全文获取类型
收费全文 | 1754篇 |
免费 | 118篇 |
国内免费 | 170篇 |
专业分类
测绘学 | 110篇 |
大气科学 | 126篇 |
地球物理 | 419篇 |
地质学 | 704篇 |
海洋学 | 245篇 |
天文学 | 221篇 |
综合类 | 61篇 |
自然地理 | 156篇 |
出版年
2024年 | 8篇 |
2023年 | 28篇 |
2022年 | 59篇 |
2021年 | 77篇 |
2020年 | 64篇 |
2019年 | 63篇 |
2018年 | 87篇 |
2017年 | 70篇 |
2016年 | 101篇 |
2015年 | 74篇 |
2014年 | 84篇 |
2013年 | 83篇 |
2012年 | 98篇 |
2011年 | 110篇 |
2010年 | 121篇 |
2009年 | 86篇 |
2008年 | 83篇 |
2007年 | 58篇 |
2006年 | 68篇 |
2005年 | 39篇 |
2004年 | 62篇 |
2003年 | 40篇 |
2002年 | 57篇 |
2001年 | 30篇 |
2000年 | 40篇 |
1999年 | 28篇 |
1998年 | 24篇 |
1997年 | 21篇 |
1996年 | 25篇 |
1995年 | 19篇 |
1994年 | 22篇 |
1993年 | 11篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 21篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 21篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有2042条查询结果,搜索用时 15 毫秒
81.
Thi Thuy Van Le Rungruang Lertsirivorakul Tran Vuong Bui Marcia K. Schulmeister 《Ground water》2020,58(6):1012-1022
The coastal aquifers and inland waters of the Long Xuyen Quadrangle and Ca Mau Peninsula of southern Vietnam have been significantly impacted by sea water intrusion (SI) as a result of recent anthropogenic activities. This study identified the evolution and spatial distribution of hydrochemical conditions in coastal aquifers at this region using Hydrochemical Facies Evolution Diagram (HFE-D) and Geographical Information System mapping. Hydraulic heads and water chemistry were measured at 31 observation wells in four layered aquifers during dry and rainy seasons in early (2005), and more recent (2016), stages of agricultural development. Hydrochemical facies associated with intrusion or freshening stages were mapped in each aquifer after assigning mixing index values to each facies. The position of groundwater freshening and SI phases differed in Holocene, Upper Pleistocene, Middle Pleistocene, and Lower Pleistocene aquifers. The geographic position of freshening and intrusion fronts differ in dry and rainy seasons, and shifted after 11 years of groundwater abstraction in all four aquifers. The spatial and temporal differences in hydrochemical facies distributions according to HFE-D reflect the relative impact of SI in the four aquifers. The study results provide a better understanding of the evolution of groundwater quality associated with SI in a peninsular coastal aquifer system, and highlight the need for improving groundwater quality and management in similar coastal regions. 相似文献
82.
G. Bergametti A.L. Dutot J.P. Quisefit R. Vie Le Sage 《Journal of Volcanology and Geothermal Research》1983,15(4):355-367
A statistical analysis of volcanic aerosol based on 1,083 variables including concentration, grain-size and site variabilities establishes correlations between sites and among chemical elements.Variation curves of element concentration show parallel behaviour. High coefficients of correlation between anions and cations confirm associations between elements. 相似文献
83.
G. Lefeuve-Mesgouez A. T. Peplow D. Le Houdec 《Soil Dynamics and Earthquake Engineering》2002,22(6):692
The transmission of vibrations over the surface of the ground, due to high-speed moving, vertical harmonic rectangular loads, is investigated theoretically. The problem is three-dimensional and the interior of the ground is modelled as an elastic half-space or a multilayered ground. The transformed solutions are obtained using the Fourier transform on the space variable. A new damping model in the spatial wavenumber domain, presented in Lefeuve-Mesgouez et al. [J. Sound. Vibr. 231 (2000) 1289] is used. Numerical results for the displacements on the surface are presented for loads moving with speeds up to and beyond the Rayleigh wave speed of the half-space. 相似文献
84.
85.
植被冠层辐射散射信号中蕴含了丰富的植被信息,通过构建植被冠层辐射散射模型,可以实现植被结构等生物物理参数的遥感定量反演。迄今为止,可见光/近红外、热红外、微波波段均已发展了大量的模型,这些模型在参数反演方面各具优势,但不同波段的模型又有其自身的局限性。跨波段的联合模拟可以实现模型间的优势互补,进而提高地表参数的反演精度,近年来已有学者专注于可见光/近红外与热红外模型,热红外与微波模型,主被动微波模型,以及可见光/近红外与微波模型的联合模拟和协同反演,但多是两两联合,且主要是基于经验模型或解析模型。基于3维场景的植被冠层辐射散射特性模拟模型可以细致刻画不同组分的结构和空间分布特征,对于由植被结构引起的多次散射和组分比例变化的考虑具有优势。本文主要介绍了3维模拟模型在可见光/近红外、热红外和微波波段,以及跨波段联合模拟方面的研究进展,从模型机理、场景统一、以及组分理化参数的统一的角度,探讨了构建多波段3维模拟系统的可行性,展望了多波段3维模拟模型的发展趋势。 相似文献
86.
87.
C. Vigny J. Chéry T. Duquesnoy F. Jouanne J. Ammann M. Anzidei J.-P. Avouac F. Barlier R. Bayer P. Briole E. Calais F. Cotton F. Duquenne K. L. Feigl G. Ferhat M. Flouzat J.-F. Gamond A. Geiger A. Harmel M. Kasser M. Laplanche M. Le Pape J. Martinod G. Ménard B. Meyer J.-C. Ruegg J.-M. Scheubel O. Scotti G. Vidal 《Journal of Geodesy》2002,76(2):63-76
The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical
investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely
unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic
problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation
between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address
these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale
GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at
each site. GPS data processing has been done by three independent teams using different software. The different solutions
have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and
2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally
smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem
to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence
between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation
of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea
that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation.
Received: 27 November 2000 / Accepted: 17 September 2001 相似文献
88.
基于典型物候特征的MODIS-EVI时间序列数据
农作物种植面积提取方法
—小区域冬小麦实验研究 总被引:10,自引:1,他引:10
利用MODIS植被指数时间序列这一特性,以北京市通州及周边为实验区,冬小麦种植面积为研究对象,提出
了农作物种植面积指数模型(Pan-CPI模型)的概念,并构造了冬小麦特征物候期植被指数与种植面积的定量函数关系,
通过样区TM影像求解关键参数,对研究区冬小麦种植面积测量方法进行了试验研究。研究结果表明:(1)Pan-CPI模
型能够很好地反映特定目标农作物种植面积状况,为基于植被指数时间序列影像识别农作物种植面积提供了新方法;
(2)精度分析结果表明:Pan-CPI模型具有很高的稳定性,且不受样本变化的影响,只要达到满足模型计算的样本量(如:
5%),多次测量结果间具有很好的一致性。选取MODIS 6×6像元大小的窗口时,TM样本的复相关系数(R2)稳定在0.85
左右,与TM结果比较,窗口相对精度稳定在95%左右,区域精度稳定在92%以上,经调整的区域精度高达96%以上;
(3)对于种植结构复杂、目标作物种植破碎的地区,Pan-CPI模型可以充分利用MODIS植被指数时间序列的优势,有效改
善TM单时相和多时相提取信息因时相缺失无法表征作物变化的不足。 相似文献
89.
Finite strain data from the Kuopio mantled gneiss domes are described. Synclines located between two domes have flattening-type strains while those situated between more than two domes exhibit constrictional strains. Cleavage trajectory patterns show that cleavage tends to parallel the dome boundaries and encloses characteristic points termed “cleavage triple points”, at junctions of synclines. The stretching lineation is generally steeply plunging in a mean southwest direction. Folds range from inclined to reclined. Their asymmetry is apparently related to irregularities in the cover-basement boundary. Two shear components of the deformation have been deduced from available data. The major one is steeply plunging and is well exhibited by cleavage fans, steeply plunging lineations and finite-strain gradients. The second shear component is horizontal, as deduced from asymmetric folds and other small-scale structures, and is controlled by bosses and dimples in the cover-basement boundaries.The described structural features are explained in terms of interference between progressively inflating neighbouring diapirs. Furthermore, some of these features, such as cleavage triple points, flattening between two domes and constriction between three or more domes, and horizontal shear components controlled by cover-basement boundary irregularities, could be used as criteria of diapirism. A model of progressive dome interference is presented in which each dome inflates and interacts with neighbours. Such a model could possibly be applied to other orogenic situations with closely spaced diapirs, e.g., Archean greenstone belts or granite-rich orogenic belts. 相似文献
90.
Activated sludge acclimation for toluene and DEHP degradation in a two-phase partitioning bioreactor
I. Béchohra J. B. Le Menn A. Couvert A. Amrane 《International Journal of Environmental Science and Technology》2016,13(8):1883-1890
The effect of activated sludge acclimation on the biodegradation of toluene in the presence of a biodegradable non-aqueous phase liquid, di (2-ethylhexyl) phthalate (DEHP), in a two-phase partitioning bioreactor was characterized. The influence of the presence of DEHP, at a ratio of 0.1 % (volume ratio), and of the acclimation of activated sludge (AS) on the biodegradation of hydrophobic VOC was studied. AS was acclimated to both toluene and DEHP simultaneously. Using acclimated cells, 73 and 96 % improvement of the mean biodegradation rates was recorded for toluene and the organic solvent (DEHP), respectively, if compared to the values recorded in the absence of acclimation, during tests performed in Erlenmeyer flasks. Degradation rates were further improved by the use of acclimated AS in a reactor with a large head space; degradation yields for toluene and DEHP were above 99 and 89 %, respectively. 相似文献