全文获取类型
| 收费全文 | 5401篇 |
| 免费 | 898篇 |
| 国内免费 | 1094篇 |
专业分类
| 测绘学 | 865篇 |
| 大气科学 | 646篇 |
| 地球物理 | 813篇 |
| 地质学 | 2864篇 |
| 海洋学 | 536篇 |
| 天文学 | 8篇 |
| 综合类 | 493篇 |
| 自然地理 | 1168篇 |
出版年
| 2024年 | 29篇 |
| 2023年 | 77篇 |
| 2022年 | 211篇 |
| 2021年 | 284篇 |
| 2020年 | 250篇 |
| 2019年 | 260篇 |
| 2018年 | 203篇 |
| 2017年 | 269篇 |
| 2016年 | 272篇 |
| 2015年 | 291篇 |
| 2014年 | 356篇 |
| 2013年 | 338篇 |
| 2012年 | 390篇 |
| 2011年 | 404篇 |
| 2010年 | 331篇 |
| 2009年 | 352篇 |
| 2008年 | 353篇 |
| 2007年 | 391篇 |
| 2006年 | 320篇 |
| 2005年 | 260篇 |
| 2004年 | 243篇 |
| 2003年 | 206篇 |
| 2002年 | 177篇 |
| 2001年 | 180篇 |
| 2000年 | 139篇 |
| 1999年 | 131篇 |
| 1998年 | 122篇 |
| 1997年 | 114篇 |
| 1996年 | 83篇 |
| 1995年 | 71篇 |
| 1994年 | 60篇 |
| 1993年 | 54篇 |
| 1992年 | 52篇 |
| 1991年 | 25篇 |
| 1990年 | 21篇 |
| 1989年 | 16篇 |
| 1988年 | 14篇 |
| 1987年 | 19篇 |
| 1986年 | 10篇 |
| 1985年 | 5篇 |
| 1984年 | 2篇 |
| 1983年 | 1篇 |
| 1982年 | 1篇 |
| 1980年 | 1篇 |
| 1979年 | 3篇 |
| 1977年 | 2篇 |
排序方式： 共有7393条查询结果，搜索用时 343 毫秒
101.
102.
The damping‐solvent extraction method for the analysis of unbounded visco‐elastic media is evaluated numerically in the frequency domain in order to investigate the influence of the computational parameters—domain size, amount of artificial damping, and mesh density—on the accuracy of results. An analytical estimate of this influence is presented, and specific questions regarding the influence of the parameters on the results are answered using the analytical estimate and numerical results for two classical problems: the rigid strip and rigid disc footings on a visco‐elastic half‐space with constant hysteretic material damping. As the domain size is increased, the results become more accurate only at lower frequencies, but are essentially unaffected at higher frequencies. Choosing the domain size to ensure that the static stiffness is computed accurately leads to an unnecessarily large domain for analysis at higher frequencies. The results improve by increasing artificial damping but at a slower rate as the total (material plus artificial) damping ratio ζt gets closer to 0.866. However, the results do not deteriorate significantly for the larger amounts of artificial damping, suggesting that ζt≈0.6 is appropriate; a larger value is not likely to influence the accuracy of results. Presented results do not support the earlier suggestion that similar accuracy can be achieved by a large bounded domain with small damping or by a small domain with larger damping. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
103.
A stochastic channel embedded in a background facies is conditioned to data observed at wells. The background facies is a fixed rectangular box. The model parameters consist of geometric parameters that describe the shape, size, and location of the channel, and permeability and porosity in the channel and nonchannel facies. We extend methodology previously developed to condition a stochastic channel to well-test pressure data, and well observations of the channel thickness and the depth of the top of the channel. The main objective of this work is to characterize the reduction in uncertainty in channel model parameters and predicted reservoir performance that can be achieved by conditioning to well-test pressure data at one or more wells. Multiple conditional realizations of the geometric parameters and rock properties are generated to evaluate the uncertainty in model parameters. The ensemble of predictions of reservoir performance generated from the suite of realizations provides a Monte Carlo estimate of the uncertainty in future performance predictions. In addition, we provide some insight on how prior variances, data measurement errors, and sensitivity coefficients interact to determine the reduction in model parameters obtained by conditioning to pressure data and examine the value of active and observation well data in resolving model parameters. 相似文献
104.
Papadimitriou P. Voulgaris N. Kassaras I. Kaviris G. Delibasis N. Makropoulos K. 《Natural Hazards》2002,27(1-2):15-33
On 7 September 1999 at 11:56 GMT a destructive earthquake (Mw = 6.0) occurred close to Athens (Greece). The rupture process is examined using data from the Cornet local permanent network, as well as teleseismic recordings. Data recorded by a temporary seismological network were analyzed to study the aftershock sequence. The mainshock was relocated at 38.105°N, 23.565°E, about 20 km northwest of Athens. Four foreshocks were also relocated close to the mainshock. The modeling of teleseismic P and SH waves provides a well-constrained focal mechanism of the mainshock (strike = 105°, dip = 55° and rake = -80°) at a depth of 8 km and a seismic moment M0 = 1.01025 dyn·cm. The obtained fault plane solution represents normal faulting indicating an almost north-south extension. More than 3500 aftershocks were located, 1813 of which present RMS < 0.1 s and ERH, ERZ < 1.0 km. Two main clusters were distinguished, while the depth distribution is concentrated between 2 and 11 km. Over 1000 fault plane solutions of aftershocks were constrained, the majority of which also correspond to N–S extension. No surface breaks were observed but the fault plane solution of the mainshock is in agreement with the tectonics of the area and with the focal mechanisms obtained by aftershocks. The hypocenter of the mainshock is located on the deep western edge of the fault plane. The relocated epicenter coincides with the fringe that represents the highest deformation observed on the differential interferometric image. The calculated source duration is 5 sec, while the estimated dimensions of the fault are 15 km length and 10 km width. The source process is characterized by unilateral eastward rupture propagation, towards the city of Athens. An evident stop phase observed in the recordings of the Cornet local stations is interpreted as a barrier caused by the Aegaleo Mountain. 相似文献
105.
The methods used for a building seismic hazard evaluation are presented with the associated results. The goals of the study are (1) to check the soil nature and the existence or not of a possible site effect around the installation and (2) to characterize the dynamic behavior of the building using ambient vibration records.
The results of the soil study with the Nakamura method are very difficult to interpret because they are not stable in space and time. The spectral ratios method has been used with regional earthquake records. The results of the application of this method allowed us to conclude that the installation was free of site effect.
The ambient vibration measurements on the building brought the conclusion to determine the first and second modes of the structure. These results have been used to calibrate numerical model. The modal shapes in plan (high roof) and in elevation (main column) have been evaluated. The damping of the building has been computed using ambient vibration records. 相似文献
106.
An scientific evaluation of annual earthquake prediction ability 总被引：1，自引：0，他引：1
Introduction There have been nearly 40 years for earthquake prediction since the research on earthquake prediction was carried out in plan by some advanced countries since 1960s. For the hard long process of earthquake prediction, Alen, American famous scientist and former president of the evaluation commission of earthquake prediction in California, USA, said that the difficulty of earthquake prediction is more than the expected and the practical progress of earthquake prediction is more sl… 相似文献
107.
108.
109.
该文基于模糊数学的理论和方法 ,从不同角度、不同层次对吉林省通榆县的旅游资源进行综合评价 ,并针对旅游资源特征 ,提出了发展旅游业的基本构思。 相似文献
110.