全文获取类型
收费全文 | 5633篇 |
免费 | 574篇 |
国内免费 | 724篇 |
专业分类
测绘学 | 92篇 |
大气科学 | 372篇 |
地球物理 | 1396篇 |
地质学 | 743篇 |
海洋学 | 2330篇 |
天文学 | 699篇 |
综合类 | 190篇 |
自然地理 | 1109篇 |
出版年
2024年 | 24篇 |
2023年 | 60篇 |
2022年 | 111篇 |
2021年 | 117篇 |
2020年 | 153篇 |
2019年 | 194篇 |
2018年 | 140篇 |
2017年 | 169篇 |
2016年 | 169篇 |
2015年 | 165篇 |
2014年 | 217篇 |
2013年 | 349篇 |
2012年 | 143篇 |
2011年 | 289篇 |
2010年 | 227篇 |
2009年 | 344篇 |
2008年 | 407篇 |
2007年 | 418篇 |
2006年 | 358篇 |
2005年 | 282篇 |
2004年 | 280篇 |
2003年 | 287篇 |
2002年 | 245篇 |
2001年 | 176篇 |
2000年 | 204篇 |
1999年 | 230篇 |
1998年 | 202篇 |
1997年 | 113篇 |
1996年 | 130篇 |
1995年 | 110篇 |
1994年 | 109篇 |
1993年 | 87篇 |
1992年 | 81篇 |
1991年 | 62篇 |
1990年 | 56篇 |
1989年 | 44篇 |
1988年 | 27篇 |
1987年 | 29篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 19篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1971年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有6931条查询结果,搜索用时 46 毫秒
121.
Incremental Differential Quadrature Method (IDQM) as a rapid and accurate method for numerical simulation of Nonlinear Shallow Water (NLSW) waves is employed. To the best of authors’ knowledge, this is the first endeavor to exploit DQM in coastal hydraulics. The one-dimensional NLSW equations and related boundary conditions are discretized in space and temporal directions by DQM rules and the resulting system of equations are used to compute the state variables in the entire computational domain. It was found that the splitting of total simulation time into a number of smaller time increments, could significantly enhance the performance of the proposed method. Furthermore, results of this study show two main advantages for IDQM compared with other conventional methods, namely; unconditional stability and minimal computational effort. Indeed, using IDQM, one can use a few grid points (in spatial or time direction) without imposing any stability condition on the time step to obtain an accurate convergent solution. 相似文献
122.
The relevant theory is presented and numerical results are compared with the analytical solution for the interaction of non-breaking waves with an array of vertical porous circular cylinders on a horizontal bed. The extension to the cases of unidirectional and multidirectional waves is obtained by means of a transfer function. The influence of the mechanical properties of porous structures and wave irregularity on wave transformation is analysed. Results for unidirectional and multidirectional wave spectra are compared to those obtained for regular waves. The model presented reproduces well the analytical results and provides a tool for analysing several engineering problems. 相似文献
123.
The effects of Coriolis force on long waves have been discussed based on gravity waves propagating in an unbounded ocean, channel and basin. In case of ocean, results show that the Coriolis effect will be significant and negligible, when the wave period is comparable to 2π/f and much shorter, respectively. Results also show in a channel, the wave amplitude and water particle velocity decrease exponentially in the positive y direction in the northern hemisphere (where f is positive). Moreover, in a basin, the Cotidal lines have been found as curves and rotate counterclockwise around the origin. 相似文献
124.
介绍了浙江东南沿海的台州市及所属玉环县、温州市及所属乐清市、瓯海区等地面实施海洋“蓝色工程”的丰富实践和新鲜经验。文中借鉴浙东南沿海大开发的成功经验,结合我国东部沿海其它地区特别是苏北沿海的实际,提出了做出滩涂开发利用、发展海洋经济的总体战略构想。 相似文献
125.
126.
This study investigates experimentally the breaking wave height of multi-directional random waves passing over an impermeable submerged breakwater. Experiments have been conducted in a three-dimensional wave basin equipped with a multi-directional random wave generator. A special type of wave gauge has been newly devised to record the water surface elevations in the breaker zone as accurately as possible. The records are analyzed to estimate the location and limit of wave breaking. Comparisons have also been made with the results of regular waves. The influence of the incident wave conditions on the breaking wave height normalized by the breakwater dimensions has been investigated. Empirical formulae have been presented to estimate the breaking limit of multi-directional random waves based on the experimental records. The formulae have been tested and found to work well not only for multi-directional random waves, but for regular waves as well. 相似文献
127.
Regeneration of sand waves after dredging 总被引:2,自引:0,他引:2
Sand waves are large bed waves on the seabed, being a few metres high and lying hundreds of metres apart. In some cases, these sand waves occur in navigation channels. If these sand waves reduce the water depth to an unacceptable level and hinder navigation, they need to be dredged. It has been observed in the Bisanseto Channel in Japan that the sand waves tend to regain their shape after dredging. In this paper, we address modelling of this regeneration of sand waves, aiming to predict this process. For this purpose, we combine a very simple, yet effective, amplitude-evolution model based on the Landau equation, with measurements in the Bisanseto Channel. The model parameters are tuned to the measured data using a genetic algorithm, a stochastic optimization routine. The results are good. The tuned model accurately reproduces the measured growth of the sand waves. The differences between the measured weave heights and the model results are smaller than the measurement noise. Furthermore, the resulting parameters are surprisingly consistent, given the large variations in the sediment characteristics, the water depth and the flow field. This approach was tested on its predictive capacity using a synthetic test case. The model was tuned based on constructed predredging data and the amplitude evolution as measured for over 2 years. After tuning, the predictions were accurate for about 10 years. Thus, it is shown that the approach could be a useful tool in the optimization of dredging strategies in case of dredging of sand waves. 相似文献
128.
This work deals with parametric resonance which poses a great danger especially for container ships sailing in following or head seas. Important parameters that are effective in roll resonance are pointed out. For this purpose, a containership is taken as an example to analyze its stability in longitudinal waves based on the method worked out by American Bureau of Shipping (ABS). Unfavorable sailing conditions such as heading and speed, which directly depend on the environmental conditions, have been determined for this particular ship. These conditions may be reported to the master to guide him to keep his ship out of parametric resonance zones. Numerical details of the procedure have been worked out and provided as well. 相似文献
129.
A higher-order non-hydrostatic model in a σ-coordinate system is developed. The model uses an implicit finite difference scheme on a staggered grid to simultaneously solve the unsteady Navier-Stokes equations (NSE) with the free-surface boundary conditions. An integral method is applied to resolve the top-layer non-hydrostatic pressure, allowing for accurately resolving free-surface wave propagation. In contrast to the previous work, a higher-order spatial discretization is utilized to approximate the large horizontal pressure gradient due to steep surface waves or rapidly varying topographies. An efficient direct solver is developed to solve the resulting block hepta-diagonal matrix system. Accuracy of the new model is validated by linear and nonlinear standing waves and progressive waves. The model is then used to examine freak (extreme) waves. Features of downshifting focusing location and wave asymmetry characteristics are predicted on the temporal and spatial domains of a freak wave. 相似文献
130.
Numerical analyses for the Bragg resonant reflection of carrier waves associated long waves due to sinusoidally varying seabeds are performed by using a set of coupled ordinary differential equations derived from the Boussinesq equations. The Boussinesq equations are firstly approximated with the Fourier decomposition. The coupled governing equations are then derived and used to simulate evolution of both short and long wave components. It is also found that wave groups are generated by two carrier waves with slightly different frequencies. The wave energy of the initial wave components is transferred to other harmonic components during propagation over a long distance. Evolution and reflection of both short and long waves were largely affected by nonlinearity. 相似文献