全文获取类型
收费全文 | 356234篇 |
免费 | 34083篇 |
国内免费 | 17640篇 |
专业分类
电工技术 | 64333篇 |
技术理论 | 56篇 |
综合类 | 44622篇 |
化学工业 | 30695篇 |
金属工艺 | 11384篇 |
机械仪表 | 18547篇 |
建筑科学 | 41880篇 |
矿业工程 | 17033篇 |
能源动力 | 17240篇 |
轻工业 | 14996篇 |
水利工程 | 16859篇 |
石油天然气 | 12294篇 |
武器工业 | 3298篇 |
无线电 | 28987篇 |
一般工业技术 | 21621篇 |
冶金工业 | 16848篇 |
原子能技术 | 4602篇 |
自动化技术 | 42662篇 |
出版年
2024年 | 573篇 |
2023年 | 3557篇 |
2022年 | 6929篇 |
2021年 | 8375篇 |
2020年 | 9185篇 |
2019年 | 7667篇 |
2018年 | 7114篇 |
2017年 | 9167篇 |
2016年 | 10779篇 |
2015年 | 12161篇 |
2014年 | 21752篇 |
2013年 | 18987篇 |
2012年 | 25471篇 |
2011年 | 27352篇 |
2010年 | 21052篇 |
2009年 | 21743篇 |
2008年 | 20598篇 |
2007年 | 26068篇 |
2006年 | 24210篇 |
2005年 | 20674篇 |
2004年 | 17403篇 |
2003年 | 15301篇 |
2002年 | 12445篇 |
2001年 | 10539篇 |
2000年 | 8739篇 |
1999年 | 6973篇 |
1998年 | 5087篇 |
1997年 | 4373篇 |
1996年 | 4192篇 |
1995年 | 3521篇 |
1994年 | 3148篇 |
1993年 | 2314篇 |
1992年 | 2019篇 |
1991年 | 1479篇 |
1990年 | 1282篇 |
1989年 | 1134篇 |
1988年 | 882篇 |
1987年 | 609篇 |
1986年 | 454篇 |
1985年 | 394篇 |
1984年 | 411篇 |
1983年 | 295篇 |
1982年 | 271篇 |
1981年 | 189篇 |
1980年 | 149篇 |
1979年 | 124篇 |
1978年 | 75篇 |
1977年 | 79篇 |
1976年 | 58篇 |
1975年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
This article is concerned with the polynomial filtering problem for a class of nonlinear stochastic systems governed by the Itô differential equation. The system under investigation involves polynomial nonlinearities, unknown‐but‐bounded disturbances, and state‐ and disturbance‐dependent noises ((x,d)‐dependent noises for short). By expanding the polynomial nonlinear functions in Taylor series around the state estimate, a new polynomial filter design method is developed with hope to reduce the conservatism of the existing results. In virtue of stochastic analysis and inequality technique, sufficient conditions in terms of parameter‐dependent linear matrix inequalities (PDLMIs) are derived to guarantee that the estimation error system is input‐to‐state stable in probability. Moreover, the desired polynomial matrix can be obtained by solving the PDLMIs via the sum‐of‐squares approach. The effectiveness and applicability of the proposed method are illustrated by two numerical examples with one concerning the permanent magnet synchronous motor. 相似文献
72.
This article presents a design methodology for linearizing GaN HEMT amplifiers based on splitting a large FET into multiple parallel FETs with same total gate periphery and by biasing them individually. By varying the biases, the magnitude and the phase of the IMD3 components at the output of FET changes. A detailed simulation methodology using commercial microwave CAD software is presented. Simulation results show that by biasing one device in Class AB and other(s) in deep Class AB mode, IMD3 components of parallel FETs can be made out of phase to each other leading to cancellation and improvement in linearity. Three prototype circuits were simulated using (a) a single 5 mm FET (1 × 5 mm), (b) two parallel 2.5 mm FETs (2 × 2.5 mm), and (c) four parallel 1.25 mm FETs (4 × 1.25 mm), for a total gate periphery of 5 mm, over the frequency range of 0.8 to 1.0 GHz. IMD3 improvement up to 20 dBc was achieved with the 4 × 1.25 mm circuit when the FET biases were optimized. Measurement results show improvement in linearity up to 20 dBc for 4 × 1.25 mm circuit. The proposed method improves linearity without a substantial penalty on the power consumption and is straightforward to implement. 相似文献
73.
The operational optimisation of coal-fired power units is important for saving energy and reducing losses in the electric power industry. One of the key issues is how to determine the benchmark values of the energy efficiency indexes of the units. Therefore, a new framework for determining these benchmark values is proposed, based on data mining methods. First, the energy efficiency key performance indicators (KPIs) associated with the net coal consumption rate (NCCR) were selected based on the domain knowledge. Second, the decision-making samples with minimal NCCR were acquired with the fuzzy C-means (FCM) clustering algorithm, and the corresponding clustering centres were employed as the benchmark values. Finally, based on the support vector regression (SVR) algorithm, the target values of the NCCR were obtained with the KPIs as input, and the energy saving potential was evaluated by comparing the target values with the historical values of the NCCR. An actual on-duty 1000 MW unit was taken as study unit, and the results show that the energy saving potential is remarkable when the operators adjust the KPIs based on the calculated benchmark values. 相似文献
74.
75.
76.
77.
南海北部陆坡区域构造地质控制着气源、流体疏导体系、富集空间及储层物性特征,因此,东沙海域、神狐海域、西沙海槽和琼东南盆地的水合物成藏条件及控制因素具有明显差异性。东沙海域深部气体可沿断层、裂缝、不整合面、砂岩疏导层和气烟囱等通道向上运移,并形成天然气水合物,具有渗漏型水合物产出特征;神狐海域水合物成藏与规模巨大的泥底辟活动相关,并与布莱克海台天然气水合物产出特征具有相似性;琼东南盆地中央坳陷带内为天然气水合物发育的重点区,底辟、泥火山或麻坑构造与天然气水合物发育密切相关。 相似文献
78.
Leading edge erosion (LEE) affects almost all wind turbines, reducing their annual energy production and lifetime profitability. This study presents results of an investigation into 18 operational wind farms to assess the validity of the current literature consensus surrounding LEE. Much of the historical research focuses on rain erosion, implying that this is the predominant causal factor. However, this study showed that the impact of excessive airborne particles from seawater aerosols or from adverse local environments such as nearby quarries greatly increases the levels of LEE. Current testing of leading edge protection coatings or tapes is based on a rain erosion resistivity test, which does little to prove its ability to withstand solid particle erosion and may drive coating design in the wrong direction. Furthermore, it was shown that there is little correlation between test results and actual field performance. A method of monitoring the expected level of erosion on an operational wind turbine due to rain erosion is also presented. Finally, the energy losses associated with LEE on an operational wind farm are examined, with the average annual energy production dropping by 1.8% due to medium levels of erosion, with the worst affected turbine experiencing losses of 4.9%. 相似文献
79.
The thermoeconomic behaviour of a nanoparticle seeded single effect LiBr‐H2O absorption refrigeration system (ARS) is investigated for a small scale application. In the proposed method, alumina nanoparticles with volume concentrations of 3%, 5%, and 7% are dispersed into an aqua lithium bromide solution. The multiobjective heat transfer search algorithm is employed to examine the design trade‐off between the coefficient of performance (COP) and total annualized cost (TAC). To analyze the overall performance of the system, the influence of five design parameters, namely the temperatures of the generator, absorber, evaporator, condenser and heat exchanger pipe diameter, are studied. It is found that with an increase in the COP, the TAC of the system is initially raised marginally, and after that, raised rigorously with further increment. The comparative results indicate that the COP and TAC of the nanofluid based ARS system are increased by about 7% and decreased by about 3.2%, respectively, corresponding to the Pareto points of the base ARS system. A lower break‐even point of about 2.6 years is achieved for the ARS system containing nanoparticles compared to the base ARS system. Overall, the ARS system containing 5% nanoparticles is the best solution from a thermodynamic and economic point of view. 相似文献
80.
《工程(英文)》2020,6(7):812-826
Renewable energy sources (RESs) are considered to be reliable and green electric power generation sources. Photovoltaics (PVs) and wind turbines (WTs) are used to provide electricity in remote areas. Optimal sizing of hybrid RESs is a vital challenge in a stand-alone environment. The meta-heuristic algorithms proposed in the past are dependent on algorithm-specific parameters for achieving an optimal solution. This paper proposes a hybrid algorithm of Jaya and a teaching–learning-based optimization (TLBO) named the JLBO algorithm for the optimal unit sizing of a PV–WT–battery hybrid system to satisfy the consumer’s load at minimal total annual cost (TAC). The reliability of the system is considered by a maximum allowable loss of power supply probability (LPSPmax) concept. The results obtained from the JLBO algorithm are compared with the original Jaya, TLBO, and genetic algorithms. The JLBO results show superior performance in terms of TAC, and the PV–WT–battery hybrid system is found to be the most economical scenario. This system provides a cost-effective solution for all proposed LPSPmax values as compared with PV–battery and WT–battery systems. 相似文献