首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4146篇
  免费   692篇
  国内免费   514篇
电工技术   613篇
综合类   790篇
化学工业   235篇
金属工艺   56篇
机械仪表   267篇
建筑科学   200篇
矿业工程   72篇
能源动力   116篇
轻工业   87篇
水利工程   119篇
石油天然气   72篇
武器工业   45篇
无线电   740篇
一般工业技术   408篇
冶金工业   38篇
原子能技术   26篇
自动化技术   1468篇
  2024年   4篇
  2023年   46篇
  2022年   66篇
  2021年   89篇
  2020年   131篇
  2019年   121篇
  2018年   98篇
  2017年   126篇
  2016年   121篇
  2015年   170篇
  2014年   238篇
  2013年   242篇
  2012年   346篇
  2011年   372篇
  2010年   267篇
  2009年   309篇
  2008年   319篇
  2007年   379篇
  2006年   323篇
  2005年   301篇
  2004年   236篇
  2003年   193篇
  2002年   193篇
  2001年   177篇
  2000年   118篇
  1999年   92篇
  1998年   61篇
  1997年   42篇
  1996年   39篇
  1995年   34篇
  1994年   26篇
  1993年   16篇
  1992年   14篇
  1991年   7篇
  1990年   9篇
  1989年   9篇
  1988年   7篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1980年   1篇
  1979年   1篇
  1975年   1篇
  1965年   1篇
  1962年   1篇
  1959年   1篇
排序方式: 共有5352条查询结果,搜索用时 15 毫秒
1.
为研究在常温(21±1)℃条件下不同搅拌方式对于厌氧氨氧化污泥复壮及运行影响,采用3组反应器(R1、R2、R3)搅拌方式分别为连续搅拌、间歇搅拌、间歇搅拌方式(R2、R3转速不同),对系统复壮及运行过程的脱氮性能、颗粒污泥性能等进行分析.结果表明,R1、R2、R3分别用10,2,2 d的时间氨氮、亚硝酸盐氮去除率接近100%,R2、R3的厌氧氨氧化速率更高,更适合厌氧氨氧化菌生长;周期实验结果可知,间歇搅拌方式形成的水流流化状态较弱,使反应器呈较低溶解氧的时间较长,更易抑制AOB活性,从而提高厌氧氨氧化菌活性;R1系统提供剪切力大,且持续与基质溶液接触,产生EPS多,稳定运行时期末,R1、R2、R3的颗粒污泥平均粒径为723,675,649μm.  相似文献   
2.
An original drying process combining air impingement and intermittent drying was studied on apple slices and mango cubes. The influence of four operating parameters (air velocity, drying/tempering periods, upper height, and air temperature) on the drying time and on the drying rate was evaluated. Continuous and intermittent drying were compared. The intermittency α = 1/7 (τon = 10 seconds and τoff = 60 seconds) gave the best results. A time savings of 54% for apple and 67% for mango was reached. In continuous drying, a time savings of 4620 seconds was observed by increasing the air velocity from 6 to 40 m s?1 for apple. Air temperatures of 328 K for apple and of 328 K or 338 K for mango were determined as optimum to prevent case‐hardening. Experimental results were fitted with the analytical solution of Fick's second law and the modified Page equation (average values R2 = 0.985 and 0.961, for apple and mango, respectively). For both products, the apparent moisture diffusivity Dapp, the drying constant k, the drying coefficient n, and the activation energy Ea, were identified. Activation energies calculated from the analytical solution were 30.3 and 36.8 kJ mol?1 and were 25.4 and 30.0 kJ mol?1 using the modified Page equation for apple and mango, respectively. Mango has an increased temperature sensitivity and thus will need less energy for drying than apple.  相似文献   
3.
This paper introduces the design of a hardware efficient reconfigurable pseudorandom number generator (PRNG) using two different feedback controllers based four-dimensional (4D) hyperchaotic systems i.e. Hyperchaotic-1 and -2 to provide confidentiality for digital images. The parameter's value of these two hyperchaotic systems is set to be a specific value to get the benefits i.e. all the multiplications (except a few multiplications) are performed using hardwired shifting operations rather than the binary multiplications, which doesn't utilize any hardware resource. The ordinary differential equations (ODEs) of these two systems have been exploited to build a generic architecture that fits in a single architecture. The proposed architecture provides an opportunity to switch between two different 4D hyperchaotic systems depending on the required behavior. To ensure the security strength, that can be also used in the encryption process in which encrypt the input data up to two times successively, each time using a different PRNG configuration. The proposed reconfigurable PRNG has been designed using Verilog HDL, synthesized on the Xilinx tool using the Virtex-5 (XC5VLX50T) and Zynq (XC7Z045) FPGA, its analysis has been done using Matlab tool. It has been found that the proposed architecture of PRNG has the best hardware performance and good statistical properties as it passes all fifteen NIST statistical benchmark tests while it can operate at 79.101-MHz or 1898.424-Mbps and utilize only 0.036 %, 0.23 %, and 1.77 % from the Zynq (XC7Z045) FPGA's slice registers, slice LUTs, and DSP blocks respectively. Utilizing these PRNGs, we design two 16 × 16 substitution boxes (S-boxes). The proposed S-boxes fulfill the following criteria: Bijective, Balanced, Non-linearity, Dynamic Distance, Strict Avalanche Criterion (SAC) and BIC non-linearity criterion. To demonstrate these PRNGs and S-boxes, a new three different scheme of image encryption algorithms have been developed: a) Encryption using S-box-1, b) Encryption using S-box-2 and, c) Two times encryption using S-box-1 and S-box-2. To demonstrate that the proposed cryptosystem is highly secure, we perform the security analysis (in terms of the correlation coefficient, key space, NPCR, UACI, information entropy and image encryption quantitatively in terms of (MSE, PSNR and SSIM)).  相似文献   
4.
鲍永胜  孙洁  宋鸿雁 《中州煤炭》2022,(11):147-153
以合理规划新能源电网,降低电网电能损耗,提升新能源消纳能力,设计了混合粒子群优化算法的新能源电网规划方法。以最小电能损耗与最大新能源消纳为目标函数,潮流功率、容量、线路输电能力、风能与太阳能出力为约束条件,建立新能源电网规划模型;通过结合自然选择机理与粒子群算法,设计混合粒子算法,在混合粒子群算法内引入混沌扰动与变异策略,避免惰性粒子陷入局部最优,优化混合粒子群算法,利用优化混合粒子群算法求解规划模型,获取最佳规划方案。实验表明,该方法可有效获取最佳规划方案,降低电能损耗,提升新能源消纳能力,提升电网断面利用率;规划后的电网日累计发电量显著提升、碳排放量显著下降。  相似文献   
5.
The traditional multilayer rigid impeller has large dead zone for the mixing of pseudoplastic non-Newtonian fluid, stable flow field interface and low mixing efficiency. A method for enhancing the chaotic mixing of non-Newtonian fluid by multilayer rigid-flexible impeller induced flow field interface instability was proposed. In the experiment, sodium carboxymethylcellulose was used as the non-Newtonian fluid system. The power characteristics were measured by the torque sensor. The mixing time was determined by the acid-base neutralization and decolorization method. The largest Lyapunov exponents were calculated by using Matlab software programming. The chaotic characteristics and mixing performance in the mixing process are analyzed. The results show that when the combination mode was RF-(PBTD+PBTD+DT), the impeller arrangement mode θ=60°, and the flexible sheet length installation ratio r=0.8, 1.2, the degree of chaos was higher and the mixing performance was better. Multilayer rigid-flexible impeller can generate multiple spiral flows, and realize the flow field interface instability under the disturbance frequency difference of the flexible sheet between the layers, the stirring dead zone was reduced, and the system enters a chaotic state at a lower speed (when the multilayer rigid-flexible impeller system N>88 r/min, LLE>0; when the multilayer rigid impeller system N>125 r/min, LLE>0). At the same speed, the mixing rate and power per unit volume of the multilayer rigid-flexible combined impeller are higher than that of the multilayer rigid impeller, but the mixing energy per unit volume is approximately the same.  相似文献   
6.
针对日益增长的小电流接地故障检测与保护装置的测试需求,研制了基于数字仿真结果的小电流接地故障模拟测试系统。搭建了能够模拟主要单相接地故障场景的典型配电系统;给出了仿真步长的选择方法;利用霍哈赖纳(Hochrainer)模型仿真电弧,对燃弧与熄弧条件进行了改进;在线路上并联一个高阻值电阻,解决ATP-EMTP中Π等效模型无法设置对地电导,使得熄弧后直流电荷无法释放的问题。通过仿真波形和实际故障波形的对比,验证了测试系统的可用性。  相似文献   
7.
科技发展背景下直播带货行业愈加深入人心,消费者足不出户就能买到心仪产品。线上直播销售农副产品能提升农村经济水平,实现产业振兴,支持我国乡村建设。但是由于行业整体起步较晚的原因,其依然存在农产品质量安全难以保证、平台发布信息不实和消费者维权途径不明确等问题。县长直播销售农产品模式作为新兴销售模式不应当仅是权宜之计,而应着力在实践中优化使之成为长久之计。本文围绕县长直播销售农产品展开,认可其弥补网红直播不足方面的优势,指出尚且存在的不足。通过完善对供应商履行义务的监督,加强对消费者合法权益的保障,规范市场秩序,整治市场乱象,使其健康平稳发展,为社会主义新农村的建设作出巨大贡献。  相似文献   
8.
采用平面激光诱导荧光技术测量双组分层式撞击流反应器撞击区浓度分布,利用混沌理论分析不同喷嘴间距、喷嘴直径和射流雷诺数下撞击流反应器浓度场混沌特征参数(关联维、Kolmogorov熵和最大Lyapunov指数)的变化规律。结果表明,撞击流反应器内浓度场混沌特征参数随喷嘴间距的增大呈上下波动的变化趋势,Kolmogorov熵在L=2d时达到最大。浓度场混沌特征参数随喷嘴直径增大呈上下波动的变化趋势,Kolmogorov熵在d=8 mm时整体上最大;射流雷诺数为Re=22 000时整体上混沌特征参数最佳。受二次撞击区的影响,撞击面上靠近二次撞击区各点的混沌特征参数有明显提高。  相似文献   
9.
冠状动脉系统的混沌现象会导致严重的健康问题。以非线性冠状动脉系统为研究对象,建立了不确定性冠状动脉系统动力学模型,提出了不确定性冠状动脉系统的微分积分终端滑模混沌抑制方法,针对该模型的不确定性设计了扰动观测器,根据Lyapunov理论证明了所设计控制系统的稳定性,通过仿真实验验证了所提出的混沌抑制方法的有效性和可行性。  相似文献   
10.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号