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   17710篇
  免费   780篇
  国内免费   1623篇
林业   1757篇
农学   1712篇
基础科学   1738篇
  2500篇
综合类   8627篇
农作物   694篇
水产渔业   393篇
畜牧兽医   1563篇
园艺   384篇
植物保护   745篇
  2024年   99篇
  2023年   296篇
  2022年   490篇
  2021年   575篇
  2020年   548篇
  2019年   669篇
  2018年   362篇
  2017年   709篇
  2016年   922篇
  2015年   799篇
  2014年   1016篇
  2013年   1072篇
  2012年   1479篇
  2011年   1363篇
  2010年   1092篇
  2009年   1044篇
  2008年   971篇
  2007年   978篇
  2006年   906篇
  2005年   695篇
  2004年   511篇
  2003年   482篇
  2002年   390篇
  2001年   344篇
  2000年   314篇
  1999年   271篇
  1998年   253篇
  1997年   215篇
  1996年   200篇
  1995年   170篇
  1994年   139篇
  1993年   145篇
  1992年   134篇
  1991年   105篇
  1990年   93篇
  1989年   95篇
  1988年   75篇
  1987年   41篇
  1986年   27篇
  1985年   6篇
  1984年   5篇
  1983年   1篇
  1982年   2篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1956年   2篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
201.
《保鲜与加工》1997,(6):58-62
In this paper,in terms of the measured data(including the deflection and slope at the ground surface of the pile,the maximum bending moment and its position),the biparameter method is used to analyze the pile-soil parameters.Two examples show that the method in present paper is reasonable and reliable,and it provides the reference value for the engineering design.  相似文献   
202.
Based on [l].this paper presents a new spline-BEM for calculating 3-D electrostatic fields,in which bi-cubic B-splines are used as basis functions. The corner problem in BEM and the extreme conditions for splines are circumvented. The numerical results presented show that the global approximation .convergence and stability of the method are satisfactory.  相似文献   
203.
This paper presents a new hierarchical and coordinative control method for reactive power optimization in large-scale interconnected power systems. It combines the interconnection forecast method for hierarchical control in large-scale steady state industrial systems with the incremental linear programming method for reactive power optimization in real time. The results of applying the method to power system examples show that the method not only solves the problem of high dimension in order, but also keeps the advantages of the incremental linear programming method. The proposed method is also suitable for the security analysis of reactive power correction in large-scale interconnected power systems.  相似文献   
204.
Based upon the eigenvalue sensitivity theory of non-self-adjoit system and the component mode synthesis method,a new technique is developed to analyze the eigenvalue sensitivity to variation of parameters of large rotor-bearing system. As an application, the influence of the journal bearing parameters on the stability of a large domestic turbine-generator set is analyzed and discussed.  相似文献   
205.
A new finite element method is presented in this paper to analyze the thermo- elastic contact problem with heat input on meshing tooth faces. The computational model of meshing gear has been established and the frictional heat input on meshing tooth faces is estimated. In addition, 2-D finite element analysis program for this kind of problem is listed. The test and practical examples are given to show the validity and versatility of this method.  相似文献   
206.
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   
207.
A fast dual algorithm is presented for the piecewise linear programming with successively increasing slopes. The concept of the pointer is used to derive the optimality and the feasibility conditions based on the dual simplex principle, which avoids enlarging the scale of the problem due to introducing piecewise variables so that storage and calculating requirements are reduced. Finally,the example is given to demonstrate the effectiveness of the presented algorithm.  相似文献   
208.
209.
The secant rigidity is used for the are-length method to solve the nonlinear finite elements problems. The advantage of this method is unnecessary of calculating the initial resistance term caused by the incremental step. The computational work is less and the programing is easier as compared with initial are-length method. This method can be widely used to solve nonlinear problems.  相似文献   
210.
In order to overcome some technical difficulties,we adopt ingenously the grey models combined with the quantitative analog method,and select the Dan Jiangkou Project which has accumulated practical operation data for a long time as the analog project to predict the economic influence for the circumjacent reservoir region of the Longtan hydropower project.On the basis of analog we have built various industrial economic grey models,and compare them with the corresponding predictions for the unconstructed reservoir case.The predictions of the former are greatly larger than the later ones.and hence provides a certain scientific basis for the central leaders to make a decision for constructing the huge hydropower project ultimateiy.  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