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   5441篇
  免费   292篇
  国内免费   614篇
林业   651篇
农学   610篇
基础科学   796篇
  1019篇
综合类   2290篇
农作物   120篇
水产渔业   114篇
畜牧兽医   315篇
园艺   59篇
植物保护   373篇
  2024年   33篇
  2023年   104篇
  2022年   135篇
  2021年   191篇
  2020年   193篇
  2019年   230篇
  2018年   158篇
  2017年   261篇
  2016年   280篇
  2015年   240篇
  2014年   299篇
  2013年   327篇
  2012年   455篇
  2011年   398篇
  2010年   362篇
  2009年   347篇
  2008年   279篇
  2007年   350篇
  2006年   314篇
  2005年   240篇
  2004年   192篇
  2003年   154篇
  2002年   138篇
  2001年   99篇
  2000年   76篇
  1999年   66篇
  1998年   56篇
  1997年   55篇
  1996年   48篇
  1995年   50篇
  1994年   46篇
  1993年   37篇
  1992年   30篇
  1991年   29篇
  1990年   22篇
  1989年   26篇
  1988年   17篇
  1987年   4篇
  1986年   5篇
  1981年   1篇
排序方式: 共有6347条查询结果,搜索用时 15 毫秒
51.
52.
This paper discusses the problem of long-range generation expansion planning. A dynamic model for long-range expansion planning is set up and an algorithm-a two-step programming is presented, which is used here in a case.  相似文献   
53.
Flowing dynamic characteristics and its temperature dynamic characteristics of a three-level sewage pipe network in Chongqing were analyzed. A mall's building whole year load was simulated. In the adverse condition of wastewater flow, the market construction peak discharge heat was compared with the sewage heat load, the balance between the most adverse flow and the building demand was found. Explored supply and demand matching method between urban sewage and city building load in flow adverse condition to take full advantage of the urban sewage cold and hot resources. the composite system was adeptcd to make up the most unfavorable flow time of sewage average heat load and the construction load difference; it also puts forward principle of load sharing and control strategy aimed at compound system.  相似文献   
54.
This paper introduces the definition of the quasi-dunamic instrument, analyzes the measuring principle of the double-theodolite space coordinate quasi-dynamic measuring system, builds the experimental system with the currency theodolite and designing the accessorial driving and orientational framework, investigates the dynamic character under variant tracking velocity of this system by the experiments and gians some elementary conclusions. These conclusions play important roles in the compensating the measuring error and in the improving the measuring precision of the measuring system.  相似文献   
55.
56.
Loss reduction is important for distribution networks and it is available to reduce loss by loads equalization. With increasing numbers of vertexes in distribution networks, compounding of loads are rapid increasing. It is hard to achieve the global optimization for load balancing by traditional model of distribution networks. Base on analyzing character of loads equalization for distribution networks, this paper provides a new method which conjugate the optimization principle and the hierarchical model of the distribution networks, can transfer the optimization issues into multi stage decision making problems,and can also achieve the optimization equalization of the distribution networks loads.  相似文献   
57.
The method and principle of the parameter design for the power train of EV is explored and discussed,then the parametersof EV. based on SC7101 are reasonably selected.The method of calculating the SOC of Lead_acid battery is provided and the relation among the electromotive force,the interior resistance, the polarized resistance and the SOC are analyzed. The capacity is compensated according to the relation between the capacity and the temperature, which is the basis on which the energy management system is designed and improved. The dynamic model which reflects the dynamic characteristics of the power train is established,then the dynamic performance of the EV based on SC7101 is simulated, and the factors that affect the continuous mileage of EV are analyzed,the measures to increase the continuous mileage are provided.The result shows that the analysis of the electric characteristics of battery and the dynamic model are correct,and the dynamic performance perfectly meets the need of the design target.  相似文献   
58.
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   
59.
Dynamic mathematical model, which is based on the character of the 200 MW tubine lbricating oil system, is established by means of modularization. On the basis of dynamic mathematical models, simulation model of the startu Pprocess of hign pressure startu Poil pum Pis created with the Visual Fortran language. The validity of this model has been verified by the simulation experiments and analysis. The simulation helps to forecast the dynamic characteristic to high pressure startu Poil pum Pand have some directive significance to design method of lubricating oil system.  相似文献   
60.
This paper researches the behavior difference among government,banks and enterprises and how it affects soft budget constraints of enterprises and non-performing loans of banks based with dynamic game.The game model suggests that government will give banks some assistance and let them refinance enterprises,especially government has strong(incentive) to sustain SOEs in China's transitional economy.Banks will do it if the assistance from government is more than the loss from refinance enterprises.In addition the value of liquidation of enterprises and the new loans affect banks' refinancing old enterprises.  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