全文获取类型
收费全文 | 2366篇 |
免费 | 294篇 |
国内免费 | 468篇 |
专业分类
测绘学 | 459篇 |
大气科学 | 466篇 |
地球物理 | 448篇 |
地质学 | 691篇 |
海洋学 | 266篇 |
天文学 | 7篇 |
综合类 | 176篇 |
自然地理 | 615篇 |
出版年
2024年 | 12篇 |
2023年 | 38篇 |
2022年 | 116篇 |
2021年 | 124篇 |
2020年 | 163篇 |
2019年 | 145篇 |
2018年 | 119篇 |
2017年 | 130篇 |
2016年 | 130篇 |
2015年 | 142篇 |
2014年 | 125篇 |
2013年 | 224篇 |
2012年 | 166篇 |
2011年 | 121篇 |
2010年 | 93篇 |
2009年 | 143篇 |
2008年 | 134篇 |
2007年 | 134篇 |
2006年 | 109篇 |
2005年 | 88篇 |
2004年 | 70篇 |
2003年 | 57篇 |
2002年 | 72篇 |
2001年 | 51篇 |
2000年 | 40篇 |
1999年 | 44篇 |
1998年 | 41篇 |
1997年 | 40篇 |
1996年 | 28篇 |
1995年 | 25篇 |
1994年 | 30篇 |
1993年 | 35篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3128条查询结果,搜索用时 15 毫秒
441.
Comparative analysis is carried out by using finite-domain power spectrum and lagged regression methods for the propagating characteristics and air-sea interaction processes of intraseasonal oscillations (ISOs) in the Asia to western Pacific (AWP) region during the boreal summer between the active and inactive tropical cyclone (TC) years from 1979 to 2004.The results show as follows.(1) There exist more significant eastward propagating characteristics of the ISO in the active TC years over the whole AWP region.The ISOs of convection propagate zonally with more eastward extension in the years with active tropical cyclone activities,during which the 20-60-day period is strengthened,western Pacific becomes an area with evident characteristics of the propagation that is closely related to TC activities.(2) The air-sea interaction processes are the same in both active and inactive TC years,and the energy exchanges between the air and the sea play a role in maintaining the northwestward propagation of ISOs.(3) The air-sea interaction is more intensive in the active TC years than in the inactive ones.It is particularly true for the latent heat release by condensation as the result of convection,which may be one of the reasons resulting in significant differences in characteristics of ISOs between the active and inactive TC years. 相似文献
442.
测站的水位流量关系由于受到多种因素的影响,没有固定的曲线线型,使得水位流量关系曲线的延长变得较为困难。多层递阶方法将预测系统视为动态系统,具有跟踪系统时变参数的特性,但没能考虑高相关影响因子的重要性。回归分析考虑到了高相关影响因子的重要性,但由于采用定常参数建模,不能反映动态系统时变参数的特性。将多层递阶方法和回归分析方法结合起来,用于单一水位流量关系曲线的高水延长。方法克服了传统的单一水位流量关系曲线高水延长时线型的需要选择、精度难以控制、效率低和不易程序化等缺点,为单一水位流量关系曲线的高水延长提供了一种新途径。 相似文献
443.
444.
ArcGIS在东昆仑西段铁矿资源预测中的应用——以矽卡岩型铁矿为例 总被引:1,自引:0,他引:1
GIS在矿产预测中的应用研究日益普及和深化,在矿产勘查领域中已成为一种快速有效成矿预测方法。本文以东昆仑西段矽卡岩型铁矿为例,从研究区的地质背景和已查明的13个矽卡岩型铁矿(点)出发,基于ArcGIS平台,建立本研究区的空间数据库,结合已知矿(点)地质资料和野外验证分析,建立找矿模型与预测区提取模型,由于矽卡岩型矿床主... 相似文献
445.
446.
新世纪上海地区相对海平面变化影响因素及预测方法 总被引:1,自引:0,他引:1
针对传统相对海平面变化分析方法均将理论海平面变化和地面沉降进行的叠加分析,本文讨论和分析了近20年来全球理论海平面上升速率加快背景下的区域海平面变化速率,利用灰色线性回归组合模型预测上海地区海平面变化趋势。考虑了上海地面沉降发展的新特点,以及长江流域来沙显著减少和河口大型工程建设对上海地区相对海平面变化的影响。在流域来沙量显著减少但来水量变化不大情况下,流域大坝的坝下冲刷使得河槽刷深,河口水位降低,同时长江口深水航道整治工程和促淤围垦工程束狭入海口,使得潮位站水位发生变化,两者的综合效应是目前研究长江口相对海平面变化时必须考虑的重要因素。 相似文献
447.
When waves impact a seawall, a vertical breakwater, an exposed jetty, a pier or a coastal bridge, they abruptly transfer their momentum into the structure. This energy transfer can be very violent and its duration exceptionally short. In the case of coastal bridges, whose spans are designed to have very short vibration period, wave impacts might have duration comparable to the natural period of oscillation of the structure, which therefore becomes prone to damage and failure. Previous forensic studies have documented the relative importance of impulsive loads on deck suspended structure, demonstrating the need to assess the effect of wave impacts on both the stability and the integrity of structural members since the early stages of the design. This requires the estimation of the dynamic characteristics of the loading pattern, and in particular the wave impulse and corresponding impact maxima and rise times. Based on the conservation of momentum, functional relationships between these parameters have been identified since pioneering work dating back to the late '30s of the 20th century. The complexity of the loading process, however, results in a significantly large variability of wave impact maxima and rise times even under similar conditions, suggesting the need for a probabilistic approach to the definition of the relationship between these two variables, to be applied when estimating the dynamic properties of wave for use in structural analysis of coastal structures. In the recent past, some effort has been made to identify functional relationships between such quantities; these require the assessment of the conditional quantiles (or similarly the conditional distribution) of wave impact maxima given the rise times. In this paper, we compare three different statistical methods proposed in the literature to accomplish this task, in order to assess the reliability of the approach and suggest guidelines for practical applications. A copula-based method, Generalized Additive Models for Location, Scale and Shape (GAMLSS), and quantile regression are applied to measurements from large-scale 3-dimensional physical model tests. The investigation suggests that quantile regression gives the simplest results to be used in practice; copula approach and GAMLSS are possible alternative when semi-parametric or fully parametric modeling is needed. 相似文献
448.
本文选择博格达-哈尔里克一带作为研究区,从区域成矿地质背景入手,鉴于该地区已知成型铜矿床较少,成矿规律研究薄弱,故作者采用ArcGIS平台下的证据权模型(WofE),以数据驱动方式为主,从断裂构造、沉积岩相与建造、火山岩建造、侵入岩岩性等方面,以学生化反差S(C)作为有利因子衡量指标,对各控矿因素进行影响程度分类,利用加权逻辑斯回归模型计算成矿后验概率,根据后验概率值的大小进行成矿远景区的圈定和分级,在博格达-哈尔里克成矿带内共圈定7个成矿远景区。最后结合区域化探资料进行了验证,结果显示所圈定的铜矿成矿远景区内化探异常明显,与Cu元素异常套合较好,说明ArcGIS证据权模型能很好地为区域矿产预测提供良好的技术支撑,为研究区铜矿找矿方向提供理论依据,文中所总结的基于ArcGIS平台的证据权计算方法流程也为区域矿产预测提供了方法借鉴。 相似文献
449.
Hazard assessment of dangerous natural phenomena is critical because of their evident results concerning loss of human life and property, especially in dense populated areas. Earthquakes are probably the most devastating phenomenon since their immediate and long-term consequences are severe. This study is focused on the earthquake data analysis in different regions of Greece, characterised by different seismicity levels. In specific, a novel model is proposed based on evolutionary computation methods, such as symbolic regression by genetic programming and genetic algorithms in order to elucidate preliminary hidden mathematical relations and patterns found in the seismological signals under study. Furthermore, the model is calibrated using reverse engineering and closes the loop from the data collection to initial hypothesis. In this way, the model formation is achieved. The presented simulation results qualitatively and quantitatively reveal some of the fundamental characteristics of each studied geographical region located in Greece that stem from its geodynamic properties. 相似文献
450.