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991.
When galvanic interactions between pyrite and chalcopyrite occur in solution, pyrite, with the higher rest potential, acts
as a cathode and is protected whereas chalcopyrite, with the lower rest potential, acts as an anode and its oxidation is increased.
In this work a three-electrode system was used to investigate the corrosion current density and mixed potential of a galvanic
cell comprising a pyrite cathode and a chalcopyrite anode in a flowing system. The results showed that with increasing concentration
of ferric ion in the solution, with increasing acidity, and with increasing flow rate of the solution, the corrosion current
density increased and the mixed potential of the galvanic cell became more positive. These experimental results are of direct
significance to the control of environmental pollution in mining activity. By using the galvanic model, mixed potential theory,
and the Butler–Volmer equation, the experimental results were explained theoretically. 相似文献
992.
Simulation-optimization approach to assess groundwater availability in Refugio County, TX 总被引:10,自引:0,他引:10
Sustainable management of groundwater resources is critical for viable development of semi-arid regions. Refugio County, TX,
is predominantly a rural community that is in close proximity to two large urban areas of Corpus Christi and San Antonio.
Large-scale water supply projects are being planned to export surplus water available in Refugio County to nearby growing
cities. Being a coastal county with several sensitive bays and estuaries, these projects have caused concerns with regard
to decreases in freshwater inflows to coastal bodies and raised the possibility of saltwater intrusion. A simulation model
characterizing groundwater flow in the shallower unconfined and the deeper semi-confined formations of the Gulf coast aquifer
was calibrated and evaluated. The model results were used in conjunction with a mathematical programming scheme to estimate
maximum available groundwater in the county. Stakeholder concerns were incorporated as constraints, which included prevention
of saltwater intrusion in the aquifer, limiting the amount of allowable drawdown in shallow aquifers, as well as maintaining
current flow gradients especially near baseflow-dependent streams and rivers. For the conditions assumed in this study, the
model results indicate that roughly 4.93 × 107 m3 of water can be extracted in a typical year. The management model was noted to be very sensitive to the imposed saltwater
intrusion constraint. 相似文献
993.
在总结大量实际工作的基础上,就区域生态环境遥感监测的指标与分类系统问题进行了探讨,提出了尽可能与现有的土地利用分类衔接,又较容易进行遥感判读和分类的土地利用分类系统;根据目前国内遥感数据获取和使用情况提出了遥感影像选择、处理以及合成的最佳方案,推荐了通过目视判读和自动分类获得土地利用状况的方法等,以期生态环境遥感监测能真正纳入环保部门常规的监测工作中. 相似文献
994.
本文首先回顾了价值链与全球生产系统的研究进展,结合跨国公司最新发展趋势对全球生产系统特征进行了总结;其次以改革开放以来上海对外贸易结构的改变,描述了90年代以来上海在全球生产系统分工中的变化,认为出口产品结构的转型并没有真正改变上海在国际劳动分工中处于低端环节的地位;最后就上海建设世界城市的差距与优势进行了总结,提出全球化发展的外部力量和地方化响应的内部力量将是上海发展世界城市的两个重要驱动力。 相似文献
995.
996.
全球城市理论与中国的国际城市建设 总被引:2,自引:0,他引:2
全球城市是多因素作用的结果,研究范式由20世纪70年代的马克思主义政治经济学向全球与地区相互作用的范式转换。全球城市体系的划分从单一指标向经济与文化结合的多指标方向发展。但如何选取指标,如何进行指标的测量,如何确定各指标的权重分配以及如何采集城市间相互作用的数据与资料,都是全球城市研究要面对的重要问题。中国的全球城市建设要从全球城市体系的等级、位序规律出发,根据社会经济发展的实际,要有步骤、有目标、分阶段,稳步推进,逐步提升城市发展的层次,促进城市国际化的步伐,建设中国的国际城市。 相似文献
997.
土地节约与集约利用评价研究——以湖南省为例 总被引:1,自引:0,他引:1
土地节约与集约利用是发展循环经济和建设节约型社会的必然要求。首先明确提出土地节约和集约利用评价方法与指标选取原则,完善节约和集约用地的评价指标结构层,特别是农用地和农村宅基地等土地利用类型的评价指标,建立区域和土地利用分区的节约与集约利用土地评价指标体系,以湖南省为例,运用层次分析法,得出湖南省土地节约与集约利用水平的动态变化发展趋势以及农用地集约利用的效益,最后利用加权求和的综合方法,计算出湖南省农用地集约利用水平的综合评价值。 相似文献
998.
W. R. OSTERKAMP J. R. GRAY J. B. LARONNE J. R. MARTIN 《国际泥沙研究》2007,22(3):238-246
A "Watershed-Scale Sediment Information Network" (WaSSIN), designed to complement UNESCO’s International Sedimentation Initiative, was endorsed as an initial project by the World Association for Sedimentation and Erosion Research. WaSSIN is to address global fluvial-sediment information needs through a network approach based on consistent protocols for the collection, analysis, and storage of fluvial-sediment and ancillary information at smaller spatial scales than those of the International Sedimentation Initiative. As a second step of implementation, it is proposed herein that the WaSSIN have a general structure of two components, (1) monitoring and data acquisition and (2) research. Monitoring is to be conducted in small watersheds, each of which has an established database for discharge of water and suspended sediment and possibly for bed load, bed material, and bed topography. Ideally, documented protocols have been used for collecting, analyzing, storing, and sharing the derivative data. The research component is to continue the collection and interpretation of data, to compare those data among candidate watersheds, and to determine gradients of fluxes and processes among the selected watersheds. To define gradients and evaluate processes, the initial watersheds will have several common attributes. Watersheds of the first group will be: (1) six to ten in number, (2) less than 1000 km2 in area, (3) generally in mid-latitudes of continents, and (4) of semiarid climate. Potential candidate watersheds presently include the Weany Creek Basin, northeastern Australia, the Zhi Fanggou catchment, northern China, the Eshtemoa Watershed, southern Israel, the Metsemotlhaba River Basin, Botswana, the Aiuaba Experimental Basin, Brazil, and the Walnut Gulch Experimental Watershed, southwestern United States. 相似文献
999.
Sensitivity of Mesoscale Model Forecast During a Satellite Launch to Different Cumulus Parameterization Schemes in MM5 总被引:1,自引:0,他引:1
The identification of the model discrepancy and skill is crucial when a forecast is issued. The characterization of the model
errors for different cumulus parameterization schemes (CPSs) provides more confidence on the model outputs and qualifies which
CPSs are to be used for better forecasts. Cases of good/bad skill scores can be isolated and clustered into weather systems
to identify the atmospheric structures that cause difficulties to the forecasts. The objective of this work is to study the
sensitivity of weather forecast, produced using the PSU-NCAR Mesoscale Model version 5 (MM5) during the launch of an Indian
satellite on 5th May, 2005, to the way in which convective processes are parameterized in the model. The real-time MM5 simulations
were made for providing the weather conditions near the launch station Sriharikota (SHAR). A total of 10 simulations (each
of 48 h) for the period 25th April to 04th May, 2005 over the Indian region and surrounding oceans were made using different
CPSs. The 24 h and 48 h model predicted wind, temperature and moisture fields for different CPSs, namely the Kuo, Grell, Kain-Fritsch
and Betts-Miller, are statistically evaluated by calculating parameters such as mean bias, root-mean-squares error (RMSE),
and correlation coefficients by comparison with radiosonde observation. The performance of the different CPSs, in simulating
the area of rainfall is evaluated by calculating bias scores (BSs) and equitable threat scores (ETSs). In order to compute
BSs and ETSs the model predicted rainfall is compared with Tropical Rainfall Measuring Mission (TRMM) observed rainfall. It
was observed that model simulated wind and temperature fields by all the CPSs are in reasonable agreement with that of radiosonde
observation. The RMSE of wind speed, temperature and relative humidity do not show significant differences among the four
CPSs. Temperature and relative humidity were overestimated by all the CPSs, while wind speed is underestimated, except in
the upper levels. The model predicted moisture fields by all CPSs show substantial disagreement when compared with observation.
Grell scheme outperforms the other CPSs in simulating wind speed, temperature and relative humidity, particularly in the upper
levels, which implies that representing entrainment/detrainment in the cloud column may not necessarily be a beneficial assumption
in tropical atmospheres. It is observed that MM5 overestimates the area of light precipitation, while the area of heavy precipitation
is underestimated. The least predictive skill shown by Kuo for light and moderate precipitation asserts that this scheme is
more suitable for larger grid scale (>30 km). In the predictive skill for the area of light precipitation the Betts-Miller
scheme has a clear edge over the other CPSs. The evaluation of the MM5 model for different CPSs conducted during this study
is only for a particular synoptic situation. More detailed studies however, are required to assess the forecast skill of the
CPSs for different synoptic situations. 相似文献
1000.