全文获取类型
收费全文 | 47437篇 |
免费 | 6141篇 |
国内免费 | 2634篇 |
专业分类
电工技术 | 8652篇 |
技术理论 | 2篇 |
综合类 | 5334篇 |
化学工业 | 2815篇 |
金属工艺 | 1632篇 |
机械仪表 | 3881篇 |
建筑科学 | 2071篇 |
矿业工程 | 1551篇 |
能源动力 | 1221篇 |
轻工业 | 2374篇 |
水利工程 | 958篇 |
石油天然气 | 1683篇 |
武器工业 | 629篇 |
无线电 | 11686篇 |
一般工业技术 | 3829篇 |
冶金工业 | 1481篇 |
原子能技术 | 332篇 |
自动化技术 | 6081篇 |
出版年
2024年 | 118篇 |
2023年 | 579篇 |
2022年 | 1088篇 |
2021年 | 1298篇 |
2020年 | 1516篇 |
2019年 | 1173篇 |
2018年 | 1157篇 |
2017年 | 1630篇 |
2016年 | 1847篇 |
2015年 | 2128篇 |
2014年 | 3023篇 |
2013年 | 2867篇 |
2012年 | 3951篇 |
2011年 | 4093篇 |
2010年 | 3161篇 |
2009年 | 3027篇 |
2008年 | 3020篇 |
2007年 | 3684篇 |
2006年 | 3180篇 |
2005年 | 2511篇 |
2004年 | 1973篇 |
2003年 | 1728篇 |
2002年 | 1435篇 |
2001年 | 1264篇 |
2000年 | 991篇 |
1999年 | 777篇 |
1998年 | 555篇 |
1997年 | 441篇 |
1996年 | 381篇 |
1995年 | 374篇 |
1994年 | 292篇 |
1993年 | 204篇 |
1992年 | 157篇 |
1991年 | 144篇 |
1990年 | 97篇 |
1989年 | 82篇 |
1988年 | 59篇 |
1987年 | 47篇 |
1986年 | 24篇 |
1985年 | 17篇 |
1984年 | 21篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1975年 | 5篇 |
1963年 | 4篇 |
1959年 | 6篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 42 毫秒
31.
Su-Il Ri Song-Il Hong Jong-Chol Kim Ju-Hyok Wi 《International Journal of Hydrogen Energy》2021,46(5):3319-3328
We investigated some properties of the hydride Mg2FeH6 substituted with yttrium by a first principles calculation. Some experimental results showed that 4d transition metal, yttrium serves as a good catalyst for magnesium based hydrogen storage alloys, but there are a few theoretical studies about magnesium based hydrides substituted with it. Mg2FeH6 is regarded as a cheaper material than pure MgH2, while it is crystalized into Fm3m structure (space group 225). Although it has high hydrogen storage capacity, many investigations have not been devoted to it due to its extremely high thermodynamic stability. The yttrium substituted Mg2FeH6 exhibits very low energy of formation, and its desorption temperature, 75 °C is very suitable for practical hydrogen storage applications. Our results showed that Mg2FeH6 is destabilized effectively by yttrium substitution and introducing vacancy defects has additive effect to the improvement of dehydrogenation performance. 相似文献
32.
余吾煤业公司作为高瓦斯矿井,瓦斯吸附能力强,属低透气性难抽放煤层。矿井目前处于新旧采区重叠期、瓦斯含量双向变化重叠期,需要立足当前、分类施策,提升采掘效率。为进一步规范掘进工作面瓦斯治理,建立规范的瓦斯治理程序,介绍了掘进工作面瓦斯分级治理相关措施,确保掘进工作面安全生产有序进行。 相似文献
33.
34.
35.
Mohammadali Kiehbadroudinezhad Ali Rajabipour Michael Cada Majid Khanali 《国际能源研究杂志》2021,45(1):429-452
People in the Middle East are facing the problem of freshwater shortages. This problem is more intense for a remote region, which has no access to the power grid. The use of seawater desalination technology integrated with the generated energy unit by renewable energy sources could help overcome this problem. In this study, we refer a seawater reverse osmosis desalination (SWROD) plant with a capacity of 1.5 m3/h used on Larak Island, Iran. Moreover, for producing fresh water and meet the load demand of the SWROD plant, three different stand‐alone hybrid renewable energy systems (SAHRES), namely wind turbine (WT)/photovoltaic (PV)/battery bank storage (BBS), PV/BBS, and WT/BBS are modeled and investigated. The optimization problem was coded in MATLAB software. Furthermore, the optimized results were obtained by the division algorithm (DA). The DA has been developed to solve the sizing problem of three SAHRES configurations by considering the object function's constraints. These results show that this improved algorithm has been simpler, more precise, faster, and more flexible than a genetic algorithm (GA) in solving problems. Moreover, the minimum total life cycle cost (TLCC = 243 763$), with minimum loss of power supply probability (LPSP = 0%) and maximum reliability, was related to the WT/PV/BBS configuration. WT/PV/BBS is also the best configuration to use less battery as a backup unit (69 units). The batteries in this configuration have a longer life cycle (maximum average of annual battery charge level) than two other configurations (93.86%). Moreover, the optimized results have shown that utilizing the configuration of WT/PV/BBS could lead to attaining a cost‐effective and green (without environmental pollution) SAHRES, with high reliability for remote areas, with appropriate potential of wind and solar irradiance. 相似文献
36.
Exposure to foot-transmitted vibration (FTV) can lead to pain and numbness in the toes and feet, increased cold sensitivity, blanching in the toes, and joint pain. Prolonged exposure can result in a clinical diagnosis of vibration-induced white foot (VIWFt). Data on the biomechanical response of the feet to FTV is limited; therefore, this study seeks to identify resonant frequencies for different anatomical locations on the human foot, while standing in a natural position. A laser Doppler vibrometer was used to measure vertical (z-axis) vibration on 21 participants at 24 anatomical locations on the right foot during exposure to a sine sweep from 10–200?Hz with a peak vertical velocity of 30?mm/s. The most notable differences in the average peak frequency occur between the toes (range: 99–147?Hz), midfoot (range: 51–84?Hz) and ankle (range: 16–39?Hz).
Practitioner Summary: The biomechanical response of the human foot exposed to foot-transmitted vibration, when standing in a natural position, was measured for 21 participants. The foot does not respond uniformly; the toes, midfoot, and ankle regions need to be considered independently in future development of isolation strategies and protective measures. 相似文献
37.
为了研究枪管结构对枪管固有频率的影响,针对枪管尤其是狙击枪管设计中约束长度、枪管外形、膛口装置以及膛线等不同结构,建立了相应的三维模型。采用以六面体为主的网格对枪管进行了网格划分,采用有限元方法对枪管进行了模态分析。计算获得了不同结构枪管的固有频率; 通过比较,得到了不同枪管结构对固有频率的影响。分析结果表明:枪管尾部螺纹长度越长,枪口振动幅度越低; 相同质量枪管,锥形外形枪管刚度最好; 加装膛口装置对枪管刚度和振动特性有不利影响。 相似文献
38.
Professor Utkin proposed an example showing that the amplitude of chattering caused by the presence of parasitic dynamics (stable actuators) in some systems governed by the First‐Order Sliding‐Mode Controller is lower than that produced by the Super‐Twisting Algorithm. This example served to motivate this paper reconsidering the problem of comparison of chattering in systems with stable actuators, and driven by Discontinuous Sliding‐Mode Controllers (DSMCs) and Continuous Sliding‐Mode Controllers (CSMCs). Comparison of chattering produced by DSMC and CSMC taking into account their amplitudes, frequencies, and average power (AP) needed to maintain the system into real‐sliding modes, allowing to conclude the following: (i) for systems with slow actuators, the amplitude of oscillations and AP produced by DSMC be smaller than those caused by CSMC; (ii) for bounded disturbances with fixed Lipschitz constant, there exist sufficiently fast actuators for which the amplitude of oscillations and AP produced by CSMC be smaller than those caused by DSMC. 相似文献
39.
40.
In the traditional sliding mode control method, there always exist the singularity due to the reduced order of the control method. In order to eliminate the singularity, I propose a new full order sliding mode control method in this article, which has been firstly applied to load frequency control. The full order sliding mode control method includes the terminal sliding mode control (TSM) and the linear sliding mode control (LSM). TSM has the good characteristic of eliminating the singularity due to the avoidance of derivative of terms with fractional power factors. While the LSM is easy to design and has fast time convergence comparing to TSM. The model is based on the system with different kinds of turbine or the same kind of turbine, which contains the nonlinearities. The control purpose is to adjust the frequency deviation to zero. Through the simulation results, it is shown that the frequency deviation can be kept to zero in the condition of different load disturbances by the two approaches, which approves the robustness of the proposed methods. In addition, we compare the two methods with the traditional sliding mode control (SMC), which proves the superiority of the two methods in terms of chattering and response time. 相似文献