全文获取类型
收费全文 | 5372篇 |
免费 | 1420篇 |
国内免费 | 1056篇 |
专业分类
测绘学 | 1145篇 |
大气科学 | 776篇 |
地球物理 | 1592篇 |
地质学 | 2495篇 |
海洋学 | 733篇 |
天文学 | 280篇 |
综合类 | 468篇 |
自然地理 | 359篇 |
出版年
2024年 | 40篇 |
2023年 | 163篇 |
2022年 | 183篇 |
2021年 | 231篇 |
2020年 | 160篇 |
2019年 | 262篇 |
2018年 | 179篇 |
2017年 | 191篇 |
2016年 | 210篇 |
2015年 | 270篇 |
2014年 | 335篇 |
2013年 | 280篇 |
2012年 | 384篇 |
2011年 | 334篇 |
2010年 | 286篇 |
2009年 | 333篇 |
2008年 | 373篇 |
2007年 | 312篇 |
2006年 | 277篇 |
2005年 | 294篇 |
2004年 | 257篇 |
2003年 | 235篇 |
2002年 | 231篇 |
2001年 | 238篇 |
2000年 | 128篇 |
1999年 | 170篇 |
1998年 | 180篇 |
1997年 | 153篇 |
1996年 | 137篇 |
1995年 | 160篇 |
1994年 | 143篇 |
1993年 | 115篇 |
1992年 | 130篇 |
1991年 | 109篇 |
1990年 | 95篇 |
1989年 | 84篇 |
1988年 | 26篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1965年 | 8篇 |
1954年 | 5篇 |
1948年 | 5篇 |
1942年 | 3篇 |
排序方式: 共有7848条查询结果,搜索用时 312 毫秒
21.
介绍了一种在任意独立直角坐标系中使用DGPS的方法。结合苏丹港泊位建设施工测量实践,分析了平面控制网的建立、观测、平差、WGS84坐标系到独立坐标系的转换参数计算。 相似文献
22.
23.
宋微波 《中国海洋大学学报(自然科学版)》1991,(1)
九脊游仆虫(Euplotes novemcarinata Wang、1930)是土壤及淡水中生活的原生动物。本文对其重要的分类特征诸如银线系及纤毛下器做了形态学研究,确认了其分类地位,并比较了国外迄今的研究工作,在此基础上,将同物异名苔藓游仆虫(E.muscicolaKahl、1932)作了归并。 相似文献
24.
The numerical mode of nonlinear wave transformation based on both the Laplace equation for water field and the Bemoulli equation for water surface is a kind of time-domain boundary problem with initial conditions. And the basis for establishing the numerical mode of nonlinear wave in time domain is to trace the position of wave free surface and to calculale the instantaneous surface height and surface potential function. This paper firstly utilizes the ‘0-1‘ combined BEM to separate the boundary by means of discretization of Green‘ s integral equation based on the Laplace equation, then separates the free surface of wave with FEM and derives the FEM equation of wave surface that satisfies the nonlinear boundary conditions. By jointly solving the above BEM and FEM equations, the wave potential and surface height could be obtained with iteration in time domain. Thus a new kind of nonlinear numerical mode is established for calculating wave transformation. The wave test in the numerical wave tank shows that the numerical simulation with this mode is of high accuracy. 相似文献
25.
利用岸基雷达站的雷达传感器以及船舶自动识别系统(Automatic Identification System,AIS)所获取的目标信息,针对近岸海域目标密集的特点,提出了一种提高雷达与AIS信息融合精度的算法。该算法在将雷达基于站心球坐标系的位置信息转换成AIS基于WGS 84坐标系的位置信息实现空间配准、以及将AIS航迹的时间通过外推法与雷达航迹时间统一起来的基础上,首先采用目标位置及航速的欧氏距离判别法,剔除一部分不符合条件的目标数据,减少参与融合的数据量,然后进一步采用模糊数学中的柯西型隶属度函数及统计加权法对航迹相似度判断。研究结果表明,本文所提出的融合算法适用于目标较密集的近海海域。 相似文献
26.
西洋东大港水道流速垂线分布研究 总被引:2,自引:0,他引:2
对辐射沙洲海域东大港4#站位连续2个潮周期的流速测量资料进行了分析、研究,拟合给出了流速垂线分布关系,并根据实际测量资料确定了该站位6个水层的浑水水流尾流函数项表达式。这些表达式表明浑水水流尾流函数是相对深度和摩阻速度的函数。探讨分析了尾流函数的空间分布和潮周期过程。非恒定流的水流尾流函数项的准确表达,对于揭示含沙水流流速结构及水、沙相影响作用规律将起到启发和推动作用。 相似文献
27.
基于EOF分析对南海西北海域水体光谱特性的研究 总被引:1,自引:0,他引:1
This study presents an analysis of the spectral characteristics of remote sensing reflectance(R_(rs)) in northwestern South China Sea based on the in situ optical and water quality data for August 2018.R_(rs)was initially divided into four classes,classes A to D,using the max-classification algorithm,and the spectral properties of whole R_(rs) were characterized using the empirical orthogonal function(EOF) analysis.Subsequently,the dominant factors in each EOF mode were determined.The results indicated that more than 95% of the variances of R_(rs) are partly driven by the back-scattering characteristics of the suspended matter.The initial two EOF modes were well correlated with the total suspended matter and back-scattering coefficient.Furthermore,the first EOF modes of the four classes of R_(rs)(A-D R_(rs)-EOF_1) significantly contributed to the total variances of each R_(rs) class.In addition,the correlation coefficients between the amplitude factors of class A-D R_(rs)-EOF_1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones.The spectral shape of class AR_(rs)-EOF_1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter(CDOM).The spectral shape of class B R_(rs)-EOF_1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM(a_g(λ)),whereas the spectral shape of class C R_(rs)-EOF_1 was governed by the back-scattering characteristics but not affected by the suspended matter.The spectral shape of class D R_(rs)-EOF_1 exhibited a relatively good correlation with all the water quality parameters,which played a significant role in deciding its spectral shape. 相似文献
28.
29.
海水中痕量苯系物的气相色谱测定的研究 总被引:1,自引:0,他引:1
Domestic polymeric microbeads GDX-502 were used to concentrate benzene hydrocarbon from seawater. The absorbed benzene hydrocarbon was removed by thermal desorption and directly injected into gas chromatograph and determined by FID detector. It was optimal for the rapid and precise determination of trace benzene hydrocarbon in seawater. In this Paper the investigation of benzene hydrocarbon in the coastal water of Jiaozhou Bay (Qingdao) is reported as well. The data for benzene hydrocarbon are listed in table 3 for 1984 and the station locations are given in figure 6. 相似文献
30.