全文获取类型
收费全文 | 22192篇 |
免费 | 567篇 |
国内免费 | 64篇 |
专业分类
财政金融 | 3154篇 |
工业经济 | 1439篇 |
计划管理 | 3258篇 |
经济学 | 3896篇 |
综合类 | 765篇 |
运输经济 | 109篇 |
旅游经济 | 219篇 |
贸易经济 | 2494篇 |
农业经济 | 1030篇 |
经济概况 | 3023篇 |
水利工程 | 3376篇 |
邮电经济 | 60篇 |
出版年
2022年 | 181篇 |
2021年 | 288篇 |
2020年 | 336篇 |
2019年 | 335篇 |
2018年 | 335篇 |
2017年 | 449篇 |
2016年 | 406篇 |
2015年 | 386篇 |
2014年 | 516篇 |
2013年 | 1557篇 |
2012年 | 1021篇 |
2011年 | 1309篇 |
2010年 | 1182篇 |
2009年 | 984篇 |
2008年 | 1086篇 |
2007年 | 1081篇 |
2006年 | 1148篇 |
2005年 | 1004篇 |
2004年 | 612篇 |
2003年 | 437篇 |
2002年 | 413篇 |
2001年 | 379篇 |
2000年 | 297篇 |
1999年 | 385篇 |
1998年 | 296篇 |
1997年 | 267篇 |
1996年 | 255篇 |
1995年 | 227篇 |
1994年 | 215篇 |
1993年 | 245篇 |
1992年 | 211篇 |
1991年 | 206篇 |
1990年 | 174篇 |
1989年 | 183篇 |
1988年 | 157篇 |
1987年 | 149篇 |
1986年 | 137篇 |
1985年 | 254篇 |
1984年 | 244篇 |
1983年 | 225篇 |
1982年 | 203篇 |
1981年 | 200篇 |
1980年 | 210篇 |
1979年 | 204篇 |
1978年 | 165篇 |
1977年 | 175篇 |
1976年 | 150篇 |
1975年 | 134篇 |
1974年 | 125篇 |
1973年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Factors affecting the activity of anammox bacteria during start up in the continuous culture reactor. 总被引:5,自引:0,他引:5
Factors affecting cultivation of extremely slow-growing bacteria (anaerobic ammonium oxidiser, doubling time 11 days) were investigated by using upflow anaerobic sludge blanket (UASB) reactors which can maintain high solid retention time. The effects of concentrations of DO, free ammonia (FA), and nitrite on activation of anammox activity were tested during the start-up period. The reactor was inoculated with granular sludge collected from a full-scale UASB reactor used for treating brewery wastewater, and sludge from a piggery wastewater treatment plant and rotating biological contactor treating sewage. Results of continuous operation showed that concentrations of DO, free ammonia (FA) and nitrite in the reactors played a key role in stimulating the anammox activity during start-up period. It is crucial to keep DO below 0.2 ppm, FA below 2 mg/L and nitrite nitrogen below 35 mg/L to cultivate anammox cells in the continuous bioreactor. When the levels of DO, FA and nitrite in the influent were controlled at less than the inhibition levels, the anammox activity increased gradually in the anaerobic condition. Addition of hydrogen sulphide into the reactor enhanced anammox activity in the continuous culture. Through the SEM, TEM and FISH analysis, anammox bacteria were detected in the granular sludge after 3 months of continuous operation. 相似文献
92.
Four experiments of coagulation and flocculation were conducted to investigate the characteristics of colloidal silica removal in a high-tech industrial wastewater treatment plant for reclamation and reuse of the effluent. Experimental results illustrated that poly-aluminium chloride (PACl) showed higher performances on colloidal silica removal than alum. Interestingly, the two coagulants demonstrated the same capacity on silica removal. The specific silica removal capacity was approximately 0.135 mg SiO2/mg Al2O3 when the dosage of coagulants was in the range 30-150 mg/L Al2O3. In addition, the silica was reduced significantly at the condition of pH above 8. Experimental data implied that precipitation of aluminium flocs was the major mechanism for colloid silica removal in PACl and alum coagulation, besides, charge adsorption was also important for improving removal efficiency. Moreover, the addition of polyacrylic acid (PAA) as a flocculant could slightly advance silica removal in the PACl coagulation. The combined PACl/PAA/flocs coagulation was effective for the removal of colloidal silica, soluble COD, and turbidity and also suitable as a pretreatment unit in wastewater reclamation and reuse processes. 相似文献
93.
The applicability of fluidised-bed reactor (FBR) based sulphate reducing bioprocess was investigated for the treatment of iron containing (40-90 mg/L) acidic wastewater at 65 degrees C. The FBR was inoculated with sulphate-reducing bacteria (SRB) originally enriched from a hot mining environment. Ethanol or acetate was supplemented as carbon and electron source for the SRB. A rapid startup with 99.9, 46 and 29% ethanol, sulphate and acetate removals, in respective order, was observed even after 6 days. Iron was almost completely removed with a rate of 90 mg/L.d. The feed pH was decreased gradually from its initial value of 6 to around 3.7 during 100 days of operation. The wastewater pH of 4.3-4.4 was neutralised by the alkalinity produced in acetate oxidation and the average effluent pH was 7.8 +/- 0.8. Although ethanol removal was complete, acetate accumulated. Later the FBR was fed with acetate only. Although acetate was present in the reactor for 295 days, its oxidation rates did not improve, which may be due to low growth rate and poor attachment ability of acetate oxidising SRB. Hence, the oxidation of acetate is the rate limiting step in the sulphidogenic ethanol oxidation by the thermophilic SRB. 相似文献
94.
中、美流域水资源管理机制比较 总被引:1,自引:0,他引:1
萨斯奎哈纳流域管理委员会的委员由美国联邦政府和其流域内纽约、宾夕法尼亚、马里兰三个州的代表组成。在《萨斯奎哈纳流域协议》(联邦法律)的授权下。该委员会有权处理流域内的任何水资源问题。相比之下.国内的流域机构没有流域内省(自治区、直辖市)的代表作为委员,流域水行政管理的职能还不能满足流域内社会经济发展的实际需要。因此,形成和完善以流域为单元的水资源管理法律框架是有效保护、开发和管理流域水资源的基础,建立包括流域内省(自治区、直辖市)为代表的流域管理委员会可以提供一个有代表性、长效的管理机构。流域管理委员会应着重加强流域水资源保护、开发和管理的综合规划,注重流域的公共利益和社会服务.重视水质、湿地、洄游鱼类、珍稀物种和文化遗产保护.切实担当起河流代言人和保护神的角色。 相似文献
95.
J H J Hulskotte H A C Denier van der Gon A J H Visschedijk M Schaap 《Water science and technology》2007,56(1):223-231
In this article we show that brake wear from road traffic vehicles is an important source of atmospheric (particulate) copper concentrations in Europe. Consequently, brake wear also contributes significantly to deposition fluxes of copper to surface waters. We estimated the copper emission due to brake wear to be 2.4 kiloton per year. For comparison, the official database for Europe (without brake wear) totals 2.6 kiloton per year. In Western Europe the brake wear emissions dominate the total emission of copper. Using the spatially resolved emission data, copper distributions over Europe were calculated with the LOTOS-EUROS model. Without brake wear the model underestimates observed copper concentrations by a factor of 3, which is in accordance with other studies. Including the brake wear emissions largely removes the bias. We find that 75% of the atmospheric copper input in the North Sea may be due to brake wear. We estimate that about 25% of the total copper input in the Dutch part of the North Sea stems from brake wear. Although the estimated brake wear copper emission is associated with a large uncertainty, it significantly improves our understanding of the copper cycle in the environment. 相似文献
96.
97.
98.
周立 《广东金融学院学报》2003,18(3):13-23
渐进转轨过程中,政府面临许多挑战,因此保持并强化国家能力十分必要.为了保持国家能力,中国政府加强了对金融业的控制,促使其行使财政职能.这体现为,在资源动员过程中,金融业具有税收替代功能;在资源配置过程中,金融业具有财政替代功能.由此,金融资源被异化为中央和地方政府的财政资金,金融业异化为"第二财政".作为"第二财政"的金融业,发挥着提供铸币收入、平衡预算赤字、替代财政投资、平衡地区差距、替代财政补贴等多项财政功能.这种替代既有逻辑上的必然性--渐进改革的必然要求,也有其现实上的不合理性--财政功能和金融功能错位.只有进行金融制度建设,促进财政到位,才能使得金融归位. 相似文献
99.
100.
An applicability of quinone biomarker to the analysis of hillslope runoff was investigated. At first, quinone profiles of three streams as well as a hillslope runoff in a forested headwater catchment were compared. The quinone composition of hillslope runoff differed from others. Moreover, there were remarkable differences in quinone profile of hillslope runoff under different rainfall conditions. Then, the behavior of quinone biomarker during the increase and decrease of hillslope runoff after a rainfall event was examined. The fractional changes in Q-9 (H2), Q-10 (H2), Q-11, MK-6 and MK-10 suggested the effect of interflow. 相似文献