全文获取类型
收费全文 | 1384篇 |
免费 | 181篇 |
国内免费 | 324篇 |
专业分类
测绘学 | 139篇 |
大气科学 | 153篇 |
地球物理 | 475篇 |
地质学 | 673篇 |
海洋学 | 181篇 |
天文学 | 82篇 |
综合类 | 57篇 |
自然地理 | 129篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 54篇 |
2021年 | 45篇 |
2020年 | 62篇 |
2019年 | 74篇 |
2018年 | 58篇 |
2017年 | 46篇 |
2016年 | 63篇 |
2015年 | 59篇 |
2014年 | 87篇 |
2013年 | 121篇 |
2012年 | 72篇 |
2011年 | 108篇 |
2010年 | 88篇 |
2009年 | 103篇 |
2008年 | 91篇 |
2007年 | 93篇 |
2006年 | 115篇 |
2005年 | 69篇 |
2004年 | 61篇 |
2003年 | 55篇 |
2002年 | 45篇 |
2001年 | 42篇 |
2000年 | 41篇 |
1999年 | 31篇 |
1998年 | 38篇 |
1997年 | 20篇 |
1996年 | 28篇 |
1995年 | 22篇 |
1994年 | 13篇 |
1993年 | 20篇 |
1992年 | 15篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1889条查询结果,搜索用时 234 毫秒
81.
Non‐associated flow rule is essential when the popular Mohr–Coulomb model is used to model nonlinear behavior of soil. The global tangent stiffness matrix in nonlinear finite element analysis becomes non‐symmetric when this non‐associated flow rule is applied. Efficient solution of this large‐scale non‐symmetric linear system is of practical importance. The standard Krylov solver for a non‐symmetric solver is Bi‐CGSTAB. The Induced Dimension Reduction [IDR(s)] solver was proposed in the scientific computing literature relatively recently. Numerical studies of a drained strip footing problem on homogenous soil layer show that IDR(s = 6) is more efficient than Bi‐CGSTAB when the preconditioner is the incomplete factorization with zero fill‐in of global stiffness matrix Kep (ILU(0)‐Kep). Iteration time is reduced by 40% by using IDR(s = 6) with ILU(0)‐Kep. To further reduce computational cost, the global stiffness matrix Kep is divided into two parts. The first part is the linear elastic stiffness matrix Ke, which is formed only once at the beginning of solution step. The second part is a low‐rank matrix Δ, which is re‐formed at each Newton–Raphson iteration. Numerical studies show that IDR(s = 6) with this ILU(0)‐Ke preconditioner is more time effective than IDR(s = 6) with ILU(0)‐Kep when the percentage of yielded Gauss points in the mesh is less than 15%. The total computation time is reduced by 60% when all the recommended optimizing methods are used. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
82.
J.M.ANDRADE D.PRADA S.MUNIATEGUI Department of Analytical Chemistry Universidade da Corun La Zapateir E- Corun Spain B.GOMEZ M.PAN Analytical Laboratory Complejo Industrial Repsol Petróleo S.A.de La Corun Poligono Bens Corun Spain Author to whom correspondence should be addressed. 《地理学报(英文版)》1993,(5)
This paper deals with a typical question encountered in all industrial analytical laboratories:are all thetests performed in the laboratory to characterize the final product really necessary?In this work the cross-validation technique,Procrustes rotation techniques and statistical variable selection have been used toreduce the 26 initial British Petroleum and ASTM kerosene specification tests to ten'essential'ones.Statistical as well as chemical considerations were used to select the optimum subset of original variablesto be retained from all the possible ones. 相似文献
83.
Thomas Striebel Wolfgang Schäfer Stefan Peiffer 《Aquatic Sciences - Research Across Boundaries》1991,53(4):346-366
A field study on the geochemical properties of a chemically-stressed limnic environment was performed in Lake Silbersee, which receives leachate water of high inorganic loading from an upgradient landfill site. The highly concentrated sulfate ion in groundwater, when entering the pore water system of the lake, gives rise to an intensive microbial sulfate reduction. A diagenetic approach was used to explain the existence of a marine-like aqueous system within a geologically slightly acidic aquifer, consisting of a well-buffered lake water and an alkalinity producing, excess sulphide containing sediment pore water system. 相似文献
84.
85.
A large extent aeromagnetic survey, covering a 9°×9° degree of a Precambrian shield area in SE Brazil, was used to analyse long wavelength magnetic anomalies with the purpose of determining the magnetic structure of the lithosphere.Data analysis based on a novel approach to the estimation of the parameters in the statistical model ofSpector andGrant (1970), reveals a highly magnetized lower crust, bounded by an essentially non-magnetic upper mantle. The highly magnetized layer can be associated with a higher density lower crust model, derived from gravity and seismic data available in the area, suggesting a compositional transition from upper to lower crust.It was also verified that the operation of reduction to the pole, which is singular at the geomagnetic equator, performs quite satisfactorily at the low geomagnetic inclination of the area, bringing into accordance the long wavelength anomalies with the structural trends. 相似文献
86.
MICHAEL BIRD SUSAN COWIE REA HAWKES† BEN HORTON† COLIN MACGREGOR JIN EONG ONG‡ AILEEN TAN SHAU HWAI§ TEH TIONG SA¶ ZULFIGAR YASIN§ 《The Geographical journal》2007,173(2):103-117
We report the results of a study of the physical characteristics and socio-economic impacts of the Indian Ocean Tsunami of 26 December 2004 on the tourist island of Langkawi, Malaysia. In comparison with many other locations struck by the tsunami, the immediate physical and socio-economic impacts in Langkawi were relatively minor. A detailed survey of the watermark and ground elevations was undertaken in the worst affected area between Sungei Kuala Teriang and Sungei Kuala Melaka. Here, the tsunami reached a maximum elevation of 4.29 m as it crossed the coast, with a maximum flow depth of 2.0 m and a very consistent run-up elevation relative to mean sea level of 300 ± 10 cm. The tsunami inundated inshore areas for 300 m and penetrated inland along creeks for 500–1000 m. Structural damage to buildings was confined to within 50–150 m of the shoreline where about 10% of the houses were completely destroyed and 60–70% suffered significant structural damage. Damage was particularly severe in areas where there was no engineered coastal protection, but while coastal revetments did provide enhanced protection for houses at the waterfront, the coastline in the study area appeared to be more heavily impacted than elsewhere in Langkawi because wave energy was focused on the area by offshore breakwaters built to protect the Langkawi port and airport. Emergency response after the tsunami was rapid and efficient but would have been improved if the local police station had not been rendered inoperative by the first wave, and if a mechanism had been in place to ensure that informal advance warnings transmitted between Phuket (Thailand), Langkawi and Penang (Malaysia) by tourist operators could have been more widely disseminated. 相似文献
87.
Non-linear seismic behavior of structures with limited hysteretic energy dissipation capacity 总被引:1,自引:0,他引:1
Pierino Lestuzzi Youssef Belmouden Martin Trueb 《Bulletin of Earthquake Engineering》2007,5(4):549-569
This paper investigates the non-linear seismic behavior of structures such as slender unreinforced masonry shear walls or
precast post-tensioned reinforced concrete elements, which have little hysteretic energy dissipation capacity. Even if this
type of seismic response may be associated with significant deformation capacity, it is usually not considered as an efficient
mechanism to withstand strong earthquakes. The objective of the investigations is to propose values of strength reduction
factors for seismic analysis of such structures. The first part of the study is focused on non-linear single-degree-of-freedom
(SDOF) systems. A parametric study is performed by computing the displacement ductility demand of non-linear SDOF systems
for a set of 164 recorded ground motions selected from the European Strong Motion Database. The parameters investigated are
the natural frequency, the strength reduction factor, the post-yield stiffness ratio, the hysteretic energy dissipation capacity
and the hysteretic behavior model (four different hysteretic models: bilinear self-centring, with limited or without energy
dissipation capacity, modified Takeda and Elastoplastic). Results confirm that the natural frequency has little influence
on the displacement ductility demand if it is below a frequency limit and vice versa. The frequency limit is found to be around
2 Hz for all hysteretic models. Moreover, they show that the other parameters, especially the hysteretic behavior model, have
little influence on the displacement ductility demand. New relationships between the displacement ductility demand and the
strength reduction factor for structures having little hysteretic energy dissipation capacity are proposed. These relationships
are an improvement of the equal displacement rule for the considered hysteretic models. In the second part of the investigation,
the parametric study is extended to multi-degree-of-freedom (MDOF) systems. The investigation shows that the results obtained
for SDOF systems are also valid for MDOF systems. However, the SDOF system overestimates the displacement ductility demand
in comparison to the corresponding MDOF system by approximately 15%. 相似文献
88.
The effectiveness of tuned mass dampers (TMD) in vibration control of buildings was investigated under moderate ground shaking caused by long‐distance earthquakes with frequency contents resembling the 1985 Mexico City (SCT) or the 1995 Bangkok ground motion. The elastic–perfectly plastic material behaviour was assumed for the main structure, with linear TMDs employed by virtue of their simplicity and robustness. The accumulated hysteretic energy dissipation affected by TMD was examined, and the ratio of the hysteretic energy absorption in the structure with TMD to that without it is proposed to be used, in conjunction with the peak displacement ratio, as a supplementary TMD performance index since it gives an indication of the accumulated damage induced in the inelastic structures. For the ground motions considered, TMD would be effective in reducing the hysteretic energy absorption demand in the critical storeys for buildings in the 1.8–2.8 s range. The consequence is reduction in damage of the buildings which would otherwise suffer heavy damage in the absence of TMD, resulting in economical restorability in the damage control limit state. This is of practical significance in view of the current trend toward performance‐based design. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
89.
Luo Yan Liu Yongsheng Hu Shenghong Gao Shan Open Laboratory of Constitution Interaction Dynamics of the Crust Mantle System Ministry of National Lands Resources China University of Geosciences Wuhan Lin Shoulin Faculty of Material Sc 《中国地质大学学报(英文版)》2001,12(3)
INTRODUCTIONLaserablationinductivelycoupledplasmamassspectrome tryisanincreasinglydevelopedanalyticaltechniqueforsolidsampleanalysis.LA ICP MSoffersattractivecharacteristicsofhighsensitivity ,lowdetectionlimits,minimalsampleprepara tion ,lessoxidesinterfe… 相似文献
90.
新疆头屯河流域水沙特性与减沙治理 总被引:2,自引:0,他引:2
本文通过对头屯河流域山区各水文实测水文,泥沙资料的分析比较,揭示了头屯河水沙运移规律,指出了头屯河上游产水,中游产沙,水沙异源的特点,进而地实才考察测量的基础上,结合流域自然特点,提出了工程,生物措施相结合的减沙治理方案和在流域不同地段的具本治理措施。 相似文献