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   17461篇
  免费   1063篇
  国内免费   1919篇
林业   1530篇
农学   1905篇
基础科学   1244篇
  2301篇
综合类   6851篇
农作物   1211篇
水产渔业   938篇
畜牧兽医   2594篇
园艺   799篇
植物保护   1070篇
  2024年   101篇
  2023年   267篇
  2022年   673篇
  2021年   791篇
  2020年   721篇
  2019年   726篇
  2018年   574篇
  2017年   771篇
  2016年   576篇
  2015年   820篇
  2014年   805篇
  2013年   1031篇
  2012年   1420篇
  2011年   1330篇
  2010年   1321篇
  2009年   1271篇
  2008年   1159篇
  2007年   1050篇
  2006年   942篇
  2005年   752篇
  2004年   408篇
  2003年   389篇
  2002年   448篇
  2001年   408篇
  2000年   345篇
  1999年   270篇
  1998年   136篇
  1997年   126篇
  1996年   125篇
  1995年   127篇
  1994年   111篇
  1993年   98篇
  1992年   73篇
  1991年   56篇
  1990年   55篇
  1989年   43篇
  1988年   32篇
  1987年   24篇
  1986年   19篇
  1985年   8篇
  1984年   6篇
  1983年   6篇
  1982年   3篇
  1981年   3篇
  1980年   4篇
  1977年   2篇
  1973年   2篇
  1968年   2篇
  1966年   2篇
  1965年   2篇
排序方式: 共有10000条查询结果,搜索用时 422 毫秒
171.
172.
In this paper, a new microcomputer distance protection scheme with high property-cost ratio has been approached. The paper presents the performance equations based on the symmetrical components of current and voltage, proposes a new (1,a) coordinate plane and derives a Fourier symmetrical component algorithem with high accuracy and less calculation amount on the (1,a) plane. The protection program is debugged on the developing system of single chip computer. The digital imitation tests indicate that the proposed relaying system is satisfactory.  相似文献   
173.
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   
174.
In the past, the criterion for calibration has almost invariably been the stellar oriented ballistic camera,the method is a point to point comparison on the identical coordinate system. Deficiencies is follows: The request of weather is severe(cloudless night); The period is often long; the measure equipment of high precision can't be calibrated. While EMBET methods is used in calibration, it does not need criterion and it demands only that the measure elements is larger than 3,and the trajectory and many system errors of the measure elements can be simultaneously calculated with the measure data sequences. The error models of related equipments' measure elements and the EMBET of typical equipment group are given. The EMBET method is successfully used in Accuracy-analysis of Satellite Launch.  相似文献   
175.
For certain types of inventory, the ordering cycle and demand may be random variants, which satisfy certain types distribution. The classical EOQ model usually neglects the fact. Based on the constant demand, under the hypothesis that the ordering cycle is a random variant which satisfies exponent distribution, average demand is a linear increasing function, this paper considers the effects of the time-value of capital and inflation on replenishment strategy of inventory system. Loosening the condition of basic economic order quantity model under deterministic state, the total cost function of the model is provided. The optimum order quantity and cycle are obtained. The application range of EOQ model under the constant demand is widened. The theoretical evidence is provided for the inventory system to make management decision.  相似文献   
176.
Intelligent recognition system of gun code is designed , which achieves online recognition of gun code. We applied video camera to get image, and some special technique in this deformed character recognition. As well, we applied dynamic template matching to get a better result.  相似文献   
177.
It is important for enterprises' inventory management to find out the optimal production cycle and the length of shortage time,so that the total cost of inventory system can be reduced and the service level can be raised.Based on the classical EPQ model,this paper develops an EPQ model for deterioration items with different lost sale factor relative to the inventory level during shortage period.The existence of unique optimal solution is discussed by mathematic analysis and a numeric example.The sensitivity analysis shows that the parameter of losing sale has different impact on the costs of inventory system.The factors must be considered for the production inventory system to make management decision.  相似文献   
178.
This paper provides a conception of brightness and puts stress upon application of brightness to science of illuminating engineering and actual illuminating engineering.  相似文献   
179.
Philosophy of science led by Popper is one of the most important contemporary scientific and philosophic theories.In addition to the science,the philosophy of science impacted contemporary social science mostly,of which the false-feasibility,circumstantial logic,anti-historical determinism and anti-scientism influenced the orientation of contemporary architecture.Just with these factors of philosophy of science,this thesis reanalyzed and reviewed Chinese contemporary architectural forms,especially the tradition inheritance.  相似文献   
180.
This paper presents a new practical criterion for voltage stability based on the real-time information at the substation and the quasi-time information from power system.By using the criterion,it is effective to predict the bus voltage stability margin.This is of great importance to raise the security operation level and prevent voltage collapse.The practical criterion for voltage stability is tested on the IEEE-14-bus test system.It needs less calculation time and is very suitable for real-time control of power systems.  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