全文获取类型
收费全文 | 21971篇 |
免费 | 1821篇 |
国内免费 | 933篇 |
专业分类
电工技术 | 3468篇 |
技术理论 | 1篇 |
综合类 | 2060篇 |
化学工业 | 1294篇 |
金属工艺 | 1891篇 |
机械仪表 | 3435篇 |
建筑科学 | 922篇 |
矿业工程 | 1224篇 |
能源动力 | 1256篇 |
轻工业 | 749篇 |
水利工程 | 352篇 |
石油天然气 | 896篇 |
武器工业 | 331篇 |
无线电 | 1733篇 |
一般工业技术 | 1368篇 |
冶金工业 | 1548篇 |
原子能技术 | 89篇 |
自动化技术 | 2108篇 |
出版年
2024年 | 47篇 |
2023年 | 213篇 |
2022年 | 472篇 |
2021年 | 484篇 |
2020年 | 591篇 |
2019年 | 409篇 |
2018年 | 450篇 |
2017年 | 619篇 |
2016年 | 702篇 |
2015年 | 769篇 |
2014年 | 1352篇 |
2013年 | 1030篇 |
2012年 | 1665篇 |
2011年 | 1797篇 |
2010年 | 1225篇 |
2009年 | 1253篇 |
2008年 | 1128篇 |
2007年 | 1550篇 |
2006年 | 1362篇 |
2005年 | 1254篇 |
2004年 | 927篇 |
2003年 | 973篇 |
2002年 | 799篇 |
2001年 | 768篇 |
2000年 | 623篇 |
1999年 | 509篇 |
1998年 | 357篇 |
1997年 | 321篇 |
1996年 | 260篇 |
1995年 | 199篇 |
1994年 | 175篇 |
1993年 | 93篇 |
1992年 | 84篇 |
1991年 | 51篇 |
1990年 | 43篇 |
1989年 | 56篇 |
1988年 | 33篇 |
1987年 | 25篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1973年 | 2篇 |
1964年 | 3篇 |
1962年 | 5篇 |
1957年 | 2篇 |
1956年 | 2篇 |
1955年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Pengfei Chen Honggang Chang Tao Peng Yongfan Tang Youquan Liu Chao Xiang 《应用聚合物科学杂志》2021,138(30):50314
Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters. 相似文献
2.
《Ceramics International》2022,48(7):9651-9657
Friction is a common clean energy and can be harvested and converted into electricity energy via triboelectricity, which can electrochemically drive dye decomposition in theory. In this work, the tribocatalytic Rhodamine B dye decomposition has been experimentally realized in strontium titanate (SrTiO3) nanofibers, which are synthesized via a hydrothermal method. In the tribocatalytic dye decomposition process, the friction is exerted in the interface between catalyst surface and a polytetrafluoroethylene (PTFE) Teflon rod setup with the different stirring speed. The RhB dye decomposition ratios of SrTiO3 nanofibers at these stirring speeds of 200 rpm, 400 rpm, 600 rpm, and 800 rpm are respectively 24.2%, 51.8%, 73.9% and 88.6%, yielding to these reaction rate constants of ~0.0112 h?1, ~0.0260 h?1, ~0.0562 h?1 and ~0.0877 h?1. The main active species, which play an important role in tribocatalytic process, are the superoxide radicals and holes on basis of the active species quenching experiment results. The excellent tribocatalysis activity makes SrTiO3 nanofibers potential for application in dye wastewater treatment through utilizing the environmental friction energy. 相似文献
3.
建立车辆动力学模型,研究车辆在高速避让工况下的路径跟踪控制策略。基于自抗扰控制设计车辆横摆角速度以及道路曲率2种不同的路径跟踪控制器;设计基于车辆偏航位移和偏航角度加权的线性二次最优控制器;对3种控制器控制效果进行仿真验证,分析路径跟踪侧向位移误差、侧向加速度、前轮转向角以及偏航角度变化。越野车实车测试结果表明,路径跟踪控制策略正确。 相似文献
4.
5.
铜目前,硫酸车间制酸一系列共有三台SO2风机,这三台风机均采用液力耦合器的调速方式,这种方式可以实现无极调速,但是存在着传动效率低,耗能大的缺点,并且这三台风机均已使用20年以上,处于设备的中晚期,工作效率已大大降低。目前行业内,均采用先进的变频调速方式。使用变频器来控制风机的转速,可以极大的节省电能,尤其是在低负荷情况下,可以实现低转速运转,大大提高硫酸系统的综合能耗指标。 相似文献
6.
An up to date review of continuously variable speed wind turbines with mechatronic variable transmissions 下载免费PDF全文
Xiuxing Yin 《国际能源研究杂志》2018,42(4):1442-1454
As a promising and potential alternative to conventional fixed or variable speed wind turbines, continuously variable speed wind turbines (CVSWTs) with variable transmissions offer improved power efficiency and enhanced power control capabilities. The CVSWTs can be generally achieved by adapting mechatronic variable transmissions in the turbine drive train for continuously variable speed operations for wind turbines. Therefore, this paper serves to provide an up to date and exhaustive review of the CVSWTs with mechatronic variable transmissions such as mechanical variable transmission, electrical variable transmission, and power splitting transmission. In this paper, the analysis of CVSWTs with different mechatronic transmission topologies is performed regarding basic configurations, dynamic characteristics, control principles, and experimental or simulation results. Review results indicate the feasibility of applying CVSWTs with such mechatronic transmissions and highlight superiorities of the CVSWTs with power splitting transmission. The CVSWT with power splitting transmission will be particularly suitable for megawatt‐scale turbine systems and will hence increase the economic competitiveness of these turbines due to its large power capacity and high reliability. The directions or challenges for future investigations of CVSWTs with such mechatronic transmissions are also presented to foster in‐depth understanding of such CVSWTs and their control strategies. 相似文献
7.
混沌识别是对非线性时间序列进行混沌预测的前提。针对时间序列风速确定性与随机性相结合的复杂非线性特征,研究了不同的混沌识别方法,并对风速时间序列进行混沌特征识别。应用随机噪声、周期运动及经典混沌系统的时间序列对所选方法进行可靠性验证。对美国国家风能研究中心M2测风塔实测时间序列风速数据进行非线性混沌特征识别。结果表明:风速时间序列具有明显的混沌特征;各风速时间序列表现出不同程度的混沌特征;各混沌识别方法对风速时间序列混沌特征的表达形式不同,互为补充,相互验证。 相似文献
8.
An innovate constant volume flow meter (ICVFM) using AAO leak element was developed, and then applied to measure the pumping speed of dry vacuum pumps. The AAO leak element was calibrated with dynamic differential pressure decay method. The results imply that the conductance of AAO leak is inversely proportional to the square root of the molecular mass, and remains unchanged with pressure varying from vacuum to atmosphere. Then the pumping speed was measured by a simple test system. In the end, the uncertainties of calibrating AAO leak element and measuring pumping speed were considered to confirm the measurement capability. The newly developed flow meter enables flow measurements at pressures ranging from vacuum through atmospheric pressure, which has potential application in the semiconductor industry. 相似文献
9.
通过对磷酸二铵生产造粒特性分析,高压中速磨粉机原理分析,结合实践生产中的工艺需求,利用高压中速磨粉系统将颗粒状不合格品磨成细粉后添加进系统重新喷浆造粒,提高返料添加量,减少不合格品的产生,腾空仓库有限货位,以获取更大的经济价值。 相似文献
10.
ABSTRACTWind turbine control is an important task to make the electricity generation secure in terms of energy demand and machine safety. It also yields to control the desired power level and optimized energy because of the assignment of turbine speed. The contactless piezoelectric wind energy harvester (CPWEH) used in this study has three piezoelectric layers located around the shaft with 120 degrees apart and they are buckled by the magnetic force without any physical contact. The superiority of this device is to generate energy for low wind speeds such as 1.5 m/s. However, for high speeds, high total harmonic distortions (THDs) govern the waveforms, thus controlling the turbine speed becomes necessary for optimizing the output power. Encouraged by this, a small low inertia dc generator is coupled with the wind turbine, and the generator terminals are connected to a resistor through a power switch to generate a braking torque that opposes to wind speed direction. By controlling the switch properly, turbine speed is ensured to remain within a certain band, which accordingly prevents the turbine from rotating very fast at damaging wind speeds. Several experiments are performed on the developed CPWEH with/without the presented control scheme which prove the existence of promising performance of our proposal. 相似文献