全文获取类型
收费全文 | 41159篇 |
免费 | 1185篇 |
国内免费 | 14篇 |
专业分类
财政金融 | 6382篇 |
工业经济 | 2520篇 |
计划管理 | 5756篇 |
经济学 | 7925篇 |
综合类 | 673篇 |
运输经济 | 245篇 |
旅游经济 | 520篇 |
贸易经济 | 5444篇 |
农业经济 | 1699篇 |
经济概况 | 4091篇 |
水利工程 | 7015篇 |
信息产业经济 | 3篇 |
邮电经济 | 85篇 |
出版年
2021年 | 305篇 |
2020年 | 483篇 |
2019年 | 744篇 |
2018年 | 892篇 |
2017年 | 914篇 |
2016年 | 925篇 |
2015年 | 627篇 |
2014年 | 952篇 |
2013年 | 3939篇 |
2012年 | 1502篇 |
2011年 | 1500篇 |
2010年 | 1154篇 |
2009年 | 1217篇 |
2008年 | 1341篇 |
2007年 | 1342篇 |
2006年 | 1254篇 |
2005年 | 1131篇 |
2004年 | 1085篇 |
2003年 | 802篇 |
2002年 | 744篇 |
2001年 | 847篇 |
2000年 | 799篇 |
1999年 | 699篇 |
1998年 | 759篇 |
1997年 | 726篇 |
1996年 | 679篇 |
1995年 | 638篇 |
1994年 | 624篇 |
1993年 | 634篇 |
1992年 | 657篇 |
1991年 | 657篇 |
1990年 | 593篇 |
1989年 | 475篇 |
1988年 | 480篇 |
1987年 | 482篇 |
1986年 | 447篇 |
1985年 | 633篇 |
1984年 | 669篇 |
1983年 | 610篇 |
1982年 | 564篇 |
1981年 | 585篇 |
1980年 | 575篇 |
1979年 | 571篇 |
1978年 | 480篇 |
1977年 | 405篇 |
1976年 | 424篇 |
1975年 | 337篇 |
1974年 | 347篇 |
1973年 | 335篇 |
1972年 | 242篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Stormwater quality simulation models are useful tools for the design and management of sewer systems. Modelling results are highly sensitive to experimental data used for calibration. This sensitivity is examined for three modelling approaches of various complexities (site mean concentration approach, event mean concentration approach and build-up, washoff and transport modelling approach) applied to a typical case study (design of a dry detention tank), accounting for the variability of calibration data and their effect on simulation results. Calibrated models with different calibration data sets were used to simulate 3 years of rainfall with different retention tank specific volumes. Annual pollutant load interception efficiencies were determined. Simulations results revealed (i) that there is no advantage in using the EMC model compared to the SMC model and (ii) that the BWT model resulted in higher design ratios than those given by the SMC/hydraulic approach. For both EMC and BWT models, using an increasing number n of events for calibration leads to narrower confidence intervals for the design ratios. It is crucial for design ratios to account for successive storm events in chronological order and to account for the maximum allowable flow to be transferred to the downstream WWTP. 相似文献
42.
An inventory analysis of rural pollution loads in China. 总被引:1,自引:0,他引:1
Rural pollution has attracted increasing attention over the past decade for its important consequences on surface and groundwater quality. This is particularly so in China due to the wide and effective control of industrial and municipal wastewater discharges over the past decade. Based on the discussion of rural activities in China, this paper develops a new method of inventory analysis through the definition of elementary unit (EU). This inventory analysis approach is then applied to estimate the total rural pollution loads of COD, TN and TP, as well as their spatial distributions in China. Further analysis is also conducted to investigate the correlations between rural pollution loads and agricultural production outputs, as well as population. It is found that China's agriculture is developing largely at the cost of environment quality, and a high population, as well as the increasing demand for agricultural products, is one of the dominant driving forces. The constructed EKC, which describes the relationship between rural pollution loads and agricultural income, also reveals that current agricultural development in China is mostly far from de-locked from the environmental problem. 相似文献
43.
D. R. Myddelton 《Economic Affairs》2003,23(1):2-6
Major tax reform to simplify the UK tax system is possible. Merging income taxes, social security taxes and corporation tax into only a single flat-rate of tax on all incomes would be a radical start. Avoiding taxes on income and expenditure which are 'too high' requires major reductions in government spending, mainly on the welfare state. Given the political will, over a period of years we really can hugely improve the UK tax system. 相似文献
44.
Lake Chivero: A management case study 总被引:1,自引:0,他引:1
C. H. D. Magadza 《Lakes & Reservoirs: Research and Management》2003,8(2):69-81
Lake Chivero in Zimbabwe was shown to be hypereutrophic. Historical data showed that the eutrophication process had been arrested in the late 1970s. However, a combination of poor planning, multiplicity of jurisdiction, mismatch between rate of urbanization and waste management investment, recent changes in the local climate and a permissive, immature political system that called for no public accountability resulted in environmental management breakdown leading to hypereutrophication of the lake. The case of Lake Chivero is presented as an example of a wider global issue regarding the status of environmental management in competition with other priorities in emerging democracies. 相似文献
45.
Flotation is a water treatment alternative to sedimentation, and uses small bubbles to remove low-density particles from potable water and wastewater. The effect of zeta potential, bubble size and particle size on removal efficiency of the electro-flotation process was investigated because previous model-simulations indicated that these attributes are critical for high collision efficiency between micro-bubbles and particles. Solutions containing Al3+ as the metal ion were subjected to various conditions. The zeta potentials of bubbles and particles were similar under identical conditions, and their charges were influenced by metal ion concentration and pH. Maximum removal efficiency was 98 and 12% in the presence and absence of flocculation, respectively. Removal efficiency was higher when particle size was similar to bubble size. These results agree with modelling simulations and indicate that collision efficiency is greater when the zeta potential of one is negative and that of the other is positive and when their sizes are similar. 相似文献
46.
V. N. Durcheva S. M. Puchkova 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2006,40(2):71-78
Operation of the dam in a transitional mode is described.
__________
Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 1, January 2006, pp. 8–15. 相似文献
47.
We argue that charismatic leadership can influence external support for the organization, particularly in making the company more attractive to outside investors. Two studies were conducted to test this general hypothesis. First, an archival study demonstrated that the stock of companies headed by charismatic leaders appreciated more than the stock of comparable companies, even after differences in corporate performance were controlled. It was also found that the effect of charismatic leadership was heightened under more difficult economic conditions. Second, an experiment was conducted in which the salience of charismatic leadership was manipulated, along with information about the prospects for an organization's turnaround. Results showed that appeals from a charismatic leader led to increased investment in the firm, and the leader's influence was greater when the prospects for an organizational turnaround were more difficult. It was also found that an endowment of stock enhanced the influence of charismatic appeals and that charismatic leadership may have affected the general risk propensities of followers. These findings were interpreted in terms of an external perspective on leadership, illustrating how leaders can manage the firm's economic and social environment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
48.
49.
50.