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   76801篇
  免费   3744篇
  国内免费   8440篇
林业   9114篇
农学   12348篇
基础科学   6839篇
  12528篇
综合类   23564篇
农作物   4004篇
水产渔业   2559篇
畜牧兽医   10170篇
园艺   2927篇
植物保护   4932篇
  2024年   161篇
  2023年   730篇
  2022年   1948篇
  2021年   2860篇
  2020年   2700篇
  2019年   2512篇
  2018年   1809篇
  2017年   2694篇
  2016年   2547篇
  2015年   3319篇
  2014年   3296篇
  2013年   4165篇
  2012年   4986篇
  2011年   5298篇
  2010年   5095篇
  2009年   4644篇
  2008年   4484篇
  2007年   4897篇
  2006年   4412篇
  2005年   3976篇
  2004年   2007篇
  2003年   1707篇
  2002年   1603篇
  2001年   1643篇
  2000年   1802篇
  1999年   1938篇
  1998年   1755篇
  1997年   1475篇
  1996年   1358篇
  1995年   1273篇
  1994年   1130篇
  1993年   1057篇
  1992年   875篇
  1991年   703篇
  1990年   612篇
  1989年   442篇
  1988年   367篇
  1987年   261篇
  1986年   139篇
  1985年   59篇
  1984年   51篇
  1983年   52篇
  1982年   38篇
  1981年   49篇
  1980年   23篇
  1979年   11篇
  1965年   4篇
  1964年   4篇
  1962年   4篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Based on the optimal control theory and Lagrange interpolation an optimal design model of plane cascades of 3D blade in an arbitrary surface of revolution is established. Using wavelet theory to solve the model, and lots of numerical results are obtained. The results show that the wavelet method is more effective than the conventional methods.  相似文献   
992.
This paper presents a detail study of bubble coalescence in inorganic salts and organic compounds of fermented solution ,and preliminary analyses the principle of bubble coalescence.The experiments show that the relationship between the solute concentration and coalescence frequency reveals the existence of sharp transition concentration.  相似文献   
993.
994.
A raseach has been done on the possibility of producing nitriochumic acid fromweathered coal of Nantong,Sichuan,oxidised by nithic acid.The optimun reacting conditions,whichare found through the way of orthogonal experiment,are suggested as follows:concentration ofHON3 35%,rate of HON3 to coal 3.5,reacting take 15 min,and reaction temperature 369 K. Thecomposition of product is Wf 2. 91 %;Ag 14.06%;HAg 78.28%;Ng 1.62%.  相似文献   
995.
996.
A new quick thinning algorithm was presented in this paper,which assigneddifferent weights to different pixels near the skeleton pixels and rules out the im possible pixels in thethinning procedure. It needs neither iteration on pixel panel nor detection on every pixel such thatthe time consumed is greatly lessened. A filling algorithm is also offered for better results.Experiment on variety of binary patterns showed that it could get both a high speed and a goodskeleton shape compared with other algorithms,This new algorithm reaches perfect result.  相似文献   
997.
998.
As a key resource, the knowledge management is becoming a research field interested by many researchers. In order to study the mathematics theory base of knowledge expression, in this paper, a knowledge expression model is given. In this model the knowledge system is expressed by multi-tuple, the single knowledge object is expressed by the tuple, a structural expression of knowledge is given using token as example and the application of the model in city water supply pipe network is presented in this paper.  相似文献   
999.
Based on the content of enterprise culture and enterprise credit, it is pointed out that the enterprise culture related to the enterprise core competitive force.In this paper, from the viewpoint of combining theory with practice, the intension, function and mutual relations between them are described and their significance in the market competition as well.The potential things,which the enterprise staffs are seeking for, from its inherent mind and the enterprise theory are the enterprise culture which becomes the enterprise core competitive force in its actual sense.The enterprise credit, as the enterprise culture in its ideological sphere, is an essential factor, which greatly affects the enterprise core competitive force.At last the authors provide some good suggestions on how to cultivate enterprise credit and to build enterprise culture.  相似文献   
1000.
In this paper the problem of energy consumption and environment in the birdhouse is introduced and the reconstructive measures aiming at energy savings are recommended. The measures include the limitation of temperature region, reconstruction of the building envelop and using the sunny board at the south side of the birdhouse roof. Finally, the energy efficiency of the reconstructive project is estimated.  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