全文获取类型
收费全文 | 105072篇 |
免费 | 6590篇 |
国内免费 | 9021篇 |
专业分类
林业 | 8029篇 |
农学 | 5541篇 |
基础科学 | 4469篇 |
9470篇 | |
综合类 | 52655篇 |
农作物 | 7833篇 |
水产渔业 | 4880篇 |
畜牧兽医 | 15320篇 |
园艺 | 8088篇 |
植物保护 | 4398篇 |
出版年
2024年 | 721篇 |
2023年 | 1991篇 |
2022年 | 4511篇 |
2021年 | 4566篇 |
2020年 | 4279篇 |
2019年 | 4269篇 |
2018年 | 3001篇 |
2017年 | 5054篇 |
2016年 | 3196篇 |
2015年 | 5057篇 |
2014年 | 5383篇 |
2013年 | 6469篇 |
2012年 | 9169篇 |
2011年 | 9114篇 |
2010年 | 8482篇 |
2009年 | 7662篇 |
2008年 | 7834篇 |
2007年 | 7338篇 |
2006年 | 5979篇 |
2005年 | 4864篇 |
2004年 | 3008篇 |
2003年 | 1821篇 |
2002年 | 2127篇 |
2001年 | 1810篇 |
2000年 | 1659篇 |
1999年 | 614篇 |
1998年 | 97篇 |
1997年 | 66篇 |
1996年 | 37篇 |
1995年 | 52篇 |
1994年 | 40篇 |
1993年 | 48篇 |
1992年 | 54篇 |
1991年 | 40篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 9篇 |
1987年 | 29篇 |
1986年 | 20篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1981年 | 9篇 |
1966年 | 5篇 |
1964年 | 5篇 |
1963年 | 5篇 |
1962年 | 18篇 |
1961年 | 6篇 |
1957年 | 11篇 |
1956年 | 37篇 |
1955年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
881.
CHEN Zuo chang 《保鲜与加工》2002,(2):93-97
With social development, the environment has become one of the major topics in human life. Although the construction project may improve economy and environment, it also may exert negative impact on environment. Cost, schedule and quality are three important objectives of construction project and on the objective of environment have not been focused. The author of this paper reiterated the importance of environmental control for the construction project and key areas to be focused on during the whole process of construction project. 相似文献
882.
In 1995, Padmanabhan and Vrat presented inventory models for deteriorating items with a constant selling price and stock dependent selling rate . Based on the result, in 2000, Kun-Jen Chung, Peter Chu and Shaw-Ping Lan devoloped the necessary and sufficient conditions of the existence and uniqueness of the optimal solutions of the profit per unit time functions without backlogging and with complete backlogging. Actually, the selling price need not be constant, it may be variable . This paper puts forward an EOQ model when the selling price is variable without backlogging, discusses the existence and uniqueness of optimum solution. The example is provided to illustrate the model. The theoretical evidence is provided for the inventory system to make management decision. 相似文献
883.
884.
Image compression is very important in picture archiving and communication system(PACS). The author studied the statistical distribution of image wavelet subimage coefficients and concluded that the distribution of wavelet subimage coefficients is similar to that of Laplasian distribution. On the other hand, in image reconstruction, the coefficient with different amplitude owns different weight, and different accuracy can be applied to different coefficients according to their different weight. Then, the author has designed a image quantization encoding scheme for PACS. In this scheme, they selected the sample-standard-deviation of coefficients in every subimage as the quantization threshold, and accurately encoded those coefficients with higher weight. Also, this algorithm utilized the visual character of human. The test has proved that the main advantages of this method are the simplicity in computing and predictable encoded coefficients, and a high compression efficiency can obtain too. 相似文献
885.
Ultra High Molecular Weight Polyethylene (UHMW-PE) is a kind of high anti-wear engineering plastic with many excellent physical and mechanical performances. It has been widely applied in the field of mechanism such as bearing and pump. Effect of load, speed, time on friction and wear properties of Ultra High Molecular Weight Polyethylene(UHMW-PE)plastic alloy bearings under different Lubricating Condition are studied by using MPV-200 model friction and wear testing machine. The test results show that water lubrication reduces the friction coefficient of bearings but increases the wear rate as compared with dry friction. At the same time, wear mechanisms are analyzed systemically. It provides a theoretic basic for practical application of plastic alloy bearings 相似文献
886.
For certain types of inventory, the ordering cycle and demand may be random variants, which satisfy certain types distribution. The classical EOQ model usually neglects the fact. Based on the constant demand, under the hypothesis that the ordering cycle is a random variant which satisfies exponent distribution, average demand is a linear increasing function, this paper considers the effects of the time-value of capital and inflation on replenishment strategy of inventory system. Loosening the condition of basic economic order quantity model under deterministic state, the total cost function of the model is provided. The optimum order quantity and cycle are obtained. The application range of EOQ model under the constant demand is widened. The theoretical evidence is provided for the inventory system to make management decision. 相似文献
887.
In order to subdivide the market during the process of project planning and orient the group of client, then determine the sale price; on the condition that the traditional orientation procedure cant grasp the payment capability of the aim client, the anthors can adapt the powerful finance analysis ability of EXEL to design the procedure of determining the purchasing power and payments ability of the aim client, and shape a set of orientation system based on quantitative analysis method. The result is, the character of the aim client can be grasp accurately depend on this orientation system, and providing a scientific gist for the accurate orientation of price and lowing the risk of investment etc. 相似文献
888.
It is important for enterprises' inventory management to find out the optimal production cycle and the length of shortage time,so that the total cost of inventory system can be reduced and the service level can be raised.Based on the classical EPQ model,this paper develops an EPQ model for deterioration items with different lost sale factor relative to the inventory level during shortage period.The existence of unique optimal solution is discussed by mathematic analysis and a numeric example.The sensitivity analysis shows that the parameter of losing sale has different impact on the costs of inventory system.The factors must be considered for the production inventory system to make management decision. 相似文献
889.
890.
This paper summarized the recent research results about the durability of structures, introduced their current application in durability design, appraisal, estimation of rest life and strategy of maintenance and strengthening as well as in other fields. 相似文献