全文获取类型
收费全文 | 325382篇 |
免费 | 38648篇 |
国内免费 | 25758篇 |
专业分类
电工技术 | 25306篇 |
技术理论 | 12篇 |
综合类 | 41886篇 |
化学工业 | 30651篇 |
金属工艺 | 16350篇 |
机械仪表 | 26799篇 |
建筑科学 | 38369篇 |
矿业工程 | 14376篇 |
能源动力 | 14051篇 |
轻工业 | 12690篇 |
水利工程 | 17228篇 |
石油天然气 | 15827篇 |
武器工业 | 5448篇 |
无线电 | 22402篇 |
一般工业技术 | 36841篇 |
冶金工业 | 11788篇 |
原子能技术 | 4344篇 |
自动化技术 | 55420篇 |
出版年
2024年 | 1020篇 |
2023年 | 4242篇 |
2022年 | 8383篇 |
2021年 | 9949篇 |
2020年 | 10755篇 |
2019年 | 9132篇 |
2018年 | 8853篇 |
2017年 | 11168篇 |
2016年 | 12846篇 |
2015年 | 13602篇 |
2014年 | 20093篇 |
2013年 | 19916篇 |
2012年 | 25231篇 |
2011年 | 26206篇 |
2010年 | 20300篇 |
2009年 | 21008篇 |
2008年 | 19805篇 |
2007年 | 23719篇 |
2006年 | 20722篇 |
2005年 | 17585篇 |
2004年 | 14288篇 |
2003年 | 12235篇 |
2002年 | 9869篇 |
2001年 | 8290篇 |
2000年 | 7289篇 |
1999年 | 5933篇 |
1998年 | 4738篇 |
1997年 | 4130篇 |
1996年 | 3637篇 |
1995年 | 3166篇 |
1994年 | 2615篇 |
1993年 | 1904篇 |
1992年 | 1631篇 |
1991年 | 1194篇 |
1990年 | 990篇 |
1989年 | 870篇 |
1988年 | 591篇 |
1987年 | 366篇 |
1986年 | 289篇 |
1985年 | 192篇 |
1984年 | 202篇 |
1983年 | 92篇 |
1982年 | 135篇 |
1981年 | 110篇 |
1980年 | 94篇 |
1979年 | 96篇 |
1978年 | 41篇 |
1977年 | 27篇 |
1959年 | 56篇 |
1951年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
61.
《Ceramics International》2020,46(17):26675-26681
DyCrxFe(1-x)O3 (0 ≤ x ≥ 0.4) nanoparticles were prepared using facile chemical route. Structural and morphological evaluation was carried out using X-ray diffraction (XRD) and electron microscopy. Formation of orthorhombic DyFeO3 nanoparticles was confirmed by XRD with crystallite size of 9–10 nm. FESEM images revealed nearly spherical morphology of the fabricated nanoparticles. Energy dispersive X-ray (EDX) technique was employed to confirm the presence of Dy, Cr, Fe and O elements in DyCrxFe(1-x)O3 nanoparticles. FTIR studies illustrated the presence of characteristics stretching and bending vibrations. UV–visible spectroscopy was used to analyze the photocatalytic performance of the DyFeO3 and Cr-substituted DyFeO3 nanoparticles and optical band gap measurements. Photocatalytic activities of the prepared substituted and un-substituted DyFeO3 nanoparticles were conducted using three different dyes. These dyes were (i) methyl orange, (ii) rhodamine B and (iii) methylene blue. Lower band gap and higher photocatalytic performance was observed for Cr-substituted DyFeO3 nanoparticles with methylene blue dye. 相似文献
62.
在内外层算法的基础上,采用联立方程思想将主塔、侧线汽提塔视为一个整体进行建模,并针对复杂炼油塔的特点对算法提出了改进。首先,由于传统内外层法简化的K值模型对组成的变化不敏感,在处理带有石油的体系时,容易出现迭代次数较多,甚至部分塔板温度更新异常的问题,因此采用了汽相分数加和式推导了简化的K值模型加权因子。其次,借鉴流量加和法思想,规定侧线汽提塔的塔底产品流量作为设计变量,增强了算法收敛的稳定性。为验证改进后算法的有效性,采用不同的算法对实际的常压塔进行了模拟,结果显示改进后的算法适合应用于复杂炼油塔的模拟计算。 相似文献
63.
64.
开关磁阻电机结构性转矩脉动抑制方法 总被引:5,自引:0,他引:5
开关磁阻电机具有结构简单、成本低和调速范围广等优势,但其双凸极结构和控制器的开关特性,导致存在转矩脉动现象,使得抑制转矩脉动成为焦点问题。首先从开关磁阻电机的结构和运行机理出发,针对线性解析方法难以分析转矩特征的问题,建立电机有限元模型求解出转矩特征并进行样机验证试验。分析样机结构参数对转矩脉动的影响,针对结构参数耦合问题,选择NSGA-Ⅱ算法在参数优化平台上对样机结构参数进行多目标寻优,在保证优化后样机的转矩脉动系数和平均转矩均优于初始电机的条件下,最终获得样机最优化结果。结果表明,不同结构参数对电机转矩的影响有较大的差异,对结构参数的优化能有效地抑制转矩脉动,该参数优化方法可以为开关磁阻电机结构性转矩脉动抑制提供参考。 相似文献
65.
针对EDEM自动划分网格较稀疏问题,采用Hypermesh划分仿真模型网格,利用Herz-Mindlin接触理论的Archard磨损模型对转载溜槽磨损问题进行仿真,在网格单元上提取出漏斗和溜管衬板的接触能量和磨损量,分析了磨损量与接触能量的关系。假设转载溜槽衬板磨损深度为物料与溜槽衬板的使用时间为线性函数,根据现场衬板磨损量的测量值,将衬板的磨损系数关系的看作隐式的单变量方程,应用EDEM软件的仿真结果求解出磨损系数的标定值。分析了漏斗和溜管的磨损机理。该方法可用于转载溜槽的磨损预测。 相似文献
66.
67.
68.
69.
Guoxiang
Zhang Junyu Xiang 《International journal for numerical methods in engineering》2020,121(15):3339-3361
A new eight-node conforming quadrilateral element with high-order completeness, denoted as QH8-C1, is proposed in this article. First, expressions for the interpolation displacement function satisfying the requirements for high-order completeness in the global coordinate system are constructed. Second, the displacement function expression in global coordinates is transformed into isoparametric coordinates, and the relationships between the two series of coefficients for the two kinds of displacement function expressions are found. Third, the displacement function expression is modified to satisfy the requirements of nodal freedom and interelement boundary continuity. The key to the new element construction is the derivation of the linear relationship expressions among 12 coefficients of element displacement interpolation polynomials in the global and isoparametric coordinate systems. As a result, the relationship between quadratic completeness and interelement continuity is explicitly given, and a proof of the completeness and the continuity was conducted to theoretically guarantee the validity of the derivation results. Furthermore, in order to verify the correctness of the theoretical work, nine numerical examples were performed. The computation results from these examples demonstrate that QH8-C1 exhibited excellent performance, including high simulation accuracy, fast convergence, insensitivity to mesh distortion, and monotonic convergence. 相似文献
70.
Yuanming Xie Tianda Yu Chaojun Deng Xuefei Hu 《Journal of Nuclear Science and Technology》2020,57(9):1074-1090
ABSTRACT In the lower chamber of pressurized water reactor (PWR), the flow distribution device is the core module to distribute coolant into the core. It has complex structure and numerous design parameters. Therefore, it has important theoretical and practical significance to optimize the device. The mesh independence verification, turbulence model selection, and data processing all can influence the numerical simulation results of the lower chamber, in order to research the influence, a numerical simulation method based on the original model of CNP1000 reactor lower chamber is proposed in this paper. In the method, an optimization design method of flow distribution device is established based on surrogate model. The main design variables and optimization objectives are determined based on the device’s structure and function characteristics. And then it respectively adopts Kriging algorithm and multi-objective genetic algorithm to establish a surrogate model of flow distribution device and optimize it globally. Finally, the optimal design variables are obtained. Compared with the device’s performance before optimization, the after optimization has smaller total pressure loss and more uniform flow. The effectiveness and practicability of proposed optimization design method can be verified. 相似文献