全文获取类型
收费全文 | 26057篇 |
免费 | 364篇 |
国内免费 | 218篇 |
专业分类
测绘学 | 521篇 |
大气科学 | 1948篇 |
地球物理 | 5203篇 |
地质学 | 9095篇 |
海洋学 | 2109篇 |
天文学 | 6025篇 |
综合类 | 47篇 |
自然地理 | 1691篇 |
出版年
2021年 | 161篇 |
2020年 | 197篇 |
2019年 | 210篇 |
2018年 | 497篇 |
2017年 | 462篇 |
2016年 | 566篇 |
2015年 | 436篇 |
2014年 | 608篇 |
2013年 | 1217篇 |
2012年 | 732篇 |
2011年 | 1016篇 |
2010年 | 876篇 |
2009年 | 1221篇 |
2008年 | 1054篇 |
2007年 | 1054篇 |
2006年 | 978篇 |
2005年 | 822篇 |
2004年 | 840篇 |
2003年 | 802篇 |
2002年 | 739篇 |
2001年 | 690篇 |
2000年 | 639篇 |
1999年 | 577篇 |
1998年 | 579篇 |
1997年 | 582篇 |
1996年 | 444篇 |
1995年 | 420篇 |
1994年 | 384篇 |
1993年 | 337篇 |
1992年 | 313篇 |
1991年 | 280篇 |
1990年 | 304篇 |
1989年 | 283篇 |
1988年 | 236篇 |
1987年 | 313篇 |
1986年 | 259篇 |
1985年 | 347篇 |
1984年 | 384篇 |
1983年 | 371篇 |
1982年 | 335篇 |
1981年 | 310篇 |
1980年 | 313篇 |
1979年 | 282篇 |
1978年 | 311篇 |
1977年 | 263篇 |
1976年 | 267篇 |
1975年 | 275篇 |
1974年 | 234篇 |
1973年 | 238篇 |
1972年 | 158篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
MICHAEL F. GOODCHILD KAREN K. KEMP 《International journal of geographical information science》2013,27(4):309-320
Abstract Education has been part of the NCGIA's mission from the earliest discussions of the concept of the Center at the National Science Foundation. To respond to the need for short-term solutions to the shortage of adequately trained personnel in GIS, the Center developed a set of teaching materials or core curriculum. The steps in its development are described and an analysis of initial distribution statistics is presented. Current efforts to develop a framework for laboratory materials are outlined. The paper ends with an assessment of the project and comparison with other disciplines. 相似文献
262.
T. K. Linsey J. F. Raper 《International journal of geographical information science》2013,27(5):435-452
Abstract The rationale, development and -implementation of a task-oriented hypertext GIS interface (HyperArc) are described. HyperArc is a fully functional interface on an Apple Macintosh computer acting as a client to a host computer running the ARC/INFO GIS. The package has been developed using the HyperCard package, and makes full use of the Apple Macintosh WIMP interface, enabling the user to perform a range of standard ARC/INFO tasks, including a variety of map displays and data queries. The key advantage of this kind of interface is that it permits the creation of tasks or sets of spatial procedures which can be easily customised and executed by the end user without any knowledge of the system command language. 相似文献
263.
Karl F. Nordstrom 《自然地理学》2013,34(2):177-196
This study compares the cyclic and seasonal geomorphic responses of oceanside and bayside beaches on Sandy Hook Spit, New Jersey. It was hypothesized that the different nature of onshore wind regimes at bayside and oceanside beaches would cause different types of beach change. On the east-facing ocean shoreline, rates of beach change are related to weather patterns associated with the passage of mid-latitude cyclonic storms. Bayside beach change is related to the influence of the prevailing westerlies. Storm erosion and post-storm deposition is more rapid on oceanside beaches. Swell waves occurring between storms rapidly reinstate pre-storm equilibrium conditions. Lower bay-side wave energies occurring between storms have little effect on profile development, and foreshore slopes inherited from previous storms undergo little change. Bayside beaches therefore appear to be more in equilibrium with storm conditions than oceanside beaches. Changes in foreshore slope, beach volume, and beach position associated with individual storm events are compared to seasonal trends to test the applicability of the Hayes cyclic model of beach development to both oceanside and bayside beaches. There is evidence of a cyclic trend of develop-ment on the more exposed ocean sites and seasonal development on the more sheltered bayside sites, which suggests that cyclic development may be causally related to the difference among the energy levels of the storm and nonstorm wave regimes. 相似文献
264.
Steve E. J. Richardson Richard J. Davies Mark B. Allen Simon F. Grant 《Basin Research》2011,23(6):702-719
The Quaternary to late Pliocene sedimentary succession along the margin of the South Caspian Basin contains numerous kilometre‐scale submarine slope failures, which were sourced along the basin slope and from the inclined flanks of contemporaneous anticlines. This study uses three‐dimensional (3D) seismic reflection data to visualise the internal structure of 27 mass transport deposits and catalogues the syndepositional structures contained within them. These are used to interpret emplacement processes occurring during submarine slope failure. The deposits consist of three linked structural domains: extensional, translational and compressive, each containing characteristic structures. Novel features are present within the mass transport deposits: (1) a diverging retrogression of the headwall scarp; (2) the absence of a conventional headwall scarp around growth stratal pinch outs; (3) restraining bends in the lateral margin; (4) a downslope increase in the throw of thrust faults. The results of this study shed light on the deformation that occurred during submarine slope failure, and highlight an important geological process in the evolution of the South Caspian Basin margin. 相似文献
265.
266.
267.
Mapping landslide susceptibility from small datasets: A case study in the Pays de Herve (E Belgium) 总被引:3,自引:1,他引:3
A landslide susceptibility map is proposed for the Pays de Herve (E Belgium), where large landslides affect Cretaceous clay outcrop areas. Based on a Bayesian approach, this GIS-supported probabilistic map identifies the areas most susceptible to deep landslides. The database is comprised of the source areas of ten pre-existing landslides (i.e. a sample of 154 grid cells) and of six environmental data layers, namely lithology, proximity to active faults, slope angle and aspect, elevation and distance to the nearest valley-floor. A 30-m-resolution DEM from the Belgian National Geographical Institute is used for the analysis. Owing to the small size of the sample, a special cross-validation procedure of the susceptibility map is performed, which uses in an iterative way each of the landslides to test the predictive power of the map derived from the other landslides. Four different sets of variables are used to produce four susceptibility maps, whose prediction curves are compared. While the prediction rates associated with the models not involving the “proximity to active fault” criterion are comparable to those of the models considering this variable, strong weaknesses inherent in the fault data on which the latter rely suggest that the final susceptibility map should be based on a model that excludes any reference to fault. This highlights the difference between a triggering factor and determining factors, and in the same time broadens the scope of the produced map. A single reactivated slide is also used to test the possibility of predicting future reactivation of existing landslides in the area. Finally, the need for geomorphological control over the mathematical treatment is underlined in order to obtain realistic prediction maps. 相似文献
268.
North End Lake is a polluted and eutrophic freshwater system located in Port Elizabeth, South Africa. Since the lake is expected
to be used for recreational/tourist purposes by 2010, a rehabilitation program will have to be designed. For this reason,
we retrieved a sediment core from the central region of the lake to decipher the effect of historical human impacts on the
water body. Pre-disturbance paleolimnological inferences indicate that the lake was likely mesotrophic. After ∼1831, when
sheep farming activities were undertaken in the catchment, increases in trophic state and changes in sediment composition
were observed. After ∼1937, increases in trace metal levels, organic matter, spheroidal carbonaceous particles (SCP) and changes
in sediment composition were recorded. The system became eutrophic as indicated by the dominance of the diatom Actinocyclus normanii, a cosmopolitan species often observed in systems where water quality has been dramatically degraded. The conditions worsened
after 1986 because of the construction of a storm-water retention system, which intentionally channeled storm-water runoff
into the lake. Because of this, extremely high values of fecal coliforms (i.e. 2 × 106 every 100 ml) have been measured in the water column. The paleolimnological information identified the sharp increase in
organic content in the uppermost section of the core, and this could be correlated to the operation of the storm-water retention
system. Therefore, as an immediate management measure, we suggest that the storm-water retention system should either no longer
be utilized, or the storm-water runoff should be treated before disposal into the lake. In addition, an effective sewage system
has to be constructed. 相似文献
269.
A. F. Howland 《Engineering Geology》2001,60(1-4):117-125
A process of urban regeneration of the former industrial dock area of east London by the London Docklands Development Corporation (LDDC) recognised the importance of geotechnical and geoenvironmental information. A systematic programme of data collection was implemented and stored in a series of bespoke computer database systems and cartographic registers. These allowed retrieval and manipulation of the data to provide rapid site assessments. The understanding of the natural setting of the area was enhanced as a consequence of the collation exercise. The data stored included geotechnical and environmental information on soil and groundwater. The hydrogeological regime was modelled by computer to determine the consequences of development on groundwater movement. In addition, a cartographic register of historic land use was developed. This gave instant detail on the potential for contamination of a site and became a fundamental tool in the UK planning process of the area. The information from the separate systems was finally combined into a geographic information system. 相似文献
270.