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   6827篇
  免费   363篇
  国内免费   1288篇
林业   612篇
农学   979篇
基础科学   1176篇
  1297篇
综合类   2848篇
农作物   416篇
水产渔业   277篇
畜牧兽医   546篇
园艺   154篇
植物保护   173篇
  2024年   59篇
  2023年   153篇
  2022年   265篇
  2021年   309篇
  2020年   287篇
  2019年   302篇
  2018年   228篇
  2017年   321篇
  2016年   377篇
  2015年   288篇
  2014年   435篇
  2013年   435篇
  2012年   533篇
  2011年   522篇
  2010年   464篇
  2009年   435篇
  2008年   392篇
  2007年   422篇
  2006年   360篇
  2005年   325篇
  2004年   227篇
  2003年   237篇
  2002年   143篇
  2001年   107篇
  2000年   96篇
  1999年   110篇
  1998年   87篇
  1997年   73篇
  1996年   74篇
  1995年   68篇
  1994年   72篇
  1993年   47篇
  1992年   66篇
  1991年   50篇
  1990年   39篇
  1989年   25篇
  1988年   19篇
  1987年   13篇
  1986年   3篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1980年   1篇
  1978年   2篇
  1977年   1篇
  1963年   1篇
  1962年   1篇
排序方式: 共有8478条查询结果,搜索用时 0 毫秒
81.
The authors discuss such questions for utility boiler as the complicated flameworks,combined quoting course, long cycle, hardly controlling the quoting veracity and so on. Based on the construction diagram of quoting design for utility boiler, Which is into the boiler sketch's construction and parameter characteristic. They are furnace construction, big screen superheater, high temperature superheater, low temperature superheater, high temperature reheater, low temperature reheater, economy coal implement, common use sign and standard sketch in boiler sketch, etc. According to demand of the quote design for utility boiler, the CAD environment of quoting system based on characteristic construction and parameter are developed. Total construction of this environment , developing characteristics and function of this system are given.  相似文献   
82.
In this paper, the machine( physical) parameters of the alternator system are on-line estimated on the basis of the derived system continuous-tims model, using Recursive Least-squares Estimation and Inverse Calculation Method proposed by Authors. Therefore, the estimated machine parameters can effectively track the changes of their true values and accomplish the fault detection for the alternator system. This paper gives a new way for machne parameter estimation and fault detection of the alternator systems.  相似文献   
83.
A digital power system stabilizer ( DPSS ) and its design method are presented in this paper. The mathematical model of a single machine infinite bus power system is obtained using off-line parameter identifications, and on the base of the identified model the control system is synthesized by generalized minimum variance control principles. Through feedback combination of several signals this control system has double functions of damping low frequency oscillation and automatic voltage regulating. In order to avoid static errors the very effective way is to combine discrete generalized minimum variance control with continuous integral control. Besides the proposed control strategy is very simple in structures and very easy to realize. Simulation results under several cases have shown the correctness and effectiveness of the proposed control strategy.  相似文献   
84.
85.
An optimization approach for multi-relational joins based on the matching concept in graph theory is introduced. The basic idea lies in constructing a join graph from an expression of N-relation query, and seeking for a maximun matching with minimun total weight. The algorithm for bipartition(X, Y) is proposed in this paper.  相似文献   
86.
Based on properties of parameters and test data of dom-estic steel,this paper analyses the reliability and partial coefficient forresistance of steel frame columns of tall builings.The result may serveas a scientific basis.It is not only for domestic steel instead of importedsteel in building tall steel structures,but also for compiling concerendstandards.  相似文献   
87.
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   
88.
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   
89.
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   
90.
In this paper,the axisymmetrical shells of suspension crosssection is studied by means of integral equation in initial parameter form.An example of the shells under uniformly distributed load is calculated.  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