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   14998篇
  免费   651篇
  国内免费   1081篇
林业   2453篇
农学   919篇
基础科学   1490篇
  1448篇
综合类   6142篇
农作物   539篇
水产渔业   435篇
畜牧兽医   2268篇
园艺   388篇
植物保护   648篇
  2024年   100篇
  2023年   283篇
  2022年   446篇
  2021年   500篇
  2020年   482篇
  2019年   621篇
  2018年   302篇
  2017年   504篇
  2016年   688篇
  2015年   559篇
  2014年   924篇
  2013年   810篇
  2012年   1374篇
  2011年   1142篇
  2010年   914篇
  2009年   894篇
  2008年   786篇
  2007年   818篇
  2006年   732篇
  2005年   546篇
  2004年   505篇
  2003年   392篇
  2002年   331篇
  2001年   302篇
  2000年   241篇
  1999年   224篇
  1998年   198篇
  1997年   167篇
  1996年   134篇
  1995年   126篇
  1994年   127篇
  1993年   94篇
  1992年   94篇
  1991年   82篇
  1990年   65篇
  1989年   60篇
  1988年   62篇
  1987年   26篇
  1986年   15篇
  1985年   7篇
  1984年   16篇
  1983年   4篇
  1982年   4篇
  1981年   4篇
  1980年   5篇
  1979年   5篇
  1978年   3篇
  1977年   6篇
  1973年   2篇
  1956年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
Critical information system in Interact is in face of increasingly security problems. More attention has been focused on the survivability of information system, which is the capability of system to continue its mission even in the presence of damage to the system. The authors first introduce the definition of survivability. According to four function properties of survivability, which are Resistance, Recognition, Recovery, and Adaption, the authors design a model of survivable system structure and then explain survivability requirement, survivability strategy in this model. Additionally, they provide possible technical solutions for the survivability of systems, categorized by different aspects of our survivability strategy.  相似文献   
202.
A new scoap-like testability measure SCTM(a signal conflict oriented testability meaure) is presented, which represents not only the difficulty to control and observe the value of a node,but also the probability to cause signal conflict in the process of test generation. A parallel calculation scheme is offered, which speeds up the calculation m/2 times. Here m is the word length of a computer.  相似文献   
203.
204.
205.
The torsion vibration of main transmission system of 1 450 rolling mill is tested:The torsion vibration frequency and amplification coefficient of torque are obtained.Basing on part of the measured date and theoretical analysis,the measure is developed for preventive method;it is of important theoretic sense and high engineering practical value for reducing accident and controlling torsion vibration.  相似文献   
206.
This paper studies an effect of high loads in Rayleigh distribution random load-ing on fatigue crack growth wi th 16 Mn steel compact tenion specimen,The results show that thehigh loads in the load spectrum close to service load of steel bridges accelerate crack growth and re-duce crack growth life,Lives predicted with constant amplitude da/dn data and equivalent loads arequite in agreement with test lives.  相似文献   
207.
The conservation of historic buildings and their environment is an unavoidable problem in urban construction. In this paper, the authors give a few new thoughts about the problem. First, the historic buildings are important part of the core power in city competition.Second,the conservation work should be combined with their development. Third, a classified and multilevel system of protection and reuse of old buildings should be set up.  相似文献   
208.
209.
In this paper, a new method of researching; the site dupleface dynamic balance of machine rigid rotator, namely duple test weightmethod is presented. Weight the new method against the existing method,namely single test weight method [1], both the efficiency increasing and theenergy-consumming dicreasing would be forty percent and over, with thebasic points of vibration theory, the formula of calculating weight andposition of the duple face dynamic unbalance of a rotator by means ofapplying the duple test weight is developed in detail. The method in handll-ing distinct bearing form is also discussed. Rightness of the new method isproved out by the living example of the simulant contrast testing carried outn the dynamic balance test machine and the site balance for a rotatorsystem of motor.  相似文献   
210.
Urbanization in China is at an essential point in its transformation from the initial stage to accelerating stage. With quick expansion of city scale and large occupation of land for urban construction, the contradiction between land resource shortage and people's living needs becomes more and more prominent. It has great affection on the grand plan of China's sustainable development of economy and society. How to adjust the relations between the development of urban construction and protect the land resource, promote the rational use of urban land, perfect and complete the protection system of land resource for improving the efficiency of urban land use. In order to conserve land resource and find a sustainable way for development of people's living and environment construction, the above mentioned problems are the most important issue for urban construction and important subject of this paper.  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