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   6259篇
  免费   529篇
  国内免费   640篇
林业   678篇
农学   469篇
基础科学   291篇
  1290篇
综合类   2570篇
农作物   166篇
水产渔业   658篇
畜牧兽医   551篇
园艺   101篇
植物保护   654篇
  2024年   67篇
  2023年   221篇
  2022年   279篇
  2021年   291篇
  2020年   351篇
  2019年   371篇
  2018年   224篇
  2017年   312篇
  2016年   309篇
  2015年   270篇
  2014年   360篇
  2013年   388篇
  2012年   475篇
  2011年   442篇
  2010年   350篇
  2009年   376篇
  2008年   291篇
  2007年   359篇
  2006年   280篇
  2005年   216篇
  2004年   199篇
  2003年   153篇
  2002年   143篇
  2001年   106篇
  2000年   88篇
  1999年   70篇
  1998年   67篇
  1997年   37篇
  1996年   40篇
  1995年   52篇
  1994年   44篇
  1993年   31篇
  1992年   38篇
  1991年   28篇
  1990年   20篇
  1989年   23篇
  1988年   19篇
  1987年   7篇
  1986年   5篇
  1984年   6篇
  1982年   6篇
  1981年   3篇
  1980年   2篇
  1979年   1篇
  1978年   3篇
  1977年   2篇
  1976年   3篇
排序方式: 共有7428条查询结果,搜索用时 62 毫秒
61.
62.
63.
The externality of surrounding is introduced into the 2-capital of economical increasing models, which includes human factors, to explore the influences of circumstances contradiction on the human capital formation. The normal and special nash equilibrium of environmental and human capital is presented through a limited boundary model of overlapping generations. The character of equilibrium trail and its economical meaning are examined. The study on the model shows that laissez faire economy will be either stagnant,growing,or collapsing in the long-run,depending on the returns of the learning technology with respect to the two kinds of capital,the initial state of economy,and the relative price of the environmental and consumption goods.  相似文献   
64.
Mathematical model of power frequency electric field is established based on Charge Simulation Method(CSM) to analyze power frequency electric field caused by EHV lines with overhead ground wires and its effect, which are entering the megalopolis. Calculative method on the electric field under the transmission lines is analyzed and validated. According to the criterion of environmental evaluation, the distributing characteristic of electric field is summarized, in case of various arrangement manners of lines. At last, some advice and methods of eliminating electric field under the transmission lines entering the megalopolis is proposed with regard to protecting environment.  相似文献   
65.
In this paper we concider the problem of stability of stochastic evolution systemsin Hilbert space drived by a cylindrical Brownian mothin. We regard the stochestic evolutionequation dXt = AXtdt +G(Xt)dBt as a deterministic system of the form dXt=AXtdt under randomperturbation,and obtain stability of its solution. It is shown that under certain assumptions,itsevolution solution and L2-contimuous evulution solution are exponertially stable.  相似文献   
66.
In this paper, the problems of bringing natural resources and environmental condition into accounting are discussed and lay emphasis on object measurement, imaging and disclosure in accounting report of environmental accounting. The author suggests that the environmental accounting is the necessary production of global economy for sustainable development in modern society; it is also a new ecological accounting subject formed by the result of environmental economies and accounting penetrating into each other. As a contribution of accounting circles to sustainable development, environmental accounting has become a hot topic in recent years.  相似文献   
67.
68.
The basic principle of infinite-dimensional dynamic system is to try to reduce the original infinite-dimensional system to an infinite-dimensional system. However,due to the unknown structure of the reduced system, it is difficult to describe its dynamical behaviour. To overcome this difficulty, the idea of approximate inertial manifolds is introduced, for NSE, the existence of AIM was studied, it is shown that the global attractor lies within a neighborhood of the graph of an Lipschitz function by the squeezing property. In this paper, by constructing a finite dimensional solution sequence, we will prove that it tends to the global attractor, theoretically, this provides a metod of constructing the asymptotic attractors, theoretically, this provides a method of constructing the asymptotic attractors for the evolution equations.  相似文献   
69.
This papar presents an evolution model in business behaviors-the L-S Business Strategies,gives some examples and predictions which support these strategies,and analyzes the relationship between the industrial organizations in China and the L-S Business strategies.  相似文献   
70.
The problem of fuzzy evaluation of environmental pollution is importantboth in environment science and in environmental protection.Usual evaluationmethods have their own characteristics.This paper puts forward a mathematicalmodel of fuzzy evaluation method in grades by means of systematic analysisfor environmental pollution.At the same time,it assigns weighted values byordering based on paired comparison.  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