首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   14576篇
  免费   306篇
  国内免费   73篇
财政金融   1568篇
工业经济   734篇
计划管理   1880篇
经济学   2153篇
综合类   543篇
运输经济   58篇
旅游经济   84篇
贸易经济   1505篇
农业经济   602篇
经济概况   1790篇
水利工程   4022篇
信息产业经济   2篇
邮电经济   14篇
  2023年   90篇
  2022年   136篇
  2021年   237篇
  2020年   250篇
  2019年   233篇
  2018年   316篇
  2017年   370篇
  2016年   318篇
  2015年   253篇
  2014年   394篇
  2013年   887篇
  2012年   789篇
  2011年   999篇
  2010年   806篇
  2009年   635篇
  2008年   721篇
  2007年   730篇
  2006年   712篇
  2005年   603篇
  2004年   359篇
  2003年   266篇
  2002年   250篇
  2001年   279篇
  2000年   221篇
  1999年   223篇
  1998年   216篇
  1997年   172篇
  1996年   159篇
  1995年   160篇
  1994年   129篇
  1993年   134篇
  1992年   135篇
  1991年   130篇
  1990年   117篇
  1989年   130篇
  1988年   118篇
  1987年   120篇
  1986年   113篇
  1985年   108篇
  1984年   126篇
  1983年   106篇
  1982年   100篇
  1981年   109篇
  1980年   118篇
  1979年   109篇
  1978年   98篇
  1977年   89篇
  1976年   95篇
  1973年   82篇
  1972年   88篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Upflow anaerobic sludge blanket (UASB) methane fermentation treatment of cow manure that was subjected to screw pressing, thermal treatment and subsequent solid-liquid separation was studied. Conducting batch scale tests at temperatures between 140 and 180 degrees C, the optimal temperature for sludge settling and the color suppression was found to be between 160-170 degrees C. UASB treatment was carried out with a supernatant obtained from the thermal treatment at the optimal conditions (170 degrees C for 30 minutes) and polymer-dosed solid-liquid separation. In the UASB treatment with a COD(Cr) loading of 11.7 kg/m3/d and water temperature of 32.2 degrees C, the COD(Cr) level dropped from 16,360 mg/L in raw water to 3,940 mg/L in treated water (COD(Cr), removal rate of 75.9%), and the methane production rate per COD(Cr) was 0.187 Nm3/kg. Using wastewater thermal-treated at the optimal conditions, also a methane fermentation treatment with a continuously stirred tank reactor (CSTR) was conducted (COD(Cr) in raw water: 38,000 mg/L, hydraulic retention time (HRT): 20 days, 35 degrees C). At the COD(Cr) loading of 1.9 kg/m3/d, the methane production rate per COD(Cr), was 0.153 Nm3/kg. This result shows that UASB treatment using thermal pre-treatment provides a COD(Cr), loading of four times or more and a methane production rate of 1.3 times higher than the CSTR treatment.  相似文献   
2.
国家行为与产权:一个新制度经济学的分析框架   总被引:1,自引:0,他引:1  
早期的产权理论侧重于微观层次的分析,较少考虑中观(利益集团)及宏观层次(国家)对产权结构形成的影响及不同层次产权的交互作用的机制。文章从新制度经济学关于国家的定义入手,通过对个体权力与国家、集体行动与国家以及法治化社会与国家的三个层次的分析,提出建立产权制度分析的国家模型,从而论证国家与产权制度变迁的关系。  相似文献   
3.
4.
The biochemical composition can be seen as a good indicator of both the biodegradability and the methane potential of a given waste. The work presented here is an attempt to elaborate a typology of wastes and to compare it to the anaerobic degradation characteristics. The first data indicate that there is a link between the ligno-cellulosic content of the waste and the biodegradability. When dealing with application to anaerobic digestion processes, having a tool to predict the ability of the waste to be degraded could be of the greatest interest for preventing failures, estimating biogas production, methane content, or for the management of co-digestion processes.  相似文献   
5.
This paper focuses on the development of a theoretical scheme describing the transformation of primary incomes into end consumption and savings in the Russian economy. This scheme is basically a system of interrelated tables reflecting the distribution of primary incomes across the institutional sectors and their further reallocation and use. The scheme makes allowances for the specific features of the Russian economy and existing statistics. In terms of methodology, it is coordinated with the interindustry balance in current buyer prices and, from the theoretical standpoint, describes the connection between Quadrant II and Quadrant III of the balance. Therefore, the proposed system of tables is treated in the paper as Quadrant IV of the interindustry balance. The theoretical scheme is used by the authors as a necessary basis for constructing an empirical model of the relationship between value added and end product, which will be published in the next issue of this journal.  相似文献   
6.
The speed with which communist China has embuaced markets has surprised Western analysis and observers, But Chinese economic progress will founder in corruption and inefficiency, argues Professor Steven Cheung of the university of Hong Kong, untess she insitutes a well-defined system of private property rights to safeguord investment and stimulate trade.  相似文献   
7.
8.
9.
Four selected azo dyes (acid orange 6, acid orange 7, methyl orange and methyl red) were completely decolourised in the presence of anaerobic granular sludge, while only methyl red was degraded in aerobic conditions using a conventional activated sludge. Additional experiments with culture broth devoid of cells showed that anaerobic decolourisation of azo dyes was performed by extracellular reducing agents produced by anaerobic bacteria. This was further confirmed by abiotic experiments with sulphide and NADH. The presence of redox mediators such as riboflavin led to dramatic acceleration of the anaerobic biodecolourisation process. The azo dye reduction products were found to be sulphanilic acid and 4-aminoresorcinol for acid orange 6; sulphanilic acid and 1-amino-2-naphthol for acid orange 7; N,N-dimethyl-1,4-phenylenediamine and sulphanilic acid for methyl orange; and N,N-dimethyl-1,4-phenylenediamine and anthranilic acid for methyl red. Anaerobic toxicity assays showed that the azo dyes were more toxic than their breakdown products (aromatic amines), except 1-amino-2-naphthol. In the presence of activated sludge, only anthranilic acid was completely mineralised while sulphanilic acid was persistent. 4-aminoresorcinol, 1-amino-2-naphthol and N,N-dimethyl-1,4-phenylenediamine underwent autooxidation in aerobic conditions yielding coloured polymeric products. On the contrary, in the presence of granular methanogenic sludge, 4-aminoresorcinol, 1-amino-2-naphthol and anthranilic acid were quantitatively methanised, sulphanilic acid was partially (70%) mineralised while N,N-dimethyl-1,4-phenylenediamine was only demethylated producing 1,4-phenylenediamine as an end product.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号