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   61725篇
  免费   9200篇
  国内免费   5231篇
电工技术   8436篇
技术理论   2篇
综合类   6327篇
化学工业   5304篇
金属工艺   2211篇
机械仪表   6132篇
建筑科学   3259篇
矿业工程   2194篇
能源动力   3070篇
轻工业   3416篇
水利工程   1681篇
石油天然气   2759篇
武器工业   859篇
无线电   4609篇
一般工业技术   5267篇
冶金工业   1899篇
原子能技术   309篇
自动化技术   18422篇
  2024年   365篇
  2023年   1432篇
  2022年   2574篇
  2021年   2733篇
  2020年   2947篇
  2019年   2529篇
  2018年   2237篇
  2017年   2738篇
  2016年   3059篇
  2015年   3414篇
  2014年   4863篇
  2013年   4595篇
  2012年   5338篇
  2011年   5387篇
  2010年   3724篇
  2009年   3933篇
  2008年   3455篇
  2007年   3915篇
  2006年   3240篇
  2005年   2579篇
  2004年   2094篇
  2003年   1677篇
  2002年   1421篇
  2001年   1143篇
  2000年   964篇
  1999年   622篇
  1998年   605篇
  1997年   503篇
  1996年   396篇
  1995年   356篇
  1994年   273篇
  1993年   212篇
  1992年   175篇
  1991年   143篇
  1990年   125篇
  1989年   100篇
  1988年   64篇
  1987年   28篇
  1986年   26篇
  1985年   17篇
  1984年   18篇
  1983年   20篇
  1982年   18篇
  1981年   8篇
  1980年   16篇
  1979年   13篇
  1978年   9篇
  1975年   5篇
  1959年   6篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 928 毫秒
61.
To minimize the mass and increase the bearing failure load of composite doublelap bolted joints, a three-step optimization strategy including feasible region reduction, optimization model decoupling and optimization was presented. In feasible region reduction, the dimensions of the feasible design region were reduced by selecting dominant design variables from numerous multilevel parameters by sensitivity analyses, and the feasible regions of variables were reduced by influence mechanism analyses. In model decoupling, the optimization model with a large number of variables was divided into various sub-models with fewer variables by variance analysis. In the third step, the optimization sub-models were solved one by one using a genetic algorithm, and the modified characteristic curve method was adopted as the failure prediction method. Based on the proposed optimization method, optimization of a double-lap single-bolt joint was performed using the ANSYS® code. The results show that the bearing failure load increased by 13.5% and that the mass decreased by 8.7% compared with those of the initial design of the joint, which validated the effectiveness of the three-step optimization strategy.  相似文献   
62.
针对多目标绿色柔性作业车间调度问题(MGFJSP)的特点,提出从碳排放量、噪声和废弃物这3个指标来综合评定环境污染程度,建立了以最小化最大完成时间和环境污染程度为优化目标的MGFJSP模型,并提出了一种改进的人工蜂群算法来求解该模型。算法的具体改进包括:设计了一种三维向量的编码和对应解码方案,在跟随蜂搜索阶段引入一种有效的动态邻域搜索操作来提高算法的局部搜索能力,在侦查蜂阶段提出产生新食物源的策略用于增加种群的多样性。最后进行了实验研究与算法对比,以验证所建模型和所提算法的有效性。  相似文献   
63.
This work presents an engineering method for optimizing structures made of bars, beams, plates, or a combination of those components. Corresponding problems involve both continuous (size) and discrete (topology) variables. Using a branched multipoint approximate function, which involves such mixed variables, a series of sequential approximate problems are constructed to make the primal problem explicit. To solve the approximate problems, genetic algorithm (GA) is utilized to optimize discrete variables, and when calculating individual fitness values in GA, a second-level approximate problem only involving retained continuous variables is built to optimize continuous variables. The solution to the second-level approximate problem can be easily obtained with dual methods. Structural analyses are only needed before improving the branched approximate functions in the iteration cycles. The method aims at optimal design of discrete structures consisting of bars, beams, plates, or other components. Numerical examples are given to illustrate its effectiveness, including frame topology optimization, layout optimization of stiffeners modeled with beams or shells, concurrent layout optimization of beam and shell components, and an application in a microsatellite structure. Optimization results show that the number of structural analyses is dramatically decreased when compared with pure GA while even comparable to pure sizing optimization.  相似文献   
64.
65.
基于FLUENT软件的流体体积(VOF)模型研究了不同壁面滑移程度以及不同流道结构参数下4层等厚熔体通过层叠器倍增为8层熔体时,流道中熔体的分层情况变化。结果表明,壁面滑移程度的降低会促使熔体在上下壁面聚集,进而导致上下壁面处熔体层厚增加;汇流段与出口段间圆角半径、汇流段扩压角和平衡段长度这3个结构参数则只会影响熔体在左右壁面的聚集,进而影响各层熔体的尺寸精度,且其中扩压角的影响程度最大,平衡段长度次之,圆角半径的影响较小。  相似文献   
66.
Central force optimization (CFO) is an efficient and powerful population-based intelligence algorithm for optimization problems. CFO is deterministic in nature, unlike the most widely used metaheuristics. CFO, however, is not completely free from the problems of premature convergence. One way to overcome local optimality is to utilize the multi-start strategy. By combining the respective advantages of CFO and the multi-start strategy, a multi-start central force optimization (MCFO) algorithm is proposed in this paper. The performance of the MCFO approach is evaluated on a comprehensive set of benchmark functions. The experimental results demonstrate that MCFO not only saves the computational cost, but also performs better than some state-of-the-art CFO algorithms. MCFO is also compared with representative evolutionary algorithms. The results show that MCFO is highly competitive, achieving promising performance.  相似文献   
67.
This paper addresses the multi-objective optimization problem arising in the operation of heat integrated batch plants, where makespan and utility consumption are the two conflicting objectives. A new continuous-time MILP formulation with general precedence variables is proposed to simultaneously handle decisions related to timing, product sequencing, heat exchanger matches (selected from a two-stage superstructure) and their heat loads. It features a complex set of timing constraints to synchronize heating and cooling tasks, derived from Generalized Disjunctive Programming. Through the solution of an industrial case study from a vegetable oil refinery, we show that major savings in utilities can be achieved while generating the set of Pareto optimal solutions through the ɛ-constraint method.  相似文献   
68.
通过计算机模拟金属配合物与核酸作用机理,对其理论模型能量计算和结构优化。在不同的化学环境条件下得到不同的实验模拟结果,对真实的化学反应过程有重要的指导意义和参考意义。通过Gaussian03,Gauss View等软件的结合应用,分别应用于优化计算和理论建模,熟悉了对化学软件操作应用。  相似文献   
69.
70.
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