全文获取类型
收费全文 | 17780篇 |
免费 | 275篇 |
国内免费 | 1篇 |
专业分类
财政金融 | 1805篇 |
工业经济 | 673篇 |
计划管理 | 1783篇 |
经济学 | 2558篇 |
综合类 | 386篇 |
运输经济 | 34篇 |
旅游经济 | 57篇 |
贸易经济 | 2305篇 |
农业经济 | 327篇 |
经济概况 | 1742篇 |
水利工程 | 6355篇 |
信息产业经济 | 3篇 |
邮电经济 | 28篇 |
出版年
2018年 | 1082篇 |
2017年 | 1041篇 |
2016年 | 736篇 |
2015年 | 175篇 |
2014年 | 321篇 |
2013年 | 888篇 |
2012年 | 563篇 |
2011年 | 1053篇 |
2010年 | 911篇 |
2009年 | 802篇 |
2008年 | 856篇 |
2007年 | 1086篇 |
2006年 | 338篇 |
2005年 | 392篇 |
2004年 | 437篇 |
2003年 | 392篇 |
2002年 | 259篇 |
2001年 | 181篇 |
2000年 | 184篇 |
1999年 | 171篇 |
1998年 | 190篇 |
1997年 | 173篇 |
1996年 | 187篇 |
1995年 | 159篇 |
1994年 | 187篇 |
1993年 | 169篇 |
1992年 | 194篇 |
1991年 | 175篇 |
1990年 | 199篇 |
1989年 | 162篇 |
1988年 | 171篇 |
1987年 | 170篇 |
1986年 | 159篇 |
1985年 | 192篇 |
1984年 | 182篇 |
1983年 | 154篇 |
1982年 | 165篇 |
1981年 | 184篇 |
1980年 | 199篇 |
1979年 | 187篇 |
1978年 | 221篇 |
1977年 | 210篇 |
1976年 | 207篇 |
1975年 | 185篇 |
1974年 | 175篇 |
1973年 | 170篇 |
1972年 | 138篇 |
1971年 | 144篇 |
1969年 | 135篇 |
1968年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 609 毫秒
101.
As far as flocculation is concerned, the agglomeration of suspended particles into flocs is highly linked to the hydraulic behaviour of the agitation. The Turbomix is a special design of mixing tank; its design was developed to better control the flow during the flocculation stage. It enables a significant decrease in footprint of the process. The combination of the Turbomix and ballasted flocculation has been studied during pilot trials in terms of treatment efficiency. Its controlled hydraulic behaviour explains the efficiency of the process as proved by CFD investigation. 相似文献
102.
An innovative technology for industrial wastewater treatment has been developed. The main focus of the new system is a transformation of persistent organic compounds (biorecalcitrant COD) into a biodegradable fraction, followed by high efficient biological elimination using specialised bacteria's. To fulfill these targets the Aqua-Biomant process integrates two treatment steps: an aerated biological upflow filter and a electrochemical oxidation technique using boron doped-diamond electrodes. The advantages of the process are high efficient COD removal with reduced energy consumption combined with low total residence time. 相似文献
103.
Increasing concern in recent years over the occurrence and fate of low-level concentrations of pharmaceuticals in the aquatic environment stimulates research on alternative treatment methods. This paper presents a study of the degradation of sulphamethoxazole, an antibiotic used on humans and animals in order to treat various bacterial infections, by ozonation. After 4.5 min of treatment, the concentration of sulphamethoxazole was below the HPLC detection limit of 0.6 mgL(-1), indicating degradation efficiency higher than 99.24%. This value is comparable and in some cases higher than published data on the degradation in drinking water. Kinetic analysis of the data indicated an overall first-order reaction with a rate constant of 1.0594 min(-1) at 20 degrees C. The reaction order differs with the second-order reaction observed by other researchers. This change of reaction order could be explained by the different treatment conditions used. Preliminary analysis using the FT-IR technique was also performed in order to obtain information on the structure of the degradation products. Further analysis using a GC-MS is needed in order to elucidate the structure of the degradation products. Finally, based on the experiments performed, ozonation seems to be a promising technique for the degradation of antibiotics, even in wastewater. 相似文献
104.
Suitability of sweet sorghum in Greece, where irrigation supply during crop development is limited as rainfall is scarce and
evapotranspiration loss is high, is examined in relation with radiation availability. A two-year field experiment was conducted,
in central Greece, imposing four soil water regimes via different irrigation treatments: (1) Highly irrigated, (2) Highly
irrigated till anthesis when irrigation stopped, (3) Medium irrigated, and (4) Low irrigated. It was found that above-ground
dry biomass production from non-water-stressed sweet sorghum plants suggests a high productivity potential among C4 crops. Under water shortage, radiation use efficiency may be significantly lower. Radiation use efficiency seems to be linearly
related to water consumption. Stressed plants (probably except severely stressed) seem to use available water more efficiently
than unstressed plants. The slope of the line relating dry matter produced and water evapotranspired increases the sooner
the stress is sensed. Yield reduction resulting from post-anthesis irrigation stopage is very little. High water use efficiency
values tend to be related with low radiation use efficiency values. 相似文献
105.
A. A. Kochetov D. D. Korzh A. V. Egorov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2007,41(1):41-46
Problems of optimum hanging of long rotor blades of the last stages of steam turbines are considered. Causes of nonuniform
erosion wear of the inlet edges connected with inaccurate location of holes for the external damper coupling on the chord
of the profile are determined. Methods for optimizing the hanging of blades for raising the reliability of the last stages
are suggested. Main results of hanging performed with the help of a specially developed “LIBRA” soft hardware are presented.
__________
Translated from élektricheskie Stantsii, No. 11, November 2006, pp. 36–41. 相似文献
106.
V C Hammen 《Water science and technology》2007,56(1):253-258
Smoke-haze episodes caused by vegetation and peat fires affect parts of Indonesia every year with significant impacts on human health and climate. The forest fires 1997/1998 were by far the largest in Indonesian history, burning between 5 and 8 million hectares before they were stopped by the monsoon rains in December 1997. Fires sprang up again in 1998 on Kalimantan when monsoon rain paused. Peat forests and peatlands are in particular severely affected. In the 1997/1998 haze event, 2.1-2.5 million hectare of peat swamp forest burnt in Indonesia. The remaining ash contains high concentrations of sulphur and sulphuric compounds which eventually leach into the groundwater, thus polluting groundwater and drinking water. The thicker the peat layer is and the higher the number of fires in the respective area the more sulphuric compounds will leach into the groundwater. Risk areas for the sulphur loads of the ash are identified. 相似文献
107.
Optimal Locations of Groundwater Extractions in Coastal Aquifers 总被引:1,自引:0,他引:1
A regional water supply management model for coastal aquifers was developed. One of its outcomes is the definition of the
optimized locations for groundwater withdrawal. Such a tool permits the analysis of alternative plans for groundwater extraction
and the sustainable use of water resources in a coastal aquifer subject to saltwater intrusion. The principal components are
the evolutionary optimization and the analytical/numerical simulation models. The optimization technique looks for the best
well locations taking into consideration the economic results and the satisfaction of the societal water demand. However these
two concerns are conditioned by trying to control the saltwater intrusion, i.e., preserving the environmental equilibrium.
The simulation model uses the governing mathematical equations for groundwater movement to find the interface between freshwater
and saltwater. Because of the non-linearity in the system and the possibility of a jumping interface, a security distance
was defined. This is a controlling variable which can be set by the decision makers. The model was applied to a typical case
with interesting results. For example, diagrams showing the relationship between the location of the wells and the security
distance(s) are of importance to the managers. It was also crucial to have an understanding of the tradeoffs between groundwater
withdrawals, positions of the wells from the coast line, and the security distance. The model was also applied to a real case
in order to relate the extractions, distances and artificial recharge (not presented in this paper). 相似文献
108.
Estrogenic personal care products in a greywater reuse system. 总被引:1,自引:0,他引:1
H R Andersen M Lundsbye H V Wedel E Eriksson A Ledin 《Water science and technology》2007,56(12):45-49
The occurrence and fate of parabens in a greywater system was assessed. The potential for removal of residual paraben concentrations in effluent greywater with chlorine dioxide was also investigated. The influent to the greywater plant was characterised by considerable variation, with concentrations from below the detection limit to 40 microg/L and the five commonly used parabens in consumer products were frequently detected. After the biological treatment only two paraben were detected with concentration from 65-120 ng/L. Chlorine dioxide treatment of the biologically treated effluent with dosages down to 0.75 mg/L resulted in more than 97% reduction of all parabens. Formation of the by-product chloroform was insignificant from the chlorine dioxide treatment. 相似文献
109.
110.
Stephen V. Marks 《Bulletin of Indonesian Economic Studies》2004,40(2):227-242
A major challenge for Indonesian economic policy makers is to avoid the recurrence of conditions that could trigger a new economic crisis. One of the important dimensions of this challenge will be to conduct fiscal policy in a way that is sustainable, given the level of interest rates and the rate of growth of the economy. This paper synthesises various approaches to the measurement of fiscal sustainability that have appeared in the economic literature, relates these measures to the fundamental concept of fiscal solvency, and applies the framework to Indonesia over the period 1991–2003. The domestic and foreign debt positions of the central government are treated separately, to capture the influence of exchange rate changes on the relative costs of domestic and foreign borrowing. The empirical analysis indicates that Indonesia has met the fiscal sustainability criterion in recent years, except when the rupiah has depreciated heavily. 相似文献