全文获取类型
收费全文 | 652篇 |
免费 | 138篇 |
国内免费 | 96篇 |
专业分类
测绘学 | 111篇 |
大气科学 | 43篇 |
地球物理 | 265篇 |
地质学 | 188篇 |
海洋学 | 103篇 |
天文学 | 10篇 |
综合类 | 36篇 |
自然地理 | 130篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 14篇 |
2021年 | 26篇 |
2020年 | 40篇 |
2019年 | 31篇 |
2018年 | 31篇 |
2017年 | 41篇 |
2016年 | 44篇 |
2015年 | 30篇 |
2014年 | 48篇 |
2013年 | 61篇 |
2012年 | 61篇 |
2011年 | 52篇 |
2010年 | 31篇 |
2009年 | 46篇 |
2008年 | 39篇 |
2007年 | 46篇 |
2006年 | 38篇 |
2005年 | 32篇 |
2004年 | 24篇 |
2003年 | 30篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 3篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有886条查询结果,搜索用时 15 毫秒
1.
Chen Guoping Yu Kuang-ming Zhang Jiachang Assistant Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing
Prof. Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing
Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1991,(4)
This paper discusses the effect of berm width and elevation of composite slope on irregular wave run-up. Based on the data obtained from model tests, the formula and distribution of irregular wave run-up on composite slope are derived. The changing of wind speed, width and elevation of the berm are considered comprehensively. The wave run-up with various exceedance probability can be es-timated utilizing the distribution curves of irregular wave run-up. 相似文献
2.
本文通过分析实验室风浪周期分布,发现风浪周期累积概率分布曲线低于Longuet-Higgins理论结果,在小概率周期区域实验结果与理论结果的差异明显。对实验结果进一步分析发现,在谱不是很窄时,在小概率处风浪周期累积概率随谱宽度的增大而降低,这与窄谱假定下的理论结果相反,Longuet-Higgins理论结果在小概率处不便于描述周期分布随谱宽度的变化。根据实验结果提出风浪周期的Weibull分布经验公式,Weibull分布中的参数依赖于谱宽度。 相似文献
3.
4.
该文分析研究了彩山小流域的区域坡度和土壤特性,并根据区内土壤性质划分出4个小区域,即:自然坡度在20°~25°内为V1区,15°~20°内为V2区,10°~15°内为V3区,5°~10°内为V4区,分别反映了不同的土壤等级及土壤抗冲能力。同时,也研究出了一个系统化、理论化的科学依据i=V(10/3)/5B,并对所有砂石山区水土保持治理工作具有借鉴性和实用性。 相似文献
5.
关于角平分线法建立线状缓冲区算法的改进 总被引:2,自引:0,他引:2
分析了用对角平分线法建立缓冲区的算法,提出了一种新的求角平分线和缓冲点的方法,实践证明其在算法实现方面是可行的,而且效果比较理想。 相似文献
6.
基于Kiwi数据格式的地图显示研究 总被引:7,自引:1,他引:7
在分析Kiwi显示数据存储组织方法的基础上,研究了Kiwi显示数据在内存中的动态组织,改进了地图显示的二级缓存方法,提出了地图显示的双缓冲池策略。试验结果表明,本文研究的数据动态组织方法和地图显示策略提高了地图显示速度。 相似文献
7.
Changes in Geomorphic characteristics in the lower reaches of the Gongola River channel following construction of Kiri dam have been investigated. The study focused on changes in the channel bankfull width and of riverbed width after the control of the river flow, variation in discharge characteristics between pre- and post- dam periods and the impact of discharge variation on post- dam river channel. Results of the analysis revealed that the main effect of the impoundment of the Gongola channel is a drastic decrease in flood peaks below the reservoir by 11.5% (from 1,420 m3/sec to 1,256 m3/sec). The low flows have on the other hand increased by 268% (from 5.7 m3/sec to 21 m3/sec). The resultant effect of decrease in the discharge was reduction in the channel bankfull and riverbed widths by 38.3% and 72.2% respectively. Also, the post- dam channel became less sinuous and braided in some of the reaches downstream. Discharges of high peaks were found during the period of maximum precipitation (June to September) whereas low discharges were recorded during the period of minimum or no precipitation (December to May). Some of the observed implications of the flow control on the geometric variables were reduction in the overall channel width, concave bank erosion and emergence of vegetation in some of the reaches. 相似文献
8.
In the Alexander von Humboldt National Park in eastern Cuba many endemic animals and plants are found in various different natural habitats, which are considered to be the most important ones for in-situ conservation in the entire Insular Caribbean. In some areas of the National Park agriculture is practised. Thus, the objective of this study was to document and analyse the different land use activities and their consequences for local resource management and conservation of biodiversity in two village areas. A particular question was: what has changed since the foundation of the National Park in 1996? As time series data for land use and aerial photographs were not available for this part of Cuba, a qualitative evaluation was carried out. For this, six different land use units were mapped in 2001 and additional information gathered for areas with special interest related to sustainable land use and resource conservation. Although most parts of the study area are influenced to various degrees by human impact, the different types of land use seem presently not to have a crucial or detrimental impact on the land resources of the Alexander von Humboldt National Park. However, exploitation of the natural resources in certain areas could be improved with different management options to reach sustainability as well as to meet the conservation objectives of the National Park. This includes reduced or abandoned agricultural use of steep slopes to reduce erosion risk as well as a facilitated regeneration of natural vegetation in many parts of the study area to be able to conserve the high valuable biodiversity of the Park. Environmental education seems to have played an important and successful role since the foundation of the Park in 1996. Since then, cropping on steep slopes as well as illegal logging and poaching could be reduced. 相似文献
9.
扩频通信技术是基于信息容量和信息传输差错概率理论而建立的先进的无线通讯方式、多次野外实地证实它具有抗干扰性强、可实现码分多址等优点。通过分析传输试验数据,我们有理由相信扩频通信技术在遥测地震台风中具有较高的应用和广阔的发展前景。 相似文献
10.