全文获取类型
收费全文 | 13715篇 |
免费 | 2852篇 |
国内免费 | 3633篇 |
专业分类
测绘学 | 2793篇 |
大气科学 | 2819篇 |
地球物理 | 3420篇 |
地质学 | 6652篇 |
海洋学 | 1919篇 |
天文学 | 473篇 |
综合类 | 934篇 |
自然地理 | 1190篇 |
出版年
2024年 | 53篇 |
2023年 | 155篇 |
2022年 | 483篇 |
2021年 | 567篇 |
2020年 | 610篇 |
2019年 | 726篇 |
2018年 | 593篇 |
2017年 | 720篇 |
2016年 | 704篇 |
2015年 | 758篇 |
2014年 | 1015篇 |
2013年 | 1080篇 |
2012年 | 1033篇 |
2011年 | 1040篇 |
2010年 | 809篇 |
2009年 | 1021篇 |
2008年 | 1028篇 |
2007年 | 1078篇 |
2006年 | 1017篇 |
2005年 | 839篇 |
2004年 | 790篇 |
2003年 | 601篇 |
2002年 | 598篇 |
2001年 | 438篇 |
2000年 | 415篇 |
1999年 | 355篇 |
1998年 | 319篇 |
1997年 | 272篇 |
1996年 | 219篇 |
1995年 | 174篇 |
1994年 | 181篇 |
1993年 | 118篇 |
1992年 | 94篇 |
1991年 | 68篇 |
1990年 | 54篇 |
1989年 | 25篇 |
1988年 | 38篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1971年 | 4篇 |
1954年 | 5篇 |
1900年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The natural human female hormones oestrone and 17β-oestradiol have been implicated in the disruption of endocrine systems in some wildlife adjacent to sewage effluents. The sorption behaviour of these two compounds under estuarine conditions was studied by spiking either 2.55 μg of oestrone or 2.65 μg of 17β-oestradiol in kinetic experiments. In equilibrium experiments, 3 ng of oestrone or 3.2 ng of 17β-oestradiol was added in each of the centrifuge tubes. Sorption onto sediment particles was relatively slow, with sorption equilibrium being reached in about 70 and 170 h for oestrone and 17β-oestradiol, respectively. The effects of a variety of environmental parameters on sorption were studied including salinity, sediment concentration (SC), the presence of a third phase, particle size and, also, surfactant concentrations. Results show that although salinity did not induce any statistically significant effect on the sorption of 17β-oestradiol, it did statistically enhance the sorption of oestrone, and a salting constant of 0.3 l mol−1 was derived. The partition coefficient for both compounds decreased with increasing sediment concentration, a phenomenon that has been widely reported and attributed to the presence of colloids (which could enhance dissolved concentrations). In this paper, the true partition coefficients for sediment particles (Kptrue) and colloidal particles (Kctrue) have been calculated, and a Kptrue value of 141 and 102 ml g−1 was obtained for oestrone and 17β-oestradiol, respectively. In addition, Kctrue values for oestrone (222×102 ml g−1) and 17β-oestradiol (135×102 ml g−1) were two orders of magnitude higher than their respective Kptrue values, suggesting that the colloidal particles are significantly stronger sorbents for natural oestrogens than sediment particles. Particles of different sizes were found to have different partition coefficients due to the strong relationships between partition coefficients for the two compounds and particulate organic carbon (POC) contents and specific surface areas (SSAs). The presence of a surfactant was shown to reduce the partition coefficients for the two compounds, although its concentrations being used were higher than those normally found in the natural environment. 相似文献
72.
本文给出了满足给定数字特征和谱的随机序列的产生方法,即用无记忆非线性变换实现非正态随机信号的模拟.该法与Gujar法相比较,放宽了变量概率分布的限制,只要求变量矩的存在。同时考虑无记忆非线性变换对谱的影响,用异于Liu的方法在频域上求解输入正态分布随机序列的谱. 相似文献
73.
74.
75.
76.
崂山花岗岩地区含锶、偏硅酸矿泉水的形成机理 总被引:1,自引:0,他引:1
报道了崂山花岗岩地区矿泉水的特征。指出其矿泉类型为含锶、偏硅酸型,并讨论了其形成机理。 相似文献
77.
使用切向流超滤系统得到粒度较均匀的Fe(OH)3胶体,进而对Fe(OH)3胶体粒子与Cu2 的作用进行了研究,并将实验结果与南沙群岛海区表层水中铜与胶体物质结合状况的调查数据进行了比较分析,得到如下结果:(1)在海水介质中,铜在Fe(OH)3胶体上结合的百分率(pH>5)随pH的升高而下降,随着Fe(OH)3胶体浓度的减小而下降?(2)在天然海水介质中,使铜在Fe(OH)3胶体上结合的百分率在50%-70%的有机物浓度为1.0mg·L-1,有机物浓度的增大使铜与无机胶体结合的百分率有下降的趋势? 相似文献
78.
Xu Shikai Wang Hongchuan Hong Guangwen
Engineer Nanjing Hydraulic Research Institute Nanjing .
Professor Research Institute of Coastal Ocean Engineering Hohai University Nanjing 《中国海洋工程》1996,(4)
To solve problems concerning wave elements and wave propagation, an effective way is the wave energy balance equation, which is widely applied in oceanography and ocean dynamics for its simple computation. The present papaer advances wave energy balance equations considering lateral energy transmission and energy loss as the governing equation for the study of wave refraction-diffraction. For the mathematical model, numerical simulation is made by means of difference method, and the result is verified with two examples. 相似文献
79.
Presented here is a compact explicit difference scheme of high accuracy for solving the extended Boussinesq equations.For time discretization,a three-stage explicit Runge-Kutta method with TVD property is used at predicting stage,a cubic spline function is adopted at correcting stage,which made the time discretization accuracy up to fourth order;For spatial discretization,a three-point explicit compact difference scheme with arbitrary order accuracy is employed.The extended Boussinesq equations derived by Beji and Nadaoka are solved by the proposed scheme.The numerical results agree well with the experimental data.At the same time,the comparisons of the two numerical results between the present scheme and low accuracy difference method are made,which further show the necessity of using high accuracy scheme to solve the extended Boussinesq equations.As a valid sample,the wave propagation on the rectangular step is formulated by the present scheme,the modelled results are in better agreement with the experimental data than those of Kittitanasuan. 相似文献
80.