全文获取类型
收费全文 | 29051篇 |
免费 | 5058篇 |
国内免费 | 7048篇 |
专业分类
测绘学 | 6194篇 |
大气科学 | 4821篇 |
地球物理 | 6647篇 |
地质学 | 12599篇 |
海洋学 | 4015篇 |
天文学 | 673篇 |
综合类 | 2367篇 |
自然地理 | 3841篇 |
出版年
2024年 | 106篇 |
2023年 | 323篇 |
2022年 | 1032篇 |
2021年 | 1213篇 |
2020年 | 1394篇 |
2019年 | 1622篇 |
2018年 | 1294篇 |
2017年 | 1565篇 |
2016年 | 1631篇 |
2015年 | 1745篇 |
2014年 | 1928篇 |
2013年 | 2161篇 |
2012年 | 2029篇 |
2011年 | 2069篇 |
2010年 | 1599篇 |
2009年 | 1835篇 |
2008年 | 1870篇 |
2007年 | 1948篇 |
2006年 | 1819篇 |
2005年 | 1623篇 |
2004年 | 1465篇 |
2003年 | 1208篇 |
2002年 | 1123篇 |
2001年 | 908篇 |
2000年 | 874篇 |
1999年 | 750篇 |
1998年 | 692篇 |
1997年 | 630篇 |
1996年 | 507篇 |
1995年 | 478篇 |
1994年 | 422篇 |
1993年 | 348篇 |
1992年 | 224篇 |
1991年 | 184篇 |
1990年 | 127篇 |
1989年 | 102篇 |
1988年 | 97篇 |
1987年 | 55篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 18篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1976年 | 3篇 |
1954年 | 13篇 |
1900年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
982.
1. IntroductionThe basic role of urban-rural boundary layer re-search is to study all kinds of physical process changesin the atmosphere boundary layer over urban and itssurrounding areas. Urban heat island (UHI) is a well-known feature of urban-rural climate. Attempts toincrease the understanding of the causes of the UHIand other urban-rural boundary layer phenomena haveused observational, theoretical and modelling methodssince long before. Seaman (1989) used a hydrostaticmodel, with real … 相似文献
983.
The contribution of areal precipitation of the catchment from Cuntan to Yichang (Three Gorges area) to eight flood peaks of the Upper Yangtze River (the upper reaches of the Yangtze River) is diagnosed for 1998 flood season. A rainfall-runoff model is employed to simulate runoffs of-this catchment. Comparison of observed and simulated runoffs shows that the rainfall-runoff model has a good capability to simulate the runoff over a large-scale river and the results describe the eight flood peaks very well. Forecast results are closely associated with the sensitivity of the model to rainfall and the calibration processes. Other reasons leading to simulation errors are further discussed. 相似文献
984.
The Application of ARGO Data to the Global Ocean Data Assimilation Operational System of NCC 总被引:11,自引:0,他引:11
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
1. Introduction It is well-known that the state of ocean plays very important role in the climate change. But there is a paucity of the ocean observation data. The data distri- bution in the space, time and different components is very inhomogeneous, even in some areas, there are no any observation data. Hence, it brings some diffcul- ties to the scientists to study many problems relevant to ocean. This situation has been being changed since ARGO (Array for Real-time Geostrophic Oceanogra-… 相似文献
985.
A model to simulate channel changes in ephemeral river channels and to test the effects of hydrological changes due to climate change and[sol ]or land use change was developed under the auspices of the EU funded MEDALUS programme (Mediterranean Desertification and Land Use). The model, CHANGISM (Channel Change GIS Simulation Model), is designed to simulate the effect of channel flow events and of climate conditions on morphology, sediment and vegetation, through sequences of events and conditions, over periods of up to several decades. The modelling is based on cellular automata but with calculations for water and sediment continuity. Process rules have both deterministic and stochastic elements. An important feature of the model is that it incorporates feedback elements between each event. The main aim of the model is to indicate the likely outcomes of events and combinations of conditions. It is linked to GIS for both input and output. The modelling is based on a channel reach and state is input as GIS layers of morphology (DEM), sediment and vegetation cover and state. Other initial conditions of soil moisture, groundwater level, and overall gradient are input. Parameters for processes are read from tables and can be easily changed for successive runs of the model. The bases for decisions on process specifications are discussed in this paper. Initial tests of the operation and sensitivity of the model were made on idealized reaches. The model was then tested using data from monitored sites in SE Spain. Simulations using clearwater flow worked well but initial simulations using events with sediment loads showed some tendency for excess deposition. Further tests and modifications are taking place. Overall, the model is one of the most sophisticated that simulates the interaction of flows with sediment and vegetation and the outcomes in terms of erosion, deposition, morphology, sediment cover, vegetation cover and plant survival over periods of up to 30 years for the scale of a channel reach. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
986.
Xiangyang Li Jianxin Yuan British Geological Survey West Mains Road Edinburgh EH LA UK. Formerly at British Geological Survey now at PGS Inc. Richmond Avenue Suite Houston TX USA. 《应用地球物理》2005,2(1)
我们业已研发了计算各向异性、非均质介质中P- SV转换波(C-波)的转换点和旅行时的新理论。据此 可以利用诸如相似性分析、迪克斯模型建模、克契 霍夫求和等常规方法来完成各向异性的处理和各向 异性处理,并使各向异性的处理成为可能。这里将 我们的新发展分作两部分来介绍。第一部分为理 论,第二部分为对速度分析和参数计算的应用。第 一部分理论包括转换点的计算和动校正的分析。 相似文献
987.
988.
Introduction Ready and Renkin (1971) were the first to make the research on anisotropy problems in magnetotellurics (MT). The progress in the research is not evident because it is more complex and difficult than isotropic problems. Now, the one-dimensional (1D) anisotropy problems in MT have been well solved, while for the two-dimensional (2D) cases, the numerical solutions have only been obtained for some particular conditions (Ready and Renkin, 1975). As to the three-dimensional (3D) ani… 相似文献
989.
WU Yaping ZHU Yuanlin GUO Chunxiang SU Qiang & MA Wei . School of Civil Engineering Lanzhou Jiaotong University Lanzhou China . State Key Laboratory of Frozen Soil Engineering Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China 《中国科学D辑(英文版)》2005,48(7)
In the construction of Qinghai-Tibet railway,to avoid diseases caused by frost heave and thaw col-lapse of frozen ground,besides the normal bridges over the rivers,a lot of dry bridge structures have been built to replace subgrade in the regions of high tem-perature and high ice content frozen soil.So,the problems on forming mechanism of bearing capacity of pile foundation in cold regions already become one of hot spot problems in frozen soil engineering.Freezing force and frost heave force ar… 相似文献
990.
We have developed new basic theories for calculating the conversion point and the travel time of the P-SV converted wave (C-wave)
in anisotropic, inhomogeneous media. This enables the use of conventional procedures such as semblance analysis, Dix-type
model building and Kirchhoff summation, to implement anisotropic processing, and makes anisotropic processing affordable.
Here we present these new developments in two parts: basic theory and application to velocity analysis and parameter estimation.
This part deals with the basic theory, including both conversion-point calculation and moveout analysis.
Existing equations for calculating the PS-wave (C-wave) conversion point in layered media with vertical transverse isotropy
(VTI) are strictly limited to offsets about half the reflector depth (an offset-depth ratio, xlz, of 0.5), and those for calculating the C-wave traveltimes are limited to offsets equal to the reflector depth (x/z=l.0). In contrast, the new equations for calculating the conversion-point extend into offsets about three-times the reflector
depth (x/z=3.0), those for calculating the C-wave traveltimes extend into offsets twice the reflector depth (x/z=2.0). With the improved accuracy, the equations can help in C-wave data processing and parameter estimation in anisotropic,
inhomogeneous media.
This work is funded by the Edinburgh Anisotropy Project (EAP) of the British Geological Survey.
First author:
Xiangyang Li, Mr. Li is currently a professorial research seismologist (Grade 6) and technical director of the Edinburgh Anisotropy Project
in the British Geological Survey. He also holds a honorary professorship in multicomponent seismology at the School of Geosciences,
University of Edinburgh. He received his BSc(1982) in Geophysics from Changchun Geological Institute, China, an MSc (1984)
in applied geophysics from East China Petroleum Institute (now known as the China University of Petroleum), and a PhD (1992)
in seismology from the University of Edinburgh. During 1984–1987, he worked as a lecturer with the East China Petroleum Institute.
Since 1991, he has been employed by the British Geological Survey. His research interests include seismic anisotropy and multicomponent
seismology. 相似文献