全文获取类型
收费全文 | 8345篇 |
免费 | 2003篇 |
国内免费 | 2039篇 |
专业分类
测绘学 | 286篇 |
大气科学 | 1091篇 |
地球物理 | 3990篇 |
地质学 | 2897篇 |
海洋学 | 3035篇 |
天文学 | 124篇 |
综合类 | 482篇 |
自然地理 | 482篇 |
出版年
2024年 | 53篇 |
2023年 | 152篇 |
2022年 | 246篇 |
2021年 | 294篇 |
2020年 | 352篇 |
2019年 | 452篇 |
2018年 | 345篇 |
2017年 | 334篇 |
2016年 | 353篇 |
2015年 | 432篇 |
2014年 | 465篇 |
2013年 | 472篇 |
2012年 | 525篇 |
2011年 | 503篇 |
2010年 | 422篇 |
2009年 | 525篇 |
2008年 | 475篇 |
2007年 | 647篇 |
2006年 | 547篇 |
2005年 | 490篇 |
2004年 | 481篇 |
2003年 | 415篇 |
2002年 | 387篇 |
2001年 | 333篇 |
2000年 | 329篇 |
1999年 | 300篇 |
1998年 | 312篇 |
1997年 | 257篇 |
1996年 | 263篇 |
1995年 | 243篇 |
1994年 | 221篇 |
1993年 | 181篇 |
1992年 | 147篇 |
1991年 | 131篇 |
1990年 | 72篇 |
1989年 | 64篇 |
1988年 | 57篇 |
1987年 | 37篇 |
1986年 | 18篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1954年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
A simple model describing the transformation of effective rainfall to direct runoff through the overland flow mechanism is presented. The model is based on the classical representation of a watershed by a combination of planes and channels. The dynamics of overland flow in each plane is simulated by the non-linear kinematic wave, but the outflow from a given plane is concentrated in the middle of the corresponding drainage channel. The water routing in the channels is carried out by a piece-wise linearized formulation in space of the kinematic wave approximation. Using synthetic events on 10 watersheds, the model was tested by comparing it with results obtained by applying the non-linear kinematic wave to all the elements of the watershed. The model was found to be adequate, even in a form that simplifies the geometric features of the planes through an averaging procedure based on the Horton–Strahler ordering scheme of the watershed. © 1998 John Wiley & Sons, Ltd. 相似文献
122.
123.
N.N.Myagkov 《Geophysical Journal International》1998,133(1):209-211
A hydrodynamic model of a strong volcanic blast associated with large (caldera-forming) ash–gas-flow eruptions is presented. We show that the mass erupted from a vent influences considerably the damping of the shock wave. If the ejected mass flux is constant, the shock amplitude as a function of distance will decrease slower (in accordance with the inverse 4/3 power law) than that of an atomic explosion (the inverse cube power law). From the modelling, we extract a relation connecting the effective energy of a blast with the mass ejected during the blast phase. The mass released during the largest explosion of the 1883 eruption of Krakatau, and the lateral blast energy at Mount St. Helens on 1980 May 18 are estimated on the basis of the equation obtained. 相似文献
124.
125.
126.
利用被动微波可穿透云层的优势,基于GCOM-W1/AMSR2(Global Change Observation Mission-Water/ Advanced Microwave Scanning Radiometer 2)星载被动微波传感器的多通道亮度温度数据,反演了2016年1月下旬“超级寒潮”过程的广东省每日地表温度,分析了寒潮过程中广东省地表温度的时空变化特征。结果表明:在寒潮前后,广东省地表温度呈现出明显的先下降而后上升的趋势,寒潮过程带来的地表最低温度在广东北部大部分地区达到了277 K(4℃),西南大部分地区为280~282 K(7~9℃),其余大部分地区278~279 K(5~6℃);降温幅度在广东南部地区达到了8~12 K(8~12℃),北部大部分地区为5~7 K(5~7℃)。此外,利用归一化植被指数(NDVI)对植被生长的指示作用,基于HJ-1 A/B卫星的CCD传感器的多通道反射率数据,计算了近3年冬季广东省典型马铃薯种植区域马铃薯叶片的NDVI值,结果表明:马铃薯叶片的NDVI值在此次寒潮过程后出现了明显的下降,大部分地区(55.4%)马铃薯NDVI降低了0.1~0.2,部分地区(17.2%)马铃薯NDVI下降了0.2~0.3;进一步对比此次“超级寒潮”后同时段的前2年数据,发现寒潮后马铃薯叶片NDVI相对于正常年份也低了0.2,表明马铃薯叶片NDVI下降的主要原因是寒潮带来的低温,而不只是马铃薯的正常老化现象。NDVI的降低表明大部分地区马铃薯生长受到了抑制,马铃薯生长状况的这一变化也通过现场调查得到了证实。 相似文献
127.
Generalised observations of wave characteristics on near‐horizontal shore platforms: Synthesis of six case studies from the North Island,New Zealand 下载免费PDF全文
Most field studies of wave processes on shore platforms in front of eroding cliffs focus on a single site, revealing aspects of wave dynamics at that location. Here, we analyse data from six platforms around northeastern New Zealand and describe the fundamental control of shore platform width, gradient and elevation on wave processes, including greater attenuation of short‐period waves at lower tidal stages and increases in longer period wave energy towards the cliff toe. These data suggest that empirical formulae developed from coral‐reef environments provide better predictions of wave height on platforms than formulae currently used in shore platform models. 相似文献
128.
129.
Traction image method for irregular free surface boundaries in finite difference seismic wave simulation 总被引:16,自引:1,他引:16
In this study, we propose a new numerical method, named as Traction Image method, to accurately and efficiently implement the traction-free boundary conditions in finite difference simulation in the presence of surface topography. In this algorithm, the computational domain is discretized by boundary-conforming grids, in which the irregular surface is transformed into a 'flat' surface in computational space. Thus, the artefact of staircase approximation to arbitrarily irregular surface can be avoided. Such boundary-conforming gridding is equivalent to a curvilinear coordinate system, in which the first-order partial differential velocity-stress equations are numerically updated by an optimized high-order non-staggered finite difference scheme, that is, DRP/opt MacCormack scheme. To satisfy the free surface boundary conditions, we extend the Stress Image method for planar surface to Traction Image method for arbitrarily irregular surface by antisymmetrically setting the values of normal traction on the grid points above the free surface. This Traction Image method can be efficiently implemented. To validate this new method, we perform numerical tests to several complex models by comparing our results with those computed by other independent accurate methods. Although some of the testing examples have extremely sloped topography, all tested results show an excellent agreement between our results and those from the reference solutions, confirming the validity of our method for modelling seismic waves in the heterogeneous media with arbitrary shape topography. Numerical tests also demonstrate the efficiency of this method. We find about 10 grid points per shortest wavelength is enough to maintain the global accuracy of the simulation. Although the current study is for 2-D P-SV problem, it can be easily extended to 3-D problem. 相似文献
130.