全文获取类型
收费全文 | 27794篇 |
免费 | 708篇 |
国内免费 | 5篇 |
专业分类
财政金融 | 4030篇 |
工业经济 | 1609篇 |
计划管理 | 3922篇 |
经济学 | 5383篇 |
综合类 | 244篇 |
运输经济 | 176篇 |
旅游经济 | 341篇 |
贸易经济 | 3768篇 |
农业经济 | 1140篇 |
经济概况 | 2595篇 |
水利工程 | 5222篇 |
信息产业经济 | 3篇 |
邮电经济 | 74篇 |
出版年
2021年 | 222篇 |
2020年 | 337篇 |
2019年 | 537篇 |
2018年 | 655篇 |
2017年 | 658篇 |
2016年 | 679篇 |
2015年 | 447篇 |
2014年 | 685篇 |
2013年 | 2635篇 |
2012年 | 1101篇 |
2011年 | 1057篇 |
2010年 | 802篇 |
2009年 | 873篇 |
2008年 | 937篇 |
2007年 | 958篇 |
2006年 | 952篇 |
2005年 | 818篇 |
2004年 | 760篇 |
2003年 | 538篇 |
2002年 | 486篇 |
2001年 | 577篇 |
2000年 | 494篇 |
1999年 | 469篇 |
1998年 | 512篇 |
1997年 | 474篇 |
1996年 | 469篇 |
1995年 | 411篇 |
1994年 | 406篇 |
1993年 | 395篇 |
1992年 | 410篇 |
1991年 | 425篇 |
1990年 | 384篇 |
1989年 | 303篇 |
1988年 | 318篇 |
1987年 | 316篇 |
1986年 | 284篇 |
1985年 | 402篇 |
1984年 | 394篇 |
1983年 | 370篇 |
1982年 | 330篇 |
1981年 | 330篇 |
1980年 | 352篇 |
1979年 | 331篇 |
1978年 | 284篇 |
1977年 | 231篇 |
1976年 | 249篇 |
1975年 | 206篇 |
1974年 | 202篇 |
1973年 | 202篇 |
1972年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
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
13.
Anaerobic co-digestion of organic wastes from households, slaughterhouses and meat processing industries was optimised in a half technical scale plant. The plant was operated for 130 days using two different substrates under organic loading rates of 10 and 12 kgCOD.m(-3).d(-1). Since the substrates were rich in fat and protein components (TKN: 12 g.kg(-1) the treatment was challenging. The process was monitored on-line and in the laboratory. It was demonstrated that an intensive and stable co-digestion of partly hydrolysed organic waste and protein rich slaughterhouse waste can be achieved in the balance of inconsistent pH and buffering NH4-N. In the first experimental period the reduction of the substrate COD was almost complete in an overall stable process (COD reduction >82%). In the second period methane productivity increased, but certain intermediate products accumulated constantly. Process design options for a second digestion phase for advanced degradation were investigated. Potential causes for slow and reduced propionic and valeric acid degradation were assessed. Recommendations for full-scale process implementation can be made from the experimental results reported. The highly loaded and stable codigestion of these substrates may be a good technical and economic treatment alternative. 相似文献
14.
15.
The Woodman Point Wastewater Treatment Plant (WWTP) in Western Australia has experienced two separate problems causing avoidable maintenance costs: the build-up of massive struvite (MgNH4PO4. 6H2O) scaling downstream of the anaerobic digester and the formation of hydrogen sulfide (H2S) levels in the digester gas to levels that compromised gas engine operation and caused high operating costs on the gas scrubber. As both problems hang together with a chemical imbalance in the anaerobic digester, we decided to investigate whether both problems could be (feasibly and economically) addressed by a common solution (such as dosing of iron solutions to precipitate both sulfide and phosphate), or by using separate approaches. Laboratory results showed that, the hydrogen sulfide emission in digesters could be effectively and economically controlled by the addition of iron dosing. Slightly higher than the theoretical value of 1.5 mol of FeCl3 was required to precipitate 1 mol of dissolved sulfide inside the digester. Due to the high concentration of PO4(3-) in the digested sludge liquor, significantly higher iron is required for struvite precipitation. Iron dosing did not appear an economic solution for struvite control via iron phosphate formation. By taking advantage of the natural tendency of struvite formation in the digester liquid, it is possible to reduce the risk of struvite precipitation in and around the sludge-dewatering centrifuge by increasing the pH to precipitate struvite out before passing through the centrifuge. However, as the Mg2+/PO4(3-) molar ratio in digested sludge was low, by increasing the pH alone (using NaOH) the precipitation of PO4(3-) was limited by the amount of cations (Ca2+ and Mg2+) available in the sludge. Although this would reduce struvite precipitation in the centrifuge, it could not significantly reduce PO4(3-) recycling back to the plant. For long-term operation, maximum PO4(3-) reduction should be the ultimate aim to minimise PO4(3-) accumulation in the plant. Magnesium hydroxide liquid (MHL) was found to be the most cost-effective chemical to achieve this goal. It enhanced struvite precipitation from both, digested sludge and centrate to the point where more than 95% PO4(3-) reduction in the digested sludge was achieved. 相似文献
16.
Managing sewerage systems is a highly complex task due to the dynamic nature of the facilities. Their performance strongly depends on the know-how applied by the operators. In order to define optimal operational settings, two decision support tools based on mathematical models have been developed. Moreover, easy-to-use interfaces have been created as well, aiding operators who presumably do not have the necessary skills to use modelling software. The two developed programs simulate the behaviour of both wastewater treatment plants (WWTP) and sewer network systems, respectively. They have essentially the same structure, including raw data management and statistical analysis, a simulation layer using the application programming interface of the applied software and a layer responsible for the representation of the obtained results. Four user modes are provided in the two software including the simulation of historical data using the applied and novel operational settings, as well as modes concerning prediction of possible operation periods and updates. Concerning the WWTP software, it was successfully installed in Nantes (France) in June 2004. Moreover, the one managing sewer networks has been deployed in Saint-Malo (France) in January 2005. This paper presents the structure of the developed software and the first results obtained during the commissioning phase. 相似文献
17.
Fares A. Ghandour Paulina Swartz Heidi M. Grenek Edward B. Roberts 《Technology Analysis & Strategic Management》2004,16(4):435-455
The number of firms using alliances as part of their corporate venturing or market entry strategies has surged over the past decade. Three common reasons cited for pursuing alliances are technology convergence, market access and alliance partners' complementary resources. This paper contrasts the alliance strategies of HP and IBM, two major competitors in electronic services (i.e. Internet-based 'e- service') businesses, using the Familiarity Matrix as a display tool to portray the strategies. Whereas the HP strategy is to attempt to establish its technology infrastructure as the standard e-services infrastructure on the Internet, IBM aims to position its IBM Global Services, rather than its technology, at the center of this ecosystem. 相似文献
18.
This paper examines monthly wage data collected by the Agro Economic Survey from seven villages in the Cimanuk River Basin of West Java, where data on agricultural and non-agricultural wages and prices of nine essential commodities were collected twice monthly between 1977 and 1983. Movements in money wages deflated by both the rice price and a weighted index of basic commodities are analysed in detail and differences between lowland and upland villages are discussed. 相似文献
19.
O Baeder-Bederski M Dürr M Borneff-Lipp P Kuschk R Netter G Daeschlein P Mosig R A Müller 《Water science and technology》2005,51(9):205-212
Different types of constructed wetlands in a pilot-plant system were fed with identical municipal waste water to compare the sanitisation process in two-stage systems. With combinations of a vertical and a horizontal flow filter an E. coli reduction of 5 log10 with an E. coli influent concentration of 10(7) MPN/100 ml was achieved. Using different filter materials in each stage the total performance of the two-stage system was independent from the sequence of these materials. However, using coarser filter material in the first stage makes the filter less prone to clogging and is thus the preferential option with regard to operational reliability. 相似文献
20.
A multi-channel continuous toxicity monitoring system developed in our laboratory, based on two-stage mini-bioreactors, was successfully implemented in the form of computer-based data acquisition. The multi-channel system consists of a series of a two-stage minibioreactor systems connected by a fiber optic probe to a luminometer, and uses genetically engineered bioluminescent bacteria for the detection of the potential toxicity from the soluble chemicals. This system can be stably and continuously operated due to the separation of the culture reactor from the test reactor and accomplish easy and long-term monitoring without system shut down by abrupt inflows of severe polluting chemicals. Four different recombinant bioluminescent bacteria were used in different channels so that the modes of the samples toxicities can be reasonably identified and evaluated based upon the response signature of each channel. The bioluminescent signatures were delivered from four channels by switching one at once, while the data is automatically logged to an IBM compatible computer. We also achieved the enhancement of the system through the manipulation of the dilution rate and the use of thermo-lux fusion strains. Finally, this system is now being implemented to a drinking water reservoir and river for remote sensing as an early warning system. 相似文献