全文获取类型
收费全文 | 47405篇 |
免费 | 7232篇 |
国内免费 | 4868篇 |
专业分类
电工技术 | 8104篇 |
技术理论 | 4篇 |
综合类 | 6121篇 |
化学工业 | 1592篇 |
金属工艺 | 1472篇 |
机械仪表 | 4170篇 |
建筑科学 | 4427篇 |
矿业工程 | 1149篇 |
能源动力 | 1091篇 |
轻工业 | 598篇 |
水利工程 | 1349篇 |
石油天然气 | 1039篇 |
武器工业 | 783篇 |
无线电 | 8557篇 |
一般工业技术 | 3786篇 |
冶金工业 | 796篇 |
原子能技术 | 327篇 |
自动化技术 | 14140篇 |
出版年
2024年 | 179篇 |
2023年 | 899篇 |
2022年 | 1490篇 |
2021年 | 1658篇 |
2020年 | 2032篇 |
2019年 | 1771篇 |
2018年 | 1538篇 |
2017年 | 1933篇 |
2016年 | 2137篇 |
2015年 | 2325篇 |
2014年 | 3525篇 |
2013年 | 3217篇 |
2012年 | 3912篇 |
2011年 | 4201篇 |
2010年 | 3127篇 |
2009年 | 3107篇 |
2008年 | 3037篇 |
2007年 | 3392篇 |
2006年 | 2829篇 |
2005年 | 2429篇 |
2004年 | 1948篇 |
2003年 | 1639篇 |
2002年 | 1309篇 |
2001年 | 1151篇 |
2000年 | 929篇 |
1999年 | 733篇 |
1998年 | 604篇 |
1997年 | 488篇 |
1996年 | 397篇 |
1995年 | 334篇 |
1994年 | 245篇 |
1993年 | 208篇 |
1992年 | 201篇 |
1991年 | 128篇 |
1990年 | 113篇 |
1989年 | 105篇 |
1988年 | 74篇 |
1987年 | 23篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1960年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
物理化学课程创新教学模式是以学生学习为中心,吐故纳新,优化精选,以新颖或变化的教学方式进行教学。调查表明创新教学模式受到绝大多数学生的肯定和认可,有效地调动学生的积极性,提高了学生对物理化学的学习和探究兴趣,学生提问问题的广度和难度发生显著变化。该教学模式能够逐步提升学生的创新意识和创新能力。 相似文献
32.
Innumerable casualties due to intrauterine hypoxia are a major worry during prenatal phase besides advanced patient monitoring with latest science and technology. Hence, the analysis of foetal electrocardiogram (fECG) signals is very vital in order to evaluate the foetal heart status for timely recognition of cardiac abnormalities. Regrettably, the latest technology in the cutting edge field of biomedical signal processing does not seem to yield the desired quality of fECG signals required by physicians, which is the major cause for the pathetic condition. The focus of this work is to extort non-invasive fECG signal with highest possible quality with a motive to support physicians in utilizing the methodology for the latest intrapartum monitoring technique called STAN (ST analysis) for forecasting intrapartum foetal hypoxia. However, the critical quandary is that the non-invasive fECG signals recorded from the maternal abdomen are affected by several interferences like power line interference, baseline drift interference, electrode motion interference, muscle movement interference and the maternal electrocardiogram (mECG) being the dominant interference. A novel hybrid methodology called BANFIS (Bayesian adaptive neuro fuzzy inference system) is proposed. The BANFIS includes a Bayesian filter and an adaptive neuro fuzzy filter for mECG elimination and non-linear artefacts removal to yield high quality fECG signal. Kalman filtering frame work has been utilized to estimate the nonlinear transformed mECG component in the abdominal electrocardiogram (aECG). The adaptive neuro fuzzy filter is employed to discover the nonlinearity of the nonlinear transformed version of mECG and to align the estimated mECG signal with the maternal component in the aECG signal for annulment. The outcomes of the investigation by the proposed BANFIS system proved valuable for STAN system for efficient prediction of foetal hypoxia. 相似文献
33.
Traditional maximum power point tracking (MPPT) methods can hardly find global maximum power point (MPP) because output characteristics curve of photovoltaic (PV) array may have multi local maximum power points in irregular shadow, and thus easily fall into the local maximum power point. To address this drawback, Considering that sliding mode variable structure (SMVS) control strategy have such advantages as simple structure, fast response and strong robustness, and P&O method have the advantages of simple principle and convenient implementation, so a new algorithm combining SMVS control method and P&O method is proposed, besides, PI controller is applied to reduce system chattering caused by switching sliding surface. It is applied to MPPT control of PV array in irregular shadow to solve the problem of multi-peak optimization in partial shadow. In order to verity the rationality of the proposed algorithm, the experimental circuit is built, which achieves MPPT control by means of the proposed algorithm and P&O method. The experimental results show that compared with the traditional P&O algorithm, the proposed algorithm can fast track the global MPP, tracking speed increases by 60% and the relative error decreased by 20%. Moreover, the system becomes more stable near the MPP, the fluctuations of output power is greatly reduced, and thus make full use of solar energy. 相似文献
34.
35.
In this paper, the development of the models for the prediction of rock mass P wave velocity is presented. For model development, the database of 53 cases including widely used and recorded drilling parameters and P wave velocity was constructed from the field studies conducted in 13 open pit lignite mines. Both conventional linear, non-linear multiple regression and Adaptive Neuro Fuzzy Inference System (ANFIS) were used for model development. Prediction performance indicators showed that ANFIS model presented the best performance and it can successfully be used for the preliminary prediction of P wave velocities of rock masses. 相似文献
36.
针对反射面成型的复杂影响因素,提出平面桁架构建的定日镜面形支撑结构优化技术路线. 利用模拟仿真、数值计算和优化算法等方法,解析20 m2定日镜面形定义技术路线的4个组成环节:面形规格及宽高比、上弦杆的截面矩、平面桁架组间距的最优值、机加工中工艺控制要点的量化. 试制小型定日镜进行实验,分析光斑形状和能流密度分布特性,并与理想球面形光斑比较,两者的拟合优度大于0.98. 实验结果表明,当反射镜宽高比取1.2,上弦杆截面矩取40 000 mm4,桁架组间距取950 mm,上弦杆和斜杆的开孔公差小于0.9 mm时,反射面形的质量提升. 研究从原理和实践上证明了该优化技术路线的可行性. 相似文献
37.
Rui
Zhang Junmin Li Jianmin Jiao 《International Journal of Adaptive Control and Signal Processing》2020,34(7):919-936
This article investigates an adaptive fuzzy tracking control problem for a class of nontriangular form systems with asymmetric time-varying full state constraints. Unknown functions are approximated by the fuzzy logic systems. A domination approach is employed to tackle the nontriangular form structure. Time-varying asymmetric barrier Lyapunov functions (ABLFs) are adopted to ensure full-state constraints satisfaction. Based on the backstepping technique and time-varying ABLFs, an adaptive controller is proposed and guarantees that all the signals in the closed-loop system are ultimately bounded and the time-varying full state constraints are met. Simulation examples are presented to further demonstrate the effectiveness of the proposed approach. 相似文献
38.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
39.
Namyong Kim 《ETRI Journal》2006,28(2):155-161
In this paper, we introduce an escalator (ESC) algorithm based on the least squares (LS) criterion. The proposed algorithm is relatively insensitive to the eigenvalue spread ratio (ESR) of an input signal and has a faster convergence speed than the conventional ESC algorithms. This algorithm exploits the fast adaptation ability of least squares methods and the orthogonalization property of the ESC structure. From the simulation results, the proposed algorithm shows superior convergence performance. 相似文献
40.
研究了由J.Bourgoin和M.Lannoo提出的半导体内Jahn-Teller畸变效应的计算理论。应用Bourgoin和Lannoo的方法研究了含中心氮杂质金刚石结构的Jahn-Teller畸变问题,计算了34C+N簇团的T2模耦合沿%111&晶向的Jahn-Teller畸变效应,结果与实验相符。 相似文献