全文获取类型
收费全文 | 33013篇 |
免费 | 729篇 |
国内免费 | 153篇 |
专业分类
财政金融 | 4676篇 |
工业经济 | 2081篇 |
计划管理 | 5110篇 |
经济学 | 5986篇 |
综合类 | 1736篇 |
运输经济 | 231篇 |
旅游经济 | 308篇 |
贸易经济 | 3540篇 |
农业经济 | 1689篇 |
经济概况 | 4156篇 |
水利工程 | 4323篇 |
信息产业经济 | 2篇 |
邮电经济 | 57篇 |
出版年
2023年 | 224篇 |
2022年 | 389篇 |
2021年 | 572篇 |
2020年 | 603篇 |
2019年 | 509篇 |
2018年 | 545篇 |
2017年 | 696篇 |
2016年 | 617篇 |
2015年 | 598篇 |
2014年 | 869篇 |
2013年 | 2284篇 |
2012年 | 1699篇 |
2011年 | 2436篇 |
2010年 | 2194篇 |
2009年 | 1707篇 |
2008年 | 1781篇 |
2007年 | 1666篇 |
2006年 | 1869篇 |
2005年 | 1629篇 |
2004年 | 733篇 |
2003年 | 673篇 |
2002年 | 588篇 |
2001年 | 552篇 |
2000年 | 418篇 |
1999年 | 499篇 |
1998年 | 379篇 |
1997年 | 363篇 |
1996年 | 376篇 |
1995年 | 322篇 |
1994年 | 319篇 |
1993年 | 257篇 |
1992年 | 279篇 |
1991年 | 263篇 |
1990年 | 216篇 |
1989年 | 184篇 |
1988年 | 173篇 |
1987年 | 146篇 |
1986年 | 192篇 |
1985年 | 268篇 |
1984年 | 282篇 |
1983年 | 266篇 |
1982年 | 233篇 |
1981年 | 241篇 |
1980年 | 204篇 |
1979年 | 223篇 |
1978年 | 194篇 |
1977年 | 161篇 |
1976年 | 149篇 |
1975年 | 137篇 |
1974年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
I Kaufmann T Meyer M Kalsch T G Schmitt H W Hamacher 《Water science and technology》2007,56(5):115-124
If technologies for decentralised sanitation and reuse (DESAR) and for natural stormwater management should at least partially replace existing systems, then intensive reconstruction work becomes essential. A conversion can only be realised successively over a long period due to high construction and financial expenses and requires new strategies. This paper presents the development and practical implementation of a mathematical tool to find an optimised strategy for the realisation of alternative and more decentralised drainage and sanitation concepts in existing urban areas. The succession of construction measures (e.g. the implementation of decentralised greywater recycling) for the whole period of consideration is determined based upon a mathematical optimisation model on the condition that the favoured future state is known. The model describes the complex interdependencies of the urban water and nutrient cycle and enables the minimisation of both financial efforts and ecological impacts on the way toward the future state. The results of the implementation for a rural area in Germany show that the mathematical optimisation is an adequate instrument to support decision-making processes in finding strategies for the realisation of sustainable urban water management. 相似文献
62.
全球气候变暖对水资源的影响 总被引:6,自引:0,他引:6
全球气候变暖加剧了干旱、洪涝、台风等自然灾害的发生,是目前各国政府和社会公众普遍关注的热点问题。根据有关资料对气候变暖研究进展情况作相关介绍,可供参考。 相似文献
63.
The secondary effluent from municipal plants in Korea generally represents higher BOD with lower SS. Therefore, more soluble forms of organics and NH4-N need to be removed to improve its effluent for reuse. In this study reuse possibility of secondary effluent and CSO (combined sewer overflow) using BAF (biological aerated filter) was evaluated. The tertiary application with 1.2 h EBCT, SS, BOD and COD showed stable concentrations less than 1.3, 1.3 and 6.2 mg/L, respectively. Nitrogen could be nitrified even at 7 degrees suggesting BAF can be used for a water reuse method as well as an effective add-on facility in cold regions. However, BAF was not stable with CSO application at increased flow rates suggesting CSO must be equalised prior to application. Disinfection was necessary even during normal weather conditions. 相似文献
64.
65.
Li Wei College of water conservancy Hydropower Engineering Wuhan Univerity Wuhan ChinaChen Wen-xue Xie Sheng-zong China Institute of Water Resources Hydropower Research Beijing China 《水动力学研究与进展(B辑)》2002,14(4)
1 . INTRODUCTIONTheturbulentstructuresinnon circularductsandopenchannelsarecharacterizedbylongitudi nalvortices .Thesevorticesareth 相似文献
66.
67.
Review of Industrial Organization - 相似文献
68.
Carl R. Chen 《The Journal of Financial Research》2001,24(2):309-310
Emerging Financial Markets, by David O. Beim and Charles W. Calomiris. McGraw‐Hill/Irwin, 2001, 364 pages, price $75.00. 相似文献
69.
This article analyzes the effects of the length of hedging horizon on the optimal hedge ratio and hedging effectiveness using 9 different hedging horizons and 25 different commodities. We discuss the concept of short‐ and long‐run hedge ratios and propose a technique to simultaneously estimate them. The empirical results indicate that the short‐run hedge ratios are significantly less than 1 and increase with the length of hedging horizon. We also find that hedging effectiveness increases with the length of hedging horizon. However, the long‐run hedge ratio is found to be close to the naïve hedge ratio of unity. This implies that, if the hedging horizon is long, then the naïve hedge ratio is close to the optimum hedge ratio. © 2004 Wiley Periodicals, Inc. Jrl Fut Mark 24:359–386, 2004 相似文献
70.
In this paper, quadratic term structure models (QTSMs) are analyzed and characterized in a general Markovian setting. The primary motivation for this work is to find a useful extension of the traditional QTSM, which is based on an Ornstein–Uhlenbeck (OU) state process, while maintaining the analytical tractability of the model. To accomplish this, the class of quadratic processes, consisting of those Markov state processes that yield QTSM, is introduced. The main result states that OU processes are the only conservative quadratic processes. In general, however, a quadratic potential can be added to allow QTSMs to model default risk. It is further shown that the exponent functions that are inherent in the definition of the quadratic property can be determined by a system of Riccati equations with a unique admissible parameter set. The implications of these results for modeling the term structure of risk-free and defaultable rates are discussed. 相似文献