全文获取类型
收费全文 | 34182篇 |
免费 | 3965篇 |
国内免费 | 2262篇 |
专业分类
电工技术 | 3949篇 |
综合类 | 3981篇 |
化学工业 | 2935篇 |
金属工艺 | 2412篇 |
机械仪表 | 3069篇 |
建筑科学 | 3280篇 |
矿业工程 | 2150篇 |
能源动力 | 1506篇 |
轻工业 | 2295篇 |
水利工程 | 1302篇 |
石油天然气 | 1929篇 |
武器工业 | 608篇 |
无线电 | 2841篇 |
一般工业技术 | 3232篇 |
冶金工业 | 1150篇 |
原子能技术 | 459篇 |
自动化技术 | 3311篇 |
出版年
2024年 | 70篇 |
2023年 | 469篇 |
2022年 | 923篇 |
2021年 | 1070篇 |
2020年 | 1136篇 |
2019年 | 966篇 |
2018年 | 941篇 |
2017年 | 1239篇 |
2016年 | 1327篇 |
2015年 | 1397篇 |
2014年 | 2088篇 |
2013年 | 2045篇 |
2012年 | 2542篇 |
2011年 | 2789篇 |
2010年 | 2104篇 |
2009年 | 2192篇 |
2008年 | 1947篇 |
2007年 | 2630篇 |
2006年 | 2260篇 |
2005年 | 1804篇 |
2004年 | 1474篇 |
2003年 | 1227篇 |
2002年 | 994篇 |
2001年 | 856篇 |
2000年 | 745篇 |
1999年 | 584篇 |
1998年 | 418篇 |
1997年 | 434篇 |
1996年 | 344篇 |
1995年 | 291篇 |
1994年 | 248篇 |
1993年 | 169篇 |
1992年 | 166篇 |
1991年 | 120篇 |
1990年 | 83篇 |
1989年 | 80篇 |
1988年 | 62篇 |
1987年 | 22篇 |
1986年 | 30篇 |
1985年 | 14篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 17篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
《International Journal of Hydrogen Energy》2021,46(80):39665-39674
The behaviors and kinetics of hydrogen evolution reaction (HER) on pure aluminum with passive film in the presence and absence of chloride ion are quantitatively investigated by using the tip generation/substrate collection mode of scanning electrochemical microscopy (SECM) with dual Al/Pt ultramicroelectrode (UME) as tip electrode and Pt UME as substrate electrode. The standard rate constants k0 and transfer coefficients αH of HER in ClO4−- and Cl−-containing solution are 6.9 × 10−7 cm/s and 0.22, 7.1 × 10−6 cm/s and 0.19, respectively. Results show that the kinetic of HER is slow and the destruction of Cl− on passive film can significantly promote the HER on Al surface. Moreover, these αH far less than commonly used 0.5 in corrosion research, can explain the great difference between theoretical Tafel slopes and experimental results. Besides, the existence of current plateau in Al electrode explains the large difference in corrosion potential during parallel testing. 相似文献
62.
63.
为解决定距螺旋桨与船用主机在船舶运行工况的机桨匹配问题,结合船舶系泊和航行试验的相关标准,分析和归纳船舶运行数据,将实船测试与船机桨匹配理论计算相结合,得出运输船和拖轮在常用工况及特殊工况下定距螺旋桨对主机外特性的定量要求,为配套不同细分市场时船用主机的优化和开发提供参考依据。 相似文献
64.
This paper presents an investigation of the age-dependent size effect and fracture characteristics of ultra-high performance concrete (UHPC). The study is based on a unique set of experimental data connecting aging tests for two curing protocols of one size and size effect tests of one age. Both aging and size effect studies are performed on notched three-point bending tests. Experimental data are augmented by state-of-the-art simulations employing a recently developed discrete early-age computational framework. The framework is constructed by coupling a hygro-thermo-chemical (HTC) model and the Lattice Discrete Particle Model (LDPM) through a set of aging functions. The HTC component allows taking into account variable curing conditions and predicts the maturity of concrete. The mechanical component, LDPM, simulates the failure behavior of concrete at the length scale of major heterogeneities. After careful calibration and validation, the mesoscale HTC-LDPM model is uniquely posed to perform predictive simulations. The ultimate flexural strengths from experiments and simulations are analyzed by the cohesive size effect curves (CSEC) method, and the classical size effect law (SEL). The fracture energies obtained by LDPM, CSEC, SEL, and cohesive crack analyses are compared, and an aging formulation for fracture properties is proposed. Based on experiments, simulations, and size-effect analyses, the age-dependence of size effect and the robustness of analytical-size effect methods are evaluated. 相似文献
65.
对煤的自燃倾向进行快速有效鉴别,有助于对煤的自燃倾向采取分级分类管理从而有效防治煤矿火灾,因而采用绝热式自燃测试方法对煤的自燃倾向进行准确分析很有必要。简要介绍绝热式自燃测试方法的测试原理及其仪器结构,模拟煤炭自燃的物理过程,通过采用包括反应器、气体预热铜管和跟踪温度控制方式等综合绝热措施以实现300 g煤样的自然发火实验,记录煤样从40℃上升到70℃的升温速率(或前30 h的升温速率),测试煤样的自燃特性曲线并分析曲线特征。即建立煤绝热氧化产热速率计算模型,结合实验数据计算所得的煤在绝热氧化条件下的升温速率和产热速率可鉴定煤自燃倾向性的强弱。采用绝热式自燃测试方法对不同煤的自燃倾向分析后表明,无烟煤和部分烟煤的自燃倾向较低,褐煤的自燃倾向较高,故而在煤矿开采时需特别注意褐煤的自燃倾向。 相似文献
66.
合成流量法对下游站流量作出预报的关键是确定各上游站流量到达下游站的时间。在实际中常采用平均传播时间,然而不同水情下真实传播时间与平均传播时间存在一定的差距,影响预报精度。对此,提出时间窗口概念,以平均传播时间为中心,向前、后各开一个时间窗口,用上游各站时间窗口内流量的线性组合表示其到达下游站的流量,以提高模型对不同水情的适应能力和预报精度。以三峡水库2009~2015年流量数据率定参数,以2016~2018年流量数据作为预报对象,试验结果表明时间窗口法能够显著改善预报精度。 相似文献
67.
With the rapid development of Internet, it is increasingly convenient to obtain real-time traffic condition information, which has greatly stimulated the improvement of urban traffic guidance. Traffic conditions are generally divided into four grades in the existing network platform, which are expressed in different colours. The understanding of traffic condition is still at the level of abstract senses. Therefore, it is difficult to grasp the characteristics of urban traffic. To this end, a new idea is proposed in this paper, and the new idea is to study the urban traffic characteristics based on real-time traffic condition information extraction with image identification technology. With this method, we can not only quantify the abstract traffic condition information, but also solve the loss of traffic condition information. In addition, an instance is analysed in this paper, it shows that it can provide references for urban traffic organization management very well. 相似文献
68.
换热单元的生成频次对换热网络优化有直接的影响,分析其机理可以指导求解算法的改进。本文采用节点非结构模型及强制进化随机游走算法,通过设置不同的换热单元生成概率与生成个数以改变换热单元的生成频次,观察并记录个体在优化过程中产生的年综合费用变化情况。发现不同生成频次下整型变量和连续变量的相对优化频率发生了变化,从而改变了整体优化过程,并且与个体当前优化状态不适应的生成频次会造成相对优化频率不平衡、优化结果较差。基于此,本文提出了一种具有生成参数动态调节策略的换热单元生成方式,在优化过程中根据个体状态实时调整换热单元的生成概率与生成个数,平衡整型变量与连续变量的相对优化频率。最后,采用15SP、10SP和20SP算例进行验证,换热网络的年综合费用较文献结果分别下降了1.06%、0.16%、0.68%,验证了该策略使得换热单元的生成频次更为合理,有效地提高了算法的优化效率。 相似文献
69.
Prakhar Jain Shubham Bauskar Manasi Gyanchandani 《International journal of imaging systems and technology》2020,30(1):112-125
Detection of anemia can be done by examining the hemoglobin concentration level in the blood using complete blood count, which is an invasive, time-consuming, and costly technique. Preliminary methods for detecting anemia include examining the color of the palpebral conjunctiva, which is a non-invasive method, but color perception may vary from person to person. This study aims to develop a computerized non-invasive technique for anemia detection. We propose a novel machine learning model using the artificial neural network to detect anemic patients from the images of eye conjunctiva. Since limited and small dataset has been used in the earlier approaches, this may cause over fitting of the model. We have improved the number of available training images using image augmentation techniques. To standardize a non-invasive method, we have used computer vision algorithms for preprocessing and feature extraction. This article derives the backpropagation rules mathematically for adjusting the weights for the proposed neural network model. After hyper parameter tuning and using the mathematically derived backpropagation rules, the model was able to achieve the best accuracy of 97.00% with sensitivity 99.21% and specificity 95.42% on the created dataset. 相似文献
70.
对于多孔质材料内的气体流动,基于Darcy定律建立其理论模型,并建立气膜间隙流场的雷诺方程,考虑速度滑移修正方程;将上述2个区域的压力分布方程进行耦合,通过有限元方法对耦合后的压力分布方程进行离散化,用超松弛迭代求解出气膜内各节点的压力分布,分析速度滑移对多孔质静压气体轴承静特性的影响。结果表明,考虑速度滑移所计算的气膜压力分布变化平稳过渡,没有较大的突变。计算轴承的承载力及刚度,结果显示在气密间隙小于15μm时,随着气膜厚度的增大偏心导致的压差增大使承载力不断增大;且当速度滑移系数小于0.1时,速度滑移对轴承承载力及刚度有较大的影响。 相似文献