全文获取类型
收费全文 | 3713篇 |
免费 | 780篇 |
国内免费 | 1069篇 |
专业分类
测绘学 | 303篇 |
大气科学 | 693篇 |
地球物理 | 972篇 |
地质学 | 2245篇 |
海洋学 | 369篇 |
天文学 | 46篇 |
综合类 | 251篇 |
自然地理 | 683篇 |
出版年
2024年 | 22篇 |
2023年 | 76篇 |
2022年 | 137篇 |
2021年 | 149篇 |
2020年 | 159篇 |
2019年 | 187篇 |
2018年 | 160篇 |
2017年 | 176篇 |
2016年 | 155篇 |
2015年 | 192篇 |
2014年 | 245篇 |
2013年 | 233篇 |
2012年 | 246篇 |
2011年 | 241篇 |
2010年 | 214篇 |
2009年 | 288篇 |
2008年 | 249篇 |
2007年 | 232篇 |
2006年 | 259篇 |
2005年 | 212篇 |
2004年 | 216篇 |
2003年 | 187篇 |
2002年 | 161篇 |
2001年 | 172篇 |
2000年 | 138篇 |
1999年 | 114篇 |
1998年 | 132篇 |
1997年 | 99篇 |
1996年 | 112篇 |
1995年 | 91篇 |
1994年 | 68篇 |
1993年 | 61篇 |
1992年 | 48篇 |
1991年 | 27篇 |
1990年 | 26篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有5562条查询结果,搜索用时 15 毫秒
221.
长江三角洲城市带扩展对区域温度变化的影响 总被引:7,自引:0,他引:7
Based on non-radiance-calibrated DMSP/OLS nighttime light imagery from 1992 to 2003, urban land area statistical data, meteorological data and land surface temperature data retrieved by MODIS and NOAA/AVHRR data, the influence of urbanization on regional cli- matic trend of temperature in the Yangtze River Delta (YRD) was analyzed. Conclusions are as follows: 1) There is a significant urbanization process from 1992 to 2003 in the YRD. Four city clusters of Nanjing–Zhenjiang–Yangzhou, Suzhou–Wuxi–Changzhou, Shanghai and Hangzhou Bay form a zigzag city belt. The increase rate of annual mean air temperature in city-belt is 0.28–0.44℃/10a from 1991 to 2005, which is far larger than that of non-city-belt. 2) The urban heat island (UHI) effect on regional mean air temperature in different seasons is summer>autumn>spring>winter. 3) The UHI intensity and the urban total population logarithm are creditably correlated. 4) The UHI effect made the regional annual mean air temperature increased 0.072℃ from 1961 to 2005, of which 0.047℃ from 1991 to 2005, and the annual maximum air temperature increased 0.162℃, of which 0.083℃ from 1991 to 2005. All these indicating that the urban expansion in the YRD from 1991 to 2005 may be regarded as a serious climate signal. 相似文献
222.
223.
前陆盆地挠曲沉降正演模型的设计与实现——以库车古近纪陆内前陆坳陷沉降分析为例 总被引:2,自引:0,他引:2
本文以二维薄板弹性挠曲模型为基础,对模型进行简化和参数优化选取,并在VC++6.0环境下采用Windows视窗设计,实现了前陆盆地挠曲沉降的正演模拟系统.应用这一系统模拟分析了库车古近纪-新近纪前陆盆地的挠曲沉降过程.模拟结果表明,库车古近纪-新近纪前陆盆地的沉降曲线总体呈上凸型,具有典型前陆盆地沉降的特点,根据沉降速率变化可以把整个沉降过程分为四个部分,分别对应盆地的四个构造层序发育阶段,每一阶段呈不同的沉降特征,相邻两阶段之间存在一盆地回弹隆升、逆冲构造活动终止期,盆地遭受广泛剥蚀形成两个构造层序之间的不整合界面.正演模拟通过将沉降过程时间离散,精细设定不同时间段的构造负载,能够精细恢复前陆盆地的沉降过程和演化. 相似文献
224.
《水文科学杂志》2013,58(5)
Abstract Some unique coupled wind–water erosion processes exist in the desert-loess transitional zone in the middle Yellow River basin. Based on data from 40 stations on 29 rivers, a study was made on the influence of such processes on suspended sediment grain-size characteristics of the tributaries of the Yellow River. Results show that the percentage of >0.05-mm grain size decreases with the increased annual mean precipitation, but increases with the increase in the annual mean number of sand-dust storm days. The percentage of <0.01-mm grain size increases with the increase in the annual mean precipitation, but decreases with the increase in the annual number of sand-dust storm days. Based on annual mean data from 40 stations, multiple regression equations were established between the percentages of >0.05-mm grain size (r >0.05) and <0.01-mm grain size (r <0.01), annual mean precipitation (P m) and annual mean number of sand-dust storm days (D ss). On this basis, the relative contributions of the variations in D ss and P m to the variation in r >0.05 and r <0.01 were estimated. The results indicate that the variation in sand-dust storm frequency exerts greater influences on the variation in grain-size characteristics of suspended load than does the variation in annual mean precipitation. With the increase in the coupled wind–water processes index, expressed by P m/D ss, the percentage of >0.05-mm grain size in suspended sediment decreases and the percentage of <0.01-mm grain size increases. With the variation in P m/D ss, different combinations of r >0.05 with r <0.01 appear, which have some influence on the formation of hyperconcentrated flows. There exist some optimal ratios of coarse to fine fractions in suspended sediment that make sediment concentrations of hyperconcentrated flows the highest. The optimal r >0.05/r <0.01 value is related to some range of the index P m/D ss. When the P m/D ss index falls in this range, the optimum combination of relative coarse with fine sediments in the suspended load appears, and thus results in the peak values of sediment concentration. 相似文献
225.
Edgar Knobloch 《地球物理与天体物理流体动力学》2013,107(6):535-536
We present three-dimensional (3D) solutions of the magnetohydrostatic equations in the co-rotating frame of reference outside a magnetized rigidly rotating cylinder. We make no symmetry assumption for the magnetic field, but to be able to make analytical progress we neglect outflows and specify a particular form for the current density. The magnetohydrostatic equations can then be reduced to a single linear partial differential equation for a pseudo-potential U, from which the magnetic field can be calculated by differentiation. The equation for U can be solved by standard methods. The solutions can also be used to determine the plasma pressure, density and temperature as functions of all three spatial coordinates. Despite the obvious limitations of this approach, it can, for example, be used as a simple tool to create 3D models for the closed field line regions of rotating magnetospheres without rotational symmetry. 相似文献
226.
This study shows the usefulness of the semivariogram for modelling sand ripples created by water flows of varied flow intensity. A combination of two mathematical functions is fitted to each sample semivariogram, that is an exponential (or stochastic) component and a periodic component. The parameters of each of these components have direct physical meaning. A non-dimensional ratio combining the two parameters of the exponential model is interpreted as a regularity index (which increases with the degree of regularity of bedform arrangement). This regularity index is inversely related to the Froude number of the flow. The non-dimensional wavelength, estimated from the dominant periodic function, is also inversely and closely related to the Froude number. The wave height, accurately estimated from properties of the two fitted components, is a direct function of flow velocity and is also proportional to the standard deviation of bed elevations. The bedform shape introduces a considerable discrepancy between the generally assumed normal frequency distribution and the empirical distributions of bed height. The series of bed elevations are generally characterized by a mixture of normal distributions having the same variance but different means. The calculation of a covariance assuming a constant and single mean (as in spectral analysis) can therefore be misleading and the problem may be avoided by using the semivariogram. 相似文献
227.
228.
The growth process, palaeoecological features and the function of organisms in reef-building of the Jukoupu bioherm in Hunan are discussed in detail. The bioherm is divided into 10 microfacies. Organisms are very abundant in the reef. Thirty-two genera Belonging to 7 phyla have been recognized. They make up 5 communities composed mainly of stromatopoids, Corals and algae, each of which has its own salient ecological features. An analysis of all communities shows that the organic functions are very complex. The same organisms may possess diverse functions simultaneously as the reef growth enters the late stage. The growth process of the reef may involve five stages' (l)biostrome stage, (2) stabilization stage, (3) frame-type reef-building stage, (4) binding and covering-type reef-building stage, and (5) baffle- type reef -building stage. 相似文献
229.
北京北山泥石流的分布受构造控制,呈北东方向展布。其分布在时间上和空间上均有一定的规律可寻。一条泥石流沟谷的形成从开始到结束,概括分为形成、位移和堆积。区内泥石流的形成主要有三种形式:以水力侵蚀为主,以坡面侵蚀为主和以沟源崩、滑塌形式触发沟床物质活动而形成的泥石流。 相似文献
230.