全文获取类型
收费全文 | 284647篇 |
免费 | 25686篇 |
国内免费 | 15859篇 |
专业分类
电工技术 | 18187篇 |
技术理论 | 7篇 |
综合类 | 29134篇 |
化学工业 | 40958篇 |
金属工艺 | 13755篇 |
机械仪表 | 15667篇 |
建筑科学 | 26715篇 |
矿业工程 | 9206篇 |
能源动力 | 8340篇 |
轻工业 | 19662篇 |
水利工程 | 9215篇 |
石油天然气 | 11671篇 |
武器工业 | 2949篇 |
无线电 | 21758篇 |
一般工业技术 | 37291篇 |
冶金工业 | 10840篇 |
原子能技术 | 4959篇 |
自动化技术 | 45878篇 |
出版年
2024年 | 692篇 |
2023年 | 2969篇 |
2022年 | 6207篇 |
2021年 | 8278篇 |
2020年 | 6987篇 |
2019年 | 6234篇 |
2018年 | 6340篇 |
2017年 | 7800篇 |
2016年 | 9934篇 |
2015年 | 11263篇 |
2014年 | 16593篇 |
2013年 | 16748篇 |
2012年 | 18081篇 |
2011年 | 18350篇 |
2010年 | 14727篇 |
2009年 | 16418篇 |
2008年 | 15786篇 |
2007年 | 19251篇 |
2006年 | 17653篇 |
2005年 | 14944篇 |
2004年 | 11872篇 |
2003年 | 10889篇 |
2002年 | 9601篇 |
2001年 | 7604篇 |
2000年 | 7411篇 |
1999年 | 6382篇 |
1998年 | 5076篇 |
1997年 | 4608篇 |
1996年 | 4423篇 |
1995年 | 4270篇 |
1994年 | 3814篇 |
1993年 | 2485篇 |
1992年 | 2379篇 |
1991年 | 1666篇 |
1990年 | 1306篇 |
1989年 | 1204篇 |
1988年 | 991篇 |
1987年 | 611篇 |
1986年 | 427篇 |
1985年 | 504篇 |
1984年 | 552篇 |
1983年 | 507篇 |
1982年 | 419篇 |
1981年 | 496篇 |
1980年 | 342篇 |
1979年 | 175篇 |
1978年 | 146篇 |
1977年 | 95篇 |
1976年 | 71篇 |
1975年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In this work, the longitudinal permeability of squarely packed dual-scale fiber preforms is studied theoretically. These fiber preforms are composed of aligned porous tows and the tows are tightly packed. The effective permeability is calculated as a parallel-like network of intra-tow permeability and inter-tow permeability, which are quantified by Darcy’s law and the inscribed radius between tows, respectively. The jump velocity at the interface between inter-tow fluids and porous tows is considered, as derived by substituting Beavers and Joseph’s correlation into Brinkman’s equation. We further examine the effects of intra-tow permeability on the effective permeability of the fibrous system with three interface conditions: (1) interface velocity = 0, (2) interface velocity = mean intra-tow velocity, and (3) interface velocity = jump velocity. The jump-velocity-based model is found to be closest to numerical data. The influence of the fiber volume fraction of tows on the effective permeability is also analyzed. 相似文献
52.
53.
针对异构计算节点组成的大规模多状态计算系统的容错性能分析问题,提出了一种计算系统容错性能的评估方法。该方法采用自定义的两级容错性能形式化描述框架进行系统描述,通过构造多值决策图(Multi-value Decision Diagram,MDD)模型对系统进行容错性能建模,并基于构造的模型高效地计算出部件故障的条件下计算系统在特定性能水平上运行的概率,减少了计算的冗余性。实验结果表明,该方法在模型的大小和构建时间上均优于传统方法。该方法的提出将对系统操作员或程序设计者具有重要意义,使其确保系统适合预期应用。 相似文献
54.
55.
56.
反应堆屏蔽计算中经常出现厚屏蔽、小探测器问题,常规蒙特卡罗方法难以有效解决。基于自动重要抽样(AIS)方法,本文提出了小探测器自动重要抽样(SDAIS)方法,并针对小探测器问题,优化了AIS方法的虚粒子赌分裂算法。该方法在自主开发的蒙特卡罗屏蔽程序MCShield上进行了实现。使用NUREG/CR-6115 PWR基准题验证该方法的正确性和计算效率。结果表明,SDAIS方法可有效地解决厚屏蔽小探测器问题,相比AIS方法及传统的重要性方法,计算效率提升1~2个量级。 相似文献
57.
不同给液方式对铜电解过程中有重要的影响,不同的循环方式会影响槽内温度分布、电解液成分及阳极泥沉降等,因此,根据铜电解生产不同情况的需要,分析对比了多种给液方式在贵冶电解车间的应用,总结了这几种给液方式的优缺点和适用条件。 相似文献
58.
A 2D computational fluid dynamics (Eulerian–Eulerian) multiphase flow model coupled with a population balance model (CFD-PBM) was implemented to investigate the fluidization structure in terms of entrance region in an industrial-scale gas phase fluidized bed reactor. The simulation results were compared with the industrial data, and good agreement was observed. Two cases including perforated distributor and complete sparger were applied to examine the flow structure through the bed. The parametric sensitivity analysis of time step, number of node, drag coefficient, and specularity coefficient was carried out. It was found that the results were more sensitive to the drag model. The results showed that the entrance configuration has significant effect on the flow structure. While the dead zones are created in both corners of the distributors, the perforated distributor generates more startup bubbles, heterogeneous flow field, and better gas–solid interaction above the entrance region due to jet formation. 相似文献
59.
The main objective of the present work is to improve the performance of bonded joints in carbon fiber composite structures through introducing Multi-Walled Carbon Nanotubes (MWCNTs) into Epocast 50-A1/946 epoxy, which was primarily developed for joining and repairing of composite aircraft structures. Results from tension characterizations of structural adhesive joints (SAJs) with different scarf angles (5–45°) showed improvement up to 40% compared to neat epoxy (NE)–SAJs. Special attention was considered to investigate the performance of SAJs with 5° scarf angle under different environments. The tensile strength and stiffness of both NE-SAJs and MWCNT/E-SAJs were dramatically decreased at elevated temperature. Water absorption showed a marginal drop of about 2.0% in the tensile strength of the moist SAJs compared to the dry one. Cracks initiation and propagation were detected effectively using instrumented-SAJs with eight strain gauges. The experimental results agree well with the predicted using three-dimensional finite element analysis model. 相似文献
60.
This paper presents the Kriging model approach for stochastic free vibration analysis of composite shallow doubly curved shells. The finite element formulation is carried out considering rotary inertia and transverse shear deformation based on Mindlin’s theory. The stochastic natural frequencies are expressed in terms of Kriging surrogate models. The influence of random variation of different input parameters on the output natural frequencies is addressed. The sampling size and computational cost is reduced by employing the present method compared to direct Monte Carlo simulation. The convergence studies and error analysis are carried out to ensure the accuracy of present approach. The stochastic mode shapes and frequency response function are also depicted for a typical laminate configuration. Statistical analysis is presented to illustrate the results using Kriging model and its performance. 相似文献