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   26091篇
  免费   738篇
  国内免费   96篇
财政金融   3377篇
工业经济   1713篇
计划管理   3982篇
经济学   4405篇
综合类   920篇
运输经济   138篇
旅游经济   311篇
贸易经济   3380篇
农业经济   1246篇
经济概况   2778篇
水利工程   4629篇
邮电经济   46篇
  2023年   126篇
  2022年   226篇
  2021年   350篇
  2020年   399篇
  2019年   410篇
  2018年   523篇
  2017年   623篇
  2016年   539篇
  2015年   453篇
  2014年   708篇
  2013年   1861篇
  2012年   1292篇
  2011年   1697篇
  2010年   1397篇
  2009年   1179篇
  2008年   1310篇
  2007年   1272篇
  2006年   1218篇
  2005年   1088篇
  2004年   632篇
  2003年   493篇
  2002年   466篇
  2001年   463篇
  2000年   427篇
  1999年   383篇
  1998年   369篇
  1997年   349篇
  1996年   344篇
  1995年   311篇
  1994年   283篇
  1993年   315篇
  1992年   291篇
  1991年   258篇
  1990年   242篇
  1989年   221篇
  1988年   183篇
  1987年   204篇
  1986年   201篇
  1985年   289篇
  1984年   307篇
  1983年   299篇
  1982年   260篇
  1981年   278篇
  1980年   247篇
  1979年   256篇
  1978年   196篇
  1977年   191篇
  1976年   172篇
  1975年   134篇
  1974年   130篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
71.
72.
73.
Transdisciplinarity: Context, contradictions and capacity   总被引:1,自引:0,他引:1  
  相似文献   
74.
Analysis of firm investment behavior during 1982–1993 shows that the Tax Reform Act of 1986 (TRA 86) Public Law No. 99-514 substantially affects both purchases and leases of depreciable assets. The changes in the regular corporate income tax rules are shown to lower asset acquisition. The effect of the alternative minimum tax (AMT) is found to vary with the debt share in firms’ capital structure and with the frequency of AMT exposure during the life of the assets acquired. On average, TRA86 depresses asset purchases less for firms that are subject to the AMT: AMT somewhat mitigates the negative effects of the regular tax rules.  相似文献   
75.
本文不仅总结了当前主要的实证研究文献提出的我国通货膨胀的种种成因,而且对每种原因给予了比较分析和新的实证分析,并在此基础上尝试进行了综合分析,以得出一些有益的结论。  相似文献   
76.
Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection.  相似文献   
77.
78.
We investigate the effects of analysts' affiliation and reputation on dealers' market making activities. We find that for a given stock, dealers who have affiliated analysts covering the stock quote and trade more aggressively than those who do not have any affiliated analysts. More important, the reputation of affiliated analysts plays an additional role in the affiliated dealer's quote and trade behavior. Dealers with affiliated star analysts post more aggressive quotes and have larger market shares than dealers with affiliated nonstar analysts. Although dealers who post more aggressive quotes also induce affiliated star analysts to cover the stocks, the positive effect of analyst reputation on the affiliated dealers' quote aggressiveness remains significant and robust after controlling for potential endogenous and simultaneous problems.  相似文献   
79.
There are four ecologically important river catchments that contain candidate Special Areas of Conservation (cSACs) under the Habitats Directive in the Lake District National Park located in the North of England. These are the rivers Ehen, Kent, Derwent and Eden. For each cSAC, there are defined ecological criteria that include water quality targets to protect the designated species. Stretches of the riverine cSACs in each catchment are failing to meet these and other water quality targets. The Environment Agency commissioned a study of each catchment to provide the underpinning scientific knowledge to allow it to deliver its statutory obligations under the Habitats Directive. SIMCAT river water quality models were produced and used to predict the water quality impacts resulting from a number of water quality planning scenarios aimed at achieving full compliance with the Habitats Directive and other national and EEC water quality targets. The results indicated that further controls on effluent discharges will allow the majority of targets to be met but other sources of pollution will also need to be controlled. The outcome of the study also recognised that water quality improvements alone will not necessarily produce the required improvement to the ecological interest features in each cSAC.  相似文献   
80.
A Discfilter with 10 and 18 microm filter openings, respectively, was placed in parallel to a flotation plant for separation of biological flocs from a post-denitrifying Kaldnes Moving Bed Process, the last treatment step at the municipal wastewater treatment plant at Sj?unda, Malm?, Sweden. The effluent concentrations from the 10 and 18 microm filter were 2-5 and 2-8 mg SS L(-1), respectively, which is comparable to, or better than, the flotation plant. Comparison with experiences from activated sludge plants shows that the Discfilter works especially well after the Kaldnes process. Particle size distribution (PSD) studies show that particles larger than the filter openings of 10 and 18 microm are separated with approximately 90% efficiency, whereas most of the smaller particles pass the filter. This fact indicates that the major particle separation mechanism is physical blocking. These findings point to the possibility of improving the prediction of the separation efficiency by combining measurements of turbidity and suspended solids with particle size analysis.  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