全文获取类型
收费全文 | 1580篇 |
免费 | 237篇 |
国内免费 | 348篇 |
专业分类
测绘学 | 91篇 |
大气科学 | 293篇 |
地球物理 | 396篇 |
地质学 | 747篇 |
海洋学 | 178篇 |
天文学 | 135篇 |
综合类 | 167篇 |
自然地理 | 158篇 |
出版年
2024年 | 11篇 |
2023年 | 28篇 |
2022年 | 83篇 |
2021年 | 91篇 |
2020年 | 61篇 |
2019年 | 99篇 |
2018年 | 68篇 |
2017年 | 82篇 |
2016年 | 87篇 |
2015年 | 59篇 |
2014年 | 95篇 |
2013年 | 71篇 |
2012年 | 74篇 |
2011年 | 71篇 |
2010年 | 95篇 |
2009年 | 92篇 |
2008年 | 93篇 |
2007年 | 81篇 |
2006年 | 57篇 |
2005年 | 65篇 |
2004年 | 25篇 |
2003年 | 42篇 |
2002年 | 36篇 |
2001年 | 41篇 |
2000年 | 68篇 |
1999年 | 80篇 |
1998年 | 55篇 |
1997年 | 44篇 |
1996年 | 57篇 |
1995年 | 45篇 |
1994年 | 43篇 |
1993年 | 33篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 23篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有2165条查询结果,搜索用时 42 毫秒
1.
This study presents a finite element (FE) micromechanical modelling approach for the simulation of linear and damage‐coupled viscoelastic behaviour of asphalt mixture. Asphalt mixture is a composite material of graded aggregates bound with mastic (asphalt and fine aggregates). The microstructural model of asphalt mixture incorporates an equivalent lattice network structure whereby intergranular load transfer is simulated through an effective asphalt mastic zone. The finite element model integrates the ABAQUS user material subroutine with continuum elements for the effective asphalt mastic and rigid body elements for each aggregate. A unified approach is proposed using Schapery non‐linear viscoelastic model for the rate‐independent and rate‐dependent damage behaviour. A finite element incremental algorithm with a recursive relationship for three‐dimensional (3D) linear and damage‐coupled viscoelastic behaviour is developed. This algorithm is used in a 3D user‐defined material model for the asphalt mastic to predict global linear and damage‐coupled viscoelastic behaviour of asphalt mixture. For linear viscoelastic study, the creep stiffnesses of mastic and asphalt mixture at different temperatures are measured in laboratory. A regression‐fitting method is employed to calibrate generalized Maxwell models with Prony series and generate master stiffness curves for mastic and asphalt mixture. A computational model is developed with image analysis of sectioned surface of a test specimen. The viscoelastic prediction of mixture creep stiffness with the calibrated mastic material parameters is compared with mixture master stiffness curve over a reduced time period. In regard to damage‐coupled viscoelastic behaviour, cyclic loading responses of linear and rate‐independent damage‐coupled viscoelastic materials are compared. Effects of particular microstructure parameters on the rate‐independent damage‐coupled viscoelastic behaviour are also investigated with finite element simulations of asphalt numerical samples. Further study describes loading rate effects on the asphalt viscoelastic properties and rate‐dependent damage behaviour. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
Wang Lifang Wu Xiangbin Zhang Baoyi Li Xuefeng Huang Anshuo Meng Fei Dai Pengyao 《Natural Resources Research》2019,28(3):587-607
Natural Resources Research - Quantitative prediction of concealed mineralization is always confronted with difficulties in comprehensive analysis between 2D and 3D data and between qualitative and... 相似文献
3.
A promising method for gas hydrates exploration incorporates pre-stack seismic inversion data, elastic properties modeling, and seismic interpretation to predict saturation of gas hydrates (Sgh). The technology can be modified slightly and used for predicting hydrate concentrations in shallow arctic locations as well. Examples from Gulf of Mexico Walker Ridge (WR) and Green Canyon (GC) protraction areas illustrate how Sgh was derived and used to support the selection of well locations to be drilled for gas hydrates in sand reservoirs by the Chevron-led Joint Industry Project (JIP) Leg II cruise in 2009. Concentrations of hydrates were estimated through the integration of seismic inversion of carefully conditioned pre-stack data, seismic stratigraphic interpretation, and shallow rock property modeling. Rock property trends were established by applying principles of rock physics and shallow sediment compaction, constrained by regional geological knowledge. No nearby sonic or density logs were available to define the elastic property trends in the zone of interest. Sgh volumes were generated by inverting pre-stack data to acoustic and shear impedance (PI and SI) volumes, and then analyzing deviations from modeled impedance trends. In order to enhance the quality of the inversion, we stress the importance of maximizing the signal to noise ratio of the offset data by conditioning seismic angle gathers prior to inversion. Seismic interpretation further plays an important role by identifying false anomalies such as hard, compact strata, which can produce apparent high Sgh values, and by identifying the more promising strata and structures for containing the hydrates. This integrated workflow presents a highly promising methodology, appropriate for the exploration of gas hydrates. 相似文献
4.
5.
本文着重论述了我国石英砂粒在冰川、水流(包括河流及潮汐)、风蚀等外营力作用下,形成的特有微结构颗粒表面的形态。据此,探索沙质沉积物的演变历史,沙物质形态结构与成因的关系,为沙漠沙物质来源提供论据。 相似文献
6.
More than 240 items of historical records containing climatic information were retrieved from official historical books, local
chronicles, annals and regional meteorological disaster yearbooks. By using moisture index and flood/drought (F/D) index obtained
from the above information, the historical climate change, namely wet-dry conditions in borderland of Shaanxi Province, Gansu
Province and Ningxia Hui Autonomous Region (BSGN, mainly included Ningxialu, Hezhoulu, Gongchanglu, Fengyuanlu and Yan’anlu
in the Yuan Dynasty) was studied. The results showed that the climate of the region was generally dry and the ratio between
drought and flood disasters was 85/38 during the period of 1208–1369. According to the frequencies of drought-flood disasters,
the whole period could be divided into three phases. (1) 1208–1240: drought dominated the phase with occasional flood disasters.
(2) 1240–1320: long-time drought disasters and extreme drought events happened frequently. (3) 1320–1369: drought disasters
were less severe when flood and drought disasters happened alternately. Besides, the reconstructed wet-dry change curve revealed
obvious transition and periodicity in the Mongol-Yuan Period. The transitions occurred in 1230 and 1325. The wet-dry change
revealed 10- and 23-year quasi-periods which were consistent with solar cycles, indicating that solar activity had affected
the wet-dry conditions of the study region in the Mongol-Yuan Period. The reconstructed results were consistent with two other
study results reconstructed from natural evidences, and were similar to another study results from historical documents. All
the above results showed that the climate in BSGN was characterized by long-time dry condition with frequent severe drought
disasters during 1258 to 1308. Thus, these aspects of climatic changes might have profound impacts on local vegetation and
socio-economic system. 相似文献
7.
8.
9.
10.
The multi‐objective land allocation problem is to optimize the selection of land for different uses based on a set of decision objectives. For most applications, a geographical information system (GIS) is either absent or loosely coupled through file exchange. In this article the evolutionary algorithm (EA), a heuristic solution method for optimization problems, is integrated with a raster GIS to form a spatial decision support system (SDSS) for multi‐objective conservation reserve design. The SDSS effectively combines the functions of a GIS for data management, analysis, and visualization, with the optimization capability of the EA; and provides a uniform way to solve conservation reserve design problems with different types of constraints and objectives. The SDSS is demonstrated through application to the creation of conservation reserves in Bolivia to protect 17 endemic mammals. 相似文献