全文获取类型
收费全文 | 2632篇 |
免费 | 554篇 |
国内免费 | 526篇 |
专业分类
测绘学 | 376篇 |
大气科学 | 618篇 |
地球物理 | 809篇 |
地质学 | 779篇 |
海洋学 | 302篇 |
天文学 | 22篇 |
综合类 | 185篇 |
自然地理 | 621篇 |
出版年
2024年 | 6篇 |
2023年 | 22篇 |
2022年 | 61篇 |
2021年 | 113篇 |
2020年 | 101篇 |
2019年 | 135篇 |
2018年 | 113篇 |
2017年 | 134篇 |
2016年 | 136篇 |
2015年 | 147篇 |
2014年 | 154篇 |
2013年 | 145篇 |
2012年 | 187篇 |
2011年 | 176篇 |
2010年 | 161篇 |
2009年 | 166篇 |
2008年 | 159篇 |
2007年 | 200篇 |
2006年 | 180篇 |
2005年 | 129篇 |
2004年 | 143篇 |
2003年 | 105篇 |
2002年 | 115篇 |
2001年 | 98篇 |
2000年 | 72篇 |
1999年 | 85篇 |
1998年 | 80篇 |
1997年 | 67篇 |
1996年 | 53篇 |
1995年 | 51篇 |
1994年 | 50篇 |
1993年 | 41篇 |
1992年 | 29篇 |
1991年 | 26篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有3712条查询结果,搜索用时 187 毫秒
71.
中国旅游资源开发模式与旅游区域可持续发展理念 总被引:38,自引:2,他引:38
从旅游资源开发与区域关系的角度,指出国内旅游资源在开发方面存在着不同的理念与方法论模式,导致不同的区域旅游开发效果;从旅游可持续发展的原则出发,旅游区域开发在理论上应该建立多元趋势分析旅游开发理论体系,在实践上应建立鞠域“大旅游”的结构系统,并提出区域旅游开发的一些理论。 相似文献
72.
中国热带东,西部地区冬季气候的差异与橡胶树的引种 总被引:8,自引:0,他引:8
由于青藏高原的动力影响,使得西部地区冬季出现下沉气流,多日照,利于橡胶树的越冬,而东部则出现上升气流,少日照,不利越冬,又由于青藏高原大山体,冬季明显地阻挡低层空气平流,导致高原南侧的西部地区冬季降温和缓,有利橡胶树越冬,而东部地区因无高大山体阻挡,寒潮初期降温剧烈,后期低温阴雨天气持续甚久,易导致橡胶树的严重寒害。 相似文献
73.
地区发展水平衡量指标体系设计及实例分析 总被引:1,自引:0,他引:1
选定地区发展水平衡量指标,测度区域社会,经济,文化发展水平或发育程度是一项有重要的工作,本文试图为量度我国西部地区发展水平提供一套昼完整的指标体系,并对一个具体实例进行衡量和计算,由此说明地区的区内发展程度的差异,划分区域发展的不同类型。 相似文献
74.
区域经济联系定量分析初探:以上海与苏锡常地区经济联系为例 总被引:49,自引:2,他引:49
针对目前区域联合日益广泛和经济联系量化研究不足的现状,在联系强度等方面提出一些新概念;阐述了经济联系量化指标的选取,建立了经济联系定量分析模型。 相似文献
75.
The seismic ground motion of a test area in the eastern district of Naples is computed with a hybrid technique based on the mode summation and the finite difference methods. This technique allows us the realistic modelling of source and propagation effects, including local soil conditions. In the modelling, we consider the 1980 Irpinia earthquake, a good example of strong shaking for the area of Naples, which is located about 90 km from the epicenter.The detailed geological setting is reconstructed from a large number of drillings. The sub-soil is mainly formed by alluvial (ash, stratified sand and peat) and pyroclastic materials overlying a pyroclastic rock (yellow neapolitan tuff), representing the neapolitan bedrock. The detailed information available on mechanical properties of the sub-soil and its geometry warrants the application of the sophisticated hybrid technique.As expected, the sedimentary cover causes an increase of the signal's amplitudes and duration. If thin peat layers are present, the amplification effects are reduced, and the peak ground accelerations are similar to those observed for the bedrock model. This can be explained by the backscattering of wave energy at such layers, that tend to seismically decouple the upper from the lower part of the structure.For SH-waves, the influence of the variations of the S-wave velocities on the spectral amplification is studied, by considering locally measured velocities and values determined from near-by down-hole measurements. The comparison between the computed spectral amplifications confirms the key role of an accurate determination of the seismic velocities of the different layers.The comparison performed between a realistic 2-D seismic response and a standard 1-D response, based on the vertical propagation of waves in a plane layered structure, shows considerable difference, from which it is evident that serious caution must be taken in the modelling of expected ground motion at a specific site. 相似文献
76.
Oscillation and numerical dispersion limit the reliability of numerical solutions of the convection-dispersion equation when finite difference methods are used. To eliminate oscillation and reduce the numerical dispersion, an optimal upstream weighting with finite differences is proposed. The optimal values of upstream weighting coefficients numerically obtained are a function of the mesh Peclet number used. The accuracy of the proposed numerical method is tested against two classical problems for which analytical solutions exist. The comparison of the numerical results obtained with different numerical schemes and those obtained by the analytical solutions demonstrates the possibility of a real gain in precision using the proposed optimal weighting method. This gain in precision is verified by interpreting a tracer experiment performed in a laboratory column. 相似文献
77.
78.
通过分析、比较1996--2003年喀什地震台站记录到的新疆伽师及附近地区发生的多次6级地震的地磁前兆异常特征,发现在这几组地震活动过程中喀什地震台的地磁表现出不同的异常特征,说明与地震破裂特征有更深层次的相关性,且地磁响应比异常和总强度差值异常在一定程度上反映了台站周围小范围的震源区介质电性结构的变化。巴楚-伽师6.8级地震前地磁异常特征并不十分突出,有别于1996—1998年伽师强震群震前地磁异常量较丰富的特点。 相似文献
79.
A regional atmospheric climate model is used toexamine the effect of changes in the roughnesslengths of momentum (z0m) and heat (z0h)on the structure of the lower atmosphere and on thesurface energy fluxes over Antarctica. Fourexperiments were carried out in which z0mand/or z0h were altered with respect to acontrol experiment. The changes consisted of (1) alowering of z0m from a field aggregated froma vegetation map with an orographic correction basedon the European Centre for Medium-Range WeatherForecasts z0m field, to a constant value of10-3 m; and (2) a lowering of z0h from a valueequal to z0m to a constant value of 10-3 mor a value dependent on the wind speed via a surfacerenewal model. A reduction of z0m results in theexpected increase in near-surface wind speed. It alsoresults in an increase in the depth of the layer in whichsouth-easterly near-surface winds prevail, and in adecrease in the strength of the large-scale flow overthe continent, in particular in summer. In theescarpment region a decrease of z0m is foundto result in too high wind speeds. Surface temperatureson average decrease while atmospheric temperaturesincrease, resulting in an increase of near-surfacestatic stability. Changes in roughness lengths donot significantly change the temperature profiles.The surface fluxes, on average found reduced, aremodelled best by using the z0h based on thesurface renewal method. 相似文献
80.
兰州CAWS600-R自动站与人工观测资料对比分析 总被引:7,自引:10,他引:7
利用2002年11月到2003年2月兰州CAWS600-R型自动站与人工观测的温度、本站气压、水汽压、相对湿度、5~320cm地温等资料,分析了对比观测资料的差值。结果表明:对气温、本站气压、水汽压、相对湿度及320cm地温等要素观测误差较小,5~160cm地温的观测误差较大。自动观测仪器的系统性偏差、测量元件的精度及对气象要素变化响应的灵敏度、观测时间的差异和人为因素的影响是造成对比观测误差的原因。 相似文献