全文获取类型
收费全文 | 10404篇 |
免费 | 4160篇 |
专业分类
财政金融 | 822篇 |
工业经济 | 1792篇 |
计划管理 | 1274篇 |
经济学 | 3292篇 |
综合类 | 155篇 |
运输经济 | 33篇 |
旅游经济 | 26篇 |
贸易经济 | 3311篇 |
农业经济 | 2596篇 |
经济概况 | 1252篇 |
邮电经济 | 11篇 |
出版年
2024年 | 183篇 |
2023年 | 417篇 |
2022年 | 258篇 |
2021年 | 187篇 |
2020年 | 512篇 |
2019年 | 1003篇 |
2018年 | 794篇 |
2017年 | 839篇 |
2016年 | 753篇 |
2015年 | 667篇 |
2014年 | 751篇 |
2013年 | 1062篇 |
2012年 | 997篇 |
2011年 | 699篇 |
2010年 | 702篇 |
2009年 | 667篇 |
2008年 | 430篇 |
2007年 | 511篇 |
2006年 | 421篇 |
2005年 | 421篇 |
2004年 | 402篇 |
2003年 | 260篇 |
2002年 | 194篇 |
2001年 | 139篇 |
2000年 | 113篇 |
1999年 | 93篇 |
1998年 | 95篇 |
1997年 | 93篇 |
1996年 | 68篇 |
1995年 | 54篇 |
1994年 | 62篇 |
1993年 | 58篇 |
1992年 | 81篇 |
1991年 | 101篇 |
1990年 | 42篇 |
1989年 | 39篇 |
1988年 | 25篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 32篇 |
1982年 | 28篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 13篇 |
1969年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Luby变换(Luby Transform,LT)码作为信道编码应用于电力线通信(Power Line Communication,PLC),可实现电信号的可靠传输。度分布对LT码编译码性能的影响至关重要。为了得到更优的度分布,首先调整二进制指数分布(Binary Exponential Distribution,BED)中的度数比例,获得一种译码性能更优的改进的二进制指数分布(Improved BED,IBED)。然后,根据IBED在冗余度较小时译码成功率高,而冗余度增大后鲁棒孤子分布(Robust Soliton Distribution,RSD)的译码性能表现更佳的特点,通过求和归一化的方式将IBED与RSD两种度分布的优势进行有机结合,提出一种新型二进制鲁棒孤子分布(Binary RSD,BRSD)。仿真结果表明,与其他方法及传统的RSD相比,采用新度分布进行LT编码,可明显降低译码开销,并节约编译码耗时。将新型度分布应用于基于LT码的PLC系统中,能有效地抑制PLC信道中各种噪声对电信号的干扰,并提高通信效率。 相似文献
2.
当前小体积远端射频单元(Remote Radio Unit,RRU)主要是皮站级别的Pico-RRU,其重量和体积仍然难以满足掌上型的要求。为此,采用高集成度的AD9361芯片来实现长期演进(Long Term Evolution,LTE)宽带收发信机功能,配合时钟同步模块、放大器模块和控制接口电路等一起构建低成本的掌上型RRU。主要解决了基于AD9516的时钟同步、低相位噪声设计和高灵敏度接收机设计三个技术难点,成功实现了掌上型、高性能、低成本的设计目标。整个RRU样机尺寸为18 cm×10 cm×2 cm,质量约500 g,量产成本千元以内。测试表明,该RRU下行误差向量幅度(Error Vector Magnitude,EVM)小于3%,优于3GPP要求的8%;10 MHz带宽时上行接收机灵敏度优于3GPP要求的-93.5 dBm。 相似文献
3.
4.
5.
This paper analyzes the issue costs and initial pricing of bonds in the international market. In particular, we investigate the determinants of three components of issue costs: underwriter fee, underwriter spread (the difference between the offering price and the guaranteed price to the issuer), and underpricing (the difference between the market price and the offering price). Total underwriter compensation increases with the bonds' credit risk and maturity, but it is insignificantly related to issue size. Interestingly, underwriters appear to price some issue characteristics directly (by adjusting the fee) and other characteristics indirectly (by setting the guaranteed price). The two compensation components (fee and spread) are negatively related to each other. We provide evidence that this trade-off is consistent with income tax considerations, as well as with two-tier pricing by underwriters. We find no evidence of underpricing. 相似文献
6.
The American Psychological Association Task Force recommended that researchers always report and interpret effect sizes for quantitative data. However, no such recommendation was made for qualitative data. Thus, the first objective of the present paper is to provide a rationale for reporting and interpreting effect sizes in qualitative research. Arguments are presented that effect sizes enhance the process of verstehen/hermeneutics advocated by interpretive researchers. The second objective of this paper is to provide a typology of effect sizes in qualitative research. Examples are given illustrating various applications of effect sizes. For instance, when conducting typological analyses, qualitative analysts only identify emergent themes; yet, these themes can be quantitized to ascertain the hierarchical structure of emergent themes. The final objective is to illustrate how inferential statistics can be utilized in qualitative data analyses. This can be accomplished by treating words arising from individuals, or observations emerging from a particular setting, as sample units of data that represent the total number of words/observations existing from that sample member/context. Heuristic examples are provided to demonstrate how inferential statistics can be used to provide more complex levels of verstehen than is presently undertaken in qualitative research. 相似文献
7.
C. Anthony Di Benedetto 《Journal of Product Innovation Management》2004,21(3):153-153
8.
In rational, efficiently functioning and complete markets, returns on derivative and underlying securities should be perfectly contemporaneously correlated. Due to market imperfections, one of these markets may reflect information faster. The use of high-frequency data and the choice for a small unit time interval to measure these lead-lag relations comes at the cost of some or many missing observations, causing traditional estimators to either under- or overestimate covariances and correlations. We use a new estimator to estimate lead-lag relationships between the cash AEX index, options and futures. We find that futures returns lead both options and cash index returns by approximately 10 minutes. The relationship between options and the cash market is not completely unidirectional. 相似文献
9.
Programme Evaluation with Unobserved Heterogeneity and Selective Implementation: The Mexican PROGRESA Impact on Child Nutrition 总被引:1,自引:0,他引:1
This paper considers the impact of Programa de Educación, Salud y Alimentación ( PROGRESA ), a large Mexican rural anti-poverty programme that had an evaluation sample in which overall treatment was randomly assigned to some communities but not others, on child nutrition. When we examine the impact of PROGRESA based on the presumption of randomized allocations, we find that PROGRESA had no or even a negative impact on child nutrition. However, not all children designated to receive nutritional supplements actually did so. Our preferred estimates – child fixed-effects estimates that control for unobserved heterogeneity that is correlated with access to the supplement – indicate a significantly positive and fairly substantial programme effect of the nutritional supplements on children 12–36 months. They imply an increase of about a sixth in mean growth per year for these children and a lower probability of stunting. Effects are somewhat larger for children from poorer communities but whose mothers are functionally literate. The long-term consequences of these improvements are non-trivial; its impact working through adult height alone could result in a 2.9% increase in lifetime earnings. 相似文献
10.
The Private Finance Initiative (PFI) was launched by the United Kingdom Government in 1992 in order to encourage the private sector in the UK to become more involved in public sector development projects. A key theme of the initiative was that the public should receive 'value for money'. This article investigates the accounting issue as to whether or not the private or the public sector should record any property related to PFI projects on balance sheet. It argues that although both HM Treasury and the Accounting Standards Board (ASB) might agree on the accounting principles, the practical impact is that in order for related properties to stay off the public sector's balance sheet, substantial risk needs to be transferred to the private sector. As a consequence of this, the objective of providing value for money to the public may not be achieved. 相似文献