全文获取类型
收费全文 | 252473篇 |
免费 | 25019篇 |
国内免费 | 16364篇 |
专业分类
电工技术 | 37967篇 |
技术理论 | 9篇 |
综合类 | 23240篇 |
化学工业 | 17143篇 |
金属工艺 | 9144篇 |
机械仪表 | 22577篇 |
建筑科学 | 21036篇 |
矿业工程 | 9708篇 |
能源动力 | 13427篇 |
轻工业 | 8658篇 |
水利工程 | 7395篇 |
石油天然气 | 8748篇 |
武器工业 | 3467篇 |
无线电 | 18836篇 |
一般工业技术 | 14455篇 |
冶金工业 | 10902篇 |
原子能技术 | 1875篇 |
自动化技术 | 65269篇 |
出版年
2024年 | 537篇 |
2023年 | 3540篇 |
2022年 | 6079篇 |
2021年 | 7173篇 |
2020年 | 8054篇 |
2019年 | 6559篇 |
2018年 | 5921篇 |
2017年 | 8009篇 |
2016年 | 9120篇 |
2015年 | 10033篇 |
2014年 | 17572篇 |
2013年 | 15706篇 |
2012年 | 19217篇 |
2011年 | 21008篇 |
2010年 | 15508篇 |
2009年 | 15740篇 |
2008年 | 15048篇 |
2007年 | 17986篇 |
2006年 | 15635篇 |
2005年 | 13326篇 |
2004年 | 10981篇 |
2003年 | 9545篇 |
2002年 | 7686篇 |
2001年 | 6393篇 |
2000年 | 5321篇 |
1999年 | 4157篇 |
1998年 | 3306篇 |
1997年 | 2788篇 |
1996年 | 2290篇 |
1995年 | 1956篇 |
1994年 | 1641篇 |
1993年 | 1206篇 |
1992年 | 975篇 |
1991年 | 747篇 |
1990年 | 584篇 |
1989年 | 509篇 |
1988年 | 359篇 |
1987年 | 210篇 |
1986年 | 163篇 |
1985年 | 186篇 |
1984年 | 219篇 |
1983年 | 174篇 |
1982年 | 182篇 |
1981年 | 97篇 |
1980年 | 86篇 |
1979年 | 79篇 |
1978年 | 57篇 |
1977年 | 53篇 |
1959年 | 17篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
针对配电自动化终端优化布局问题,提出了一种基于重要度排序的终端优化布局方法。首先以等年值综合费用为目标函数,供电可靠性和投入产出比为双重约束建立了配电自动化终端优化布局模型。然后通过分析配电自动化终端对供电可靠性提升的影响,给出各个节点的“二遥”及“三遥”终端安装重要度定义及计算公式。最后采用枚举法确定最优终端安装数量,基于节点终端安装重要度排序确定终端的最优安装位置。该方法考虑了已布局节点对剩余节点终端安装重要度的影响,能够在降低计算量的同时兼顾布局合理性。运用所提方法RBTS-BUS2系统及扩充模型进行终端优化布局并与智能优化算法的布局结果进行对比,验证了本文方法的有效性及优越性。 相似文献
22.
23.
《International Journal of Hydrogen Energy》2022,47(43):18831-18856
This study represents the results of the analysis and optimization of an integrated system for cogenerating electricity and freshwater. This setup consists of a Solid Oxide Fuel cell (SOFC) for producing electricity. Unburned fuel of the SOFC is burned in the afterburner to increase the temperature of the SOFC's outlet gasses and operate a Gas turbine (GT) to produce additional power and operate the air compressor. At the bottom of this cycle, a combined setup of a Multi-Effect Desalination (MED) and Reverse Osmosis (RO) is considered to produce freshwater from the unused heat capacity of the GT's exhaust gasses. Also, a Stirling engine is used in the fuel supply line to increase the fuel's temperature. Using LNG and the Stirling engine will replace the fuel compressor with a pump which increases the system performance and eliminates the need for the expansion valve. To study the system performance a mathematical model is developed in Engineering Equation Solver (EES) program. Then, the system's simulated data from the EES has been sent to MATLAB to promote the best operating condition based on the optimization criteria. An energetic, exergetic, economic, and environmental analysis has been performed and a Non-dominated Sorting Genetic Algorithm (NSGA-II) is used to achieve the goal. The two-objective optimization is performed to maximize the exergetic efficiency of the proposed system while minimizing the system's total cost of production. This cost is a weighted distribution of the Levelized Cost of Electricity (LCOE) and Levelized Cost of freshwater (LCOW). The results showed that the exergetic and energetic efficiencies of the system can reach 73.5% and 69.06% at the optimum point. The total electricity production of the system is 99 MW. The production cost is 11.71 Cents/kWh, of which 1.04 Cents/kWh is emission-related and environmental taxes. The freshwater production rate is 42.44 kg/s which costs 4.38 USD/m3. 相似文献
24.
《International Journal of Hydrogen Energy》2022,47(64):27680-27689
The low performance of open-cathode proton-exchange-membrane fuel cells (OCPEMFCs) is attributed to the low-humidity ambient air supplied to the cathode using electric fans. To improve the OCPEMFC performance, this paper proposes a novel humidification method by collecting water purged from the anode and supplying it to the open cathode. The OCPEMFC performance is evaluated at various humidifier distances from the cathode inlet, and it is compared with that where no humidifier is used when the OCPEMFC operates under three different current levels of 1, 5, and 8 A. The results show that the novel design improves the stack power, and optimal performance is achieved at a humidifier distance of 2 cm. The energy efficiency achieves an improvement between 1.4% and 1.8% when a humidifier is used. 相似文献
25.
26.
《中国稀土学报(英文版)》2022,40(11):1691-1698
White light-emitting diodes (WLEDs) fabricated by single-phase full color emitting phosphor are an emerging solution for health lighting. The crystallographic site occupation of activators in a proper host lattice is crucial for sophisticated design of such phosphor. Here, we report a high quality white light-emitting phosphor Ba2Ca(BO3)2:Ce3+(K+),Eu2+,Mn2+ with spectral distribution covering whole visible region. Blue light emission originates from Ce3+ ions occupying preferentially Ba2+ site by controlling synthesis conditions. Green and red lights are obtained from Eu2+ occupying Ba2+ (and Ca2+) site and Mn2+ occupying Ca2+ site, respectively. In this triple-doped phosphor, strong red emission with a low concentration of Mn2+ is realized by the efficient energy transfer from Ce3+ and Eu2+ to Mn2+. Furthermore, high quality white light is accomplished by properly tuning the relative doping amount of Ce3+(K+)/Eu2+/Mn2+ based on efficient simultaneous energy transfer. The results indicate that Ba2Ca(BO3)2:Ce3+(K+),Eu2+,Mn2+ is a promising white light-emitting phosphor in WLEDs application. 相似文献
27.
《Mechatronics》2022
This paper considers the shared path following control of an unmanned ground vehicle by a single person. A passive measure of human intent is used to blend the human and machine inputs in a mixed initiative approach. The blending law is combined with saturated super-twisting sliding mode speed and heading controllers, so that exogenous disturbances can be counteracted via equivalent control. It is proven that when the proposed blending law is used, the combined control signals from both the human and automatic controller respect the actuator magnitude constraints of the machine. To demonstrate the approach, shared control experiments are performed using an unmanned ground vehicle, which follows a lawn mower pattern shaped path. 相似文献
28.
《Ceramics International》2021,47(22):31590-31596
In this study, the high ferroelectric hysteresis loss of (Pb0·93La0.07)(Zr0·82Ti0.18)O3 (PLZT 7/82/18) antiferroelectric (AFE) ceramics was reduced by employing a combinatorial approach of Mn acceptor doping followed by thick film fabrication via an aerosol deposition (AD) process. The grains of the as-deposited PLZT 7/82/18 AFE AD thick films were grown by thermal annealing at 550 °C to enhance their electrical properties. Investigation of the electrical properties revealed that Mn-doping results in improved dielectric and ferroelectric properties, increased dielectric breakdown strength (DBS), and energy-storage properties. The Mn-doped PLZT AFE AD films possess a frequency-independent high dielectric constant (εr ≈ 660) with low dielectric loss (tan δ ≈ 0.0146), making them suitable candidates for storage capacitor applications. The bipolar and unipolar polarization vs. electric field (P-E) hysteresis loops of PLZT 7/82/18 AFE AD thick films were found to be slimmer than those of their bulk form (double hysteresis) with significantly reduced ferroelectric hysteresis loss, which is attributed to the AD-induced mixed grain structure. The Mn-doped PLZT 7/82/18 AFE AD thick films exhibited a low remnant polarization (Pr ≈ 9.22 μC/cm2) at a high applied electric field (~2750 kV/cm). The energy-storage density and energy efficiency of the Mn-doped PLZT AFE AD thick films were calculated from unipolar P-E hysteresis loops and found to be ~38.33 J/cm3 and ~74%, respectively. 相似文献
29.
Wen-Sen He Jiaxin Rui Qingzhi Wang Zhen-Yu Chen 《European Journal of Lipid Science and Technology》2021,123(7):2000398
Piceatannol has shown to be a strong antioxidant in vivo, however, its ability to suppress lipid oxidation in foods has not been examined. The present study is to examine the antioxidant effect of piceatannol on heated canola oil compared with that of butylated hydroxytoluene (BHT). The oxidation of canola oil is conducted at 60, 90, 120, and 150 °C by monitoring the depletion of oxygen, the decrease in unsaturated fatty acids, and the changes of primary and secondary oxidation products. Results demonstrated that piceatannol can suppress lipid oxidation of canola oil in a dose-dependent manner with its effect being more effective than BHT. Practical Applications: Lipid oxidation is a major factor in the deterioration of food quality. Synthetic antioxidants, such as BHT and butylated hydroxyanisole, are used to inhibit oxidation in foods, but their safety has been always concerned. Piceatannol has exhibited a strong antioxidant activity to attenuate lipid oxidation and it should be further explored for use as a natural antioxidant in foods. 相似文献
30.
Form selection of concomitant polymorphs: A case study informed by crystallization kinetics modeling
Weiwei Tang Yufeng Quan Junbo Gong Jingkang Wang Qiuxiang Yin Tonglei Li 《American Institute of Chemical Engineers》2021,67(4):e17129
Molecular mechanisms and process kinetics of crystallizing concomitant polymorphs remain poorly understood. Solvent-mediated phase transformation and concomitant crystallization are difficult to be distinguished in practice, as multiple forms can be detected at the same time. Herein, we developed a population balance model to simulate a concomitant crystallization process of two polymorphs of tolfenamic acid. Our kinetic modeling aims to understand concomitant crystallization and help guide form selection of such a molecular system. Crystallization kinetics of ethanolic solutions were uncovered from induction time measurements, as well as seeded and unseeded crystallization experiments. Experimental and simulation results demonstrate that the stable form I crystallizes concomitantly with the metastable form II. The faster growing form II results in an intermediate decline in the composition of form I in crystallized samples, a characteristic feature of the concomitantly crystallized system. A four-quadrant scheme of attainable polymorph outcome was simulated under various crystallization conditions. 相似文献