全文获取类型
收费全文 | 2784篇 |
免费 | 651篇 |
国内免费 | 609篇 |
专业分类
测绘学 | 424篇 |
大气科学 | 354篇 |
地球物理 | 963篇 |
地质学 | 1170篇 |
海洋学 | 349篇 |
天文学 | 29篇 |
综合类 | 223篇 |
自然地理 | 532篇 |
出版年
2024年 | 10篇 |
2023年 | 34篇 |
2022年 | 80篇 |
2021年 | 119篇 |
2020年 | 123篇 |
2019年 | 153篇 |
2018年 | 135篇 |
2017年 | 143篇 |
2016年 | 148篇 |
2015年 | 153篇 |
2014年 | 174篇 |
2013年 | 189篇 |
2012年 | 191篇 |
2011年 | 205篇 |
2010年 | 177篇 |
2009年 | 172篇 |
2008年 | 153篇 |
2007年 | 230篇 |
2006年 | 197篇 |
2005年 | 140篇 |
2004年 | 162篇 |
2003年 | 103篇 |
2002年 | 126篇 |
2001年 | 103篇 |
2000年 | 90篇 |
1999年 | 79篇 |
1998年 | 88篇 |
1997年 | 69篇 |
1996年 | 49篇 |
1995年 | 34篇 |
1994年 | 47篇 |
1993年 | 46篇 |
1992年 | 30篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 15篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1954年 | 4篇 |
排序方式: 共有4044条查询结果,搜索用时 31 毫秒
11.
本文提出了一种地震折射液的虚拟射线理论,根据该理论,只要已知地表层的速度,即可直接由折射波信息提取地震参数,从而可实现折射界面的反演。 文中通过实际介质模型的计算机实验结果,验证了该理论的正确性。 相似文献
12.
The architecture of macrofaunal burrows and the total area of the sediment-water interface created by biogenic structure were
investigated in the Donggeomdo tidal flat on the west coast of Korea. Resin casting methods were applied to recover burrows
of four dominant species, Macrophthalmus japonicus, Cleistostoma dilatatum, Perinereis aibuhitensis, and Periserrula leucophryna,
and whole burrows within the casting area at three sites in different tidal levels.P. leucophryna excavated the largest burrow in terms of a surface area among them. In the case of whole burrow casting, the space occupied
by the biogenic structure was extended into deeper and expanded more greatly at the higher tidal level. In the uppermost flat,
the burrow wall surface area within sediment was more extensive than the sediment surface area. Increased oxygen supply through
the extended interface could enhance the degradation rates of organic carbon and also change the pathways of degradation.
Quantifying the relationship between the extended interface and mineralization rate and pathway requires more extensive study. 相似文献
13.
14.
15.
引入差比关系法分析西北太平洋TOPEX/POSEIDON卫星高度计测高数据 总被引:7,自引:0,他引:7
TOPEX/POSEIDON(T/P)卫星高度计数据信息中存在周期成分混淆问题.对其中的一类混淆引入差比关系方法对混淆的分潮进行分离.卫星轨道交叉点资料包括升轨和降轨资料,资料量比沿轨点资料多1倍,经分析发现:在已有为期6a多的观测资料时间序列中,在沿轨处混淆的分潮如K1和SSA在交叉点处不再混淆,可以直接分离.因此首先对交叉点资料进行调和分析.然后由交叉点的分析结果得到分潮间的差比关系,处理到相近的沿轨点处,从而得到沿轨点的调和常数.用引入差比关系方法,对西北太平洋海区6a多的T/P卫星高度计资料进行了潮汐分析,并与沿岸及岛屿验潮站资料进行了比较,所得结果较满意. 相似文献
16.
运用扫描电镜(SEM)和X-射线衍射(XRD)技术研究了电化学脱盐处理对钢样-砂浆界面微观结构的影响。试验结果表明,经电化学脱盐处理后,钢样-砂浆界面的微观形貌特征与组成发生了明显的变化。 相似文献
17.
1 .IntroductionTomeasurethereflectionofincidentwavesproducedbyaphysicalmodelinawaveflumeisacommonproblemwithphysicaltestsofwaveactiononcoastalstructures .Wavesgeneratedbythewave makerpropagateforwardinthewaveflumeandarereflectedbythephysicalmodel,andthe… 相似文献
18.
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
19.
A new three-dimensional, non-hydrostatic free surface flow model is presented. For simulating water wave motions over uneven bottoms, the model employs an explicit project method on a Cartesian the staggered gird system to solve the complete three-dimensional Navier–Stokes equations. A bi-conjugated gradient method with a pre-conditioning procedure is used to solve the resulting matrix system. The model is capable of resolving non-hydrostatic pressure by incorporating the integral method of the top-layer pressure treatment, and predicting wave propagation and interaction over irregular bottom by including a partial bottom-cell treatment. Four examples of surface wave propagation are used to demonstrate the capability of the model. Using a small of vertical layers (e.g. 2–3 layers), it is shown that the model could effectively and accurately resolve wave shoaling, non-linearity, dispersion, fission, refraction, and diffraction phenomena. 相似文献
20.
Sloshing in a two-dimensional rectangular tank in horizontal motion is analysed based on the velocity potential theory. It is found that even when the first-order excitation is away from all the natural frequencies of the tank, second-order resonance can still occur when the sum-frequency or the difference-frequency is equal to one of the natural frequencies corresponding to the even mode. However, such resonance is not excited when the sum or difference frequency is equal to the natural frequency of an odd mode. 相似文献