全文获取类型
收费全文 | 25137篇 |
免费 | 2626篇 |
国内免费 | 1592篇 |
专业分类
电工技术 | 859篇 |
技术理论 | 2篇 |
综合类 | 3606篇 |
化学工业 | 3830篇 |
金属工艺 | 2226篇 |
机械仪表 | 1460篇 |
建筑科学 | 1315篇 |
矿业工程 | 191篇 |
能源动力 | 1833篇 |
轻工业 | 1705篇 |
水利工程 | 185篇 |
石油天然气 | 123篇 |
武器工业 | 300篇 |
无线电 | 2118篇 |
一般工业技术 | 4076篇 |
冶金工业 | 440篇 |
原子能技术 | 610篇 |
自动化技术 | 4476篇 |
出版年
2024年 | 145篇 |
2023年 | 893篇 |
2022年 | 951篇 |
2021年 | 963篇 |
2020年 | 1161篇 |
2019年 | 1040篇 |
2018年 | 825篇 |
2017年 | 1168篇 |
2016年 | 1218篇 |
2015年 | 1369篇 |
2014年 | 2086篇 |
2013年 | 1941篇 |
2012年 | 2460篇 |
2011年 | 2329篇 |
2010年 | 1776篇 |
2009年 | 1954篇 |
2008年 | 1150篇 |
2007年 | 1568篇 |
2006年 | 1136篇 |
2005年 | 548篇 |
2004年 | 217篇 |
2003年 | 243篇 |
2002年 | 259篇 |
2001年 | 233篇 |
2000年 | 245篇 |
1999年 | 228篇 |
1998年 | 126篇 |
1997年 | 68篇 |
1996年 | 98篇 |
1995年 | 78篇 |
1994年 | 56篇 |
1993年 | 56篇 |
1992年 | 55篇 |
1991年 | 46篇 |
1990年 | 55篇 |
1989年 | 34篇 |
1988年 | 87篇 |
1987年 | 140篇 |
1986年 | 151篇 |
1985年 | 38篇 |
1984年 | 30篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 23篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1959年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
《Materials Letters》2007,61(4-5):1109-1113
We report the synthesis of a nanostructured γ-LiAlO2 network in an Al-based metal matrix composite (MMC) by arc-melting a powder compact of Al–15 wt.%Li2O. During synthesis, chemical reactions between Al and Li2O occurred, and a two-phase Al-γ-LiAlO2 MMC was produced. The γ-LiAlO2 was in the form of nano-network extended evenly in the Al matrix. The apparent density and Vickers' hardness number of the MMC were determined to be 2.31 gcm− 3 and 143, respectively, and having a relative density of 0.87. The MMC was made nano-porous by etching away Al with a 2 M NaOH solution. The sizes of pores were about 150 nm and the width of the branches in the γ-LiAlO2 network was about 90 nm. Atomic force microscopy revealed that the branches were composed of fine grains of 50 nm in diameter. Microstructure of the network was not altered even after prolonged etching, and this suggested that γ-LiAlO2 was chemically inert to NaOH corrosion. Specific surface area of the γ-LiAlO2 nano-network was measured to be 79 m2/g, and its porosity was determined to be 43.7%. 相似文献
62.
《Cement and Concrete Composites》2007,29(4):330-336
The relatively simple to measure ‘time constant’ is presented as an index for characterizing the level of corrosion experienced by steel in concrete. This communication, largely in the form of a technical note, explicitly illustrates that the time constant determined from electrochemical testing has significant merit for monitoring corrosion of steel in concrete, and appears to be insensitive to the area of electrode being probed. In this work, the time constant, κ, is determined following a galvanostatic excitation signal, revealing a good correlation between the value of κ and corrosion status across specimens of widely varying geometry. Although this notion has been suggested in the past, this work presents both a survey and consolidated review to indicate the utility of the parameter as an index to corrosion rate on-site. 相似文献
63.
64.
65.
66.
《Journal of power sources》2006,158(1):169-176
A fuel cell is a device that can convert chemical energy into electricity directly. Among various types of fuel cells, both polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) can work at low temperature (<80 °C). Therefore, they can be used to supply power for commercial portable electronics such as laptop computers, digital cameras, PDAs and cell phones. The focus of this paper is to investigate the performance of a miniaturized DMFC device using a micropump to deliver fuel. The core of this micropump is a piezoelectric ring-type bending actuator and the associated nozzle/diffuser for directing fuel flow. Based on the experimental measurements, it is found that the performance of the fuel cell can be significantly improved if enough fuel flow is induced by the micropump at anode. Three factors may contribute to the performance enhancement including replenishment of methanol, decrease of diffusion resistance and removal of carbon dioxide. In comparison with conventional mini pumps, the size of the piezoelectric micropump is much smaller and the energy consumption is much lower. Thus, it is very viable and effective to use a piezoelectric valveless micropump for fuel delivery in miniaturized DMFC power systems. 相似文献
67.
《Journal of power sources》2006,162(2):943-948
This paper describes a novel method of modelling an energy store used to match the power output from a wind turbine and a solar PV array to a varying electrical load. The model estimates the fraction of time that an energy store spends full or empty. It can also estimate the power curtailed when the store is full and the unsatisfied demand when the store is empty. The new modelling method has been validated against time–stepping methods and shows generally good agreement over a wide range of store power ratings, store efficiencies, wind turbine capacities and solar PV capacities.Example results are presented for a system with 1 MW of wind power capacity, 2 MW of photovoltaic capacity, an energy store of 75% efficiency and a range of loads from 0 to 3 MW average. 相似文献
68.
《Journal of power sources》2006,160(1):657-661
The cathode-active materials, layered Li[Ni0.333Co0.333Mn0.293Al0.04]O2−zFz (0 ≤ z ≤ 0.1), were synthesized from a sol–gel precursor at 900 °C in air. The influence of Al–F co-substitution on the structural and electrochemical properties of the as-prepared samples was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical experiments. The results showed that Li[Ni0.333Co0.333Mn0.293Al0.04]O2−zFz has a typical hexagonal structure with a single phase, the particle sizes of the samples tended to increase with increasing fluorine content. It has been found that Li[Ni0.333Co0.333Mn0.293Al0.04]O1.95F0.05 showed an improved cathodic behavior and discharge capacity retention compared to the undoped samples in the voltage range of 3.0–4.3 V. The electrodes prepared from Li[Ni0.333Co0.333Mn0.293Al0.04]O1.95F0.05 delivered an initial discharge capacity of 158 mAh−1 g and an initial coulombic efficiency is 91.3%, and the capacity retention at the 20th cycle was 94.9%. Though the F-doped samples had lower initial capacities, they showed better cycle performances compared with F-free samples. Therefore, this is a promising material for a lithium-ion battery. 相似文献
69.
《International Journal of Heat and Mass Transfer》2006,49(21-22):3831-3845
In lost foam casting of aluminum, pressure equilibrium between the liquid metal and the decomposing foam can produce a variety of different shapes for the metal flow front, ranging from convex to concave. In extreme cases, the flow front can become so strongly concave that small pieces of the foam pattern begin to break off inside the concave hollow of the flow front and become enveloped by the advancing liquid metal. When this happens, the entire mechanism of foam decomposition changes from steady ablation to a more chaotic motion in which the metal seems to “chew” its way through the pattern, creating large bubbles of vaporizing polymer liquid in its wake. These bubbles usually lead to undesirable anomalies in the final casting. In most cases, the nonlinear equations that govern the shape of the flow front depend on a single nondimensional number, which relates the onset of the engulfing motion to specific material, geometric, and process parameters. Numerical solutions to these equations are obtained for several special cases. These solutions help to explain a number of experimental observations that until now have been poorly understood. 相似文献
70.