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   150830篇
  免费   3742篇
  国内免费   26篇
财政金融   25808篇
工业经济   11539篇
计划管理   21739篇
经济学   29084篇
综合类   1458篇
运输经济   958篇
旅游经济   2480篇
贸易经济   23450篇
农业经济   6085篇
经济概况   16838篇
水利工程   14876篇
信息产业经济   7篇
邮电经济   276篇
  2021年   1066篇
  2020年   1800篇
  2019年   2627篇
  2018年   2630篇
  2017年   2704篇
  2016年   3043篇
  2015年   2378篇
  2014年   3787篇
  2013年   16293篇
  2012年   4709篇
  2011年   4483篇
  2010年   3972篇
  2009年   4632篇
  2008年   4170篇
  2007年   3588篇
  2006年   3942篇
  2005年   3869篇
  2004年   3482篇
  2003年   3087篇
  2002年   3089篇
  2001年   2944篇
  2000年   2797篇
  1999年   2689篇
  1998年   2538篇
  1997年   2637篇
  1996年   2464篇
  1995年   2249篇
  1994年   2269篇
  1993年   2238篇
  1992年   2329篇
  1991年   2198篇
  1990年   2030篇
  1989年   1903篇
  1988年   1805篇
  1987年   1827篇
  1986年   1843篇
  1985年   2632篇
  1984年   2536篇
  1983年   2334篇
  1982年   2222篇
  1981年   2157篇
  1980年   2155篇
  1979年   2096篇
  1978年   1901篇
  1977年   1831篇
  1976年   1645篇
  1975年   1499篇
  1974年   1399篇
  1973年   1403篇
  1972年   1100篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
11.
12.
Demand for disclosures on environmental, social, and governance (ESG) issues has increased dramatically. Using corporate political spending disclosures as our setting, we conduct a detailed inquiry of 541 political spending‐related shareholder proposals from 2004 to 2012 to highlight the role of shareholder activism as a mechanism to motivate ESG disclosure. Unlike earlier studies, we examine both proposals that went to a vote and proposals that were withdrawn by the activist, allowing us to assess more comprehensively the success of shareholder activism. We find that 20 percent of firms targeted by disclosure proposals begin disclosing in the subsequent year, although implementation rates vary by proposal type—8 percent for proposals subject to a vote versus 56 percent for proposals withdrawn. The sponsor is also important: unions and public pension funds are less likely than other activists to target firms with agency problems and are less successful in having proposals withdrawn, and the implementations they obtain are viewed more negatively by the broader investor base. Our findings highlight shareholder proposals as one mechanism through which investors can successfully express their preferences for corporate disclosure policies. Given activists' long‐standing interest in environmental and social disclosure policies, we believe our findings generalize to a broader set of ESG disclosures.  相似文献   
13.
Dreissenid mussel veligers compose a substantial component of pelagic biomass in the Great Lakes, yet their dynamics are poorly understood. To evaluate seasonal, spatial, and inter-annual variation in veliger density, we used a 64-μm mesh plankton net (2008, 2013–2016) and a 153-μm mesh plankton net (2007–2016) to collect dreissenid veligers at nearshore (15–25?m depth), transitional (45?m) and offshore (93–110?m) sites in southeast Lake Michigan during March–December. We also evaluated trends in density of recently settled mussels relative to veliger abundance and the density of the standing stock of adult mussels. Veliger density peaked during both summer and fall at all sites, but peak densities in summer were generally higher nearshore, whereas peak densities in the fall were generally higher offshore. The density of veligers in the 153-μm net was overall 28% of that in the 64-μm net, but there was high variability in this comparison among months. Smaller veligers were much more abundant in the 64-μm net, but there was little difference in the size distribution and abundance between nets for the 210–300?μm size classes. Thus, the 153-μm net could still be a useful tool for assessing density trends of larger veligers just prior to their settlement. Newly settled mussels (≤2?mm) were most abundant in summer or fall at the nearshore and offshore sites but were nearly absent at the transitional site despite the high density of veligers there. Factors other than veliger density must play an important role in mussel recruitment.  相似文献   
14.
15.
16.
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   
17.
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   
18.
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   
19.
In this paper, we consider the feasibility of constructing online sentiment indices, using large amounts of media data, as an alternative to the conventional survey method used to create the consumer confidence index in South Africa. A clustering framework is adopted to provide an indication of possible candidate sentiment indices constructed from a combination of different text sources and dictionaries that best mimic the traditional survey-based consumer confidence index from the South African Bureau for Economic Research (BER). The results conclude that it is possible to create an index using sentiment analysis using online editorial data that does resemble the BER’s consumer confidence index. The different media-based sentiment indices (MSI) show a significant level of correlation and co-movement with the BER’s CCI. Impulse responses and cross-correlation functions indicate that the MSI could potentially lead the survey-based method up to two quarters. Furthermore, Granger-causality tests show that the media-based indices are good predictors of future consumer confidence index values. The results provide motivation for further study on the use of sentiment-based techniques and online media data sources to track consumer confidence within an emerging market such as South Africa.  相似文献   
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