全文获取类型
收费全文 | 5006篇 |
免费 | 209篇 |
国内免费 | 93篇 |
专业分类
测绘学 | 157篇 |
大气科学 | 534篇 |
地球物理 | 1390篇 |
地质学 | 2156篇 |
海洋学 | 231篇 |
天文学 | 612篇 |
综合类 | 82篇 |
自然地理 | 146篇 |
出版年
2022年 | 42篇 |
2021年 | 71篇 |
2020年 | 64篇 |
2019年 | 42篇 |
2018年 | 162篇 |
2017年 | 151篇 |
2016年 | 234篇 |
2015年 | 162篇 |
2014年 | 244篇 |
2013年 | 299篇 |
2012年 | 249篇 |
2011年 | 207篇 |
2010年 | 244篇 |
2009年 | 258篇 |
2008年 | 195篇 |
2007年 | 152篇 |
2006年 | 135篇 |
2005年 | 130篇 |
2004年 | 107篇 |
2003年 | 85篇 |
2002年 | 90篇 |
2001年 | 93篇 |
2000年 | 87篇 |
1999年 | 85篇 |
1998年 | 104篇 |
1997年 | 65篇 |
1996年 | 83篇 |
1995年 | 65篇 |
1994年 | 65篇 |
1993年 | 47篇 |
1992年 | 39篇 |
1991年 | 39篇 |
1990年 | 42篇 |
1989年 | 44篇 |
1988年 | 28篇 |
1987年 | 45篇 |
1986年 | 34篇 |
1985年 | 39篇 |
1984年 | 45篇 |
1983年 | 61篇 |
1982年 | 43篇 |
1981年 | 40篇 |
1980年 | 40篇 |
1979年 | 45篇 |
1978年 | 45篇 |
1977年 | 39篇 |
1976年 | 28篇 |
1975年 | 44篇 |
1974年 | 38篇 |
1973年 | 40篇 |
排序方式: 共有5308条查询结果,搜索用时 31 毫秒
921.
Christian Betzler Jörn Fürstenau Thomas Lüdmann Christian Hübscher Sebastian Lindhorst Andreas Paul John J. G. Reijmer André W. Droxler 《Basin Research》2013,25(2):172-196
Multichannel high‐resolution seismic and multibeam data were acquired from the Maldives‐isolated carbonate platform in the Indian Ocean for a detailed characterization of the Neogene bank architecture of this edifice. The goal of the research is to decipher the controlling factors of platform evolution, with a special emphasis on sea‐level changes and changes of the oceanic currents. The stacking pattern of Lower to Middle Miocene depositional sequences, with an evolution of a ramp geometry to a flat‐topped platform, reflects variations of accommodation, which here are proposed to be primarily governed by fluctuations of relative sea level. Easterly currents during this stage of bank growth controlled an asymmetric east‐directed progradation of the bank edge. During the late middle Miocene, this system was replaced by a twofold configuration of bank development. Bank growth continued synchronously with partial bank demise and associated sediment‐drift deposition. This turnover is attributed to the onset and/or intensification of the Indian monsoon and related upwelling and occurrence of currents, locally changing environmental conditions and impinging upon the carbonate system. Mega spill over lobes, shaped by reversing currents, formed as large‐scale prograding complexes, which have previously been interpreted as deposits formed during a forced regression. On a regional scale, a complex carbonate‐platform growth can occur, with a coexistence of bank‐margin progradation and aggradation, as well as partial drowning. It is further shown that a downward shift of clinoforms and offlapping geometries in carbonate platforms are not necessarily indicative for a sea‐level driven forced regression. Findings are expected to be applicable to other examples of Cenozoic platforms in the Indo‐Pacific region. 相似文献
922.
Ionuţ Iosifescu Enescu Vassilios Vescoukis Cristina M. Iosifescu Enescu Fabian Müller Nadia H. Panchaud Lorenz Hurni 《The Cartographic journal》2013,50(2):137-148
The geospatial field significantly influences the development of the environmental domain, including a wide range of geospatial and cartographic information systems, such as Geographic Information Systems (GIS), Multimedia Atlas Information Systems (MAIS) and more recently web-based GIS (Web-GIS). In this context, we introduce web-based environmental geospatial information systems (Web-EGIS) as a special case of Web-GIS, aiming to integrate the functionalities of geospatial information systems with the enormous quantity of specialized, distributed and highly heterogeneous environmental geo-referenced data and services. We define three main characteristics of the Web-EGIS. The first is a generic hypercube-based data organization and visualization. The next characteristic is a standard-based, three-tier service-oriented architecture. The third and last characteristic is the traceability of the architectural and design decisions, for which we introduce the new concept of an ‘Environmental Application Context’, arguing that not only the functional but also the non-functional requirements (NFRs) have an important role in defining the architecture, software components and data services of such systems. In a nutshell, a Web-EGIS is characterized by a coherent user experience through the hypercube-based visualization concept, technically supported by a service-oriented architecture that is structured according to an extensive analysis of NFRs. On this basis, we introduce the Geodata visualization and interactive training environment (GeoVITe) Platform for Interdisciplinary Environmental Research as a reference implementation of a Web-EGIS with its basic design requirements, integrative hypercube-based visualization for heterogeneous data sources, extended web cartography functionalities, and its de facto system architecture. The concept of the hypercube-based visualization is better transferred to the system architecture by understanding the ‘Environmental Application Context’ of this particular Web-EGIS, which also makes it easier to maintain and enhance. The resulting system is a support platform for research activities in the environmental domain. 相似文献
923.
Within the confines of Earth Observation Scientific Knowledge and Technology Transfer in Hungary (EKAT) titled ESA PECS project we gained forum for utilization of our earth observation (EO) knowledge and possibility for further development of experiences. The project aims the horizontal preparation of Hungary for ESA membership – for a dynamically developing sphere in the common part of science, technology and business. For the efficient transfer and dissemination, we preconceived target groups and principles to reach main take-up points and to open new forums of information exchange. Nowadays, user-friendly service, complex supply and real-validation process all have great importance. Joining units of suitable data choice, entire ingestion–processing chains and ergonomic interfaces can only offer a timely and professional solution for the challenges of industry and business sectors. It has to be clearly seen, that information and communication technologies (ICT) and information control becomes a more and more significant part of EO services. 相似文献
924.
925.
利用1961-2019年三江源地区19个气象台站逐日气温、降水量等气象观测数据,分析了三江源地区降雪量、降雪日数和雪雨比的时空演变特征及其对径流量的影响。结果表明:(1)1961-2019年三江源地区平均降雪量为146.5 mm,降雪量以14.8 mm·(10a)-1的速率在减少,1985-1999年为降雪量偏多期,2000年以来为降雪量偏少期;(2)三江源地区年平均雪雨比以4.0%·(10a)-1的速率在减少,长江源区西部及黄河源区西部是雪雨比减少最为明显的区域,其余地区减少速率相对缓慢;(3)三江源地区年平均降雪日数为91天,曲麻莱、五道梁、沱沱河一带以及黄河源区中西部是降雪日数的大值区,降雪日数以14 d·(10a)-1的速率在减少,黄河源区西部是降雪日数减少最为明显的区域;(4)三江源地区各月降雪量及降雪日数均呈双峰型分布,降雪量和降雪日数最多出现在5月,小雪易出现在3月或4月,中雪和大雪以上量级在秋末、春季出现的概率最高;(5)随着海拔的抬升,降雪量和降雪日数增加,随经度的增加而减少;冷季降雪量多的年份,径流量也随之增大,且径流量相... 相似文献
926.
新疆小热泉子铜(锌)矿床硫化物显微结构及稀土、微量元素研究 总被引:2,自引:0,他引:2
新疆小热泉子铜(锌)矿床位于大南湖晚古生代岛弧带内,矿体主要赋存于一套凝灰质火山碎屑沉积岩中,矿石类型主要为块状黄铜矿矿石、闪锌矿矿石和脉状硫化物矿石。硫化物的显微结构研究表明,黄铁矿主要发生脆型变形,形成碎裂结构、细粒化结构、充填交代结构、"布丁"结构以及变斑晶结构,黄铜矿和闪锌矿发生塑性变形,黄铜矿表现为"S型"面理结构以及在闪锌矿中呈团斑状结构,电子探针结果表明黄铜矿发生明显的活化迁移富集作用。硫化物的稀土微量元素研究表明,闪锌矿中Mn、Ga、As等元素含量很低,Ga/In<<1,Ge/In多数小于1,174相似文献
927.
A GIS-implemented, deterministic approach for the automated spatial evaluation of geometrical and kinematical properties of
rock slope terrains is presented. Based on spatially distributed directional information on planar geological fabrics and
DEM-derived topographic attribute data, the internal geometry of rock slopes can be characterized on a grid cell basis. For
such computations, different approaches for the analysis and regionalization of available structural directional information
applicable in specific tectonic settings are demonstrated and implemented in a GIS environment. Simple kinematical testing
procedures based on feasibility criteria can be conducted on a pixel basis to determine which failure mechanisms are likely
to occur at particular terrain locations. In combination with hydraulic and strength data on geological discontinuities, scenario-based
rock slope stability evaluations can be performed. For conceptual investigations on rock slope failure processes, a GIS-based
specification tool for a 2-D distinct element code (UDEC) was designed to operate with the GIS-encoded spatially distributed
rock slope data. The concepts of the proposed methodology for rock slope hazard assessments are demonstrated at three different
test sites in Germany. 相似文献
928.
An experimental investigation has been carried on the solubility of CO2 in water and 1 M NaCl between 0.3 and 4 MPa, in order to test the validity of the results given by various modelling codes. In addition to experiments with pure fluids, the effect of a range of likely reservoir minerals on CO2–water interactions, including K-feldspar, kaolinite, calcite, Ca-montmorillonite and Na-montmorillonite were also investigated. In addition to measurements of CO2 solubility, the pH of the CO2-saturated suspensions was also measured directly at pressures of up to 1 MPa. The results demonstrate that predictions of CO2 solubility made with PHREEQC and Geochemist’s Workbench agree to within 20% with the experimental value, provided corrections are first made off-line for the fugacity coefficient of CO2, while predictions from standalone models are slightly more accurate. In the presence of mineral suspensions, PHREEQC and Geochemist’s Workbench give good results for calcite and kaolinite but underestimate the pH of montmorillonite-bearing assemblages while slightly overestimating the pH of K-feldspar suspensions. These results are significant because they indicate that CO2-charged fluids reacted with clays may be less acidic than indicated by the models, which will impact predictions of the potential for dissolution of reservoir and cap rock minerals, as well as the potential for leaching of toxic metals. 相似文献
929.
Comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges 总被引:2,自引:1,他引:1
Süleyman Adanur Ahmet Can Altuni?ik Alemdar Bayraktar Mehmet Akk?se 《Natural Hazards》2012,64(1):593-614
This paper presents a comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges. Bo?azi?i (The First Bosporus) and Fatih Sultan Mehmet (Second Bosporus) suspension bridges built in Istanbul, Turkey, are selected as numerical examples. Both bridges have almost the same span. While Bo?azi?i Suspension Bridge has inclined hangers, Fatih Sultan Mehmet Suspension Bridge has vertical hangers. Geometric nonlinearity including P-delta effects from self-weight of the bridges is taken into account in the determination of the dynamic behavior of the suspension bridges for near-fault and far-fault ground motions. Near-fault and far-fault strong ground motion records, which have approximately identical peak ground accelerations, of 1999 Chi-Chi, 1999 Kocaeli, and 1979 Imperial Valley earthquakes are selected for the analyses. Displacements and internal forces of the bridges are determined using the finite element method including geometric nonlinearity. The displacements and internal forces obtained from the dynamic analyses of suspension bridges subjected to each fault effect are compared with each other. It is clearly seen that near-fault ground motions are more effective than far-fault ground motion on the displacements and internal forces such as bending moment, shear force and axial forces of the suspension bridges. 相似文献
930.
In Europe, the Wide Wheel abrasion (WWA) test and the B?hme abrasion (BA) test are among the most widely used standard test
methods for determining abrasion resistance of natural stones, the former being the reference test method in EN 14157 Standard.
However, it is stated in the Annex-A (Informative) of EN 14157 Standard that very limited data are available to provide correlations
between these two test methods. To be able to fill this gap, in this study, 25 different natural stones belonging to sedimentary,
metamorphic and igneous groups were tested for their abrasion resistance as well as physico-mechanical properties. Also, for
a better interpretation of abrasion resistance characteristics of the tested stone materials, relationships between abrasion
resistance and physico-mechanical properties were statistically examined. A statistically significant linear correlation (R
2 = 0.85; P value = 0.000) was established between the WWA test and the BA test, which could be used in practice for converting the measured
abrasion resistance values from one testing method to another. It was also found that the correlation between these two test
methods improved significantly (R
2 = 0.93; P value = 0.001) when relatively high-porosity stone materials (porosity ≥1%) were separately evaluated. Both methods of abrasion
resistance employed in the present study showed statistically significant linear correlations with uniaxial compressive strength
and Brazilian tensile strength, the former proving to be a more influencing parameter on resistance to abrasion. Also, from
the point view of representing actual abrasion mechanism of stone materials in practice, the necessity of simulating multi-directional
foot traffic in abrasion testing methods was discussed. In this respect, the reference test method in the EN 14157 Standard
was criticized for not fully meeting this requirement. It was also pointed out that the reference method could have some drawbacks
when applied to coarse-grained granitic rocks having cleavable minerals such as plagioclase and orthoclase feldspars. 相似文献