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   29823篇
  免费   1476篇
  国内免费   2939篇
林业   3514篇
农学   2394篇
基础科学   1794篇
  4726篇
综合类   13285篇
农作物   1817篇
水产渔业   1459篇
畜牧兽医   2392篇
园艺   856篇
植物保护   2001篇
  2024年   270篇
  2023年   681篇
  2022年   1221篇
  2021年   1268篇
  2020年   1233篇
  2019年   1436篇
  2018年   931篇
  2017年   1427篇
  2016年   1750篇
  2015年   1431篇
  2014年   1848篇
  2013年   1783篇
  2012年   2381篇
  2011年   2324篇
  2010年   1869篇
  2009年   1804篇
  2008年   1478篇
  2007年   1578篇
  2006年   1256篇
  2005年   946篇
  2004年   738篇
  2003年   639篇
  2002年   490篇
  2001年   430篇
  2000年   388篇
  1999年   336篇
  1998年   280篇
  1997年   285篇
  1996年   251篇
  1995年   272篇
  1994年   219篇
  1993年   215篇
  1992年   165篇
  1991年   159篇
  1990年   129篇
  1989年   134篇
  1988年   85篇
  1987年   51篇
  1986年   21篇
  1985年   7篇
  1984年   3篇
  1982年   3篇
  1981年   5篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
  1963年   2篇
  1962年   4篇
  1956年   3篇
  1955年   6篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
[目的]奶冻在储存过程中常出现失水现象,为提高奶冻贮藏中的品质和保水性。[方法]以不同时间下奶冻质构特性、持水力、感官品质指标评价奶冻品质,探究明胶添加量以及明胶-卡拉胶复配对奶冻品质的影响。[结果]随明胶添加量增大,水析率、回复性和弹性逐渐减小,硬度和咀嚼度逐渐增大,感官品质先提升后下降,明胶添加量为1.8%时奶冻品质最好;在总胶体用量为1.8%情况下,卡拉胶比例增大,水析率和弹性变化幅度小,硬度先增大后减小再增大,咀嚼度先减小后增大,回复性减小,感官品质先降低后提升最后持续降低,卡拉胶比例为7%时其奶冻品质最好。[结论]1.8%的胶体添加量下添加7%的卡拉胶与明胶复配提高了奶冻的贮藏品质,胶体复配可改善奶冻贮藏中品质下降问题。  相似文献   
122.
微热光电系统燃烧室内截面突变对燃烧的影响   总被引:1,自引:0,他引:1  
微燃烧室是微热光电(MTPV)系统的重要组成部分。微燃烧室的外表面必须产生一个高而均匀的温度分布,以尽可能高地输出辐射能。通过对截面突变的微燃烧室的试验研究,得到了不同氢氧混合气流量、氢氧体积混合比下燃烧室内的燃烧状况,壁面和出口端面的温度分布。试验结果表明:采用截面突变的燃烧室能很好地控制火焰中心位置,获得稳定的外壁面温度分布规律,可以在截面突变处产生涡流,增强氢气和氧气的混合。  相似文献   
123.
The test of functional groups of microorganisms in Spiral Up-flow Reactor System and the correlation between microorganisms in the water and the main environmental factors are studied.The results show that the diversity of microorganisms population in the SUFR system is complex and the bio-community formed in the SUFR system is stable.The close relations between abundance of bacteria and nutrients are found.The correlation between heterotrophic bacteria and COD is 0.949.The correlation between organic phosphate bacteria and TP is 0.815. The correlation between nitrosobacteria and NH_3-N is 0.909. The correlation between disnitrifier bacteria and TN is 0.653.  相似文献   
124.
弱光条件下桃光合作用的动态变化及品种差异分析   总被引:3,自引:1,他引:3  
于桉  孔云  姚允聪 《中国农学通报》2005,21(9):242-248,254
就日光温室桃树光合生理进行了详尽的研究,结果表明:1d中叶温与气温以14:00时较高。遮阴明显地降低了到达叶片表面的有效光合辐射、叶温与气温。桃叶片的光合速率日变化为双峰曲线,峰值大约出现在上午10:00与下午14:00时;不同品种弱光下的光合速率有明显的差异,以NJN较高,其次为五月火与麦香。遮阴降低了桃叶片的光合速率,以NJN光合速率降低的较少,说明NJN能适应设施栽培。气孔阻力与蒸腾速率则随着遮阴程度的增加而增加。桃中位叶的光合速率较幼叶高。  相似文献   
125.
A theoretical model is developed for the dropwise condensation heat transfer on the horizontal circular surface with radial gradient surface energy based on the heat transfer model of individual condensate drop and the size distribution model of condensate drop on homogeneous condensation surface.The effect of variation of contact angle on the gradient surface on condensation heat transfer and condensate drop size distribution is taken account of in this model.The theoretical calculation method was obtained to predict the dropwise condensation heat transfer coefficient on the horizontal circular surface with radial gradient surface energy under various wall subcooled temperature,contact angle profile on wall surface,and working fluid.The effects of surface energy gradient,wall subcooled temperature,and thermophysical properties of condensate on the condensation heat transfer are discussed respectively.The calculation results show that the condensation heat transfer coefficient increases slightly with the increase of wall subcooled temperature.As latent heat and surface tension increasing,the condensation heat transfer coefficient increases.A larger surface energy gradient induces a larger condensation heat transfer coefficient.  相似文献   
126.
The traditional scheduling for vehicle is option in the fixed network. But it can't satisfy the real time environment. The demand of order is changeable and uncertain in real environment. It is convenient for scheduling transforming it into static data, but can't get the advantage on time. This paper proposes a real time vehicle scheduling on the study of traditional scheduling and discusses the model structure and the key technology for the real time system that establishes the base for develop teal time system.  相似文献   
127.
Distribution Network Structure planning is a complex combinatorial optimization problem,which is difficult to solve properly by using traditional optimization methods.In order to solve this problem,Improved Immune Genetic Algorithm is introduced to the distribution network optimal planning. Improved Immune Genetic Algorithm draws into the immune diversity and antibody's density mechanism to maintain the individual's diversity and remains evolution algorithm's global stochastic searching ability,so it can promote diversity and the whole optimal-searching ability of genetic algorithm.The optimal module takes the minimum annual cost as its object,and the capacity and voltage drop of feeder and the radiation of distribution network as its restrictions.According to the require of radiation of distribution network,the spanning tree of the alternative network is taken as the initial solution to speed up the calculation.And the branch-exchange method is used in designing crossover operator and mutation operator to avoid the radiation checking and enhance the optimizing ability.This algorithm has been illustrated effectively by examples,at the same time,the calculation example demonstrates that,the algorithm has higher calculation speed than the traditional immune genetic algorithm.  相似文献   
128.
The deformation characteristics of the fine-sandstone is studied under the loading and unloading conditions at the three different deformation-rates and the two different stress-levels. The experimental results show that there is really the plastic-loop in the deformation curve for the loading deformation curve is different from the unloading deformation curve. But the plastic-loop is nearly unchangeable since the second circulate loading. The residual-deformation is be almost zero since the second circulate loading, and that the slope of the deformation curve increases as the deformation-rate increases, and that the residual-deformation increases as the stress-levels increases.  相似文献   
129.
In general, the process of synthesis the refractory nanoparticles Is classified as solid state, liquid state and gaseity. The new progress and development in the study of refractory nanoparticles are investigated. The synthesis technology of the refrectory nanoparticle in liquid state is discussed mostly. The refrectory nanoparticles is synthesized by the liquid state. The characteristics and the structure of the refrectory nanoparticles have been studied in this paper.  相似文献   
130.
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