全文获取类型
收费全文 | 4408篇 |
免费 | 969篇 |
国内免费 | 808篇 |
专业分类
测绘学 | 762篇 |
大气科学 | 753篇 |
地球物理 | 1587篇 |
地质学 | 1765篇 |
海洋学 | 560篇 |
天文学 | 39篇 |
综合类 | 334篇 |
自然地理 | 385篇 |
出版年
2024年 | 26篇 |
2023年 | 57篇 |
2022年 | 148篇 |
2021年 | 184篇 |
2020年 | 238篇 |
2019年 | 255篇 |
2018年 | 205篇 |
2017年 | 240篇 |
2016年 | 232篇 |
2015年 | 248篇 |
2014年 | 340篇 |
2013年 | 367篇 |
2012年 | 381篇 |
2011年 | 336篇 |
2010年 | 263篇 |
2009年 | 255篇 |
2008年 | 273篇 |
2007年 | 308篇 |
2006年 | 277篇 |
2005年 | 263篇 |
2004年 | 180篇 |
2003年 | 159篇 |
2002年 | 137篇 |
2001年 | 124篇 |
2000年 | 107篇 |
1999年 | 111篇 |
1998年 | 70篇 |
1997年 | 65篇 |
1996年 | 64篇 |
1995年 | 42篇 |
1994年 | 51篇 |
1993年 | 54篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有6185条查询结果,搜索用时 15 毫秒
991.
《水文科学杂志》2013,58(4):655-664
Abstract Palaeohydraulic modelling is presented for Athabasca Vallis, the youngest known catastrophic flood channel on Mars. This modelling incorporates three significant advantages over previous modelling of Martian channels: a step-backwater hydraulic model; more accurate topography; and improved flood height indicators. The maximum modelled palaeodischarge is between 1 × 106 and 2 × 106m3s?1 depending on the friction coefficient selected. An anomalously high palaeostage indicator suggests a region of ponded backwater in the channel in which streamlined forms were created through deposition, with the additional possibility of post-flood subsidence/lowering of the channel slope due to magma extrusion. 相似文献
992.
《水文科学杂志》2013,58(2):387-400
Abstract The effects of spatial variation of the saturated hydraulic conductivity (K s ) of the soil on the variation of overland flow were tested by analysing 2000 synthetic rainfall—runoff events, all generated from real, observed rainfall events but with runoff modelled by a two-dimensional distributed model using different spatially variable K s fields in a small (12 ha) agricultural catchment. The purpose is to determine the influence of spatial variation in K s on runoff generation. The statistical measures used to describe the variation in the generated K s were its coefficient of variation and correlation length. Both of these had two levels of typical values obtained from field measurements in other studies. The storms were analysed at a general event level, first using simple graphical and statistical methods and then using analysis of variance (ANOVA). The observed scale of the spatial variation of K s does cause statistically significant variation in overland flow. The graphical analysis showed that the first flow peak in a multi-event storm had the largest variation and that differences were greater in the rising part of the hydrograph than in its recession. The greatest variation in overland flow was produced by the combination of the greater coefficient of variation and the longer correlation lengths. The smallest variation in overland flow was produced by the combination of the smaller coefficient of variation and the shorter correlation lengths. ANOVA showed that the coefficient of variation and correlation length alone did not explain all the variation of the total flow. ANOVA was not very useful due to the many restrictive assumptions that were not satisfied by the nature of the data and therefore analysis methods with less restrictive assumptions need to be tested. 相似文献
993.
比赛用游泳馆泳池长度必须满足相应国际标准,对其精度有严格的质量控制。根据日照市游泳馆工程设计的特点及精度要求,提出了运用TCA2003型全站仪对游泳池长度进行全过程长度控制的方法,并进行了精度分析。 相似文献
994.
995.
针对油田联合站的主要工艺流程、生产要求及自动化仪表的配置情况,在现有力控组态软件的基础上,探讨了一种利用GIS技术特点的组态图应用模式,结合组态软件采集的实时生产数据,结合GIS化的工艺流程,为油田各级领导提供宏观与微观的生产状态展示与分析,辅助生产决策。 相似文献
996.
论述了双鸭山市测绘行业对双鸭山市连续运行卫星定位服务系统(SYS-CORS)暨南方NRS系统的需求,介绍了系统建设过程,同时介绍了系统测试状况,最后叙述系统的功能、本系统的创新点及系统为社会提供信息服务的前景。 相似文献
997.
为了适应测绘科学技术的信息化、自动化应用发展的需求,掌上电脑(PersonalDigitalAssistant,PDA)在测绘野外数据采集得到广泛应用,本文运用面向对象的思想设计并开发了野外数据采集成果预处理系统。该系统主要由数据通信、数据记录与检查、测量数据概算、原始成果记录表格自动生成、数据格式转换五个模块组成。将该系统与全站仪结合可实现野外测量数据的高效自动化数据采集及预处理概算,为内外业数据处理一体化奠定基础。 相似文献
998.
Rivers in drylands typically are characterized by extreme flow variability, with long periods of little or no flow interspersed with occasional large, sometimes extreme, floods. Complete adjustment of river form and process is sometimes inhibited, resulting in a common assumption that equilibrium conditions may rarely, if ever, exist in dryland rivers, and that transient and unstable (nonequilibrium) behavior is the norm. Examples from the Channel Country and the Northern Plains in central Australia challenge that notion. Along the middle reaches of these intermediate and large, low-gradient rivers, where long duration floods generate moderate to low unit stream powers and boundary resistance is high as a result of indurated alluvial terraces, cohesive muds or riparian vegetation, there is evidence that: (1) channels have remained essentially stable despite large floods; (2) sediment transport discontinuities, while present at a catchment scale, are largely insignificant for channel form and process in individual reaches; (3) there are strong correlations between many channel form and process variables; and (4) many rivers appear to be adjusted to maximum sediment transport efficiency under conditions of low gradient, abundant within-channel vegetation and declining downstream discharge. In these middle reaches, rivers are characterized by equilibrium conditions. However, in the aggradational lower reaches of rivers on the Northern Plains, where upstream terraces are buried by younger sediments and channels are less confined, nonequilibrium conditions prevail. Here, channels sometimes undergo sudden and substantial changes in form during large floods, sediment transport discontinuities are readily apparent, and landforms such as splays remain out-of-balance with normal flows. Hence, dryland rivers can exhibit both equilibrium and nonequilibrium conditions, depending on factors such as catchment size, channel gradient, flood duration, unit stream power, channel confinement, sediment cohesion, and bank strength. [Key words: dryland rivers, floods, equilibrium, nonequilibrium, central Australia.] 相似文献
999.
1000.