全文获取类型
收费全文 | 12056篇 |
免费 | 319篇 |
国内免费 | 29篇 |
专业分类
财政金融 | 2018篇 |
工业经济 | 698篇 |
计划管理 | 1653篇 |
经济学 | 2093篇 |
综合类 | 323篇 |
运输经济 | 66篇 |
旅游经济 | 173篇 |
贸易经济 | 1468篇 |
农业经济 | 434篇 |
经济概况 | 1359篇 |
水利工程 | 2113篇 |
邮电经济 | 6篇 |
出版年
2022年 | 94篇 |
2021年 | 134篇 |
2020年 | 137篇 |
2019年 | 187篇 |
2018年 | 223篇 |
2017年 | 248篇 |
2016年 | 213篇 |
2015年 | 196篇 |
2014年 | 242篇 |
2013年 | 1135篇 |
2012年 | 442篇 |
2011年 | 502篇 |
2010年 | 406篇 |
2009年 | 371篇 |
2008年 | 440篇 |
2007年 | 424篇 |
2006年 | 432篇 |
2005年 | 391篇 |
2004年 | 305篇 |
2003年 | 214篇 |
2002年 | 243篇 |
2001年 | 217篇 |
2000年 | 189篇 |
1999年 | 171篇 |
1998年 | 175篇 |
1997年 | 176篇 |
1996年 | 168篇 |
1995年 | 131篇 |
1994年 | 141篇 |
1993年 | 159篇 |
1992年 | 177篇 |
1991年 | 182篇 |
1990年 | 130篇 |
1989年 | 141篇 |
1988年 | 111篇 |
1987年 | 132篇 |
1986年 | 137篇 |
1985年 | 170篇 |
1984年 | 153篇 |
1983年 | 179篇 |
1982年 | 154篇 |
1981年 | 151篇 |
1980年 | 167篇 |
1979年 | 145篇 |
1978年 | 118篇 |
1977年 | 133篇 |
1976年 | 125篇 |
1975年 | 125篇 |
1974年 | 118篇 |
1973年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 423 毫秒
51.
The relationship between the number of employees in a firm, their rank, and the level of professionalism among firm members is evaluated in 19 accounting firms, involving 325 accountants engaged in public practice. Professionalism is measured using five individual traits plus a composite. Results indicate that one trait (i.e. a belief that the profession provides a service to society) and the composite were inversely related to firm size. Rank or position in the firm hierarchy demonstrated an even stronger, independent effect on three professionalism traits and the composite, with higher member rank associated with higher levels of professionalism. Issues related to the future study of professionalism among accountants are discussed. 相似文献
52.
全面整合旅游资源,推进广州旅游业的深度发展 总被引:5,自引:0,他引:5
<正> 广州旅游业发展到今天,已经完成了“基本原始积累” 的数量型发展阶段,实现了旅游产业化的飞跃。而在新的形势下,如何提升旅游业的综合竞争力,促进其向效益型、质量型的产业转变,引发新的飞跃,出路在于:全面整合旅游资源,推进旅游业的深度发展。 相似文献
53.
This paper deals with an economic comparison between costs and incomes in small wastewater treatment plants where the anaerobic co-digestion process of sludge and biowaste with energy recovery is operated. Plants in the size range 1,000-30,000 persons equivalent (pe) were considered in the study: typical costs, comprehensive of capital and operating costs, were in the range euro69-105 per person per year depending on the plant size: the smaller the size the higher the specific cost. The incomes deriving from taxes and fees for wastewater treatment are generally in the range euro36-54 per person per year and can only partially cover costs in small wastewater treatment plants. However, the co-treatment of biowaste and the use of produced energy for extra credits (green certificates) determine a clear improvement in the possible revenues from the plant. These were calculated to be euro23-25 per person per year; as a consequence the costs and incomes can be considered comparable for wastewater treatment plants (WWTPs) with size larger than 10,000 pe. Therefore, anaerobic co-digestion of biowaste and sludge can also be considered a sustainable solution for small wastewater treatment plants in rural areas where several different kinds of biowaste are available to enhance biogas production in anaerobic reactors. 相似文献
54.
55.
New climate change scenarios for the Netherlands. 总被引:4,自引:0,他引:4
B van den Hurk A K Tank G Lenderink A van Ulden G J van Oldenborgh C Katsman H van den Brink F Keller J Bessembinder G Burgers G Komen W Hazeleger S Drijfhout 《Water science and technology》2007,56(4):27-33
A new set of climate change scenarios for 2050 for the Netherlands was produced recently. The scenarios span a wide range of possible future climate conditions, and include climate variables that are of interest to a broad user community. The scenario values are constructed by combining output from an ensemble of recent General Climate Model (GCM) simulations, Regional Climate Model (RCM) output, meteorological observations and a touch of expert judgment. For temperature, precipitation, potential evaporation and wind four scenarios are constructed, encompassing ranges of both global mean temperature rise in 2050 and the strength of the response of the dominant atmospheric circulation in the area of interest to global warming. For this particular area, wintertime precipitation is seen to increase between 3.5 and 7% per degree global warming, but mean summertime precipitation shows opposite signs depending on the assumed response of the circulation regime. Annual maximum daily mean wind speed shows small changes compared to the observed (natural) variability of this variable. Sea level rise in the North Sea in 2100 ranges between 35 and 85 cm. Preliminary assessment of the impact of the new scenarios on water management and coastal defence policies indicate that particularly dry summer scenarios and increased intensity of extreme daily precipitation deserves additional attention in the near future. 相似文献
56.
Floods cause environmental hazards and influence on socio‐economic activities. In this study, we evaluated the historic flood frequency at a confluence in the middle Yellow River, China. A non‐parametric, multivariate, empirical, orthogonal function matrix model, which consists of time correlation coefficients of flood discharge at different gauge stations and flood events was used for the analysis of flood frequency. The model addresses the characteristics of confluent floods such as frequency and the probability in multiple tributary rivers. Flood frequency analysis is often coupled with studies of hydrological routing processes that reduce the flood capacity of the rivers. Flood routing to the confluence were simulated using kinematic wave theory. Results of this flood frequency analysis showed that flooding frequency has intensified in the past 500 years, especially during the 19th century. Flooding in streams above the confluence was more frequent than in streams below the confluence. Over the last 2000 years, concurrent flooding in multiple tributary rivers accounted for 67.5% of the total flooding in the middle Yellow River. Simulation of flood routing processes shows that the decreased flooding capacity and elevated river bed of the shrunken main channel leads to an increased flood wave propagation time (24–52.3 h) in the study area after 1995. The model indicates that human activities, such as constructions of the Sanmenxia Dam, have changed flood routing boundary conditions and have contributed to the increased flood frequency at the confluence. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
57.
Poor sanitation and insufficient disposal of sewage and faeces are primarily responsible for water associated health problems in developing countries. Domestic sewage and faeces are prevalently discharged into surface waters which are used by the inhabitants as a source for drinking water. This paper presents a decentralized anaerobic process technique for handling of such domestic organic waste. Such an efficient and compact system for treating faeces and food waste may be of great benefit for developing countries. Besides a stable biogas production for energy generation, the reduction of bacterial pathogens is of particular importance. In our research we investigated the removal capacity of the reactor concerning pathogens, which has been operated under thermophilic conditions. Faecal coliforms and intestinal enterococci have been detected as indicator organisms for bacterial pathogens. By the multiple regression analysis technique an empirical mathematical model has been developed. The model shows a high correlation between removal efficiency and both, hydraulic retention time (HRT) and temperature. By this model an optimized HRT for defined bacterial pathogens effluent standards can be easily calculated. Thus, hygiene potential can be evaluated along with economic aspects. In this paper not only results for describing the hygiene potential of a thermophilic anaerobic bioreactor are presented, but also an exemplary method to draw the right conclusions out of biological tests with the aid of mathematical tools. 相似文献
58.
Oxidation and mineralisation of substituted phenols by Fenton's reagent and catalytic wet oxidation.
Catalytic abatement of solutions of 1,000 mg/L in phenol, ortho and para nitrophenol and ortho and para cresols was acomplished by using two catalytic systems. Fenton's reagent was used at 50 degrees C by adding 10 mg/L of ferrous cation and different dosages of H2O2. The mixture was reacting isothermically in a batch way during 3 hours. Catalytic wet oxidation (CWO) was carried out by using a commercial Activated Carbon, Industrial React FE01606A, CWO runs were carried out in a fixed bed reactor (FBR) with concurrent upflow. Temperature and oxygen pressure of the reactor were set to 160 degrees C and 16 bar, respectively. While phenols are quicky oxidised by the Fenton reagent higher mineralisation was obtained in the CWO process. 相似文献
59.
Optimal Locations of Groundwater Extractions in Coastal Aquifers 总被引:1,自引:0,他引:1
A regional water supply management model for coastal aquifers was developed. One of its outcomes is the definition of the
optimized locations for groundwater withdrawal. Such a tool permits the analysis of alternative plans for groundwater extraction
and the sustainable use of water resources in a coastal aquifer subject to saltwater intrusion. The principal components are
the evolutionary optimization and the analytical/numerical simulation models. The optimization technique looks for the best
well locations taking into consideration the economic results and the satisfaction of the societal water demand. However these
two concerns are conditioned by trying to control the saltwater intrusion, i.e., preserving the environmental equilibrium.
The simulation model uses the governing mathematical equations for groundwater movement to find the interface between freshwater
and saltwater. Because of the non-linearity in the system and the possibility of a jumping interface, a security distance
was defined. This is a controlling variable which can be set by the decision makers. The model was applied to a typical case
with interesting results. For example, diagrams showing the relationship between the location of the wells and the security
distance(s) are of importance to the managers. It was also crucial to have an understanding of the tradeoffs between groundwater
withdrawals, positions of the wells from the coast line, and the security distance. The model was also applied to a real case
in order to relate the extractions, distances and artificial recharge (not presented in this paper). 相似文献
60.
This paper presents a preliminary study for the removal of COD and suspended solids in wastewater treatment by combining magnetic field and electrocoagulation (EC) technology. The experiments were carried out using batch apparatus and setup in the static method. Batch experiments with two monopolar iron (Fe) plate anodes and cathodes were employed as electrodes. Wastewater samples were prepared from milk powder with an initial COD of 1,140 mgL(-1) and suspended solids of 1,400 mgL(-1) and acidic conditions were employed (pH approximately 3). DC current was varied from 0.5-0.8 A and operating times were between 30 and 50 min. The results show that the effluent wastewater was very clear (turbidity approximately 9 NTU) and its quality exceeded the direct discharge standard. The suspended solids and COD removal efficiencies were as high as 30.6 and 75.5%, respectively. In addition, the experimental results also show that the electrocoagulation could neutralise the pH of wastewater. 相似文献