞杆回程撞击缸体强制停止运动瞬间,尾部产生的应力集中值为3 339.28 MPa,导致其破坏;优化改进后,活塞杆上下端直径比为17/16、尾部圆弧直径为60 mm,活塞杆体内的应力集中值为1 419.66 MPa,较改进前活塞杆的应力集中值减小58%。试验验证表明,优化后的活塞能大幅提高使用寿命和耐久性。 相似文献
104.
庐江-枞阳矿集区深部结构与成矿 总被引:22,自引:1,他引:21
为探测长江中下游成矿带庐江?枞阳白垩纪火山岩盆地和铁、硫矿集区深部构造和地壳结构, 探讨成矿深部控制条件, 作者完成了穿越火山岩盆地的深反射地震剖面(记录30 s)和罗河铁矿区浅层高分辨反射地震剖面, 揭示了矿集区全地壳精细结构, 同时开展区域构造测量和应力场反演研究, 获得了新的认识。证实“耳状”的庐?枞火山岩盆地是一个沿北东向罗河断裂向东发育的非对称火山盆地, 排除了另一半被断在西侧红层之下的判断;罗河断裂是一条切穿MOHO的深断裂, 倾向南东, 是引导地幔流体和岩浆上涌和喷发的通道;鉴别出多层界面, 火山岩?侏罗系砂岩厚约4?5 km(其中火山岩厚度约3 km), 三叠系?震旦系变形层底界深度大致18?20 km, 变质基底组成中下地壳, MOHO平缓向西北倾, 深度33?31 km;追踪郯?庐断裂带的深部产状, 陡立延伸到MOHO, 宽约10 km。 相似文献
105.
京石客运专线石家庄明挖隧道工程与既有京广铁路线近距离并行长达5 km,为了摸清列车动载对桩锚支护结构的影响,以及不同锚固形式对动载的响应特点,特在该隧道设立压力分散型锚索试验段,与现场普遍采用的拉力集中型锚索锚固段相对照,进行长期应力、应变量测。在此基础上,对实测数据进行了系统的整理和分析,对比了压力分散型锚索与拉力集中型锚索在应对动载方面的不同特性。研究表明,压力分散型锚索的抗振性能是拉力集中型锚索的5倍,而且具有应力调整时间短、长期抗振性能稳定,预应力损失幅度小、比例低的优点。 相似文献
106.
107.
108.
In this paper, the application of an efficient, transparent and accurate kinematic-cyclic constitutive model based on the fuzzy-set concepts and incremental plasticity theory is presented to show its capability in modeling cyclic mobility of saturated granular soil. The nature and kinematic mechanism of the membership functions in the fuzzy-set constitutive model are illustrated. The model’s capability of modeling soil dilatancy is investigated. Important features of volume change and pore water pressure build-up related to soil cyclic mobility are captured. The formulation of the proposed model is relatively simple and it can be readily implemented in finite element codes. The enhanced fuzzy-set model is capable of simulating ground motion problems particularly related to cyclic mobility, soil liquefaction, and spreading behavior. 相似文献
109.
Marco A. Lardies José Luis Muñoz Kurt A. Paschke Francisco Bozinovic 《Marine Ecology》2011,32(1):42-51
The colonisation of the terrestrial environment by crustaceans is more apparent in tropical latitudes because of the high diversity of semi‐terrestrial and terrestrial crabs. However, in temperate regions there are also great numbers of crustaceans that inhabit ecological niches at the water–air interface. Grapsidae crabs (Decopoda) are especially important in studies of water‐to‐land transition as the family contains species occupying the intertidal and adjacent regions. A way to evaluate the ability of intertidal invertebrates to breathe air is to measure the aerial/aquatic oxygen consumption ratio. The objective of this study was to test the effect of thermal variation on the aquatic and aerial metabolism. We selected as study model the decopoda crab Cyclograpsus cinereus Dana and utilised five populations of the species spread over 2000 km along the Chilean coast. To determine the compensation capacity in respiration with respect to latitude, we evaluated metabolic rate at the same temperature in a common garden design in the laboratory, to examine the extent to which variation in crab physiology is environmentally determined. Whereas in our study, mb (body mass) varied significantly with latitude, the difference in mass‐independent metabolism both in air and water persisted, indicating that observed differences in MR (Metabolic Rate) were not an effect of differences in body size. We demonstrated that C. cinereus is able to breath oxygen from air and water as expected for an amphibious crab. Almost all the studied populations of C. cinereus show a aerial/aquatic metabolism ratio near 1. The pattern found indicates an increase in metabolic rate, both aerial and aquatic, in low latitudes and therefore does not support the latitudinal compensation hypothesis for temperate habitats. Finally, these kinds of studies are required to make the necessary link between ecological physiology and macroecology and to help develop a global understanding of organismal function in marine systems. 相似文献
110.