全文获取类型
收费全文 | 149565篇 |
免费 | 3731篇 |
国内免费 | 25篇 |
专业分类
财政金融 | 25464篇 |
工业经济 | 11541篇 |
计划管理 | 21495篇 |
经济学 | 28817篇 |
综合类 | 1438篇 |
运输经济 | 951篇 |
旅游经济 | 2484篇 |
贸易经济 | 23311篇 |
农业经济 | 6046篇 |
经济概况 | 16786篇 |
水利工程 | 14725篇 |
信息产业经济 | 8篇 |
邮电经济 | 255篇 |
出版年
2021年 | 1067篇 |
2020年 | 1797篇 |
2019年 | 2617篇 |
2018年 | 2632篇 |
2017年 | 2679篇 |
2016年 | 3043篇 |
2015年 | 2362篇 |
2014年 | 3786篇 |
2013年 | 16294篇 |
2012年 | 4665篇 |
2011年 | 4432篇 |
2010年 | 3955篇 |
2009年 | 4626篇 |
2008年 | 4117篇 |
2007年 | 3541篇 |
2006年 | 3903篇 |
2005年 | 3821篇 |
2004年 | 3417篇 |
2003年 | 3049篇 |
2002年 | 3076篇 |
2001年 | 2909篇 |
2000年 | 2743篇 |
1999年 | 2667篇 |
1998年 | 2497篇 |
1997年 | 2595篇 |
1996年 | 2431篇 |
1995年 | 2231篇 |
1994年 | 2245篇 |
1993年 | 2209篇 |
1992年 | 2304篇 |
1991年 | 2156篇 |
1990年 | 2009篇 |
1989年 | 1902篇 |
1988年 | 1781篇 |
1987年 | 1804篇 |
1986年 | 1815篇 |
1985年 | 2615篇 |
1984年 | 2481篇 |
1983年 | 2310篇 |
1982年 | 2174篇 |
1981年 | 2116篇 |
1980年 | 2119篇 |
1979年 | 2039篇 |
1978年 | 1872篇 |
1977年 | 1822篇 |
1976年 | 1644篇 |
1975年 | 1478篇 |
1974年 | 1396篇 |
1973年 | 1401篇 |
1972年 | 1100篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
41.
Thomas S. Lowry John C. Bright Murray E. Close Christina A. Robb Paul A. White Stewart G. Cameron 《国际水资源开发杂志》2003,19(4):579-592
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
42.
43.
The paper examines the relationship between transitory terms‐of‐trade shocks and private saving. Using a model allowing for nonseparability between the consumption of tradables and nontradables, the paper estimates the intertemporal elasticity of substitution while accounting for the intratemporal elasticity of substitution between the consumption of tradables and nontradables. Empirical analysis of data for five industrial countries indicates that in response to transitory terms‐of‐trade shocks, intertemporal substitution of consumption and intratemporal substitution of consumption between tradables and nontradables both have large effects on private saving. 相似文献
44.
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
45.
46.
We consider the problem of estimating a probability density function based on data that are corrupted by noise from a uniform distribution. The (nonparametric) maximum likelihood estimator for the corresponding distribution function is well defined. For the density function this is not the case. We study two nonparametric estimators for this density. The first is a type of kernel density estimate based on the empirical distribution function of the observable data. The second is a kernel density estimate based on the MLE of the distribution function of the unobservable (uncorrupted) data. 相似文献
47.
An approach is presented to satisfy the demand for simple criteria, guidelines and models for the preliminary sizing of horizontal subsurface flow (SF) constructed wetland systems. This approach eliminates time-consuming calculations and iterations by providing graphical solutions for wetland system sizing. Therefore, it can be used for the preliminary assessment of new or performance evaluation of existing subsurface flow constructed wetland systems. The validity of this methodology is checked with data from existing systems and is found to be quite satisfactory. This methodology is combined with simple equations predicting the maximum wetland capacity in summer, so as to assist designers in sizing installations in tourist areas with increased summer populations. Furthermore, based on this methodology, a sensitivity analysis is performed of the area requirements for wastewaters of various strengths and various design conditions and performance criteria. The results provide a useful overview to engineers and further simplify the design methodology of new subsurface flow constructed wetland systems. 相似文献
48.
Membrane separation technology represents an alternative way to achieve biomass retention in anaerobic bioreactors for wastewater treatment. Due to high biomass concentrations of anaerobic reactors, cake formation is likely to represent a major cause of flux decline. In the presented research, experiments are performed on the effect of biomass concentration and level of gas sparging on the hydraulic capacity of a submerged anaerobic membrane bioreactor. Both parameters significantly affected the hydraulic capacity, with biomass exerting the most pronounced effect. After 50 days of continuous operation the critical flux remained virtually unchanged, despite an increase in membrane resistance, suggesting that biomass characteristics and hydraulic conditions determine the bio-layer formation rather than the membrane's fouling level. The concept of bio-layer management is introduced to describe the programmed combination of actions performed in order to control the formation of biomass layer over membranes. 相似文献
49.
C. Anthony Di Benedetto 《Journal of Product Innovation Management》2004,21(3):153-153
50.
许多情况说明,用于组织中数据存储的消费已经成爆炸状态。产生这种情况的主要因素是电子邮件和电子商务对数据的质量和数量的要求提高了,并且这种数据大部分是分散的、非结构性的,这就增加了对组织中数据管理的要求。本文是在澳大利亚进行的一次调查的基础上做出的,该调查是关于组织中如何处理数据增长和由于数据增长所带来的问题。调查的结果显示人们对该问题表现出高度的关注,同时显示出一种乐观的趋势,即技术将对未来出现的各种各样的问题提供解决方案。 相似文献