全文获取类型
收费全文 | 194642篇 |
免费 | 19206篇 |
国内免费 | 13741篇 |
专业分类
电工技术 | 32348篇 |
技术理论 | 11篇 |
综合类 | 19606篇 |
化学工业 | 9785篇 |
金属工艺 | 6895篇 |
机械仪表 | 17369篇 |
建筑科学 | 16968篇 |
矿业工程 | 7390篇 |
能源动力 | 5322篇 |
轻工业 | 5090篇 |
水利工程 | 5810篇 |
石油天然气 | 6143篇 |
武器工业 | 3003篇 |
无线电 | 17507篇 |
一般工业技术 | 9704篇 |
冶金工业 | 8043篇 |
原子能技术 | 1267篇 |
自动化技术 | 55328篇 |
出版年
2024年 | 355篇 |
2023年 | 2395篇 |
2022年 | 3835篇 |
2021年 | 4805篇 |
2020年 | 5658篇 |
2019年 | 4485篇 |
2018年 | 4013篇 |
2017年 | 5745篇 |
2016年 | 6386篇 |
2015年 | 7199篇 |
2014年 | 13322篇 |
2013年 | 11596篇 |
2012年 | 14504篇 |
2011年 | 15523篇 |
2010年 | 11864篇 |
2009年 | 12104篇 |
2008年 | 12073篇 |
2007年 | 14529篇 |
2006年 | 13120篇 |
2005年 | 11353篇 |
2004年 | 9420篇 |
2003年 | 8287篇 |
2002年 | 6583篇 |
2001年 | 5470篇 |
2000年 | 4698篇 |
1999年 | 3610篇 |
1998年 | 2749篇 |
1997年 | 2335篇 |
1996年 | 1901篇 |
1995年 | 1607篇 |
1994年 | 1353篇 |
1993年 | 983篇 |
1992年 | 786篇 |
1991年 | 585篇 |
1990年 | 455篇 |
1989年 | 392篇 |
1988年 | 278篇 |
1987年 | 164篇 |
1986年 | 119篇 |
1985年 | 112篇 |
1984年 | 162篇 |
1983年 | 124篇 |
1982年 | 121篇 |
1981年 | 84篇 |
1980年 | 58篇 |
1979年 | 66篇 |
1978年 | 49篇 |
1977年 | 52篇 |
1964年 | 15篇 |
1959年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Tundong Liu Linjing Liu Jing Chen Hao Jiang Qiao Sun 《Journal of Modern Optics》2018,65(14):1680-1687
This paper introduces an evolutionary algorithm, Shuffled Frog Leaping Algorithm (SFLA), to solve the optimization problem in designing the multi-pumped Raman Fibre Amplifier (RFA). SFLA is a powerful optimizer tool because of its efficient mathematical expressions and global search capability. We utilize SFLA to determine the optimal pump wavelengths and pump powers by minimizing the gain ripple of RFA. To accelerate calculations, a terminal value optimization strategy (TVOS) is incorporated into the evolution of SFLA. This proposed strategy takes the terminal power values of pumps as the decision variables in optimization. Then, the optimal original power values of the pumps are obtained by solving the Power Coupled Equations once, without using the traditional method of repetitive guesses.The combination of SFLA and TVOS enhances the efficiency of optimization and accelerates calculation, while satisfying the design requirements of RFA.The simulation results show that nearly 65% of computational time has been saved compared with the traditional average power analysis. The 4-pumped C+L band of backward multi-pumped RFA with the average net gain of 0 dB, 1 dB and 2 dB are designed individually, where the gain ripple is less than 0.64 dB. The combination of SFLA and TVOS enhance the optimization efficiency and improve the performance of RFA with good gain profile. 相似文献
92.
Ali Maghami Dominik Schillinger 《International journal for numerical methods in engineering》2020,121(5):967-989
We explore a truncation error criterion to steer adaptive step length refinement and coarsening in incremental-iterative path following procedures, applied to problems in large-deformation structural mechanics. Elaborating on ideas proposed by Bergan and collaborators in the 1970s, we first describe an easily computable scalar stiffness parameter whose sign and rate of change provide reliable information on the local behavior and complexity of the equilibrium path. We then derive a simple scaling law that adaptively adjusts the length of the next step based on the rate of change of the stiffness parameter at previous points on the path. We show that this scaling is equivalent to keeping a local truncation error constant in each step. We demonstrate with numerical examples that our adaptive method follows a path with a significantly reduced number of points compared to an analysis with uniform step length of the same fidelity level. A comparison with Abaqus illustrates that the truncation error criterion effectively concentrates points around the smallest-scale features of the path, which is generally not possible with automatic incrementation solely based on local convergence properties. 相似文献
93.
某出口型号交流电力机车牵引控制系统要求变流器控制逻辑具备接触器控制、牵引系统数据交互、变流器故障保护、变流器启动自检等功能。针对以上功能,基于MATLAB中的Simulink/Stateflow可视化编程工具进行牵引控制模型的搭建,遵循模块化编程理念,采用较少的程序代码编写实现复杂的逻辑控制模型,生成逻辑清晰的控制功能流程图,进行半实物仿真测试,增强控制模型的可靠性。通过该变流器产品型式试验检验,验证变流器控制逻辑的功能可以满足控制系统的需求。 相似文献
94.
Shaohui Li Jingwei Chen Jiaqing Xiong Xuefei Gong Jinghao Ciou Pooi See Lee 《纳微快报(英文)》2020,(3):55-68
Sodium-ion capacitors(SICs)have received increasing interest for grid stationary energy storage application due to their affordability,high power,and energy densities.The major challenge for SICs is to overcome the kinetics imbalance between faradaic anode and nonfaradaic cathode.To boost the Na+reaction kinetics,the present work demonstrated a high-rate MnS-based anode by embedding the MnS nanocrystals into the N,S-co-doped carbon matrix(MnS@NSC).Benefiting from the fast pseudocapacitive Na+storage behavior,the resulting composite exhibits extraordinary rate capability(205.6 mAh g−1 at 10 A g−1)and outstanding cycling stability without notable degradation after 2000 cycles.A prototype SIC was demonstrated using MnS@NSC anode and N-doped porous carbon(NC)cathode;the obtained hybrid SIC device can display a high energy density of 139.8 Wh kg−1 and high power density of 11,500 W kg−1,as well as excellent cyclability with 84.5%capacitance retention after 3000 cycles.The superior electrochemical performance is contributed to downsizing of MnS and encapsulation of conductive N,S-co-doped carbon matrix,which not only promote the Na+and electrons transport,but also buffer the volume variations and maintain the structure integrity during Na+insertion/extraction,enabling its comparable fast reaction kinetics and cyclability with NC cathode. 相似文献
95.
ABSTRACTLearning parameters of a probabilistic model is a necessary step in machine learning tasks. We present a method to improve learning from small datasets by using monotonicity conditions. Monotonicity simplifies the learning and it is often required by users. We present an algorithm for Bayesian Networks parameter learning. The algorithm and monotonicity conditions are described, and it is shown that with the monotonicity conditions we can better fit underlying data. Our algorithm is tested on artificial and empiric datasets. We use different methods satisfying monotonicity conditions: the proposed gradient descent, isotonic regression EM, and non-linear optimization. We also provide results of unrestricted EM and gradient descent methods. Learned models are compared with respect to their ability to fit data in terms of log-likelihood and their fit of parameters of the generating model. Our proposed method outperforms other methods for small sets, and provides better or comparable results for larger sets. 相似文献
96.
申建光 《工业仪表与自动化装置》2020,(1):54-57,64
为提高环形供热管网水力工况运行稳定性,提出了基于模糊PID控制的环形供热管网水力工况控制方法。构建环形供热管网水力工况控制的约束参量模型,在此基础上采用回归模型逼近方法构建其测试指标集,结合自适应融合反馈跟踪方法进行环形供热管网水力工况信息的融合处理,并从中提取分布特征量;采用模糊PID控制方法调节提取结果的输出稳定性,实现环形供热管网水力工况优化设计和自适应控制。仿真结果表明,采用该方法进行环形供热管网水力工况控制的稳定性较好,自适应控制能力较强,实现了环形供热管网水力工况优化调节。 相似文献
97.
针对臂式斗轮取料机运行中抖动现象,进行了故障分析和排除,并对其液压原理和元件选型进行了优化及改进,为相关液压系统的故障分析和设计选型提供参考。 相似文献
98.
本文通过对两级伸缩式液压缸与四柱滑轨结合使用中所出现问题及处理过程的阐述,提出了在液压系统设计与制造中,准确的原理仅仅是基础,其上还有许许多多的细枝末节需要仔细修剪,比如污染、噪声、温度、泄漏以及与机械的协调等等。 相似文献
99.
富水条件下软岩巷道容易出现大变形及围岩强度大幅度降低等情况,对矿井的生产安全造成极大威胁。为探索富水软岩巷道稳定性控制技术,结合新上海一号煤矿113082工作面运输巷工程实例,采用理论分析方法研究了地下水对巷道围岩及支护结构的影响,提出围岩稳定性控制对策,并对控制方案进行数值模拟验证。针对富水软岩巷道,首先采取导、疏结合的控水措施,减小对原有围岩强度的影响,降低对支护结构的损害;其次采用全断面、多手段联合加固的支护措施,控制围岩变形。工程实际及数值模拟结果表明,对于富水软岩巷道采取以上技术措施,能够有效保证巷道的稳定性。 相似文献
100.
In this paper, a robust controller for a Six Degrees of Freedom (6 DOF) coaxial octorotor helicopter control is proposed in presence of actuator faults. Radial Base Function Neural Network (RBFNN), Fuzzy Logic Control approach (FLC) and Sliding Mode Control (SMC) technique are used to design a controller, named Fault Tolerant Control (FTC), for each subsystem of the octorotor helicopter. The proposed FTC scheme allows avoiding difficult modeling, attenuating the chattering effect of the SMC, reducing the rules number of the fuzzy controller, and guaranteeing the stability and the robustness of the system. The simulation results show that the proposed FTC can greatly alleviate the chattering effect, good tracking in presence of actuator faults. 相似文献