全文获取类型
收费全文 | 6888篇 |
免费 | 991篇 |
国内免费 | 1147篇 |
专业分类
测绘学 | 773篇 |
大气科学 | 1634篇 |
地球物理 | 1477篇 |
地质学 | 1963篇 |
海洋学 | 1016篇 |
天文学 | 35篇 |
综合类 | 430篇 |
自然地理 | 1698篇 |
出版年
2024年 | 22篇 |
2023年 | 92篇 |
2022年 | 250篇 |
2021年 | 325篇 |
2020年 | 328篇 |
2019年 | 412篇 |
2018年 | 284篇 |
2017年 | 329篇 |
2016年 | 355篇 |
2015年 | 395篇 |
2014年 | 434篇 |
2013年 | 516篇 |
2012年 | 408篇 |
2011年 | 468篇 |
2010年 | 367篇 |
2009年 | 481篇 |
2008年 | 467篇 |
2007年 | 505篇 |
2006年 | 404篇 |
2005年 | 318篇 |
2004年 | 249篇 |
2003年 | 254篇 |
2002年 | 199篇 |
2001年 | 182篇 |
2000年 | 158篇 |
1999年 | 135篇 |
1998年 | 120篇 |
1997年 | 113篇 |
1996年 | 84篇 |
1995年 | 87篇 |
1994年 | 74篇 |
1993年 | 54篇 |
1992年 | 45篇 |
1991年 | 25篇 |
1990年 | 15篇 |
1989年 | 22篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1971年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有9026条查询结果,搜索用时 31 毫秒
21.
Prediction of coastal hazards due to climate change is fraught with uncertainty that stems from complexity of coastal systems, estimation of sea level rise, and limitation of available data. In-depth research on coastal modeling is hampered by lack of techniques for handling uncertainty, and the available commercial geographical information systems (GIS) packages have only limited capability of handling uncertain information. Therefore, integrating uncertainty theory with GIS is of practical and theoretical significance. This article presents a GIS-based model that integrates an existing predictive model using a differential approach, random simulation, and fuzzy set theory for predicting geomorphic hazards subject to uncertainty. Coastal hazard is modeled as the combined effects of sea-level induced recession and storm erosion, using grid modeling techniques. The method is described with a case study of Fingal Bay Beach, SE Australia, for which predicted responses to an IPCC standard sea-level rise of 0.86 m and superimposed storm erosion averaged 12 m and 90 m, respectively, with analysis of uncertainty yielding maximum of 52 m and 120 m, respectively. Paradoxically, output uncertainty reduces slightly with simulated increase in random error in the digital elevation model (DEM). This trend implies that the magnitude of modeled uncertainty is not necessarily increased with the uncertainties in the input parameters. Built as a generic tool, the model can be used not only to predict different scenarios of coastal hazard under uncertainties for coastal management, but is also applicable to other fields that involve predictive modeling under uncertainty. 相似文献
22.
23.
24.
25.
Oleg Zaytsev Rafael Cervantes-Duarte Orzo Montante Artemio Gallegos-Garcia 《Journal of Oceanography》2003,59(4):489-502
High primary productivity on the Pacific coast of the Baja California Peninsula is usually related to coastal upwelling activity
that injects nutrients into the euphotic zone in response to prevailing longshore winds (from the northwest to north). The
upwelling process has maximum intensity from April to June, with the coastal upwelling index varying from 50 to 300 m3/s per 100 m of coastline. Along the entire coast of the peninsula, the upwelling intensity changes in accordance with local
wind conditions and bottom topography. Spatial variability can also be modulated by the influence of mesoscale meanders of
the California Current. We have identified the seasonal and synoptic variability of upwelling signatures on the Baja California
shelf, using averaged monthly and weekly sea surface temperature (SST) distributions obtained from remote sensing imagery
from the Advanced Very High Resolution Radiometer in the period from 1996 to 2001. Analysis of SST distribution and direct
experimental data on temperature and nutrient concentration shows that the areas with the coldest SST anomalies were closely
related to the bottom slope, shelf width, and coastline orientation relating to wind direction. We also assume that the nutrient
transport into the coastal lagoons may be forced by the coupling of coastal upwelling and tidal pumping of surface waters
into the lagoon system.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
26.
2.4拟庸蝶食性的对应分析2.4.1观察量和变量的分组观察量(捕食鱼类)依不同季节(冬、夏季)、不同性别(雌雄性)和不同性成熟状态(幼鱼和成鱼)来分组,因此得到8(23)个观察量。对应分析的变量(饵料)首先根据个体生态的不同分为6个类型:游走多毛类,隐居多毛类,双壳类,不大游动的甲壳类(端足目和等足目),爬行甲壳类(十足国短尾部)和棘皮动物。其他6个类型的饵料生物(类、纽虫类、小型游泳甲壳类、腔肠动物、鱼类及苔藓虫类顺在分组时剔除,其原因为它们的出现可能少了些。考虑到捕食鱼类和饵料双壳类贝壳厚度… 相似文献
27.
In this paper, a new definition of structure system redundancy is proposed in view of the various measures for structure redundancy. By introducing the terms of structure system failure at the mechanism level and equivalent reliability index, the safety for existing offshore platforms can be evaluated by the semi-probabilistic method presented in this paper. Some numerical examples are given and satisfactory results have been obtained. 相似文献
28.
海洋生态环境监测的指标体系研究 总被引:1,自引:0,他引:1
本文在总结国内外各种海洋生态监测方法的基础上,构建生物分布指数、生物暴露指数和生物反应指数,并由此确定生态质量总指教。生态质量总指数可以综合反映特定海洋环境的生物群落特征,典型污染物在生物体内的蓄积特征以及生物体对环境污染的生理生化反应特征,因此可以应用于近岸海洋环境质量的生态监测。 相似文献
29.
30.
Yu Xiaodong Yan Shuwang Sun Wanhe
Postgraduate Student Tianjin University Tianjin Professor Tianjin University Tianjin Senior Engineer Tianjin Port Engineering Institute Tianjin 《中国海洋工程》1997,(2)
At pesent,it is very popular to estimate pile bearing capacity by use of empirical formula andphysical indexes of soil provided in the design codes for civil construction in China.This paper attempts toapply mechanical indexes of soil and semi-empirical formulas,which are based on soil mechanical theoriesand were summarized and presented by Meyerhof in 1976,to calculate the axial pile bearing capacity.Lo-ading test results of 24 single piles in Tianjin area have been collected and compared with the proposed cal-ulation approach. 相似文献