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   3249篇
  免费   216篇
  国内免费   477篇
林业   204篇
农学   830篇
基础科学   124篇
  499篇
综合类   1450篇
农作物   369篇
水产渔业   113篇
畜牧兽医   174篇
园艺   97篇
植物保护   82篇
  2024年   28篇
  2023年   85篇
  2022年   110篇
  2021年   134篇
  2020年   171篇
  2019年   170篇
  2018年   111篇
  2017年   131篇
  2016年   149篇
  2015年   150篇
  2014年   196篇
  2013年   188篇
  2012年   239篇
  2011年   271篇
  2010年   211篇
  2009年   216篇
  2008年   197篇
  2007年   183篇
  2006年   173篇
  2005年   171篇
  2004年   125篇
  2003年   79篇
  2002年   77篇
  2001年   63篇
  2000年   75篇
  1999年   44篇
  1998年   41篇
  1997年   19篇
  1996年   26篇
  1995年   17篇
  1994年   17篇
  1993年   11篇
  1992年   15篇
  1991年   11篇
  1990年   6篇
  1989年   8篇
  1988年   4篇
  1987年   5篇
  1986年   3篇
  1984年   1篇
  1977年   1篇
  1963年   1篇
  1962年   7篇
  1955年   2篇
排序方式: 共有3942条查询结果,搜索用时 15 毫秒
961.
Using semidifferentiable concept for set-valued mapping and defining strong semiconpact for set-valued mapping. The article studies the existence of positive fixed point for semidifferentiable and Upper semicontinuous set-valued 1-set-contractive mapping.  相似文献   
962.
Architecture of Logistics system is the interior operation environment and business platform for Logistics companies, which is to steer to build special logistics system and tactics frame-saw to realize the company's objectives. Further more, characteristic and design principle of architecture are mentioned. There are 4 levels in this article to discuss the architecture of TPL system. Six elements contained in the architecture are mentioned: information platform, tech-equipment platform, knowledge platform, organization platform, business platform and functional platform, Furthermore, the mutual connection among which is analyzed as a whole. In conclusion, measure of the transfer from traditional storage and transportation to modern logistics is discussed.  相似文献   
963.
In this paper, the factors influencing the foundation scheme of high-rise buildings are analyzed. In accordance with the complex hierarchical structure and the uncertainty of foundation scheme, a knowledge base of hierarchical structure is set up and an inexact reasoning is realized. Then, the expert system for high-rise buildings foundation scheme (TBFES) is built on the knowledge base with the expert system tool CLIPS.  相似文献   
964.
A customer segmentation method based on dynamic SOM and RFM indicators is presented. Firstly, customer clusters is generated by DSOM clustering analysis. Secondly, customer loyalty, customer scale and customer credit are simulated by RFM behaviors of customer, and then customer clusters are identified. Finally, the value of customers can be decided according to the customer segmentation results, and enterprises are able to provide better different service levels to different customers. It provides customer strategies of enterprises with an effective support and decision-making.  相似文献   
965.
In this paper, we obtained one implicit function theorm,which, in the inverse function cases, becomes to the necessary and sufficient condition for the mapping is a homeomorphism.  相似文献   
966.
967.
Data-mining is a composite and multi - disciplinary technology newly developed. This paper will start by describing the fundamentals and basic methods of the technology followed by an overview of the latest development of its applications, problems and hurdles currently facing and the way forward and future work.  相似文献   
968.
From the topological angle and byintroducing the definitions of continuous mapping, open mapping, closed mapping,homeomorphic mapping, submatroid and quotient matroids, under which the qualities of matroids are studied, and some equivalent condictions are obtained. Inadditional, whether the independent set,dependent set and circuit of matroids are held under these mappings is discussed.  相似文献   
969.
Literature searching instruments are available via the Internet, but one has to conduct several individual searches to retrieve relevant scholarly materials for research. This scenario led information experts from the Consultative Group on International Agricultural Research (CGIAR) to find ways to make life easier for scientists. The collaboration among Information and IT managers resulted in the launch of the CGIAR Virtual Library (CGVLibrary) in 2006. CGIAR supports 15 diverse international centers, located worldwide, which generate scholarly research results that are considered as public goods and must be shared freely with the international community. The CGVLibrary enables federated searching of catalogs and databases and carries hyperlinks to full-text CGIAR documents. This article provides an analysis of the content of the CGVLibrary, of the various information avenues it opens for improving access to agricultural research, and of how the tool is being improved and marketed to promote awareness and worldwide use.  相似文献   
970.
Several botanical studies have been conducted in different parts of Oman, but knowledge about agro-biodiversity in the rapidly decaying ancient mountain oases of this country remains scarce. To fill this gap we assessed the genetic resources of three mountain oases in the al-Hajar range using a GIS-based field survey and farmer interviews. While arid conditions prevail throughout the mountain range, the different elevations of Balad Seet (950–1020 m a.s.l.), Maqta (930–1180 m a.s.l.) and Al Jabal al Akhdar (1750–1930 m a.s.l.) provide markedly differing agro-climatic conditions. Overall, 107 different crop species were identified belonging to 39 families. Species number was highest among fruits (33 spp.), followed by vegetables (24 spp.). Intensive irrigation allows cultivation of a broad range of species at all oases. However, the number of species varied significantly between sites. Fruit species diversity and homogeneity of distribution of individual fruit species was highest at Balad Seet and lowest at Maqta as indicated by respective Shannon indices of 1.00 and 0.39 and evenness values of 32% and 16%. Century plant (Agave americana L.), faba bean (Vicia faba L. var. minor Peterm. em. Harz) and lentil (Lens culinaris Medik.) were identified as relict crops, supporting oral reports of past cultivation and providing evidence of genetic erosion. Some species, such as the temperate fruits of Al Jabal al Akhdar, were exclusively found at the coolest site, while others only occurred at the hotter locations. Overall greatest species similarity was found between Balad Seet and Al Jabal al Akhdar as indicated by a Sørensen coefficient of similarity of 67%. At all oases a multilayered vegetation structure dominated with a canopy, an understory and a ground layer. Greatest species richness was recorded in the lowest stratum. Overall the study shows a location-specific but surprisingly diverse mosaic of crops in Omani mountain oases which merits further studies and conservation efforts.  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