全文获取类型
收费全文 | 11782篇 |
免费 | 692篇 |
国内免费 | 204篇 |
专业分类
财政金融 | 1140篇 |
工业经济 | 462篇 |
计划管理 | 1932篇 |
经济学 | 1629篇 |
综合类 | 991篇 |
运输经济 | 90篇 |
旅游经济 | 122篇 |
贸易经济 | 1941篇 |
农业经济 | 486篇 |
经济概况 | 752篇 |
水利工程 | 2991篇 |
信息产业经济 | 1篇 |
邮电经济 | 141篇 |
出版年
2024年 | 26篇 |
2023年 | 91篇 |
2022年 | 203篇 |
2021年 | 378篇 |
2020年 | 236篇 |
2019年 | 203篇 |
2018年 | 332篇 |
2017年 | 374篇 |
2016年 | 377篇 |
2015年 | 424篇 |
2014年 | 535篇 |
2013年 | 949篇 |
2012年 | 864篇 |
2011年 | 834篇 |
2010年 | 769篇 |
2009年 | 701篇 |
2008年 | 727篇 |
2007年 | 735篇 |
2006年 | 761篇 |
2005年 | 644篇 |
2004年 | 371篇 |
2003年 | 242篇 |
2002年 | 246篇 |
2001年 | 229篇 |
2000年 | 164篇 |
1999年 | 85篇 |
1998年 | 67篇 |
1997年 | 51篇 |
1996年 | 50篇 |
1995年 | 54篇 |
1994年 | 38篇 |
1993年 | 52篇 |
1992年 | 39篇 |
1991年 | 30篇 |
1990年 | 40篇 |
1989年 | 30篇 |
1988年 | 36篇 |
1987年 | 37篇 |
1986年 | 43篇 |
1985年 | 54篇 |
1984年 | 46篇 |
1983年 | 36篇 |
1982年 | 40篇 |
1981年 | 37篇 |
1980年 | 32篇 |
1979年 | 28篇 |
1978年 | 32篇 |
1977年 | 28篇 |
1976年 | 36篇 |
1971年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
71.
Strategy for olive mill wastewater treatment and reuse with a sewage plant in an arid region. 总被引:1,自引:0,他引:1
This study was conducted to evaluate the treatability of OMW (olive mill wastewater) with sewage and sewage sludge, which could supplement nutrients and microbes required for OMW treatment and reduce its possible toxicity. The amount of OMW added to an aeration tank was based on the loading difference between the designed and actual COD loads, while the amount added to anaerobic digestion for energy recovery was determined by CH4 production. The COD removal efficiencies were 70-85% for both systems. Compost of OMW with dried sewage sludge also showed a similar temperature profile without OMW addition. This strongly suggested that OMW can be treated at a sewage plant without pretreatment and the treated effluent can be reused in irrigation for an arid region. 相似文献
72.
Domestic wastewater is a significant source of nitrogen and phosphorus, which cause lake eutrophication. Among the wastewater treatment technologies, constructed wetlands are a promising low-cost means of treating point and diffuse sources of domestic wastewater in rural areas. However, the sustainable operation of constructed wetland treatment systems depends upon a high rate conversion of organic and nitrogenous loading into their metabolic gaseous end products, such as N2O and CH4. In this study, we examined and compared the performance of three typical types of constructed wetlands: Free Water Surface (FWS), Subsurface Flow (SF) and Vertical Flow (VF) wetlands. Pollutant removal efficiency and N2O and CH4 emissions were assessed as measures of performance. We found that the pollutant removal rates and gas emissions measured in the wetlands exhibited clear seasonal changes, and these changes were closely associated with plant growth. VF wetlands exhibited stable removal of organic pollutants and NH3-N throughout the experiment regardless of season and showed great potential for CH4 adsorption. SF wetlands showed preferable T-N removal performance and a lower risk of greenhouse gas emissions than FWS wetlands. Soil oxidation reduction potential (ORP) analysis revealed that water flow structure and plant growth influenced constructed wetland oxygen transfer, and these variations resulted in seasonal changes of ORP distribution inside wetlands that were accompanied by fluctuations in pollutant removal and greenhouse gas emissions. 相似文献
73.
机电排灌工程是丘陵、滨湖地区的主要灌溉设施,必须建立适应市场经济的管理新机制,确保工程良性运行和巩固发展,满足不断发展的工农业生产需要。 相似文献
74.
75.
Amin Y Kamete 《Development Southern Africa》2004,21(4):663-686
This analysis is a reappraisal of two perspectives in urban development in Zimbabwe: environmental sustainability and human sustenance. The discussion seeks to reposition the conservation–survival debate by broadening it to the wider urban and national macroeconomic and sociopolitical context. It re‐examines Zimbabwe's environmental problems by examining the challenges posed by urbanisation, industrialisation and informalisation. To these ‘permanent’ strands are added the ‘transient’ phenomena of structural adjustment and indigenisation. The analysis is done within the overall national macroeconomic and sociopolitical environment. The article examines environmental sustainability and human sustenance as the two policy challenges that have to be reconciled in the quest for sustainable urban settlements in Zimbabwe. The analysis stresses that the exercise of striking a balance between the needs of humankind and those of nature has to take cognisance of the complexity of issues and the processes going on elsewhere in the urban and national context. 相似文献
76.
Siu Y. Chan 《Abacus》2001,37(2):248-266
Although International Quality Standards 9000 certification is one of the most popular quality assurance systems in the world, its contribution to a firm's value is still a controversial issue. This project re-examines this issue by using stock market reactions to the announcements of the award of certification made by a sample of Hong Kong listed companies, as a proxy for its contribution to a firm's value. The results suggest that on average certification increased a firm's value. However, most of this value increase was incorporated into stock prices before formal announcements were published in newspapers. In addition, the contribution of certification to value was greater in smaller firms than in larger ones. This can be attributed to fewer stock traders and professional analysts following smaller firms. 相似文献
77.
This paper deals with on-line computation—or step-wise learning—of Pareto optimal insurance contracts. Our approach tolerates that the loss distribution might be unknown, intractable, or not well specified. Thus we accommodate fairly inexperienced parties. Losses are here simulated or observed, one at a time, and they cause iterated revisions of the premium. The mechanical and global nature of probability calculus thereby yields to more tentative, myopic procedures, possibly closer to how humans operate or reason in face of risk. Sequential revisions may also reduce the expense of insurers' time and money in seeking sufficient statistics. Emphasized below is the remarkable simplicity and stability of the resulting adaptive procedures. Special attention goes to catastrophic risks, and to subsidized or competitive insurance. 相似文献
78.
Meng Jun min Ocean University of Qingdao Qingdao China Zhang Zi li Zhao Jun sheng First Institute of Oceanography State Oceanic Administration Qingdao China Zhang Jie Key Laboratory of Marine Science Numerical Modelling 《水动力学研究与进展(B辑)》2001,(3)
1 . INTRODUCTIONOceaninternalwaveisakindofgravitywavegeneratedinthestratifiedocean .Itproducebytheinteractionoftidecurrentandtopography ,seaquakeandmovingshipwhenthestrong ,shallowpycnoclineis present.Theinternalwavesinthecontinentalshelfarealmosttideprod… 相似文献
79.
正交曲线坐标下三维代数应力通量模型 总被引:7,自引:1,他引:6
针对弯曲及不规则明渠的水动力及物质输运特性,本文建立了曲线坐标系下的三维代数应力通量数学模型,对平面上弯曲及不规则复杂边界情形,采用Poisson方程进行正交曲线坐标变换,各向异性的湍流代数应力通量模型被引用于本文的模拟计算中,以体现复杂边界条件引起的水动力及物质输运特性的变化。通过180度强弯曲明渠水槽及贵溪电厂不规则边界河段物理模型试验两个实例计算表明,实测值与计算吻合良好,效果令人满意。 相似文献
80.
In this paper we illustrate how certain design problems can be simplified by reparametrization of the response function. This alternative viewpoint provides further insights than the more traditional approaches, like minimax, Bayesian or sequential techniques. It will also improve a practitioner’s understanding of more general situations and their “classical” treatment. 相似文献