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   13909篇
  免费   875篇
  国内免费   1489篇
林业   2133篇
农学   1052篇
基础科学   815篇
  1949篇
综合类   6088篇
农作物   676篇
水产渔业   1221篇
畜牧兽医   1289篇
园艺   333篇
植物保护   717篇
  2024年   135篇
  2023年   318篇
  2022年   469篇
  2021年   535篇
  2020年   532篇
  2019年   577篇
  2018年   374篇
  2017年   560篇
  2016年   749篇
  2015年   605篇
  2014年   741篇
  2013年   772篇
  2012年   1069篇
  2011年   1113篇
  2010年   859篇
  2009年   867篇
  2008年   764篇
  2007年   816篇
  2006年   702篇
  2005年   534篇
  2004年   473篇
  2003年   362篇
  2002年   323篇
  2001年   320篇
  2000年   260篇
  1999年   191篇
  1998年   171篇
  1997年   150篇
  1996年   150篇
  1995年   140篇
  1994年   104篇
  1993年   105篇
  1992年   103篇
  1991年   82篇
  1990年   77篇
  1989年   59篇
  1988年   48篇
  1987年   22篇
  1986年   19篇
  1985年   3篇
  1984年   3篇
  1983年   1篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1973年   3篇
  1962年   4篇
  1956年   3篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
Based on the analysis of the status of building construction in China, the development of Assembled Structure System (ASS) can solve not only the problems in construction, but also is the key for realization of building industrialization. On the basis of technique innovations, a study on the structural performance, construction method and precast production of ASS should be carried out to inherit the old one and overcome its demerits. The process reengineering should be done in the construction enterprise to promote the development of building industrialization.  相似文献   
134.
Based on a cable -stayed bridge girder as an example, the structure and function, the operating principle and calculation model of the main elements of the Basket of wide - stayed bridge were described in detail. A further discussion was carried out on the Basket of Cantilever construction of the main beam in the structure.  相似文献   
135.
In system controlled,Sampling these parameters and with parameters for controller in time, it is an object to adaptive control. The article presents a scheme that the structure parameters on it's model and model parameters is robust identified by on line, while to optimal of algorithm on adaptive control is fulfilled. In control scheme, method of intelligent identifying to the structure parameters(levels of model) and algorithm of robust pole placement are introduced also It is advancer for already mentioned scheme. Whole scheme presents new model on adaptive control.  相似文献   
136.
Bill of material of product is data about product structure, and plays an important role in product information management. The paper analyzed characteristics of product BOM, and put forward a product BOM management method based on single layer BOM, witch can well meet requirements of product BOM.  相似文献   
137.
According to the graphics characteristics of metallic doors & windows design and based on the research of graphics dimension restriction problems. This paper provides a new method for parameterized design of metallic doors & windows in virtue of expression solution. In this method, the restrictions of graphic elements have been changed into the parameter expressions of sizes and positions of graphic elements. Through the calculation of such expressions, the parameter driven method has been reached. Thus the parameterization of graphics can be easier and quicker than before. It can be used to setup the open parameterized graphics libraries.  相似文献   
138.
The Crossing Entropy is defined to scale the similar level of two probability distribution. In many papers on learning BN structure,the Crossing Entropy was used as an indicator of measuring the learning accuracy of an algorithm.The known scoring metrics for learning BN structure is analyzed in this paper,then a new scoring metrics Sum of Mutual Information is proposed based on the information theory.At last,two algorithm for learning BN structure by SIM is represented.  相似文献   
139.
In this paper,notions on appropriate technology for the Steel Construction Congregated Apartments are proposed in order to deal with the technical impediment that arises from applying steel structural techniques to the congregated apartments.The appropriate technology for the steel construction congregated apartments is defined as systematic technologies that are in harmony with the status quo of Chinese productive force level,social culture and building technology,and as the strategies of choosing or balancing technology according to sustainable development principle.The principal design and constructing strategies of appropriate technology are as follows:(1) organization of residential space combined with steel construction techniques,(2) suitable structural system,(3) a new idea of fire resistance,and(4) kit building technique etc.A technological concept analysis about an ideal model of a steel construction system congregated apartment combined with the appropriate technology is also presented.  相似文献   
140.
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