首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   13989篇
  免费   172篇
  国内免费   2篇
财政金融   1915篇
工业经济   826篇
计划管理   1863篇
经济学   2596篇
综合类   136篇
运输经济   76篇
旅游经济   126篇
贸易经济   1528篇
农业经济   501篇
经济概况   1475篇
水利工程   3065篇
邮电经济   56篇
  2021年   105篇
  2020年   140篇
  2019年   230篇
  2018年   266篇
  2017年   308篇
  2016年   323篇
  2015年   177篇
  2014年   298篇
  2013年   1122篇
  2012年   445篇
  2011年   462篇
  2010年   315篇
  2009年   407篇
  2008年   390篇
  2007年   417篇
  2006年   394篇
  2005年   420篇
  2004年   381篇
  2003年   281篇
  2002年   227篇
  2001年   239篇
  2000年   240篇
  1999年   246篇
  1998年   249篇
  1997年   272篇
  1996年   218篇
  1995年   193篇
  1994年   195篇
  1993年   248篇
  1992年   272篇
  1991年   217篇
  1990年   212篇
  1989年   200篇
  1988年   191篇
  1987年   194篇
  1986年   191篇
  1985年   219篇
  1984年   206篇
  1983年   200篇
  1982年   198篇
  1981年   206篇
  1980年   201篇
  1979年   217篇
  1978年   174篇
  1977年   170篇
  1976年   156篇
  1975年   118篇
  1974年   133篇
  1973年   125篇
  1972年   96篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Local and regional governments account for an important share of total government spending and, given the decentralization trend in OECD nations, this is likely to increase. How should this spending be governed? This article argues that direct democracy is best suited to organize decision–making at the state and local level. To support this, we present the main theoretical arguments on why and how referenda and initiatives affect fiscal policy outcomes. The basic argument concerns voter control. Under representative democracy, citizens only have direct control at election time. With referenda and initiatives, citizens can selectively control their representatives on specific policies whenever they deviate sufficiently from citizens' preferences. As a result, fiscal policy outcomes are likely to more closely reflect voter preferences. We empirically test this on Swiss data since Switzerland provides a 'natural laboratory' for local governance. The governance structures of Swiss cantons and localities with respect to fiscal issues range from classic parliamentary democracy to pure direct democracy, and an important part of spending and taxation is controlled at these levels. Specifically, we estimate an econometric model of fiscal behaviour using data from 1986 to 1997 for the 26 Swiss cantons, and 1990 data on 134 local communities. It is shown that mandatory referenda on fiscal issues at both levels have a dampening effect on expenditure and revenue, and at the local level also on public debt. Combining this with existing empirical evidence leads to a relatively uncontested result, namely that elements of direct democracy are associated with sounder public finances, better economic performance and higher satisfaction of citizens.  相似文献   
52.
53.
A pilot-scale fluidised pellet bed (FPB) bioreactor, which combines chemical coagulation, biological degradation, particle pelletisation and separation in one unit, was applied for onsite wastewater treatment and reuse. As a result of rational use of inorganic coagulant and organic polymer and moderate mechanical agitation, spherical particles were generated in the upflow column and a well-fluidised bed was formed. With a continuous supply of dissolved oxygen through a recycling loop, an aerobic condition was kept in the bottom section of the FPB column. Under such conditions the pellets in the FPB column showed the following characteristics: (1) compact structure and high density; (2) rich in microorganisms; and (3) high MLSS and MLVSS concentrations. Therefore, the FPB bioreactor achieved more than 90% removal of SS, COD, BOD and TP from raw domestic wastewater within a total hydraulic retention time (HRT) of only about 30 minutes. It also showed nitrification and denitrification ability and the TN removal could be about 50% as the recycling ratio was increased to 1:1. The treated water quality is generally competitive with the secondary effluent from a conventional activated sludge process. With these advantages the FPB bioreactor is recommendable as a compact system for onsite wastewater treatment and reuse.  相似文献   
54.
Posting or closing of swimming beaches because of faecal contamination is a widespread problem reported in many locations. In a risk-based approach to this problem, the risk to swimmers' health is assessed by field monitoring of indicator bacteria and the associated risks are managed by source controls and other remedial measures. In risk assessment, great advances have been made in recent years with the introduction of microbial source tracking (MST) techniques. Two such techniques, antibiotic resistance analysis and DNA fingerprinting, were applied in a study of causes of faecal contamination at two lake beaches in Toronto, Ontario. Both methods identified bird faeces as the dominant sources of E. coli. Coping with this type of pollution presents a major environmental challenge.  相似文献   
55.
Cytostatic agents are applied in cancer therapy and subsequently excreted into hospital wastewater. As these substances are known to be carcinogenic, mutagenic and toxic for reproduction, they should be removed from wastewater at their source of origin.In this study the fate and effects of the cancerostatic platinum compounds (CPC) cisplatin, carboplatin, oxaliplatin, 5-fluorouracil (5-FU) and the anthracyclines doxorubicin, daunorubicin and epirubicin were investigated in hospital wastewater. Wastewater from the in-patient treatment ward of a hospital in Vienna was collected and monitored for the occurrence of the selected drugs. A calculation model was established to spot the correlation between administered dosage and measured concentrations. To investigate the fate of the selected substances during wastewater treatment, the oncologic wastewater was treated in a pilot membrane bioreactor system (MBR) and in downstream advanced wastewater treatment processes (adsorption to activated carbon and UV-treatment). Genotoxic effects of the oncologic wastewater were assessed before and after wastewater treatment followed by a risk assessment.Monitoring concentrations of the selected cytostatics in the oncologic wastewater were in line with calculated concentrations. Due to different mechanisms (adsorption, biodegradation) in the MBR-system 5 - FU and the anthracyclines were removed < LOD, whereas CPC were removed by 60%. In parallel, genotoxic effects could be reduced significantly by the MBR-system. The risk for humans, the aquatic and terrestrial environment by hospital wastewater containing cytostatic drugs was classified as small in a preliminary risk assessment.  相似文献   
56.
Power Technology and Engineering - The paper presents the results of developing a high-speed semiconductor transformer voltage regulator (STVR) intended for a real-time voltage regulation of 0.4 kV...  相似文献   
57.
Employment,schooling and productivity growth   总被引:1,自引:1,他引:0  
Summary This paper presents an empirical analysis of labour demand and labour productivity growth in The Netherlands. Assuming an aggregate production function with as factors capital and 3 types of labour, distinguished by educational attainment, cost minimization leads to a set of 3 labour demand relations to be estimated on time series data. Using the estimates and the implied elasticities, aggregate labour productivity growth is decomposed into factor substitution, autonomous factors, labour time shortening, economies of scale, utilization rates and the increased educational level of the working population. The contributions of substitution, utilization rates and education appear to be substantial, notably in the seventies.

List of symbols

Variables a i Efficiency index of skill leveli - C production - h i working-time index for skill leveli - g i steady-state growth rate of skill leveli - K capital stock - L i employment volume of skill leveli - L i * desired level of labour skill leveli - p output price - p * desired output price - s i * long-run static labour shares in the production value - p k rental price of capital - P index of total factor productivity - P l index of labour productivity - u i utilization rate of skill leveli - u k utilization rate of capital - w i wage rate for skill leveli - y production volume - y yij Hicks partial elasticities of complementarity - i steady-state cost share of skill leveli - k Bk steady-state cost share of capital - f lf highest level price index in cost function nesting - g 4 intermediate level price index in cost function nesting - h 4 lowest level price index in cost function nesting - i steady-state relative wage share of skill leveli - ij Allen partial elasticities of substitution Parameters d i l adjustment speed of skill leveli - d p price adjustment speed - M mark-up on marginal costs - scale elasticity of production - i distribution parameter in cost function,i = 3, g - i distribution parameter in cost function,i = k, h - i distribution parameter in cost function,i =1, 2 - i autonomous labour productivity growth for skill leveli - i cost share of skill level in base year - f production cost index in base year - i hours elasticity in labour efficiency index - group elasticity of substitution betweenL 3 and (K, (L 1,L 2)) - g Og group elasticity of substitution betweenK and (L 1,L 2) - h 6h group elasticity of substitution betweenL 1 andL 2 We would like to thank B. Downey, G.M.M. Gelauff, A. Nieuwenhuis, J.M.M. Ritzen, J.C. Siebrand and an unknown referee for helpful comments on earlier drafts.  相似文献   
58.
1.  When ventilating complex underground hydraulic systems during their construction it is necessary to take into account the natural draft.
2.  The method presented for calculating the natural draft pressure drop of single tunnels (formulas 1–6) reflects the specific characteristics of hydrotechnical construction in mountainous areas and for the first time takes into account the direction of movement of the ventilation flow.
3.  For the particular conditions of constructing the Rogun hydrostation the values of the lapse rates were established, which can be used in calculations to take into account the natural draft when designing the ventilation of underground workings.
4.  For calculating the natural draft pressure drop of a complex network of underground workings, an algorithm was developed which makes it possible to calculate by a standard program on a computer the air distribution in the underground complex being constructed in relation to a number of technological and natural factors.
5.  On the basis of analyzing the results of different variants of the air distribution, the selection of the types and arrangement of the ejector fans (including in the future) was optimized, making it possible to increase the quality of ventilation and safety of underground operations, as well as to obtain a substantial technical-economic effect.
Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 8, pp. 26–29, August, 1988.  相似文献   
59.
The author examines recent urban development in Indonesia. "Analysis of urban developments in Indonesia has been hampered in the past by weak data. Recently, the National Urban Development Strategy (NUDS) project has generated a set of improved data. This paper aims at elaborating and supplementing the NUDS study. After a discussion of definitional problems, an analysis is carried out of urban growth rates at the provincial level. Private investment is shown to be a principal determinant of urban growth rates. Other significant determinants are rural immigration and the present level of urbanisation. Private investment is shown to be strongly biased towards provinces with large urban areas. In addition, polarisation is studied at the level of individual cities. It is found that a period of rapidly increasing polarisation has come to an end during the last decade."  相似文献   
60.
Conclusions On the basis of the particular examples of geodetic works in the region of design and construction of the Bartogai and Bestyuba reservoirs we can recommend the following sequence of studying CVCM in highly seismic regions of constructing large hydraulic structures:A study of the geological structure of the region from literature sources (morphostructural plan, fault tectonics, contemporary crustal movements);Study of the contemporary crustal movements from the results of precision levelings of the state vertical control network. Study of the degree of activity of large faults in the crust of the region in connection with strong earthquakes;Creation of networks of the first level — deformation areas — in the region of the site of the dam and other large structures, regime observations for studying the small-block structure of the construction region (microregionalization) and activity of microfractures and cracks;Equipping the networks of the second level and establishment of the initial stage of observations on long profiles around the bed of the future reservoir and across the shores. Repeat, as required, of leveling of sections of the line of the state vertical control network for determining the tendencies of the secular crustal movements;Analysis of the data of the observations and development of recommendations aimed at refining the designs, safe operation of the hydraulic structures, and further development of geodetic works at the stage of using the objects in the economy.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 3, pp. 27–30, March, 1987.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号