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   84435篇
  免费   4132篇
  国内免费   9183篇
林业   9338篇
农学   12215篇
基础科学   7110篇
  13122篇
综合类   27745篇
农作物   4637篇
水产渔业   2928篇
畜牧兽医   11705篇
园艺   3540篇
植物保护   5410篇
  2024年   229篇
  2023年   907篇
  2022年   2311篇
  2021年   3282篇
  2020年   2856篇
  2019年   2891篇
  2018年   2043篇
  2017年   2969篇
  2016年   2750篇
  2015年   3893篇
  2014年   3768篇
  2013年   4513篇
  2012年   5589篇
  2011年   5974篇
  2010年   5944篇
  2009年   5444篇
  2008年   5023篇
  2007年   5152篇
  2006年   4815篇
  2005年   4238篇
  2004年   2057篇
  2003年   1958篇
  2002年   1706篇
  2001年   1702篇
  2000年   1750篇
  1999年   1974篇
  1998年   1718篇
  1997年   1545篇
  1996年   1414篇
  1995年   1270篇
  1994年   1084篇
  1993年   1115篇
  1992年   876篇
  1991年   738篇
  1990年   624篇
  1989年   501篇
  1988年   382篇
  1987年   230篇
  1986年   127篇
  1985年   66篇
  1984年   44篇
  1983年   40篇
  1982年   49篇
  1981年   48篇
  1980年   32篇
  1979年   14篇
  1965年   15篇
  1964年   11篇
  1963年   12篇
  1956年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
The feasible control problem is presented for the day-operation of the Three-Gorge Caseade Hydropower Station. The significance of the problem is explained. Basic propetties ofthe problem and the approaches to study it are discussed. Two methfods are given for solving theproblem. which are calculus of variation and linear programming. In the former. the Euler equationwith time-lag and the generalised two-point boundary conditions are obtained and the correspondingpractical implication is interpreted. In the latter. the rationality for the discrete model is exptainedand the computalional details are given for the implement software. some questions which should bepaid much attentfon and the corresponding propeels are prasented based on the numerical results andtheoretical analysis  相似文献   
984.
面对全球、我国和我省种子产业的发展趋势,分析了我国高校近年来建立种子学科的现状和广东有关高校种子学科建设的可能性,提出了一些仅供参考的设想.  相似文献   
985.
Gymnasium in Harbin Normal University Sports Center is a large-scale gymnasium. This paper analyzes unfavorable factors in its acoustics and illustrates different kinds of intention of the design. At the same time, the questions about the project operation and technique are pondered one by one, it is expected that these thinking can provide some experience to the similar project.  相似文献   
986.
987.
This paper analyzes the current situation of university students' credit evaluation and set up an evaluation index system of university students' credit to compensate a loan.Based on this index system,this paper sets up a matter-element evaluation model on the individual credit of university students loan by means of extensible engineering method.The grade of individual credit and the index for evaluating the level of individual credit are made as matter-element,meanwhile,the classical field,the segment field,the weight coefficient are obtained.Dependence function is established based on the grade of individual credit and then the grade is judged by calculating the synthetic dependence degree.Finally,this paper presents the evaluation method by giving an example.This method is simple in calculation,reasonable in evaluation with high applicability.  相似文献   
988.
Along with the establishment of the constructor association,how to locate the constructor association is extremely important at present,which is not only related to the efficiency of the constructor trade management,but also related to the future development of the constructor trade.This paper launches the discussion on the constructor association's localization from three aspects,namely the legal localization,the profession localization and the relation localization with the government and its members,and puts forward some proposals and individual opinions.  相似文献   
989.
MA Li  TANG Qi 《保鲜与加工》2002,(2):124-127
According to the present research situation of conductive polymer materials- polyaniline (PAN) ,we reviewed the structure and properties of PAN, the effecting factors and the best conditions of electrochemical synthesis and chemical synthesis of PAN , the doping mechanism of PAN, inorganic and organic acid doping,secondary doping, the method of increase soublity and processability of PAN and the broad application of PAN. The development derection and prospect of PAN are pointed out.  相似文献   
990.
The preparation method of transparent film of electrochromism polyaniline on the glass supporter is studied by a dipping polymerization. The electric and optic properities of the resulting film are measured as a function of oxidant,dopant,reaction time and temperature.The optimum technology term is obtained in the normal atmospheric temperature.The experimental result is testified by fuzzy set theory.  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