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   604篇
  免费   20篇
  国内免费   35篇
林业   61篇
农学   60篇
基础科学   44篇
  106篇
综合类   299篇
农作物   9篇
水产渔业   13篇
畜牧兽医   38篇
园艺   9篇
植物保护   20篇
  2023年   7篇
  2022年   6篇
  2021年   3篇
  2020年   13篇
  2019年   10篇
  2018年   6篇
  2017年   11篇
  2016年   14篇
  2015年   11篇
  2014年   34篇
  2013年   39篇
  2012年   34篇
  2011年   49篇
  2010年   41篇
  2009年   41篇
  2008年   36篇
  2007年   42篇
  2006年   48篇
  2005年   26篇
  2004年   23篇
  2003年   38篇
  2002年   22篇
  2001年   12篇
  2000年   16篇
  1999年   19篇
  1998年   8篇
  1997年   7篇
  1996年   13篇
  1995年   6篇
  1994年   4篇
  1993年   7篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   2篇
  1988年   3篇
排序方式: 共有659条查询结果,搜索用时 9 毫秒
31.
提出了利益均衡机制的构造框架:研究目标、政企分开的基础研究,政企分开时银行、企业、政府三方决策过程研究,政企分开后的效果评价、实证研究、关键问题,提出了相应的构建思路.  相似文献   
32.
Non equity Strategic Alliance is one of the middle organization forms between enterprises and the market. It is loosely coupled and agile based on the restriction and coordination by contract. Relative to Equity Strategic Alliance, it shows the agile character. But, this character causes the instability and complexity. The authors did a research of dynamic stabilization in Non-equity Strategic Alliance supported by the theories of institution equilibrium from New Institutional Economics. Presuming a control management institute M, the dynamic stabilization model of Non-equity Strategic Alliance under conditions of complete information and incomplete information is established. The author hopes to help Chinese enterprises establish Non equity Strategic Alliance was established under the changing environment.  相似文献   
33.
The externality of surrounding is introduced into the 2-capital of economical increasing models, which includes human factors, to explore the influences of circumstances contradiction on the human capital formation. The normal and special nash equilibrium of environmental and human capital is presented through a limited boundary model of overlapping generations. The character of equilibrium trail and its economical meaning are examined. The study on the model shows that laissez faire economy will be either stagnant,growing,or collapsing in the long-run,depending on the returns of the learning technology with respect to the two kinds of capital,the initial state of economy,and the relative price of the environmental and consumption goods.  相似文献   
34.
为研究气候变化对粮食生产、消费及经济增长影响,将气候变化影响粮食产量的研究结果作为一般均衡模型的政策模拟方案,通过构建的基期模拟预测研究了到2050年中国粮食生产、消费及其经济增长两个方面的内容。模拟结果显示:(1)到2050年,中国粮食生产总量在A2情景(高排放)下为629185×103 t,在B2(中低排放)情景下为601859×103 t。总需求在B2情景下为626609×103 t,在B2情景下为561093×103 t,不考虑损耗及库存,粮食供需基本平衡,供给略大于需求。(2)考虑CO2的肥效作用,到2050年,气候变化对中国宏观经济和部门经济产生有利影响,实际工资、实际GDP、投资、家庭消费、出口等宏观指标相比于基期都有所上升,对主要农业部门及工业和服务业部门的产出、消费、进出口也是有利影响。而不考虑CO2的肥效作用则会得到相反的结论。(3)在A2情景下气候变化对中国宏观经济和部门经济的有利影响要大于B2情景下的影响。(4)从气候变化对产出和需求影响的变化结果来看,从总体上来说,考虑CO2的肥效作用,无论是A2还是B2情景下,都导致供给增加,进口减少,增加的供给量大于需求。因此,考虑CO2肥效的作用,会增强供给的保障,有利于维护中国的粮食安全。而不考虑CO2的肥效作用,无论是A2还是B2情景下,都导致供给减少,进口增加,减少的供给量大于需求的变化量,不利于维护中国的粮食安全。  相似文献   
35.
There are a large number of malicious attack nodes and collusion groups in P2P(peer to peer) network, and the existing trust models improve the P2P network environment to some extent, but the emphasis of the models are different, which are unable to fully solve large-scale malicious attacks and deception. Therefore, a P2P trust model based on equilibrium theory is presented. The model consists of the construction of the trust structure, the malicious node detection and trust speculation. It constructs trust network according to the equilibrium theory, uses the equilibrium theory to define nodes balance factor, detects balance malicious nodes by calculating the impact of malicious behavior on the network, and adopts trust inference algorithm to estimate trust nodes to prevent distrust network nodes being added. Experimental results show that the model is reliable, and the algorithm is efficient and robust.  相似文献   
36.
首先分析了技术-环境贸易壁垒的定义和特征,描述了中国农产品遭受到的技术-环境贸易壁垒,然后通过采用局部均衡分析的方法来分析技术-环境贸易壁垒对中国农产品出口的影响,结果表明:技术-环境贸易壁垒会使中国的社会福利减少,同时能够产生较高的遵循成本,该遵循成本在出口国的生产者和进口国的消费者这件进行分摊。最后通过这种分析指出企业在遭受技术-环境贸易壁垒时应根据不同的情况以做出相应的决策。  相似文献   
37.
Abstract

For most markets for wood, it is used without any treatments or modifications. When wood is used in adverse environments, it may be treated with chemicals to help prevent decay, improve water resistance, reduce the effects of ultraviolet radiation or increase fire retardancy. Many of these treatments involve the use of toxic or corrosive chemicals that can harm the environment. Chemical modification of wood provides an alternative by providing protection against water, decay, UV and thermal degradations by bonding chemicals to the cell wall polymers that do not leach out. Dimensional stability and decay resistance are two major properties that can be greatly improved by simple reactions with acetic anhydride.  相似文献   
38.
Computable general equilibrium (CGE)model's solving is important for its reseachers . Though there are many softwares to solve the CGE model, it is very important for its reseachers to understand CGE model's solving principle. The paper introduces the methods,principles and problems of CGE model's solving.The software -MATLAB is used to solve CGE Model, and reseach the existing problem of CGE model's solving.  相似文献   
39.
The Brinell hardness and equilibrium moisture content (EMC) were measured from thinning-aged silver birch wood. Wood material both from the trees harvested in the first commercial thinning and from trees remaining on site after the thinning was included. The average Brinell hardness was 19.40 MPa. It correlated significantly with the basic density of wood. With respect to the distance from the pith, the Brinell hardness of air-dried wood was higher than that of artificially dried wood. The average EMC of the conditioned (20°C, 65% relative humidity) wood was 12.0%. The EMC of the wood also varied, with the EMC being higher for air-dried wood than for kiln-dried wood. EMC was the highest at a distance of 30–40 mm from the pith, decreasing towards both pith and log surface. Seasonal variation in both the Brinell hardness and the EMC of the wood was found. It was presumed to be a consequence of season-dependent physiological changes in trees.  相似文献   
40.
螺旋离心式潜水排污泵叶轮的加工   总被引:1,自引:1,他引:1  
高小芬 《排灌机械》2002,20(2):21-23
对引进意大利技术生产的螺旋离心式水泵中的关键零件螺旋式叶轮的结构特点进行了分析,讨论了叶轮的加工工艺、夹具及工装设计对叶轮精度的影响,确定了螺旋式叶轮的加工工艺、校平衡的方法及加工中应注意的问题。  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