全文获取类型
收费全文 | 4713篇 |
免费 | 812篇 |
国内免费 | 627篇 |
专业分类
测绘学 | 718篇 |
大气科学 | 570篇 |
地球物理 | 1510篇 |
地质学 | 1088篇 |
海洋学 | 574篇 |
天文学 | 414篇 |
综合类 | 436篇 |
自然地理 | 842篇 |
出版年
2024年 | 7篇 |
2023年 | 37篇 |
2022年 | 122篇 |
2021年 | 150篇 |
2020年 | 158篇 |
2019年 | 213篇 |
2018年 | 146篇 |
2017年 | 190篇 |
2016年 | 181篇 |
2015年 | 195篇 |
2014年 | 225篇 |
2013年 | 260篇 |
2012年 | 279篇 |
2011年 | 284篇 |
2010年 | 227篇 |
2009年 | 304篇 |
2008年 | 254篇 |
2007年 | 337篇 |
2006年 | 328篇 |
2005年 | 262篇 |
2004年 | 241篇 |
2003年 | 225篇 |
2002年 | 180篇 |
2001年 | 182篇 |
2000年 | 151篇 |
1999年 | 142篇 |
1998年 | 171篇 |
1997年 | 91篇 |
1996年 | 94篇 |
1995年 | 95篇 |
1994年 | 92篇 |
1993年 | 81篇 |
1992年 | 55篇 |
1991年 | 38篇 |
1990年 | 25篇 |
1989年 | 47篇 |
1988年 | 21篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有6152条查询结果,搜索用时 62 毫秒
961.
Study on Probability Distributions of Multi-Timescale Aerosol Optical
Depth Using AERONET Data
下载免费PDF全文
![点击此处可从《大气和海洋科学快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The probability distribution analysis is per-formed for multi-timescale aerosol optical depth (AOD) using AErosol RObotic NETwork (AERONET) level 2.0 data.The maximum likelihood estimation is employed to determine the best-fit probability density function (PDF),and the statement that the fitting Weibull distribution will be light-tailed is proved true for these AOD samples.The best-fit PDF results for multi-site data show that the PDF of AOD samples with longer timescale in most sites tends to be stably represented by lognormal distribution,while Weibull distribution is a better fit for AOD samples with short timescales.The reason for this difference is ana-lyzed through tail characteristics of the two distributions,and an indicator for the selection between Weibull and lognormal distributions is suggested and validated.The result of this research is helpful for determining the most accurate AOD statistics for a given site and a given time-scale and for validating the retrieved AOD through its PDF. 相似文献
962.
针对夏季高温极值分布存在偏态性,利用Box-Cox变换,得到一种偏态概率分布拟合函数。基于偏态分布函数中的偏态指数和最概然高温极值,揭示了我国夏季高温极值的概率分布特征及其在20世纪80年代前后的变化规律,发现我国夏季高温极值的概率分布主要呈正偏分布型,最概然高温极值变化较好地反映了分布型的改变。研究不同时间尺度内极值对偏态指数和最概然高温极值的影响发现,最概然高温极值较为稳定,10年尺度内受极值影响较小,而偏态指数所受影响随着时间尺度的增大而越发显著。 相似文献
963.
964.
965.
Because a conventional isolation system with constant isolation frequency is usually a long‐period dynamic system, its seismic response is likely to be amplified in earthquakes with strong long‐period wave components, such as near‐fault ground motions. Seismic isolators with variable mechanical properties may provide a promising solution to alleviate this problem. To this end, in this work sliding isolators with variable curvature (SIVC) were studied experimentally. An SIVC isolator is similar to a friction pendulum system (FPS) isolator, except that its sliding surface has variable curvature rather being spherical. As a result, the SIVC's isolation stiffness that is proportional to the curvature becomes a function of the isolator displacement. By appropriately designing the geometry of the sliding surface, the SIVC is able to possess favorable hysteretic behavior. In order to prove the applicability of the SIVC concept, several prototype SIVC isolators, whose sliding surfaces are defined by a sixth‐order polynomial function, were fabricated and tested in this study. A cyclic element test on the prototype SIVC isolators and a shaking table test on an SIVC isolated steel frame were all conducted. The results of both tests have verified that the prototype SIVC isolators do indeed have the hysteretic property of variable stiffness as prescribed by the derived formulas in this study. Moreover, it is also demonstrated that the proposed SIVC is able to effectively reduce the isolator drift in a near‐fault earthquake with strong long‐period components, as compared with that of an FPS system with the same friction coefficient. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
966.
967.
968.
969.
受降水丰枯变化不确定性和差异性的影响,南水北调中线工程水源区与受水区降水的丰枯遭遇状态各不相同,给南水北调工程水资源调度运行带来风险。联合copula函数和贝叶斯网络理论,建立了南水北调中线工程水源区和受水区降水丰枯遭遇风险分析模型,对南水北调中线工程调水最不利的丰枯遭遇风险概率进行了研究。利用copula函数建立了水源区和受水区年降水量联合分布函数,计算条件概率,结合贝叶斯网络进行丰枯遭遇风险分析。结果表明南水北调中线4个受水区调水风险的概率均在25%以下,并对不同情景的调水风险进行了仿真分析。 相似文献
970.