全文获取类型
收费全文 | 156篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 15篇 |
地球物理 | 34篇 |
地质学 | 79篇 |
海洋学 | 9篇 |
天文学 | 14篇 |
自然地理 | 2篇 |
出版年
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 15篇 |
2013年 | 14篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2010年 | 12篇 |
2009年 | 14篇 |
2008年 | 5篇 |
2007年 | 3篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 5篇 |
2002年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1979年 | 1篇 |
排序方式: 共有165条查询结果,搜索用时 31 毫秒
101.
H. Abdul Aziz M. Böhme A. Rocholl A. Zwing J. Prieto J. R. Wijbrans K. Heissig V. Bachtadse 《International Journal of Earth Sciences》2008,97(1):115-134
A detailed integrated stratigraphic study was carried out on middle Miocene fluvial successions of the Upper Freshwater Molasse
(OSM) from the North Alpine Foreland Basin, in eastern Bavaria, Germany. The biostratigraphic investigations yielded six new
localities thereby refining the OSM biostratigraphy for units C to E (sensu; Heissig, Actes du Congres BiochroM’97. Mem Trav
EPHE, Inst Montpellier 21, 1997) and further improving biostratigraphic correlations between the different sections throughout eastern Bavaria. Radioisotopic
ages of 14.55 ± 0.19 and 14.88 ± 0.11 Ma have been obtained for glass shards from the main bentonite horizon and the Ries
impactite: two important stratigraphic marker beds used for confirming our magnetostratigraphic calibration to the Astronomical
Tuned Neogene Time Scale (ATNTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). Paleomagnetic analysis was performed using alternating field (AF) and thermal (TH) demagnetization methods. The AF method
revealed both normal and reverse polarities but proofs to yield unreliable ChRM directions for the Puttenhausen section. Using
the biostratigraphic information and radioisotopic ages, the magnetostratigraphic records of the different sections are tentatively
correlated to the Astronomical Tuned Neogene Time Scale (ATNTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University
Press, 2004). This correlation implies that the main bentonite horizon coincides to chron C5ADn, which is corroborated by its radioisotopic
age of 14.55 Ma, whereas the new fossil locality Furth 460, belonging to OSM unit E, probably correlates to chron C5Bn.1r.
The latter correlation agrees well with the Swiss Molasse locality Frohberg. Correlations of the older sections are not straightforward.
The Brock horizon, which comprises limestone ejecta from the Ries impact, possibly correlates to C5ADr (14.581–14.784 Ma),
implying that, although within error, the radioisotopic age of 14.88 ± 0.11 Ma is somewhat too old. The fossil localities
in Puttenhausen, belonging to the older part of OSM unit C, probably coincide with chron C5Cn.2n or older, which is older
than the correlations established for the Swiss Molasse.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
102.
选取塔克拉玛干沙漠腹地塔中地区和北缘过渡带肖塘地区2013年土壤热通量观测资料,初步比较分析了塔克拉玛干沙漠两种下垫面的土壤热通量变化特征。结果表明:(1)在日变化尺度上,两个站点都有明显的日变化特征,1月份塔中站土壤热通量日平均变化幅度小于肖塘站,日较差分别为58.9 W.m2和72.4 W.m2,4月份两站土壤热通量变化幅度较为接近,日较差分别为88.1W.m2、100.1 W.m2。7、10月份塔中站土壤热通量变化幅度明显高于肖塘站,日较差分别为99.0 W.m2、53.7W.m2,100.3 W.m2、73.3W.m2。(2)不同天气条件下两个站点土壤热通量变化都有很大差异。晴天,塔中站和肖塘站土壤热通量变化都呈现出单峰型,变化幅度较一致,日较差分别为119.7 W.m2、119.1 W.m2。沙尘天和雨天受云层或降水的影响土壤热通量变化波动较大,沙尘天塔中站变化幅度小于肖塘站,日较差分别为83.6 W.m2、133.1 W.m2;雨天塔中站和肖塘站变化幅度都很剧烈,日较差分别为70.6 W.m2、66.6 W.m2。(3)年变化尺度上,塔中站土壤热通量在7月份达到最大值(7.7 W.m2),在11月出现最小值(-5.3 W.m2),肖塘站7月份出现最大值(4.2 W.m2),11月份出现最小值(-10.2 W.m2)。塔中站和肖塘站土壤热通量年总量差异很大,塔中站为16.8 W.m2,能量由大气向土壤传递,土壤为热汇,而肖塘站则为-34.9 W.m2,能量由土壤向大气传播,土壤表现为热源。 相似文献
103.
104.
105.
Ramin Vaghei Farzad Hejazi Hafez Taheri Mohd Saleh Jaafar Farah Nora Aznieta Abdul Aziz 《地震工程与工程振动(英文版)》2017,16(1):97-117
The Industrialized Building System (IBS) was recently introduced to minimize the time and cost of project construction. Accordingly, ensuring the integration of the connection of precast components in IBS structures is an important factor that ensures stability of buildings subjected to dynamic loads from earthquakes, vehicles, and machineries. However, structural engineers still lack knowledge on the proper connection and detailed joints of IBS structure construction. Therefore, this study proposes a special precast concrete wall-to-wall connection system for dynamic loads that resists multidirectional imposed loads and reduces vibration effects (PI2014701723). This system is designed to connect two adjacent precast wall panels by using two steel U-shaped channels (i.e., male and female joints). During casting, each joint is adapted for incorporation into a respective wall panel after considering the following conditions: one side of the steel channel opens into the thickness face of the panel; a U-shaped rubber is implemented between the two channels to dissipate the vibration effect; and bolts and nuts are used to create an extension between the two U-shaped male and female steel channels. The developed finite element model of the precast wall is subjected to cyclic loads to evaluate the performance of the proposed connection during an imposed dynamic load. Connection performance is then compared with conventional connections based on the energy dissipation, stress, deformation, and concrete damage in the plastic range. The proposed precast connection is capable of exceeding the energy absorption of precast walls subjected to dynamic load, thereby improving its resistance behavior in all principal directions. 相似文献
106.
Elemental characterization of black shales of Khyber Pakthunkhawa (KPK) region of Pakistan using AAS 总被引:1,自引:0,他引:1
Black shale samples were collected from Chimiari Khyber Pakthunkhawa region of Pakistan and were analyzed for elemental compositions. Atomic Absorption Spectrophotometry (AAS) was utilized for the determination of elements in the digested solutions. The analysis of black shale was performed precisely with relative standard deviation (RSD) lower than 2%. Results showed that the samples contained high concentrations of Ca (11.98 %), Al (7.09%), Fe (3.03%), Mg (0.59%) and Ti (0.58%). 相似文献
107.
The authors derived the normalized difference vegetation index (NDVI) from the NOAA/AVHRR Land dataset, at a spatial resolution of 8km and 15-day intervals, to investigate the vegetation variations in China during the period from 1982 to 2001. Then, GIS is used to examine the relationship between precipitation and the Normalized Difference Vegetation Index (NDVI) in China, and the value of NDVI is taken as a tool for drought monitoring. The results showed that in the study period, China’s vegetation cover had tended to increase, compared to the early 1980s; mean annual NDVI increased 3.8%. The agricultural regions (Henan, Hebei, Anhui and Shandong) and the west of China are marked by an increase, while the eastern coastal regions are marked by a decrease. The correlation between monthly NDVI and monthly precipitation/temperature in the period 1982 to 2001 is significantly positive (R2=0.80, R2=0.84); indicating the close coupling between climate conditions (precipitation and temperature) and land surface response patterns over China. Examination of NDVI time series reveals two periods: (1) 1982–1989, marked by low values below average NDVI and persistence of drought with a signature large-scale drought during the 1982 and 1989; and (2) 1990–2001, marked by a wetter trend with region-wide high values above average NDVI and a maximum level occurring in 1994 and 1998. 相似文献
108.
The development of automated morphological classification schemes can successfully distinguish between morphological types of galaxies and can be used for studies of the formation and subsequent evolution of galaxies in our universe. In this paper, we present a new automated machine supervised learning astronomical classification scheme based on the Nonnegative Matrix Factorization algorithm. This scheme is making distinctions between all types roughly corresponding to Hubble types such as elliptical, lenticulars, spiral, and irregular galaxies. The proposed algorithm is performed on two examples with different number of image (small dataset contains 110 image and large dataset contains 700 images). The experimental results show that galaxy images from EFIGI catalog can be classified automatically with an accuracy of ~93% for small and ~92% for large number. These results are in good agreement when compared with the visual classifications. 相似文献
109.
R. K. Somashekar P. Ravikumar S. V. Sowmya Mubhashir Aziz Dar A. S. Ravikumar 《Journal of the Indian Society of Remote Sensing》2011,39(1):95-106
The study area, Hesaraghatta watershed is located between 77° 20′ to 77° 42′ E longitude and 13° 10′ to 13° 24′ N latitude
with an area of 600.01 km2. Thematic layers such as Land Use/Land Cover, drainage, soil and hydrological soil group were generated from IRS–1D LISS
III satellite data (FCC). An attempt was made to estimate runoff using Soil Conservation Service (SCS) curve number model
and it was estimated to be 1960, 2066, 1870 and 1810 mm for sub-watersheds 1, 2, 3 and 4 respectively. Quantitative morphometric
analysis was carried out for the entire watershed and the four sub-watersheds independently by estimating their (a) linear
aspects like stream order, stream length, stream length ratio, bifurcation ratio, length of overland flow, drainage pattern
(b) aerial aspects like shape factor, circulatory ratio, elongation ratio and drainage density and (c) relief aspects like
basin relief, relief ratio, relative relief and ruggedness number. Drainage density was estimated to be 1.23 km/km2 designating the study area as a very coarse textured watershed. 相似文献
110.
The variation of the shear strength of infilled rock joints under cyclic loading and constant normal stiffness conditions is studied. To simulate the joints, triangular asperities inclined at angles of 9.5° and 18.5° to the shear movement were cast using high-strength gypsum plaster and infilled with clayey sand. These joints were sheared cyclically under constant normal stiffness conditions. It was found that, for a particular normal stiffness, the shear strength is a function of the initial normal stress, initial asperity angle, joint surface friction angle, infill thickness, infill friction angle, loading direction and number of loading cycles. Based on the experimental results, a mathematical model is proposed to evaluate the shear strength of infilled rock joints in cyclic loading conditions. The proposed model takes into consideration different initial asperity angles, initial normal stresses and ratios of infill thickness to asperity height. 相似文献