全文获取类型
收费全文 | 24447篇 |
免费 | 172篇 |
国内免费 | 916篇 |
专业分类
测绘学 | 1410篇 |
大气科学 | 1978篇 |
地球物理 | 4515篇 |
地质学 | 11605篇 |
海洋学 | 1003篇 |
天文学 | 1642篇 |
综合类 | 2161篇 |
自然地理 | 1221篇 |
出版年
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 4763篇 |
2017年 | 4039篇 |
2016年 | 2579篇 |
2015年 | 238篇 |
2014年 | 82篇 |
2013年 | 27篇 |
2012年 | 989篇 |
2011年 | 2732篇 |
2010年 | 2014篇 |
2009年 | 2314篇 |
2008年 | 1890篇 |
2007年 | 2365篇 |
2006年 | 54篇 |
2005年 | 198篇 |
2004年 | 403篇 |
2003年 | 410篇 |
2002年 | 249篇 |
2001年 | 48篇 |
2000年 | 51篇 |
1999年 | 13篇 |
1998年 | 21篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1989年 | 1篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1976年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
251.
Pitthaya Jamsawang Phermphorn Boathong Warakorn Mairaing Pornkasem Jongpradist 《Landslides》2016,13(5):939-955
This paper presents an analysis of the slope failure of a Suvarnabhumi drainage canal during construction. The Suvarnabhumi drainage canal project includes a large drainage canal with a road on both sides. The width of the bottom of the drainage canal is 48.0 m, the depth of the drainage canal is 3.0 m, and the length of the drainage canal is 10.5 km. Because the project was constructed on very soft Bangkok clay, deep cement mixing (DCM) columns were employed to increase the stability of the excavated canal. The failure of the drainage canal slope occurred 25 days after the end of excavation. The field monitoring data show that lateral movement of the canal slope continuously increased with time, which caused failure due to the instability of the canal slope. The time-dependent deformation and undrained creep behavior of very soft clay was suspected to be the cause of the canal failure. A laboratory investigation of undrained creep behavior and a finite element analysis (FEA) using the soft soil creep (SSC) model were performed to confirm the causes of the canal failure. The results indicate that very soft clay specimens that are subjected to deviator creep stress levels of 70 and 100 % of the peak strength failed by creep rupture within 60 days and 8 min, respectively. The factor of safety for the canal slope, which was obtained from the FEA, shows significant reduction from the initial value of 1.710 to 1.045 within 24 days after the end of excavation due to the effect of undrained creep. This paper also describes a solution method that is applied to a new section of the canal. Field monitoring and an FEA of the new trial section were performed to prove the effectiveness of the solution method. 相似文献
252.
253.
254.
The main purpose of this paper is to describe ways to improve the microstructure of expansive soil by adding nanomaterials. Mechanical tests were done to explore the changes in shear strength and compression index of expansive soil that was modified by adding different amounts of two kinds of nanomaterials (nano-alumina and nano-silica). The test results show that adding 1.2% nano-alumina and about 2% nano-silica to expansive soil provides the optimal compression index. The test results show that adding 1.2% nano-alumina and about 1.5% nano-silica to expansive soil provides the optimal unconfined compression stress. Scanning electron microscopy of the microstructure of expansive soil modified by nanomaterials provided a deeper understanding of the effects of nanomaterials on improving expansive soil. 相似文献
255.
256.
Elvis A. Shukla Jagdish Prasad M. S. S. Nagaraju Rajeev Srivastava D. L. Kauraw 《Journal of the Indian Society of Remote Sensing》2009,37(1):129-137
Soil resource characterization of Dhamni micro-watershed in Chandrapur district of Maharashtra was carried out using IRS-1D
LISS-III data in conjunction with field survey and ancillary data. The study indicates that nearly 84.2 per cent of the total
geographical area of the watershed is under cultivation. Forest (mainly degraded) occupy only 4.5 per cent area Whereas wasteland
with scrub cover 9.4 per cent area of the watershed. Nine soil series were tentatively identified and mapped as soil series
association in to five mapping units. These soils belong to order Inceptisol, Vertisol and Mollisol. Except the soils of wasteland
with scrub, other soils are moderately suitable for pigeonpea and soybean and have average to good productivity. 相似文献
257.
Sushan Konar 《Journal of Astrophysics and Astronomy》2017,38(3):47
This article briefly reviews our current understanding of the evolution of magnetic fields in neutron stars, which basically defines the evolutionary pathways between different observational classes of neutron stars. The emphasis here is on the evolution in binary systems and the newly emergent classes of millisecond pulsars. 相似文献
258.
259.
Ice-core samples from Upper Fremont Glacier (UFG), Wyoming, were used as proxy records for the chemical composition of atmospheric
deposition. Results of analysis of the ice-core samples for stable isotopes of nitrogen (δ15N, ) and sulfur (δ34S, ), as well as and deposition rates from the late-1940s thru the early-1990s, were used to enhance and extend existing National Atmospheric
Deposition Program/National Trends Network (NADP/NTN) data in western Wyoming. The most enriched δ34S value in the UFG ice-core samples coincided with snow deposited during the 1980 eruption of Mt. St. Helens, Washington.
The remaining δ34S values were similar to the isotopic composition of coal from southern Wyoming. The δ15N values in ice-core samples representing a similar period of snow deposition were negative, ranging from -5.9 to -3.2 ‰ and
all fall within the δ15N values expected from vehicle emissions. Ice-core nitrate and sulfate deposition data reflect the sharply increasing U.S.
emissions data from 1950 to the mid-1970s. 相似文献
260.
NILANJAN DASGUPTA TARITWAN PAL JOYDEEP SEN TAMOGHNO GHOSH 《Journal of Earth System Science》2011,120(4):617-626
The study involves the characterization of pegmatoidal granite, southeast of Beawar, Ajmer district, Rajasthan. Earlier researchers
had described this granite as part of the BGC, basement to the Bhim Group of the Delhi Super Group rocks. However, the present
study indicates that it is younger than the rocks of Bhim Group of South Delhi Fold Belt, into which it is intrusive. The
intrusion is structurally controlled and the outcrop pattern is phacolithic. The granite had intruded post-D2 deformation of the Delhi orogeny along the axial planes of D2 folds. The intrusion has also resulted in the formation of a contact aureole about the calc gneisses. 相似文献