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   103577篇
  免费   5530篇
  国内免费   10220篇
林业   8826篇
农学   10008篇
基础科学   4570篇
  13113篇
综合类   45047篇
农作物   7289篇
水产渔业   6934篇
畜牧兽医   12846篇
园艺   4189篇
植物保护   6505篇
  2024年   572篇
  2023年   1625篇
  2022年   3073篇
  2021年   3394篇
  2020年   3478篇
  2019年   4139篇
  2018年   2938篇
  2017年   4361篇
  2016年   5346篇
  2015年   5154篇
  2014年   5471篇
  2013年   6193篇
  2012年   8314篇
  2011年   8040篇
  2010年   6344篇
  2009年   5910篇
  2008年   5672篇
  2007年   6496篇
  2006年   5775篇
  2005年   4522篇
  2004年   3473篇
  2003年   2585篇
  2002年   2101篇
  2001年   1808篇
  2000年   1711篇
  1999年   1461篇
  1998年   1241篇
  1997年   1097篇
  1996年   976篇
  1995年   982篇
  1994年   807篇
  1993年   793篇
  1992年   742篇
  1991年   620篇
  1990年   603篇
  1989年   441篇
  1988年   339篇
  1987年   218篇
  1986年   175篇
  1985年   77篇
  1984年   40篇
  1983年   25篇
  1982年   22篇
  1981年   39篇
  1980年   20篇
  1979年   20篇
  1978年   15篇
  1962年   14篇
  1956年   10篇
  1955年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
CHEN An-ming 《保鲜与加工》2007,(8):149-152159
Based on the widening of definition of talent effectiveness, using the indexes of talent structure and economic output types, many indexes of talent effectiveness are built up. A synthetic evaluation of regional talent utilization efficiency is presented based on principal components analyses. The result indicates that the talent utilization efficiency in east China is higher distinctly than in middle and west China and the talent utilization efficiency in middle is close to in west China without obvious hierarchy distribution  相似文献   
973.
Comparison between Calibration Procedure and Econometric Estimation   总被引:1,自引:0,他引:1  
The two methods of estimating parameter in computable general equilibrium(CGE) model are introduced and compared:the calibration procedure and econometric estimation. The conclusions are:the estimation of parameter in CGE model must use the calibration procedure coupled with the econometric estimation method;the elasticity of output with respect to labor input,the marginal expenditure share for households and price elasticity of export demand are estimated by econometric estimation method;and other parameters of the CGE model can be get by calibration procedure.  相似文献   
974.
This article briefly introduces the principle and the character of the leverage buyouts since the rate of finance lever and the risk is high in the LBO, this article gives a game-theory analysis on the financing process between the purchaser and the investor in LBO by using the ROSS model. It is expected that some beneficial proposal to either side can be put forward by parting the equilibrium.in the last, it poses that LBO can be a way of broadening the financing channel on the annexation between the enterprises in our country.  相似文献   
975.
Frequency refining is an important spectrum analyzing tool, and is one of the main function of signal processing and the virtual instrument. This paper introduces several typical frequency refining analysis methods including DFT and multiple modulation and so on. It also probes into their advantages and disadvantages, and proposes a new frequency refining method combining subband decomposing DFT and multiple modulation, which inherits the advantages of multiple modulation, needs not to design a specific filter, reduces the amount of calculation, and is fit for real-time refining analysis. At last, it exhibits several frequency refining algorithm and their effects with applications in virtual instruments.  相似文献   
976.
The exact three di me nsional temperatu re distribution and thermal analysiS to inte-grated circuit substrates have been presen ted by means of numerical method of a fin ite difference.Thismethed.which will overcome the di fficuItv of mathematical deduction mav be consltieredas an analytical way aided by com puters for thermal design of electron ic compon ents.  相似文献   
977.
The wavelet analysis are used in the detection of edges within the cross sectionfrom projections of parallel beams. This method can be applied in computerized tomography (CT) inorder to reduce the noise and the number of projections.  相似文献   
978.
In order to research the state of energy bands and gain and loss of electrons on the surface of ZnSnO_(3),it is put forward that Pinning theory of Fermi energy is applied to development of gas sensitive materials.The relative position between surface state and conduction band on surface of zinc tin complex oxide(ZnSnO_(3)) gas sensitive material has been investigated by utilizing oxidation redox couple,FeCl_(2)/ FeCl_(3),which have high surface state.Fermi energy is pinned at about 0.2 eV below conduction band E_(cs)on the surface of ZnSnO_(3).It has been determined that additives doping ratio,addition concentration and working atmosphere have no effect on this value.Therefore,pinning theory of Fermi energy has been verified by using this method.  相似文献   
979.
A novel edge detection algorithm is proposed by implementing fuzzy image enhancement at different scales.The implement of this algorithm can reduce the negative influence bring from the non-maximum suppression algorithm which select only one threshold.The success of the approach depends on the selection of a general fuzzy operator(GFO) for the enhancement of contrast of region after smoothing of image at different scales.Consequently,it is more obvious that coarse intensity changes are obtained at a large scale whereas the fine details of intensity changes are obtained at a small scale.A pretty performance is obtained by used this work.  相似文献   
980.
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   
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