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   159361篇
  免费   4152篇
  国内免费   211篇
财政金融   26158篇
工业经济   12020篇
计划管理   23015篇
经济学   30079篇
综合类   2454篇
运输经济   1050篇
旅游经济   2547篇
贸易经济   24341篇
农业经济   6547篇
经济概况   18367篇
水利工程   16893篇
信息产业经济   11篇
邮电经济   242篇
  2021年   1458篇
  2020年   2119篇
  2019年   2818篇
  2018年   2821篇
  2017年   3011篇
  2016年   3261篇
  2015年   2739篇
  2014年   4204篇
  2013年   16880篇
  2012年   5500篇
  2011年   5553篇
  2010年   4952篇
  2009年   5342篇
  2008年   5017篇
  2007年   4328篇
  2006年   4671篇
  2005年   4495篇
  2004年   3576篇
  2003年   3226篇
  2002年   3253篇
  2001年   3037篇
  2000年   2806篇
  1999年   2726篇
  1998年   2484篇
  1997年   2585篇
  1996年   2434篇
  1995年   2213篇
  1994年   2227篇
  1993年   2188篇
  1992年   2250篇
  1991年   2094篇
  1990年   1977篇
  1989年   1880篇
  1988年   1784篇
  1987年   1792篇
  1986年   1791篇
  1985年   2577篇
  1984年   2473篇
  1983年   2264篇
  1982年   2141篇
  1981年   2082篇
  1980年   2095篇
  1979年   2009篇
  1978年   1847篇
  1977年   1815篇
  1976年   1620篇
  1975年   1472篇
  1974年   1393篇
  1973年   1401篇
  1972年   1098篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Hypoxia formation and breakdown were tracked during 2015 in Muskegon Lake estuary at multiple locations, and five years (2011–2015) of time-series buoy observatory data were evaluated for the effect of episodic wind-events on lake mixing. Bi-weekly water temperature and dissolved oxygen (DO) profiles at four locations revealed that hypoxia occurred at all sites and persisted for 2–3 months during summer 2015. On one date in late-summer, up to 24% of the lake’s volume was estimated to be mildly hypoxic (DO < 4 mg L?1) as defined by lake sturgeon requirements. Patterns of wind speed and water column stability in late spring indicated that high winds and low stability delayed the onset of hypoxia while in late summer low winds and high stability delayed degradation of hypoxia. Wind speeds appear to play a great role in the interannual variability of stratification and subsequent hypoxia. Water temperature and DO profiles taken before and after one mid-summer mixing event (wind speed >7.7 m s?1 for 10 h), indicated that while the wind was unable to completely mix the entire water column, it deepened the epilimnion by ~1.5 m and sheared a thin layer from the upper hypolimnion. By entraining internally loaded nutrients, such episodic wind-events may initiate and sustain algal blooms in nutrient limited surface waters. Quantifying the variable role of wind and mixing events will be key to integrating limnological processes into climate models of the future.  相似文献   
12.
Various aspects of sustainable development and quality of life are considered, including the impact of standardization. Particular attention is paid to the study of the role played by standardization in improving environmental protection. In this connection the significance of standardization is shown as a factor of improving the technological potential of an enterprise and the quality of life. Various approaches to methods for assessing the effective impact of standardization on the quality of life are analyzed.  相似文献   
13.
A growing literature finds evidence that flood risk salience varies over time, spiking directly following a flood and then falling off individuals' cognitive radar in the following years. In this article, we provide new evidence of salience exploiting a hurricane cluster impacting Florida that was preceded and followed by periods of unusual calm. Utilizing residential property sales across the state from 2002 through 2012, our main estimate finds a salience impact of ?8%, on average. The salience effect persists when we base estimation only on spatial variation in prices to limit confounding from other simultaneous changes due to shifting hedonic equilibria over time. These effects range from housing prices decreases of 5.4–12.3% depending on the year of sale. Understanding flood risk salience has important implications for flood insurance and disaster policy, the benefits transfer literature, and, more broadly, our understanding of natural disaster resilience. JEL Classification: Q51, Q54, R21  相似文献   
14.
Water Resources Management - A number of models have been developed to simulate seawater intrusion in coastal aquifers, which differ in the accuracy level and computational demands, based on the...  相似文献   
15.
16.
17.
The prospect for electric vehicles as a climate change solution hinges on their ability to reduce gasoline consumption. But this depends on how many miles electric vehicles are driven and on how many miles would have otherwise been driven in gasoline-powered vehicles. Using newly-available U.S. nationally representative data, this paper finds that electric vehicles are driven considerably fewer miles per year on average than gasoline-powered vehicles. The difference is highly statistically significant and holds for both all-electric and plug-in hybrid vehicles, for both single- and multiple-vehicle households, and both inside and outside California. The paper discusses potential explanations and policy implications. Overall, the evidence suggests that today’s electric vehicles imply smaller environmental benefits than previously believed.  相似文献   
18.
This study quantifies the moral hazard effect of health insurance on medical expenditure by estimating a dynamic model of within‐year medical care consumption that allows for insurance selection, endogenous health transitions, and individual uncertainty about medical care prices in an environment where insurance has nonlinear cost‐sharing features. The results suggest that moral hazard accounts for 53.1%, on average, of total annual medical expenditure when insured. This estimate is significantly different, and generally larger, than that produced by an alternative model that is representative of the annual medical care decision‐making models commonly found in the literature.  相似文献   
19.
20.
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