全文获取类型
收费全文 | 3200篇 |
免费 | 472篇 |
国内免费 | 596篇 |
专业分类
测绘学 | 378篇 |
大气科学 | 258篇 |
地球物理 | 865篇 |
地质学 | 1134篇 |
海洋学 | 303篇 |
天文学 | 1001篇 |
综合类 | 147篇 |
自然地理 | 182篇 |
出版年
2024年 | 20篇 |
2023年 | 57篇 |
2022年 | 88篇 |
2021年 | 112篇 |
2020年 | 124篇 |
2019年 | 146篇 |
2018年 | 102篇 |
2017年 | 125篇 |
2016年 | 157篇 |
2015年 | 172篇 |
2014年 | 179篇 |
2013年 | 162篇 |
2012年 | 160篇 |
2011年 | 160篇 |
2010年 | 153篇 |
2009年 | 240篇 |
2008年 | 210篇 |
2007年 | 270篇 |
2006年 | 234篇 |
2005年 | 185篇 |
2004年 | 193篇 |
2003年 | 171篇 |
2002年 | 137篇 |
2001年 | 131篇 |
2000年 | 98篇 |
1999年 | 98篇 |
1998年 | 96篇 |
1997年 | 31篇 |
1996年 | 51篇 |
1995年 | 30篇 |
1994年 | 29篇 |
1993年 | 36篇 |
1992年 | 23篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有4268条查询结果,搜索用时 15 毫秒
981.
铁路干线下的隧道施工关键技术 总被引:2,自引:0,他引:2
结合泰安抽水蓄能电站工程实例,介绍隧洞在穿越京沪铁路的施工过程中,采用震动监测技术优化爆破参数,顺利通过的施工技术。 相似文献
982.
研究了地震资料的特征参数与储层参数间的神经网络模型。建立了相互之间的非线性映射,可以横向预测目的层的储层参数,实现地震资料和测井资料联合预测储层参数的空间分布规律。实验结果表明,该方法是可行的。 相似文献
983.
The magnitude of kriging errors varies in accordance with the surface properties. The purpose of this paper is to determine the association of ordinary kriging (OK) estimated errors with the local variability of surface roughness, and to analyse the suitability of probabilistic models for predicting the magnitude of OK errors from surface parameters. This task includes determining the terrain parameters in order to explain the variation in the magnitude of OK errors. The results of this research indicate that the higher order regression models, with complex interaction terms, were able to explain 95 per cent of the variation in the OK error magnitude using the least number of predictors. In addition, the results underscore the importance of the role of the local diversity of relief properties in increasing or decreasing the magnitude of interpolation errors. The newly developed dissectivity parameters provide useful information for terrain analysis. Our study also provides constructive guides to understanding the local variation of interpolation errors and their dependence on surface dissectivity. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
984.
Existing empirical models for estimating liquefaction-induced lateral spread displacement (DLL) have been derived from a dataset poorly distributed with respect to earthquake magnitude and source distance, and also produced from different tectonic source types and faulting mechanisms. Both the poor distribution and mixed tectonic source types and faulting mechanisms of the data have an adverse impact on the reliability of the empirical models. To overcome these problems in the development of empirical models, we replace the direct use of magnitude and source distance with pseudo-displacement derived from spectral acceleration attenuation models that are well supported by earthquake data, and use a modification factor to account for effects of the non-linear soil response. Attenuation models derived from very large and reasonably well-balanced datasets have been selected, one being a Japanese attenuation model and other being a combination of the Sadigh et al. model and the Youngs et al. model. These models are capable of accounting for the effects of earthquake tectonic source type and faulting mechanism. We determined the model coefficients by selecting the pseudo-displacements calculated for a number of spectral periods to achieve an unbiased distribution of residuals with respect to earthquake magnitude and source distance. Sensitivity analyses have been carried out based on the new and existing models, and show that the new model is more robust than the existing models. Comparison with a limited number of data from the 1997 Kocaeli, Turkey earthquake suggests our model provides comparable liquefaction-induced lateral displacement DLL estimates. 相似文献
985.
Marcos A. E. Chaparro Juan M. Lirio Héctor Nuñez Claudia S. G. Gogorza Ana M. Sinito 《Environmental Geology》2005,49(1):30-43
Magnetic properties of lagoon and stream sediments from Chascomús area (Buenos Aires Province) and the relevance of various magnetic parameters as giving pollution status are studied in the present work. This work is focussed on magnetic parameters, such as concentration-dependent (magnetic susceptibility, saturation anhysteric and isothermal remanent magnetisation) and feature-dependent parameters (S-ratio, coercivity of remanence, anhysteric susceptibility/magnetic susceptibility-ratio), as pollution indicators. Firstly and most importantly, different magnetic parameters and chemical measurements were correlated in order to investigate their goodness, obtaining the best results for feature-dependent magnetic parameters. Coercivity of remanence correlate very well with chemical variables, showing correlations at high level of significance up to 0.9094, and the anhysteric susceptibility/magnetic susceptibility-ratio also shows very good correlations (up to 0.8376). Some results and advantages of using a new experimental method in order to discriminate hard and soft magnetic phases are also shown. This method uses alternately backfield isothermal remanent magnetisation and alternating field demagnetisation. From the experimental separation, the presence of hard magnetic phases in some samples was confirmed. 相似文献
986.
本文利用半经验、半理论的方法对世界各主要地震汇集和研究机构所给出的集集主震基本震源参数进行了综合计算和评定。根据这些参数重新计算了集集主震的标量地震矩、破裂面积、应力降等。根据这些参数之间的内在联系,从地震分类学的角度,判定集集地震是发生于板块边缘的大地震。可供研究台湾岛上地震活动性以及台湾地区板块构造演化问题参考。 相似文献
987.
The earthquake swarm that struck Shadwan Island at the entrance of the Gulf of Suez in 2001 August included 408 events. Almost all of these events (94 per cent) were microearthquakes and only 6 per cent had small measurable magnitudes (5.0 > M L ≥ 3.0) . Most of the earthquakes were weak and followed each other so closely in time that they could not be identified at more distant stations. The fault plane solutions of the strongest events of the swarm show almost identical focal mechanisms, predominately normal faulting with a significant sinistral strike-slip component for nodal planes trending NW–SE. A comparison with the mechanisms of the 1969 and 1972 events which took place 20 km north of the swarm epicentral region shows similarities in faulting type and orientation of nodal planes. The azimuths of T -axes determined from focal mechanisms in this study are oriented in the NNE–SSW direction. This direction is consistent with the present-day stress field derived from borehole breakouts in the southern Gulf of Suez and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS results.
The source parameters of the largest ( ML ≥ 3.0) events of the 2001 August Shadwan swarm have been estimated from the P -wave spectra of the Egyptian National Seismograph Network (ENSN). Averaging of the values obtained at different stations shows relatively similar source parameters, including a fault length of 0.65 ≤ L ≤ 2 km , a seismic moment of 7.1 × 1012 ≤ Mo ≤ 3.0 × 1014 N m and a stress drop of 0.4 ≤Δσ≤ 10 bar. 相似文献
The source parameters of the largest ( M
988.
由地震活动参数分析龙门山-岷山断裂带的现今活动习性与强震危险性 总被引:38,自引:0,他引:38
根据最近28年的区域台网地震资料,利用b值空间分布及断裂带分段的多地震活动参数值的组合方法,结合历史强震背景,分析了沿川北龙门山-岷山断裂带不同断裂段的现今活动习性,并初步判别出了潜在的强震危险段落。研究结果表明:龙门山断裂带中-南段存在6个具有不同现今活动习性的段落,其中,绵竹-茂县段处于相对高应力背景下的频繁中-小震活动状态,被认为是龙门山断裂带上未来最可能发生强震的地段;江油-平武段处于相对高应力背景下的稀疏中-小震活动状态,未来有可能发生中强地震。而岷山断裂带中的岷江断裂段和虎牙断裂段,以及叠溪隐伏逆断层地区均具有相对偏低的应力水平,可能与其不久前分别发生过大地震和强震有关,未来不太长的时期内复发大地震的可能性较小。 相似文献
989.
990.
Zafeiria Roumelioti Anastasia Kiratzi Nikos Theodoulidis Christos Papaioannou 《Journal of Seismology》2002,6(2):219-236
S-wave spectral analysis is applied to 174 strong motion accelerationrecords to obtain the source parameters of 27 aftershocks(3.1 ML 4.3) of the May 13, 1995, Mw 6.6,Kozani-Grevena (NW Greece) earthquake. The data are derived from atemporary network, of three-component digital accelerographs, deployedwithin the strongly affected area some days after the mainshock occurrence.Site effects were evident in the strong motion records at 3 out of the 4stations used, and a correction was applied to account for theoverestimation of seismic moment due to amplification of thelow-frequency part of the spectrum. The data from this analysis arecomplimented with previously obtained source parameters for earthquakesin Greece, in order to study the applicability of the empirical scalingrelations used so far, towards smaller magnitudes. In general, a goodcorrelation was observed in most cases, validating the use of empiricalrelations that are applicable to the Aegean area. Empirical relations aredetermined between seismic moment and seismic slip, as well as, betweenseismic moment and stress drop, applicable to small magnitude earthquakes(ML < 4.3). Stress drop values were found to be relatively small,ranging from 2 to 41 bars, indicative of inter-plate environments. Thevalues of fc and of fmax were found in good agreement withrelations based on observations from larger worldwide earthquakes. 相似文献