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   30176篇
  免费   755篇
  国内免费   21篇
财政金融   4347篇
工业经济   1627篇
计划管理   3640篇
经济学   5112篇
综合类   486篇
运输经济   125篇
旅游经济   278篇
贸易经济   4172篇
农业经济   818篇
经济概况   3238篇
水利工程   7067篇
信息产业经济   4篇
邮电经济   38篇
  2021年   204篇
  2020年   311篇
  2019年   414篇
  2018年   1366篇
  2017年   1316篇
  2016年   1009篇
  2015年   380篇
  2014年   600篇
  2013年   2284篇
  2012年   979篇
  2011年   1569篇
  2010年   1238篇
  2009年   1140篇
  2008年   1226篇
  2007年   1445篇
  2006年   786篇
  2005年   794篇
  2004年   828篇
  2003年   601篇
  2002年   494篇
  2001年   484篇
  2000年   461篇
  1999年   448篇
  1998年   461篇
  1997年   401篇
  1996年   358篇
  1995年   378篇
  1994年   341篇
  1993年   376篇
  1992年   418篇
  1991年   391篇
  1990年   337篇
  1989年   340篇
  1988年   305篇
  1987年   309篇
  1986年   289篇
  1985年   367篇
  1984年   395篇
  1983年   369篇
  1982年   335篇
  1981年   327篇
  1980年   325篇
  1979年   306篇
  1978年   293篇
  1977年   249篇
  1976年   252篇
  1975年   256篇
  1974年   195篇
  1973年   220篇
  1972年   184篇
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
61.
62.
本文介绍了网络预算管理是如何有效地克服传统预算方法的缺点,通过有效的控制去解决企业预算管理工作中的实际问题,指出了该预算方法能大大提高工作效率和管理效率。  相似文献   
63.
The primary objective of this project is to identify gaps, whether real or perceived, that hinder effective groundwater management in New Zealand. These gaps show as gaps in information, gaps in implementation, gaps in technological and management tools, and gaps in understanding of fundamental processes. The secondary objective is to propose a management strategy to close the identified gaps. Several methods are used to meet these objectives: surveys distributed to selected staff in each regional council; the review of various written reports; the analysis of land-use databases; and private consultation within each regional council. Results show that groundwater management in New Zealand is generally reactionary with the main gaps being in strategic planning and national guidelines. Most gaps appear to be predominantly information and implementation issues. In some cases there are gaps in the understanding of fundamental processes within an aquifer system, including the long-term effects of land-use on groundwater quality. An adaptive management approach is suggested as a means of closing these gaps.  相似文献   
64.
Recent studies revealed that organic acids such as citric and oxalic acids seemed to be more promising as chemical extracting agents for removal of heavy metals from contaminated sludge, since they are biodegradable and can attain a higher metal extraction efficiency at mildly acidic pH compared to other extracting agents. Results of a lab-scale study on the efficiency of citric acid in the extraction of chromium (Cr), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn) from anaerobically digested sludge, revealed that citric acid seemed to be highly effective in extracting Cr (at 100%), Cu (at 88%), Ni (at 98%) and Zn (at 100%) at pH 2.33, mostly at 5 days leaching time except for Cu and Zn, which are at 1 day and 2 h contact times respectively. Lead removal at the same pH was also high at 95% but at a longer leaching time of 11 days. At pH 3, citric acid seemed to be highly effective in extracting Pb (at 100%) at 1 day leaching time, although higher removals were also attained for Ni (70%) and Zn (80%) at only 2 h leaching time. Chemical speciation studies showed that Cr, Cu and Ni in the sludge sample seem to predominate in residual fractions, while Pb and Zn were found mostly bound to organic and inorganic matter forms, hence the potential of the sludge for land application.  相似文献   
65.
Construction kits have played a significant part in nurturing the growth and development of the minds and manipulation-based skills of children (and adults) in formal and non-formal education settings. These kits have origins rooted in the representation of the built world and now have a diversity of form and function, including technical versions with moving parts. This article examines some of the historically based ideas that lie behind the role that kits may have in terms of physical modelling. The article traces the transformation of kits from simple bricks and blocks into more complicated pieces for space-filling and achieving the transfer of forces and motion. This transformation occurred during the Victorian era when the influence of the ideas of educationalists and, perhaps rather strangely, exponents of early aviation, played major roles in determining the diversity of forms of construction kit and modelled possibilities that are now to be seen in classrooms and homes. The article ends with a review of some of the lessons from the past and present that will need to be considered in relation to concrete modelling in schools for the future. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
66.
In this paper we will analyze the relationship between the value and duration moments of a cash flow and movements in the yield curve. We will show that for changes in the yield curve which can be related to tn , the 1st order changes in the net present value of a cash flow are linearly dependent on the n + lth duration moments, and that the 2nd order changes are dependent on the sum of duration moments of order 2 n + 1 and 2 n + 2. We will use this relationship to tilt tracking portfolios so as to protect them against specific changes in the yield curve.  相似文献   
67.
In this paper, we examine the warrant price and stock price reactions to the announcement of warrant life extensions by REITs. As predicted by option pricing theory, warrant prices increase in response to these extensions. The stocks of REITs making the extension announcements experience average abnormal returns that are not significantly different from zero. Thus, total firm value appears to increase, with the gains accruing primarily to the warrantholders.  相似文献   
68.
69.
1. INTRODUCTIONThemaingoalofthispaperistoexplorethepossibilitytolearnmoreaboutthemechanismofturbulentboundarylayerflowinteractionsanditseffectsoncompliantwallperformance.Therearecertainprerequisiteconditionstofurtherthestudyonthemechanism,i.e.theco…  相似文献   
70.
Conclusion On the basis of data of model tests it can be stated that substantial deformation of the Usoi landslide will not be observed as a result of a surge overtopping it with the proposed parameters.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 8, pp. 38–40, August, 1993.  相似文献   
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