全文获取类型
收费全文 | 5506篇 |
免费 | 98篇 |
国内免费 | 1篇 |
专业分类
财政金融 | 511篇 |
工业经济 | 171篇 |
计划管理 | 471篇 |
经济学 | 593篇 |
综合类 | 43篇 |
运输经济 | 18篇 |
旅游经济 | 28篇 |
贸易经济 | 407篇 |
农业经济 | 151篇 |
经济概况 | 479篇 |
水利工程 | 2732篇 |
信息产业经济 | 1篇 |
出版年
2018年 | 114篇 |
2017年 | 111篇 |
2016年 | 139篇 |
2015年 | 71篇 |
2014年 | 122篇 |
2013年 | 396篇 |
2012年 | 177篇 |
2011年 | 166篇 |
2010年 | 117篇 |
2009年 | 112篇 |
2008年 | 149篇 |
2007年 | 189篇 |
2006年 | 161篇 |
2005年 | 136篇 |
2004年 | 137篇 |
2003年 | 84篇 |
2002年 | 82篇 |
2001年 | 88篇 |
2000年 | 70篇 |
1999年 | 77篇 |
1998年 | 79篇 |
1997年 | 84篇 |
1996年 | 75篇 |
1995年 | 61篇 |
1994年 | 92篇 |
1993年 | 75篇 |
1992年 | 93篇 |
1991年 | 71篇 |
1990年 | 98篇 |
1989年 | 80篇 |
1988年 | 93篇 |
1987年 | 73篇 |
1986年 | 74篇 |
1985年 | 94篇 |
1984年 | 93篇 |
1983年 | 75篇 |
1982年 | 83篇 |
1981年 | 89篇 |
1980年 | 102篇 |
1979年 | 103篇 |
1978年 | 112篇 |
1977年 | 91篇 |
1976年 | 96篇 |
1975年 | 89篇 |
1974年 | 81篇 |
1973年 | 88篇 |
1972年 | 64篇 |
1971年 | 68篇 |
1969年 | 61篇 |
1968年 | 69篇 |
排序方式: 共有5605条查询结果,搜索用时 15 毫秒
1.
J Comas I Rodríguez-Roda M Poch K V Gernaey C Rosen U Jeppsson 《Water science and technology》2006,53(4-5):303-311
Wastewater treatment plant operators encounter complex operational problems related to the activated sludge process and usually respond to these by applying their own intuition and by taking advantage of what they have learnt from past experiences of similar problems. However, previous process experiences are not easy to integrate in numerical control, and new tools must be developed to enable re-use of plant operating experience. The aim of this paper is to investigate the usefulness of a case-based reasoning (CBR) approach to apply learning and re-use of knowledge gained during past incidents to confront actual complex problems through the IWA/COST Benchmark protocol. A case study shows that the proposed CBR system achieves a significant improvement of the benchmark plant performance when facing a high-flow event disturbance. 相似文献
2.
Y S Cao C M Ang K S Raajeevan A K Kiran K C Lai S W Ng I Zulkifli Y L Wah 《Water science and technology》2006,54(8):237-246
This paper analyses the performance of the anaerobic selector (A/O process) in a full-scale activated sludge process receiving mostly industrial sewage discharge (> 60%) in Singapore. In addition to the sludge settleability, enhanced biological phosphorus removal (EBPR) was studied. The sludge volume index (SVI) reduced from 200 to 80 ml g(-1) and foaming was suppressed significantly, indicating the effectiveness of the anaerobic selector in improving sludge settleability. The phosphorus removal efficiency was 66%, and 7.5 mg HAc-COD was consumed per mg PO4(3-) -P removed. In the anaerobic compartment, 31% of the SCOD and 73% of the acetic acid in the settled sewage were removed with PO4(3-) -P release of 14.1 mg PO4(3-)-P l(-1). The linear correlation between PO4(3-) -P release in the anaerobic compartment and PO4(3-) -P uptake in the aerobic compartment indicates that there is about 0.8 mg PO4(3-) -P release in the anaerobic compartment per mg PO34(3-) -P uptake in the aerobic compartment. The fates of volatile fatty acids (VFAs) and its short chain acids (SCAs) in the process were studied and discussed. 相似文献
3.
At the present time, organic solid wastes from industries and agricultural activities are considered to be promising substrates for biogas production via anaerobic digestion. Moreover solids stabilisation is required before reutilization or disposal. Slaughterhouses are among the most important industries in Uruguay and produce 150,000 tons of ruminal content (RC) and 30,000 tons of blood per year. In order to determine the influence of the solids and blood contents, the ammonia inhibition and the inoculum adaptation co-digestion batch tests were performed. A set of experiences with TS concentration of 2.5%, 5% and 7.5% and different ratios of RC/blood were carried out using an inoculum from an UASB reactor. In all experiences fast blood hydrolisation was observed. A higher methane production was detected in the experiences with higher TS content. However, the fraction of solids degradation was lower in these experiences. A plateau in the biogas production was found. The free ammonia level, which was above the reported inhibitory levels, could explain this behaviour. After the inhibition period the biogas production restarted probably due to the biomass acclimatisation to the ammonia. In order to determine the inoculum adaptation a new experiment was performed. The inoculum used was the sludge coming from the first set of experiences. Based upon batch tests a 3.5 m3 pilot reactor was designed and started up. Ammonia inhibition was avoided by the start-up strategy and in two weeks the biogas production was 3.5 m3/d. The VS stabilisation with a solid retention time of 20 days was of 43%. The pilot reactor working at steady state had a TS concentration of 3-4% with a ratio of RC/blood of 10:1 at the entrance. 相似文献
4.
An Imhoff tank was reconstructed into a 250 m3 UASB reactor in order to treat a malting plant wastewater. The UASB was inoculated with sludge from an anaerobic lagoon used for slaughterhouse wastewater treatment. After two months of operation the reactor achieved full load with an HRT of 17 h, a COD removal higher than 80% and a biogas production of 300 m3/day (77% average methane content), with an organic loading rate of 3.6 kgCOD/m3.d (0.24 kgCOD/kgVSS.d). A yield coefficient of 0.09 gVSS/gCODrem was found from a mass balance. The fat present in the inoculated sludge (48 mg/gSSV) did not affect the start up performance. Sludge from the inoculum with high content of fat (270 mg/gSSV), was separated by flotation in the first week of operation. The COD removal efficiency was scarcely influenced by the reactor operation temperature (17-25 degrees C). 相似文献
5.
6.
V. I. Shtykov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》1998,32(8):459-462
Conclusions 1. Use of dewatering systems based on voidless drainage is most effective when dewatering slightly permeable soils in regions
with a deep seasonal frost.
2. Two-story drainage with the upper and lower stories spaced 30 m apart accelerates the discharge of gravitational water
from the arable layer. Results of observations on two-story drainage in experimental-production sections indicated that it
discharges 2 – 3.8 times more water than systematic tubular drainage with an interdrain spacing of 10 m and a 0.2-m thick
three-dimensional filter of a sandy-gravelly mixture.
3. It is recommended to use crushed stone and porous-clay gravel with a fineness of 10 – 20 mm as a filler. In that case,
protection of the drain filler is, as a rule, required only from the intrusion of soil from above during construction in cohesive
soils with a plasticity indexW
p≥7.
4. seepage rate in a voidless drain should be lower than the scouring velocity for the soil in which the voidless drainage
is placed. In the opposite case, it is necessary to lower the grade of the drains or select a filler gradation such that the
seepage rate in the drain be lower than the scouring velocity.
Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 8, pp. 41–43, August, 1998. 相似文献
7.
8.
9.
Fermentative hydrogen production in a system using anaerobic digester sludge without heat treatment as a biomass source. 总被引:3,自引:0,他引:3
Hydrogen produced from anaerobic fermentation of organic matter is a sustainable energy source. Anaerobic hydrogen-producing systems have been typically seeded with heat-treated inocula to eliminate hydrogen-consuming methanogens. This can be both energy- and economically-intensive. In this work, operational parameters were modified to determine if operating a reactor at low pH (5.5) and low SRT (10 hours) would result in a hydrogen-producing system free of methanogens using anaerobic digester sludge with no heat treatment as an inoculum. Initially, the reactor exhibited a hydrogen productivity of approximately 7.9% when fed glucose. After purging was begun with 10% CO2/90% N2, the hydrogen productivity increased to > 20% for the first day. Hydrogenotrophic methanogens then established themselves in the reactor, reducing the hydrogen productivity in the second non-purged phase by 80%. The operational controls examined were not sufficient to eliminate hydrogen-consuming methanogens for longer than approximately one week, and thus further methods must be developed. 相似文献
10.