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   94342篇
  免费   5123篇
  国内免费   7595篇
林业   10791篇
农学   7235篇
基础科学   6691篇
  13957篇
综合类   46153篇
农作物   3906篇
水产渔业   3092篇
畜牧兽医   8232篇
园艺   2292篇
植物保护   4711篇
  2024年   532篇
  2023年   1518篇
  2022年   2319篇
  2021年   2400篇
  2020年   2455篇
  2019年   3044篇
  2018年   1747篇
  2017年   3034篇
  2016年   3788篇
  2015年   3439篇
  2014年   4489篇
  2013年   4659篇
  2012年   6778篇
  2011年   7182篇
  2010年   5903篇
  2009年   5784篇
  2008年   5428篇
  2007年   6391篇
  2006年   5636篇
  2005年   4746篇
  2004年   3615篇
  2003年   3125篇
  2002年   2412篇
  2001年   2095篇
  2000年   1915篇
  1999年   1552篇
  1998年   1360篇
  1997年   1254篇
  1996年   1206篇
  1995年   1186篇
  1994年   1093篇
  1993年   956篇
  1992年   890篇
  1991年   752篇
  1990年   673篇
  1989年   593篇
  1988年   440篇
  1987年   293篇
  1986年   137篇
  1985年   50篇
  1984年   27篇
  1983年   23篇
  1982年   20篇
  1981年   19篇
  1980年   26篇
  1979年   16篇
  1978年   16篇
  1977年   7篇
  1976年   10篇
  1962年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
In earlier calculation models,the stiffness centers in frame-shear wall structures have been located by the structural torsion stiffness.However,the results are illogical owing to the difference between the distortion character and the shears distribute mechanism of the frames and shear walls.In this paper,a new formula for calculating story stiffness is introduced,which can consider the stiffness of the frames and shear walls at the same time.The structural stiffness centers,the torsion eccentric distances and torsion effect are calculated,and the stiffness of elements is considered also.It is shown that the concept of the presented stiffness model is clear and the results are reasonable,which can be used to calculate the appreciative torsion effect.  相似文献   
942.
According to the investigations of urban barrier free facilities, there have been lots of progresses in constructions of barrier free in cities recently. But there are no systematic barrier free facilities in these cities, which would restrict the function and effect of urban barrier free facilities for the handicapped and the elder. This paper puts forward that there should be a development from the urban barrier free facilities to the urban barrier free environment. There are two parts in the barrier free environment,that is the hardy environment and soft environment. Finally,an in-series connection two-core model of barrier free environment has been designed and discussed.  相似文献   
943.
944.
945.
946.
The datum line and mainly three profile height parameters of surface roughness are briefly introduced and the operation principle and system structure of AFM. IPC - 208B with high-resolution, which was successfully developed by Chongqing University, are described in detail, and the emphasis is laid on its application on the nanometer scale surface roughness. Taking stainless steel for example, its micro-structure was observed, and the surface data were analyzed and transacted by special evaluator and the values of three profile height parameters were obtained. Finally the experimental results are briefly analyzed.  相似文献   
947.
Valuation based on the bill of quantifies will change the existing valuation mode of tender and bidding. For the standardized management of tender and bidding for power projects and the inteUigentized information management of power enterprises, it is an inevitable trend of reform to apply the valuation mode based on the bill of quantifies. According to the characteristics of power projects, this paper expounds the working process of the valuation mode based on the bill of quantities and analyzes the goal and function need of the tender and bidding management system. Considering the calculation procedure of the valuation and the quote strategy of quantities bill, the composition of fees for the valuation is settled and the calculation method is designed. To establish the management system of tender and bidding with a valuation based on the bill of quantities is beneficial for the costing reform of power projects and the perfection of the tender and bidding market. Therefore it is of great significance to spread the new management mode of project costing with a valuation based on the bill of quantities.  相似文献   
948.
949.
Based on by typical coding schemes such as EZW,SPIHT, EBCOT,3D-IEZW,3D-SPIHT and 3D-ESCOT,a context model(3D-OWNER) of wavelet coefficients is proposed,which makes use of partial order,self-similarity between subbands of wavelet coefficients and the correlation of neighboring wavelet coefficients.Experimental results show that the model can achieve higher PSNR than 3D-ESCOT.  相似文献   
950.
为降低建筑能耗影响因素间复杂相关性对模型性能的影响,建立了一种基于KPCA-WLSSVM的建筑能耗预测模型。利用核主元分析(KPCA)对输入变量进行数据压缩,消除变量之间的相关性,简化模型结构;进一步采用加权最小二乘支持向量机(WLSSVM)方法建立建筑能耗预测模型,同时结合一种新型混沌粒子群-模拟退火混合优化(CPSO-SA)算法对模型参数进行优化,以提高模型的预测性能及泛化能力。通过将KPCA-WLSSVM模型方法应用于某办公建筑能耗的预测中,并与WLSSVM、LSSVM及RBFNN模型相比,实验结果表明,KPCA-WLSSVM模型方法能有效提高建筑能耗预测精度。  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