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51.
ac losses have been investigated experimentally as well as theoretically in tapes having on the surface several normal conducting and/or superconducting layers. The superconducting layers under investigation have been Nb3Sn on a niobium substrate and Nb3Ge on a stainless steel substrate. It has been proved that the layered structure of the tapes is well reflected by the stepwise character of the ac losses dependence on the amplitude of the surface magnetic field. The magnetic flux passing through a surperconducting layer or surface barrier into the inside of the tape enhances the losses in the passed barrier or layer. 相似文献
52.
Tea Tušar Peter Korošec Gregor Papa Bogdan Filipič Jurij Šilc 《Applied Intelligence》2007,27(2):101-111
The efficiency of universal electric motors that are widely used in home appliances can be improved by optimizing the geometry
of the rotor and the stator. Expert designers traditionally approach this task by iteratively evaluating candidate designs
and improving them according to their experience. However, the existence of reliable numerical simulators and powerful stochastic
optimization techniques make it possible to automate the design procedure. We present a comparative study of six stochastic
optimization algorithms in designing optimal rotor and stator geometries of a universal electric motor where the primary objective
is to minimize the motor power losses. We compare three methods from the domain of evolutionary computation, generational
evolutionary algorithm, steady-state evolutionary algorithm and differential evolution, two particle-based methods, particle-swarm
optimization and electromagnetism-like algorithm, and a recently proposed multilevel ant stigmergy algorithm. By comparing
their performance, the most efficient method for solving the problem is identified and an explanation of its success is offered. 相似文献
53.
The insertion of the communication network in the feedback control loop makes the analysis and design of a network control system more complex, and induces some issues that degrade the control system’s performance and even cause system instability. The main aspects are focused on the stability analysis of Network Control Systems (NCSs) with network-induced delays, data packet dropouts, and multiple-packet transmission. These issues must be considered in the design of an NCS. This work summarizes the main research results, and remarks on some related handling approaches and techniques. The main purpose of the survey is to present the new research state of NCSs and to point out some fields of future work. 相似文献
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56.
Water management remains a significant challenge for the Proton Exchange Membrane Fuel Cell (PEMFC) with respect to performance, lifetime and operational flexibility. In recent years, microporous layers (MPL) have been widely used on the cathode side of the PEMFC in order to improve fuel cell performance and water management capabilities. Many modeling and experimental studies have with limited success attempted to analyze the underlying mechanisms that are responsible for the performance improvement due to the MPL. In this study, porous inserts along with various in-situ experimental techniques are used to investigate the MPLs. It was observed that the anode pressure drop increased when a cathode MPL was present, indicating water cross-over from the cathode towards the anode side. Further testing identified that the MPL improved cell performance due to the reduction of water saturation in the cathode catalyst layer, which resulted in enhanced oxygen diffusion. The influence of the MPL on the anode side was also studied with the aid of porous inserts and other techniques, and it was observed that the anode MPL improves cell voltage stability and reduces water accumulation in the anode catalyst layer. The present investigation provides further important information on the critical role of the MPL in the PEMFC. 相似文献
57.
Storage studies were conducted in 2009 and 2010 on large round (1.83 m × 1.53 m) and square (1.22 m × 1.22 m × 2.44 m) switchgrass bales stored for 6 months. Round and square bales were stored outside under different conditions: tarped (on pallets, gravel and ground) and untarped (on pallets, gravel and ground). Round and square bales were also stored inside and served as a control treatment. During both years, outside tarped bales resisted moisture accumulation and thus dry matter losses were equivalent to bales stored inside. The average dry matter loss for the round and square bales stored inside was 0.6% compared to 0.9 and 2.8% for the tarped round and square bales stored outside, respectively. However, untarped round (11.3%) and square (32.7%) bales on an average had greater dry matter loss than the tarped round (0.9%) and square (2.8%) bales. The untarped square bales consistently had higher moisture contents than untarped round bales which resulted in greater dry matter loss in untarped square bales. Hemicellulose content was more severely affected than cellulose content during storage. In 2010, untarped square bales stored on gravel, ground and pallets lost 30%, 24% and 16% of hemicellulose content, respectively. 相似文献
58.
Piotr Lampart 《热科学学报(英文版)》2000,9(2):115-121
IntroductionLP turbines operate over some range of flow regimeson both sides of the nominal operating conditions. Acharacteristic feature of LP tUrbines are strong radial gradients of pressure, Mach number and flow angle, especially downstream of the stator, Where these gradientsdetechne inlet now conditions for the moving bladerow. The changing swirl velocity and swirl angle spanwise require considerable twist of the rotor blades. Forlow loads, low pressures at the inlet to the rotor at th… 相似文献
59.
复合生态系统的降雨截留过程模拟 总被引:7,自引:0,他引:7
在水文水资源分析计算中,对降雨损失的处理,往往只对蒸散发和土壤下渗量进行计算,忽视了植被的降雨截留损失,这样至少说在理论上是不完善的。因而,在水文分析计算中,准确模拟植被的降雨截留过程,对合理评价水资源量,具有现实意义和理论价值。在系统分析复合生态系统的降雨截留过程的基础上,建立了半理论的复合生态系统截留计算模型,用于小型生态流域模拟降雨截留过程,不仅丰富了水文学的内容,而且完善了降雨损失计算的理论。 相似文献
60.
Optimal reactive power dispatch (ORPD) is a complex and non-linear problem, and is one of the sub-problems of
optimal power flow (OPF) in a power system. ORPD is formulated as a single-objective problem to minimize the
active power loss in a transmission system. In this work, power from distributed generation (DG) is integrated into a
conventional power system and the ORPD problem is solved to minimize transmission line power loss. It proves
that the application of DG not only contributes to power loss minimization and improvement of system stability
but also reduces energy consumption from the conventional sources. A recently proposed meta-heuristic algorithm
known as the JAYA algorithm is applied to the standard IEEE 14, 30, 57 and 118 bus systems to solve the newly
developed ORPD problem with the incorporation of DG. The simulation results prove the superiority of the JAYA
algorithm over others. The respective optimal values of DG power that should be injected into the four IEEE test
systems to obtain the minimum transmission line power losses are also provided. 相似文献