全文获取类型
收费全文 | 409篇 |
免费 | 61篇 |
国内免费 | 95篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 136篇 |
地球物理 | 85篇 |
地质学 | 220篇 |
海洋学 | 33篇 |
天文学 | 14篇 |
综合类 | 18篇 |
自然地理 | 44篇 |
出版年
2023年 | 7篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 21篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 21篇 |
2013年 | 21篇 |
2012年 | 22篇 |
2011年 | 24篇 |
2010年 | 23篇 |
2009年 | 21篇 |
2008年 | 24篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 7篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 22篇 |
1999年 | 24篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 18篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1938年 | 1篇 |
1936年 | 4篇 |
排序方式: 共有565条查询结果,搜索用时 328 毫秒
31.
江淮地区北部晚太古宙TTG质片麻岩 总被引:5,自引:1,他引:5
江淮地区北部的灰色片麻岩是深成侵入的英云闪长岩-奥长花岗岩-花岗闪长岩,以高铝型为主,具弱的负Eu异常或不明显。从英云闪长岩到奥长花岗岩,TiO_2、FeO、Ca0、MgO减少,而稀土元素分馏程度增加。形成于晚太古宙华北陆台南东大陆边缘挤压的构造环境下,由斜长角闪岩部分熔融而成。 相似文献
32.
我国月平均气温场遥相关结构的观测研究 总被引:1,自引:0,他引:1
研究了我国月平均气温场的遥相关结构。指出,我国冬季月份的气温场的跷跷板特征不明显。夏季月季有明显的遥相关结构。给出了各月的遥相关模态及强度。指出,月平均气温遥相关表现为从南向东北,西北方向的辐射状。在105°E以东呈东北-西南向。在105°E以西呈西北-东南向。这种遥相关结构是由环流异常造成的。而且可以在区域的月平均气温场预报中使用。 相似文献
34.
A time-domain method for the analysis of arch dam-foundation rock dynamic interaction during earthquake was proposed, and
the dynamic relaxation technique was adopted to obtain the initial static response for dynamic analysis by [Du et al. (2005).
The paper has been contributed to Bulletin of earthquake engineering]. In this paper, a nonlinear explicit method in time
domain considering the opening and closing effect of contact joints on arch dam during earthquake is further proposed by introducing
the dynamic contact force model into the method. The simulation accuracy of dynamic contact force model is verified by comparing
its calculation result and test result of scale model on shaking table. Finally, the influence of joints on the seismic response
of Xiaowan arch dam is studied by the proposed method and some conclusions are given. 相似文献
35.
多窗谱分析方法及其在全球变暖研究中的应用 总被引:12,自引:0,他引:12
多窗谱分析方法是一种低方差、高分辨的谱分析方法 ,尤其适合于非线性气候系统中高噪声背景下弱信号、时频演变信号的诊断分析。文中简要地介绍了多窗谱分析方法的基本原理 ,并将其用于近 1 5 0 a来全球及南、北半球温度变化的研究。结果表明 :(1 )在温度呈线性变暖的背景趋势下 ,北半球、全球年平均温度还具有显著的 40~ 70 a的准周期低频振荡 ,它们与变暖过程中的波动性密切相关 ;(2 )年代际振荡信号在北半球温度序列中也相当明显 ,南半球则存在多种低于 5 a尺度的显著振荡周期 ,半球或全球 ENSO振荡分量、QBO周期信号的振幅都具有缓变包络的特性 ;(3 )与传统功率谱估计、最大熵谱估计结果的对比表明 ,多窗谱分析方法方法得到的谱估计分辨力高 ,稳定性强。 相似文献
36.
陕西凤县金矿类型与金的预富集及找矿方向 总被引:1,自引:0,他引:1
陕西凤县地区金矿主要有蚀变岩与石英脉型。地层预富集是金矿形成的物质基础;岩体为金矿形成提供了Au源,而且沿构造蚀变带提供了热源,是Au活化成矿的一个重要条件;多期次热液沿构造破碎带进行交代改造形成蚀变预富集,是金矿成矿的关键。庞家河成矿模式为层预富集+蚀变预富集+后期多次热液交代富集成矿;佐家庄成矿模式为岩体(脉)预富集+构造蚀变预富集+多种热液叠加成矿。NNW向断裂带是寻找蚀变岩型金矿的主要标志;印支期与华力西期花岗岩-闪长岩带的内外接触带是寻找石英脉型及蚀变岩型金矿的主要构造带;金的预富集带是金矿成矿的有利部位,紧靠商丹大断裂南侧续分布的残余存小岩块旁侧都发现金矿床。 相似文献
37.
考虑湿度影响的城市气溶胶夜晚温度效应 总被引:10,自引:0,他引:10
本文利用一维非定常模式,研究了城市上空干、湿气溶胶粒子对夜间边界层温度的影响。结果表明,湿气溶胶粒子对低层大气有明显的升温作用,而对中上层大气则起降温作用,同时改变了贴地逆温层结构和边界层稳定度。 相似文献
38.
The geometrical and scaling properties of the energy flux of the turbulent kinetic energy in the solar wind have been studied. Using present experimental technology in solar wind measurements we cannot directly measure the real volumetric dissipation rate, <varepsilon>(t), but are constrained to represent it by its surrogate the energy flux near the dissipation range at the proton gyro scale. There is evidence for the multifractal nature of the so defined dissipation field <varepsilon>(t), a result derived from the scaling exponents of its statistical moments. The generalized dimension D q has been determined and reveals that the dissipation field has a multifractal structure, which is not compatible with a scale-invariant cascade. The related multifractal spectrum f(<alpha>) has been estimated for the first time for MHD turbulence in the solar wind. Its features resemble those obtained for turbulent fluids and other nonlinear multifractal systems. The generalized dimension D q can for turbulence in high-speed streams be fitted well by the functional dependence of the p-model with a comparatively large parameter p 1=0.87, indicating a strongly intermittent multifractal energy cascade. The experimental value for D p/3 used in the scaling exponent s(p) of the velocity structure function gives an exponent that can describe some of the observations. The scaling exponent <mu> of the autocorrelation function of <varepsilon>(t) has also been directly evaluated, being 0.37. Finally, the mean dissipation rate was determined, which could be used in solar wind heating models. 相似文献
39.
An extended structure-function model is developed by including the new effect in the p-model of Meneveau and Sreenivasan which shows that the averaged energy cascade rate changes with scale, a situation which has been found to prevail in nonfullydeveloped turbulence in the inner solar wind. This model is useful for the small-scale fluctuations in the inner heliosphere, where the turbulence is not fully developed and cannot be explained quantitatively by any of the previous intermittency turbulence models. With two model parameters, the intrinsic index of the energy spectrum <alpha>, and the fragmentation fraction P 1, the model can fit, for the first time, all the observed scaling exponents of the structure functions, which are calculated for time lags ranging from 81 s to 0.7 h from the Helios solar wind data. From the cases we studied we cannot establish for P 1 either a clear radial evolution trend, or a solar-wind-speed or stream-structure dependence or a systematic anisotropy for both the flow velocity and magnetic field component fluctuations. Generally, P 1 has values between 0.7 and 0.8. However, in some cases in low-speed wind P 1 has somewhat higher values for the magnetic components, especially for the radial component. In high-speed wind, the inferred intrinsic spectral indices (<alpha>) of the velocity and magnetic field components are about equal, while the experimental spectral indices derived from the observed power spectra differ. The magnetic index is somewhat larger than the index of the velocity spectrum. For magnetic fluctuations in both high- and low-speed winds, the intrinsic exponent <alpha> has values which are near 1.5, while the observed spectral exponent has much higher values. In the solar wind with considerable density fluctuations near the interplanetary current sheet near 1 AU, it is found that P 1 has a comparatively high value of 0.89 for V x . The impact of these results on the understanding of the nature of solar wind fluctuations is discussed, and the limitations in using structure functions to study intermittency are also described. 相似文献
40.