全文获取类型
收费全文 | 21625篇 |
免费 | 3380篇 |
国内免费 | 1233篇 |
专业分类
电工技术 | 6218篇 |
技术理论 | 2篇 |
综合类 | 1423篇 |
化学工业 | 1689篇 |
金属工艺 | 348篇 |
机械仪表 | 1439篇 |
建筑科学 | 511篇 |
矿业工程 | 202篇 |
能源动力 | 2946篇 |
轻工业 | 238篇 |
水利工程 | 475篇 |
石油天然气 | 772篇 |
武器工业 | 105篇 |
无线电 | 3234篇 |
一般工业技术 | 2129篇 |
冶金工业 | 370篇 |
原子能技术 | 106篇 |
自动化技术 | 4031篇 |
出版年
2024年 | 118篇 |
2023年 | 482篇 |
2022年 | 773篇 |
2021年 | 946篇 |
2020年 | 991篇 |
2019年 | 871篇 |
2018年 | 772篇 |
2017年 | 1038篇 |
2016年 | 1049篇 |
2015年 | 1078篇 |
2014年 | 1544篇 |
2013年 | 1367篇 |
2012年 | 1648篇 |
2011年 | 1904篇 |
2010年 | 1253篇 |
2009年 | 1366篇 |
2008年 | 1216篇 |
2007年 | 1282篇 |
2006年 | 1109篇 |
2005年 | 957篇 |
2004年 | 766篇 |
2003年 | 599篇 |
2002年 | 509篇 |
2001年 | 455篇 |
2000年 | 419篇 |
1999年 | 312篇 |
1998年 | 242篇 |
1997年 | 193篇 |
1996年 | 177篇 |
1995年 | 150篇 |
1994年 | 125篇 |
1993年 | 110篇 |
1992年 | 93篇 |
1991年 | 68篇 |
1990年 | 50篇 |
1989年 | 41篇 |
1988年 | 20篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 25篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
It is expected that demand response might provide soon ancillary services to the power system. This could be done, for example, by managing the use of Electric Vehicles (EV) batteries, or the production of flexible energy commodities such as hydrogen (H2), that can be used for fuel cell vehicles (H2EV) or in industrial processes. This paper analyses the impact of a transition to H2EV as an alternative to EV for passengers’ cars on a Spanish-like power sector. A simple H2 demand estimation is developed and provided to CEVESA, an operation and expansion model for the Iberian Power System Electricity Market (MIBEL). For this study, CEVESA was extended to include the investments and operation decisions of H2 production. Simulations were performed to determine the optimal evolution of the H2 production capacity and of the electricity generation mix, considering scenarios with different shares of EV and H2EV. The impact of H2EV vs EV mobility is assessed based on the recent Spanish National Plan for Energy and Climate (NECP) as the base case scenario. Results show that, even if H2EV mobility alternative is still more costly than EV, H2 production could provide a significant flexibility to the system that should also be appraised. Indeed, H2EV mobility could become a feasible and complementary alternative to decarbonize mobility by powering H2 production with the renewable generation surplus. This, together with the on-going learning process of this technology that will decrease its production costs and increase its efficiency in the coming years, could boost, even more, the development of the H2 economy. 相似文献
12.
The intermittent wind power in isolated hybrid distributed generation (IHDG) may cause serious problems associated with frequency (f) and power (P) fluctuation. Energy storage devices such as battery, super capacitor, and superconducting magnetic energy storage (SMES) may be used to reduce these fluctuations associated with f and P. This paper presents a study of IHDG power system for improving both f and P deviation profiles with the help of SMES. The studied IHDG power system is consisted of wind turbine generator and diesel engine generator. Both f and P control problems of the studied power system model are addressed in presence or absence of SMES. Fuzzy logic based proportional–integral–derivative (PID) controller with SMES is used for the purpose of minimization of f and P deviations. The different tunable parameters of the PID controller and those of the SMES are tuned by a novel quasi-oppositional harmony search algorithm. Performance study of the IHDG power system model is carried out under different perturbation conditions. The results demonstrate minimum f and P deviations may be achieved by using the proposed fuzzy logic based PID controller along with SMES. 相似文献
13.
AbstractBa0.95Ca0.05Ti1-xZrxO3 (BCTZO) ceramics were prepared by a solid state reaction method. The samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray absorption near edge structure (XANES). The ceramics exhibit a pure perovskite structure. The average grain size gradually decreases with increasing Zr concentration. XANES results indicate that the intensities of pre-edge peaks dropped with increasing Zr concentration. The BCTZO ceramic of x?=?0.05 has the optimum electrical properties with the maximum dielectric constant (ε'm), remanent polarization (2Pr), coercive electric field (2Ec) and piezoelectric charge constant (d33) of 7,244, 12.54 (μC/cm2), 5.29 (kV/cm) and 288 (pC/N), respectively. 相似文献
14.
Short-term generation scheduling is an important function in daily operational planning of power systems. It is defined as optimal scheduling of power generators over a scheduling period while respecting various generator constraints and system constraints. Objective of the problem includes costs associated with energy production, start-up cost and shut-down cost along with profits. The resulting problem is a large scale nonlinear mixed-integer optimization problem for which there is no exact solution technique available. The solution to the problem can be obtained only by complete enumeration, often at the cost of a prohibitively computation time requirement for realistic power systems. This paper presents a hybrid algorithm which combines Lagrangian Relaxation (LR) together with Evolutionary Algorithm (EA) to solve the problem in cooperative and competitive energy environments. Simulation studies were carried out on different systems containing various numbers of units. The outcomes from different algorithms are compared with that from the proposed hybrid algorithm and the advantages of the proposed algorithm are briefly discussed. 相似文献
15.
For rechargeable wireless sensor networks, limited energy storage capacity, dynamic energy supply, low and dynamic duty cycles cause that it is unpractical to maintain a fixed routing path for packets delivery permanently from a source to destination in a distributed scenario. Therefore, before data delivery, a sensor has to update its waking schedule continuously and share them to its neighbors, which lead to high energy expenditure for reestablishing path links frequently and low efficiency of energy utilization for collecting packets. In this work, we propose the maximum data generation rate routing protocol based on data flow controlling technology. For a sensor, it does not share its waking schedule to its neighbors and cache any waking schedules of other sensors. Hence, the energy consumption for time synchronization, location information and waking schedule shared will be reduced significantly. The saving energy can be used for improving data collection rate. Simulation shows our scheme is efficient to improve packets generation rate in rechargeable wireless sensor networks. 相似文献
16.
17.
Activity-directed synthesis (ADS) is a structure-blind, functional-driven molecular discovery approach. In this Concept, four case studies highlight the general applicability of ADS and showcase its flexibility to support different medicinal chemistry strategies. ADS deliberately harnesses reactions with multiple possible outcomes, and allows many chemotypes to be evaluated in parallel. Resources are focused on bioactive molecules, which emerge in tandem with associated synthetic routes. Some of the future challenges for ADS are highlighted, including the realisation of an autonomous molecular discovery platform. The prospects for ADS to become a mainstream lead generation approach are discussed. 相似文献
18.
19.
20.
Industrialized white organic light-emitting diodes (OLEDs) currently require host-guest doping, a complicated process necessitating precise control of the guest concentration to get high efficiency and stability. Two doping-free, hybrid white OLEDs with fluorescent blue, and phosphorescent green and red emissive layers (EMLs) are reported in this work. An ultra-thin red phosphorescent EML was situated in a blue-emitting electron transport layer (ETL), while the ultra-thin green phosphorescent EML was placed either in the ETL (Device 1), or the hole transport layer (HTL) (Device 2). Device 2 exhibits higher efficiency and more stable spectrum due to the enhanced utilization of excitons by ultra-thin green EML at the exciton generation zone within the HTL. Values of current efficiency (CE), power efficiency (PE), and CRI obtained for the optimized hybrid white OLEDs fabricated through a doping-free process were of 23.2 cd/A, 20.5 lm/W and 82 at 1000 cd/m2, respectively. 相似文献