全文获取类型
收费全文 | 104883篇 |
免费 | 6751篇 |
国内免费 | 8924篇 |
专业分类
林业 | 8029篇 |
农学 | 5541篇 |
基础科学 | 4458篇 |
9428篇 | |
综合类 | 52613篇 |
农作物 | 7822篇 |
水产渔业 | 4870篇 |
畜牧兽医 | 15311篇 |
园艺 | 8088篇 |
植物保护 | 4398篇 |
出版年
2024年 | 607篇 |
2023年 | 1991篇 |
2022年 | 4502篇 |
2021年 | 4566篇 |
2020年 | 4278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 | 7337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 93 毫秒
991.
An equivalent model for hollowing-center grounding device is proposed, the hollowing-center grounding device resistance is calculated with the surface charge simulation method and the computer programme is programmed based on this model. The accuracy of the model and method is validated by experimentation. 相似文献
992.
This paper analyzes the fluid flow and heat transfer of the heat exchanger, and obtainsd the distribution of fluid field, heat field and pressure field in heat exchanger. According the analysis result, some modify measure is adopted, such as decreasing the number of tube bundle, the size of baffle plate and increasing the diameter of exchange heat tube. In the new heat exchanger, the resistance decreased 32.3%, is 103.2 Pa and the temperature of the exit is 130 K. The new heat exchanger satisfies the requirement of exchanging heat. The study indicates that adopting the numerical simulation method could get temperature, pressure and fluid - velocity of anywhere of the heat exchanger, and understand effecfing of structure parameter on fluid flied and heat flied of the heat exchanger. Therefore, it provides a new method for optimization design of heat exchanger. 相似文献
993.
994.
The monitoring and assessment scheme of the Caiyuanba Yangtze Bridge is present by sensitivity analysis. The mechanics character of the six ties is studied by numerical simulation, and then the sensor location and selection are discussed considering the technique of sensor and construction situation. The trend of the displacement at the sensor location is analyzed according to different damage level of ties, the pattern associating with several displacements which are sensitive to damage at ties is bring forward to improve assessment reliability. The result can assist implement of structural health monitoring system to the same type as this bridge. 相似文献
995.
In view of the important effect of clustering analysis in data mining, the clustering rules and its curve are studied to solve the problem of determining clustering number. A kind of self-adaptation clustering ANN is presented based on SOFM ANN, which can automatically determine the clustering number. Based on practical sales data, the time feature analysis of power user consumption are carried out by using the self-adaptation clustering ANN, whose conclusion has the important referenced values for adjusting power price correspondingly and arranging power producing reasonably. 相似文献
996.
This paper analyzes the questions that are likely to exist in comprehensive evaluation of commercial bank's internal control.On the basis of the analysis,the valuation indexes are divided into two levels.And maximizing deviation method,is introduced to get a evaluation method that can evaluate commercial bank's internal control more impersonally and more impartially. 相似文献
997.
The activation of black soil (analog the lignite) by electro-hydraulic impulse is proposed. The abundant insoluble nitrogen, phosphorus, potassium and other organic elements in black soil are activated as the green fertilizer by this way. The new method is provided for activating sludge produced by treating wastewater. For several kinds of black soil, the experiment result indicates that electro-hydraulic impulse increases the percentage of absorbable nitrogen by 1 to 4 times and the percentage of insoluble organic elements by 4 times, which is a valuable reference to sludge treatment. 相似文献
998.
999.
1000.