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   7453篇
  免费   321篇
  国内免费   734篇
林业   762篇
农学   678篇
基础科学   668篇
  1069篇
综合类   3659篇
农作物   409篇
水产渔业   133篇
畜牧兽医   558篇
园艺   243篇
植物保护   329篇
  2024年   48篇
  2023年   120篇
  2022年   186篇
  2021年   209篇
  2020年   194篇
  2019年   303篇
  2018年   160篇
  2017年   295篇
  2016年   335篇
  2015年   335篇
  2014年   350篇
  2013年   409篇
  2012年   574篇
  2011年   566篇
  2010年   493篇
  2009年   517篇
  2008年   467篇
  2007年   532篇
  2006年   417篇
  2005年   352篇
  2004年   248篇
  2003年   207篇
  2002年   136篇
  2001年   128篇
  2000年   106篇
  1999年   117篇
  1998年   101篇
  1997年   75篇
  1996年   83篇
  1995年   80篇
  1994年   79篇
  1993年   65篇
  1992年   48篇
  1991年   44篇
  1990年   35篇
  1989年   45篇
  1988年   31篇
  1987年   10篇
  1986年   5篇
  1985年   1篇
  1956年   2篇
排序方式: 共有8508条查询结果,搜索用时 287 毫秒
51.
52.
In order to consider the effect of non-coincidence of torsion center and gravity center,the rectangular variable-curvature-box girder with vertical symmetrical axis is studied. Considering the influence of shear deflection and non-coincidence of torsion center and gravity center, the elastic equilibrium formulas are established. Based on deformation equations of the girder and the relations of inner forces and deformations,the flexure-torsion differential equations are developed. The equilibrium differential equations and Galerkin methods formulas for clothoid curved box girder are presented.  相似文献   
53.
According to the diffusion equation of carburizing process and its boundary conditionand initial condition, various shapes steel parts are modeled under various case carburize craft parameters, concentration distribution curves have been obtained. Various craft parameters are compared, and carburizing temperature has more influence on carbon concentration distribution. Various shapes steel parts' carbon concentration distribution curves have some difference. According to the carbon concentration distribution curve, craft parameters can be adjusted in order to obtain the best carburizing craft.  相似文献   
54.
Nonlinear characteristic of servo value is the important factor influencing hydraulic system, the model of electro-hydraulic servo pressure control system is designed. In this model, flux-equation of servo valve is specially applied and some non-linear characteristics are considered. Furthermore, SIMULINK toolbox of MATLAB language software is applied to solve mathematic model and simulation curves of some variables are obtained. The calculation results are in good agreement with the experimental results.  相似文献   
55.
A three critical point theorem is proved. As its applications, Dirichlet problem for a class of quasilinear elliptic equations cf second order is considered.  相似文献   
56.
Several aspects of the conditional equation derived from the accumulative equation are discussed in detail. The results indicate that the conditional equation not only is well consistent with the principles of electronegativity and absolute hardness equalization, but also satisfies the bonding of a full -prerequisite condition, e. g. two like electronic charge species repel and unlike attract each other'. In addition these principles are in the accumulative state. Mathematically, some other aspects of the conditional equation are worth studying based on the generalization of this equation.  相似文献   
57.
In this paper, taking a D1201 spindle as an example, we discuss the dynamic analysis of spindle by using the theory of the complex model, we also analyse the factors which effect the dynamic characterics of spindle and give results which arc reference value to improving the structure of spindle,  相似文献   
58.
59.
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   
60.
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