全文获取类型
收费全文 | 43671篇 |
免费 | 8350篇 |
国内免费 | 9948篇 |
专业分类
测绘学 | 3607篇 |
大气科学 | 8425篇 |
地球物理 | 11441篇 |
地质学 | 20867篇 |
海洋学 | 5533篇 |
天文学 | 2245篇 |
综合类 | 4308篇 |
自然地理 | 5543篇 |
出版年
2024年 | 239篇 |
2023年 | 724篇 |
2022年 | 1869篇 |
2021年 | 2218篇 |
2020年 | 1849篇 |
2019年 | 2237篇 |
2018年 | 2394篇 |
2017年 | 2298篇 |
2016年 | 2663篇 |
2015年 | 2443篇 |
2014年 | 2892篇 |
2013年 | 2888篇 |
2012年 | 2720篇 |
2011年 | 2795篇 |
2010年 | 2794篇 |
2009年 | 2556篇 |
2008年 | 2428篇 |
2007年 | 2247篇 |
2006年 | 1773篇 |
2005年 | 1678篇 |
2004年 | 1283篇 |
2003年 | 1239篇 |
2002年 | 1187篇 |
2001年 | 1234篇 |
2000年 | 1370篇 |
1999年 | 1730篇 |
1998年 | 1388篇 |
1997年 | 1320篇 |
1996年 | 1221篇 |
1995年 | 1067篇 |
1994年 | 949篇 |
1993年 | 848篇 |
1992年 | 691篇 |
1991年 | 561篇 |
1990年 | 404篇 |
1989年 | 383篇 |
1988年 | 327篇 |
1987年 | 196篇 |
1986年 | 173篇 |
1985年 | 118篇 |
1984年 | 117篇 |
1983年 | 91篇 |
1982年 | 91篇 |
1981年 | 72篇 |
1980年 | 47篇 |
1979年 | 40篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 15篇 |
1958年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Spatial Modeling and Analysis for Shoreline Change Detection and Coastal Erosion Monitoring 总被引:3,自引:0,他引:3
Coastal erosion presents a serious problem throughout U.S. coastal areas. The Ohio Geological Survey estimates that more than 3,200 acres of Ohio's Lake Erie shore have been lost to erosion since the 1870s, resulting in economic losses exceeding tens of millions of dollars per year. This article presents research results of a project that monitors shoreline erosion using high-resolution imagery and examines erosion causes. Spatial modeling and analysis methods are applied to the project area along the south shore of Lake Erie. The shoreline is represented as a dynamically-segmented linear model that is linked to a large amount of data describing shoreline changes. A new method computes an instantaneous shoreline using a digital water level model, a coastal terrain model, and bathymetric data. This method provides an algorithm for deriving the Mean-Lower Low Water (MLLW) and the Mean High Water (MHW) shorelines that are essential to navigation charts. The results describe a part of our effort towards a coastal spatial information infrastructure to support management and decision-making in the dynamic coastal environment. 相似文献
142.
143.
144.
Frequency-selective attenuation of sound propagaion and reverberation in shallow waterTXFrequency-selectiveattenuationofsoundp... 相似文献
145.
146.
Despite the fact that BaP is a carcinogen, mammalian immunosuppressant, and ubiquitous aquatic pollutant, knowledge regarding the effects of BaP on the immune system of fish is still lacking. To begin to fill this gap, studies were conducted in medaka to examine the effects and mechanisms by which BaP exposure might alter host immunocompetence. Fish, exposed by IP injection of BaP (2-600 microg/g BW), were examined after 48 h for effects upon immune function and CYP1A expression/activity. Benzo[a]pyrene, at a concentration below that which increased levels of CYPIA expression/activity (2 microg BaP/g BW) suppressed lymphocyte proliferation. Concentrations of BaP at 20 and 200 microg/g BW. suppressed antibody-forming cell (AFC) numbers, superoxide production, and host resistance against bacteria. In contrast, exposure to the low affinity aryl hydrocarbon receptor (AhR) agonist, benzo[e]pyrene (BeP), neither induced CYP1A expression nor altered immune function. Given the lack of immunosuppressive effects produced by BeP, and the fact that exposure to the AhR antagonist (and CYP1A inhibitor) alpha-naphthoflavone (ANF) ameliorated the suppressive effects of BaP upon AFC numbers, the AhR pathway (including CYP1A-mediated production of reactive BaP metabolites) appears important in mediating BaP-induced immunotoxicity in fish, as in mammals. In the past, the medaka has proven a successful model for assessing carcinogenic agents. These studies have demonstrated its utility for also determining the immunosuppressive effects of an important aquatic contaminant. 相似文献
147.
148.
本方案采用850、700、500hPa三个层次的环境平均流场作控制点法。综合考虑这些层次上的引导气流在不同时、空域中的相对重要性。试验结果表明,其效果比单一取某层作引导为佳。且对用来预测台风的未来24小时路径是否异常具有一定的参考价值。 相似文献
149.
SeaWiFS航空模拟器(SAS)是专门为在水面之上测量水体表观光学参数的现场设备。文章在介绍SAS现场测量以及数据处理基本方法的基础上,分析了2002年黄海试验SAS的应用效果,并与剖面法测量数据进行了比对。 相似文献
150.