全文获取类型
收费全文 | 14396篇 |
免费 | 2914篇 |
国内免费 | 4116篇 |
专业分类
测绘学 | 1213篇 |
大气科学 | 2820篇 |
地球物理 | 3573篇 |
地质学 | 8102篇 |
海洋学 | 1949篇 |
天文学 | 598篇 |
综合类 | 1411篇 |
自然地理 | 1760篇 |
出版年
2024年 | 82篇 |
2023年 | 246篇 |
2022年 | 692篇 |
2021年 | 824篇 |
2020年 | 691篇 |
2019年 | 895篇 |
2018年 | 888篇 |
2017年 | 817篇 |
2016年 | 884篇 |
2015年 | 859篇 |
2014年 | 987篇 |
2013年 | 955篇 |
2012年 | 988篇 |
2011年 | 1044篇 |
2010年 | 984篇 |
2009年 | 938篇 |
2008年 | 907篇 |
2007年 | 869篇 |
2006年 | 719篇 |
2005年 | 590篇 |
2004年 | 511篇 |
2003年 | 442篇 |
2002年 | 402篇 |
2001年 | 387篇 |
2000年 | 418篇 |
1999年 | 489篇 |
1998年 | 392篇 |
1997年 | 407篇 |
1996年 | 324篇 |
1995年 | 288篇 |
1994年 | 312篇 |
1993年 | 240篇 |
1992年 | 186篇 |
1991年 | 146篇 |
1990年 | 112篇 |
1989年 | 85篇 |
1988年 | 104篇 |
1987年 | 58篇 |
1986年 | 46篇 |
1985年 | 42篇 |
1984年 | 38篇 |
1983年 | 33篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1975年 | 2篇 |
1958年 | 7篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The incompressible viscous uniform and shear flow past a circular cylinder is studied. The two-dimensional Navier-Stokes equations are solved by a finite element method. The governing equations are discretized by a weighted residual method in space. The stable three-step scheme is applied to the momentum equations in the time integration. The numerical model is firstly applied to the computation of the lid-driven cavity flow for its validation. The computed results agree well with the measured data and other numerical results. Then, it is used to simulate the viscous uniform and shear flow over a circular cylinder for Reynolds numbers from lO0 to lO00. The transient time interval before the vortex shedding occurs is shortened considerably by introduction of artificial perturbation. The computed Strouhal number, drag and lift coefficients agree well with the experimental data. The computation shows that the finite element model can be successfully applied to the viscous flow problem. 相似文献
72.
AbstractBased on hydrological data obtained during the 7th to 9th Chinese National Arctic Research Expeditions in the summers of 2016–2018, the main water structure on the shelf of the northern Bering Sea and the volume and heat fluxes of the Bering Strait throughflow were analyzed. Distinct variability was identified in the three Pacific water masses feeding the strait - Anadyr Water (AW), Bering Shelf Water (BSW) and Alaskan coastal water (ACW). Overall, the temperature and salinity of the entire section increased each year, with 2018 showing significant anomalies, i.e., a temperature anomaly of up to 1?°C and a maximum salinity anomaly of 2. From 2016 to 2018, the extent of the ACW gradually narrowed in the eastern part of this section, while the AW expanded eastward each year. The net volume transport through each of the three sections increased poleward from 1.65?Sv to 2.76?Sv, with the AW increasing from 0?Sv to 1.03?Sv, the BSW varying between 0.52–1.65?Sv, and the ACW gradually decreasing from 1.04?Sv to disappearing completely. The net heat fluxes were also poleward, varying between 25.77 TW and 61.50 TW, and showing a significant increase. Significant variations in magnitude and extent were observed in each water mass of the Bering Strait throughflow, which could produce widespread effects in the Arctic Ocean and the global ocean beyond. 相似文献
73.
The interaction of a solitary wave with an array of surface-piercing vertical circular cylinders is investigated numerically. The wave motion is modeled by a set of generalized Boussinesq equations. The governing equations are discretized using a finite element method. The numerical model is validated against the experimental data of solitary wave reflection from a vertical wall and solitary wave scattering by a vertical circular cylinder respectively. The predicted wave surface elevation and the wave forces on the cylinder agree well with the experimental data. The numerical model is then employed to study solitary wave scattering by arrays of two circular cylinders and four circular cylinders respectively. The effect of wave direction on the wave forces and the wave runup on the cylinders is quantified. 相似文献
74.
The aim of this paper is to investigate the shape and tension distribution of fishing nets in current. A numerical model is developed, based on lumped mass method to simplify the net. The motion equation is set up for each lumped mass. The Runge–Kutta–Verner fifth-order and sixth-order method is used to solve these simultaneous equations, and then the displacement and tension of each lumped mass are obtained. In order to verify the validity of the numerical method, model tests have been carried out. The results by the numerical simulation agree well with the experimental data. 相似文献
75.
76.
在连云港近岸海域计算潮流场基础上建立拉格朗日余流模型,并对连云港市两大堤建成前后的拉格朗日余流变化进行了分析,且选择有代表性的排污口进行了数值跟踪。 相似文献
77.
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
78.
本文研究模糊矩阵传递闭包的化简问题。通过定义 1类典型阵 ,给出传递闭包能够进一步化简的充要条件 ,为网络最大流分析提供了 1种新的模式。 相似文献
79.
作者根据大量试验和调查数据的分析,提出烟单14号夏玉米在高产条件下,亩穗数、穗粒数、千粒重三因素的最佳取值范围。 亩穗数:3569~4980 穗/亩; 穗粒数:423~526 粒/穗; 千粒重:259~278 克/1000粒。 相似文献
80.
珠江河口湾伶仃洋的地形 总被引:8,自引:7,他引:8
河口湾是河流终止于大陆前缘的半围圈的海域,河水和海水分别从河口湾的两端注入并混合为冲淡水。河口湾通常是由于冰后期海面上涨被海水淹没的河流下游部分。伶仃洋就是珠江的河口湾,为华南最大的河口湾。 相似文献