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   5362篇
  免费   1327篇
财政金融   927篇
工业经济   462篇
计划管理   1249篇
经济学   1164篇
综合类   10篇
运输经济   120篇
旅游经济   50篇
贸易经济   1464篇
农业经济   313篇
经济概况   604篇
水利工程   315篇
邮电经济   11篇
  2023年   14篇
  2022年   9篇
  2021年   93篇
  2020年   222篇
  2019年   562篇
  2018年   281篇
  2017年   433篇
  2016年   417篇
  2015年   421篇
  2014年   426篇
  2013年   695篇
  2012年   438篇
  2011年   403篇
  2010年   364篇
  2009年   257篇
  2008年   270篇
  2007年   207篇
  2006年   184篇
  2005年   154篇
  2004年   150篇
  2003年   131篇
  2002年   116篇
  2001年   95篇
  2000年   82篇
  1999年   38篇
  1998年   20篇
  1997年   17篇
  1996年   14篇
  1995年   13篇
  1994年   13篇
  1993年   11篇
  1992年   12篇
  1991年   20篇
  1990年   13篇
  1989年   8篇
  1988年   3篇
  1987年   15篇
  1986年   12篇
  1985年   8篇
  1984年   4篇
  1983年   5篇
  1982年   5篇
  1981年   7篇
  1980年   4篇
  1979年   6篇
  1978年   2篇
  1977年   6篇
  1975年   2篇
  1974年   3篇
  1973年   2篇
排序方式: 共有6689条查询结果,搜索用时 31 毫秒
61.
A feature transformation method based on domain knowledge for arti?cial neural networks (ANNs) is proposed. The method of feature transformation based on domain knowledge converts continuous values into discrete values in accordance with the knowledge of experts in speci?c application domains. This approach effectively ?lters data, trains the classi?er, and extracts the rules from the classi?er. In addition, it reduces the dimensionality of the feature space, which not only decreases the cost and time in the operation but also enhances the generalizability of the classi?er. The experimental results of the proposed approach will be compared and tested statistically with the results of the linear transformation method. The results show that the method of feature transformation based on domain knowledge outperforms the linear transformation in modelling of ANNs. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
62.
The Cuban economy has experienced a significant increase in foreign direct investment over the past decade due to the end of the Soviet Union and the establishment of more liberal trade policies. Although the U.S. embargo of trade with Cuba still exists, there has been movement lately that suggests the end of the four‐decades‐old policy. The purpose of this article is to analyze the current Cuban business environment and to identify potential entrepreneurial opportunities in the service sector. Major trade partners are also reviewed and managerial implications discussed. © 2006 Wiley Periodicals, Inc.  相似文献   
63.
We examine the neglected area of internationalisation by VCs. Using a representative sample of 195 VCs, we show that the decision of a European VC firm to invest internationally is driven by its human resources. Having more VC executives in general and more VC executives with previous international experience in specific, results in a higher probability of investing internationally. In contrast, more VC executives with experience in the VC industry or with an engineering background lead to a higher probability of remaining domestic.  相似文献   
64.
Book Reviews     
Richard Robison, Indonesia: The Rise of Capital, Allen and Unwin, Sydney, 1986 pp. xxv + 425. Indexed. $19.95.

W.L. Korthals Altes, Changing Economy in Indonesia: Volume 7: Balance of Payments, 1822–1939, Amsterdam: The Royal Tropical Institute. pp. 167.

Trade Statistics, Java, 1823–73: Trade Statistics, Indonesia 1874–1937. Mededeelingen van het Centraal Kantoor voor de Statistiek nos 160 and 161

Om Prakash, The Dutch East India Company and the Economy of Bengal, 1630–1720, Princeton: Princeton University Press, 1985 pp. xii + 291, map, tables. graphs, glossary, index. Cloth $38.50.

Sediono M.P. Tjondronegoro, Social Organization and Planned Development in Rural Java, Singapore, Oxford University Press for the Institute of Southeast Asian Studies, 1984, pp. xv + 326.

A. Fujimoto and F. Matsuda (eds), An Economic Study of Rice Farming in West Java, Tokyo: NODAI Research Institute, Tokyo, University of Agriculture, 1986.

A. Fujimoto and T. Matsuda (eds), A Comparative Study of the Structure of Rice Productivity and Rural Society in Southeast Asta Two Village Studies in Indonesta and Thailand, Tokyo: University of Agriculture, 1985. Reviewed by C.L J. van der Meer (1986) Bulletin of Indanesian Economic Studies, 22(2) pp. 124–27

David Jenkins, Suharto and His Generals: Indonesian Military Politics, 1975–1983, Ithaca: Cornell Modern Indonesia Project, Monograph Series No. 64, 1984, pp. xiii + 280. US$12.50. David Bourchier, Dynamics of Dissent in Indonesia Sawito and the Phantom Coup, Ithaca: Cornell Modern Indonesia Project, Interim Reports Series, 1984, pp. 128. US$9.00.

Linda G. Martin (ed), The ASEAN Success Story: Social, Economic, and Political Dimensions, East-West Center, distributed by the University of Hawaii Press, Honolulu, 1987, pp. xviii + 253. $15.00.

Mubyarto and Edy Suandy Hamid (eds), Kredit Pedesaan di Indonesia, Badan Penerbit Fakultas Ekonomi, U.G.M., 1986 pp, 160.

Ron Hatley, et al., Other Javas Away from the Kraton, Melbourne: Monash University, 1984, pp. 60.

K.S. Nathan and M. Pathmanathan (eds), Trilateralism in Asia: Problems and Prospects in US-Japan-ASEAN Relations, Antara Book Company, Kuala Lumpur, 1986, pp. xviii + 205. $18.00 (cloth): $12.00 (paper).  相似文献   

65.
Discharge measurement is a critical task for gravel‐bed channels. Under high‐flow conditions, the elevation of the riverbed changes significantly by intensive torrential flow. The stage–discharge relations commonly used for stream discharge estimation may no longer be adequate. The contact‐type velocity measuring is also subject to measurement errors and/or instrument failures by the high‐flow velocities, driftwood, stumps, and debris. This study developed a new real‐time method to estimate river discharge in gravel‐bed channels. A systematic measuring technology combining ground‐penetrating radar and surface‐velocity radar was employed. The rating curves representing the relations of water surface velocity to the channel cross‐sectional mean velocity and flow area were established. Stream discharge was then deduced from the resulting mean velocity and flow area. The proposed method was examined in a steep gravel‐bed reach of the Cho‐Shui River in central Taiwan. The estimated stream discharge during three flood events were compared to the prediction by using the stage–discharge relation and the index‐velocity method. The proposed method of this study is capable of computing reasonable values of discharge for an entire flood hydrograph, whereas the other two methods tend to produce large extrapolation errors. Moreover, when the computed discharge is used in 2D flood flow simulation, the proposed method demonstrates better performance than the commonly used stage–discharge and index‐velocity methods.  相似文献   
66.
The Dokan Reservoir dam is a concrete cylindrical arch with gravity abutments, located on the Lesser Zab River about 60 km from the city of Sulaimani in north‐eastern Iraq. A bathymetric survey was conducted in November 2014 for a period of 10 days, using an echo sounder of 200‐kHz single beam. The survey results indicated an annual average sediment deposition of 3.8 million m3. Thirty‐two sediment samples were collected from the reservoir bed. The ratio of gravel, sand, silt and clay was 15:14:48:23, respectively. The reservoir bed is covered mainly with silt. The sediments are composed of silty clay (77.6%), silty sandy clay (10%), sandy gravely silty clay (1.2%) and gravely sandy silty clay (1%).  相似文献   
67.
This study presents a methodology for the development of a water balance model that uses publicly available data in a manner useful to water scientists and managers who manage complex lake and reservoir watersheds. The approach was applied to Coeur d'Alene Lake, a naturally occurring lake that is controlled by a dam located on its outlet (Spokane River) in North Idaho, USA. As in many other areas, the region surrounding Coeur d'Alene Lake has experienced high rates of population growth in recent years, and there is concern that, as consumptive water use increases, the lake will eventually not be able to be managed to simultaneously maintain the federally mandated minimum flow requirements in the Spokane River and also maintain the target summertime elevation of 2128 feet (648.6 m) for recreation and hydropower purposes. The complexity caused by the competing uses at Coeur d'Alene Lake makes it an excellent case study for similarly characterized watersheds. Both a natural flow model and regulated elevation model were developed, and sensitivity analysis was conducted on both models to evaluate which lake processes have the greatest effects on lake elevation, thereby requiring the most attention. A ‘low‐flow’ scenario was modelled to demonstrate the usefulness of the model and to inform Coeur d'Alene Lake regional stakeholders regarding the interrelationship between current water policy and the lake's physical behaviour under stressed conditions that could result from climate change. Model result indicates that, while lake elevation may be maintained at the summertime elevation of 2128 feet (648.6 m) under a low‐flow scenario, the outflows in the Spokane River start to approach the minimum flow requirements in the month of August. The developed approach is useful where publicly available data exist and allows for economic, yet rigorous, water resources systems evaluation without requiring significant field data collection.  相似文献   
68.
Multi‐temporal analysis of river‐floodplain processes is a key tool for the identification of reference conditions or benchmarks and for the evaluation of deviations or deficits as a basis for process‐based river restoration in large modified rivers. This study developed a methodology for benchmarking fluvial processes at river segment level, focusing on those interrelations between morphodynamics (aggradation, erosion, channel shift) and vegetation succession (initial, colonization, transition) that condition habitat structure. Habitat maps of the free‐flowing Upper Rhine River downstream from Iffezheim dam (France–Germany border) were intersected with a geographic information system‐based approach. Patches showing trajectories of anthropization, changeless, progression and regression allowed for the identification of natural and human‐induced processes over almost 200 years. Before channelization, the riverine system was characterized by a shifting habitat mosaic with natural heterogeneity, high degree of surface water connectivity and equilibrium between progression and regression processes. On the other hand, the following 175 years of human interventions led to severe biogeomorphologic deficits evidenced by loss of natural processes and habitat heterogeneity, hydrological disconnection between the river and its floodplain and imbalance of progression versus regression dynamics. The main driving forces of change are found in hydromorphological impacts (channelization, regulation and hydropower plant construction). Regression processes are now almost absent and have to be the objective of process‐based river restoration measures for the studied river‐floodplain system. A sustainable view on water management and river restoration should aim at a more resilient riverine system by balancing the recovery of natural processes with societal needs. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
69.
70.
Water supply systems are critical infrastructure that provides food and energy security for developed societies. The operation of reservoirs (flow regulation) and water intakes (water diversion) has known negative impacts on aquatic ecosystems; however, quantification of ecological impacts and examination of these two types of flow alteration remain a developing area of research. We investigated the individual and combined impact of flow regulation and water diversion on stream ecosystem integrity, the freshwater macroinvertebrate community, and the population structure of flow‐sensitive insects. For 2 years, we monitored quarterly discharge, physical and chemical stream conditions, and benthic invertebrates of four high‐altitude tropical streams that are part of the water supply system of Quito, Ecuador. Flow regulation caused a loss of the hydrological seasonality of these streams, including a decrease in stream depth and biotic quality. Water diversion caused a decrease in dissolved oxygen and overall ecosystem integrity. Freshwater invertebrate density and richness decreased as a result of water diversion and flow regulation. The combined flow alteration in these streams decreased the density of nymphal stages of the widely distributed mayfly Andesiops peruvianus. Given the societal needs for food and energy security, water management for diversion (e.g., irrigation) and in‐line storage practices (e.g., hydroelectric dams) are anticipated to increase. This research suggests that the negative environmental impacts of flow alteration could be mitigated with discharge releases designed to approximate the natural hydrologic regime of undisturbed streams.  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