全文获取类型
收费全文 | 45812篇 |
免费 | 4560篇 |
国内免费 | 2796篇 |
专业分类
电工技术 | 1033篇 |
综合类 | 2682篇 |
化学工业 | 8379篇 |
金属工艺 | 5010篇 |
机械仪表 | 4554篇 |
建筑科学 | 2423篇 |
矿业工程 | 1151篇 |
能源动力 | 1487篇 |
轻工业 | 1579篇 |
水利工程 | 285篇 |
石油天然气 | 1295篇 |
武器工业 | 533篇 |
无线电 | 4298篇 |
一般工业技术 | 14153篇 |
冶金工业 | 2267篇 |
原子能技术 | 365篇 |
自动化技术 | 1674篇 |
出版年
2024年 | 196篇 |
2023年 | 994篇 |
2022年 | 1100篇 |
2021年 | 1551篇 |
2020年 | 1858篇 |
2019年 | 1556篇 |
2018年 | 1435篇 |
2017年 | 1631篇 |
2016年 | 1611篇 |
2015年 | 1675篇 |
2014年 | 2411篇 |
2013年 | 2601篇 |
2012年 | 2924篇 |
2011年 | 3654篇 |
2010年 | 2611篇 |
2009年 | 2809篇 |
2008年 | 2561篇 |
2007年 | 3067篇 |
2006年 | 2742篇 |
2005年 | 2561篇 |
2004年 | 2080篇 |
2003年 | 1865篇 |
2002年 | 1495篇 |
2001年 | 1152篇 |
2000年 | 1009篇 |
1999年 | 730篇 |
1998年 | 654篇 |
1997年 | 497篇 |
1996年 | 413篇 |
1995年 | 325篇 |
1994年 | 310篇 |
1993年 | 212篇 |
1992年 | 166篇 |
1991年 | 167篇 |
1990年 | 140篇 |
1989年 | 112篇 |
1988年 | 58篇 |
1987年 | 39篇 |
1986年 | 32篇 |
1985年 | 25篇 |
1984年 | 36篇 |
1983年 | 21篇 |
1982年 | 31篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1955年 | 5篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
This paper presents the development of an optimization and a computer-simulation model to evaluate the process plans of a manufacturing center by analyzing the effect of tool failure on system performance. The GPSS/PC simulation program that is used in this study has been built with variables, functions and matrices so that many experiments could be conducted with the model. Sensitivity analysis is presented and the developed model has proven to be useful in determining optimum sequencing of parts for various operating policies. 相似文献
122.
123.
A one–dimensional, transient thermal degradation heat transfer model for the response of composite materials when exposed to fire is presented. The model can handle layers of different materials. Material properties are functions of temperature. The reaction can be specified using Arrhenius‐type parameters or by inputting a density–temperature relationship determined by any experimental technique such as thermogravimetric analysis. The model is validated against the experimental data presented in Boyer's 1984 dissertation. Overall, the model provides excellent agreement with the experimental data. It is shown that very little difference is found between results arrived at by Arrhenius kinetics and results obtained by specifying the easier to measure density–temperature relationship. From this it is concluded that this technique is a viable alternative to Arrhenius‐type models. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
124.
L. J. Singh S. Choudhury S. Singha Roy K. P. Ghatak 《Electrical Engineering (Archiv fur Elektrotechnik)》2005,87(1):1-9
An attempt is made to study the Einstein relation for the diffusivity–mobility ratio (DMR) in quantum wells (QWs) and quantum well wires (QWWs) of tetragonal compounds on the basis of a newly formulated electron energy spectrum taking into account the combined influences of the anisotropies in effective electron mass, the spin–orbit splitting, and the presence of crystal field splitting, respectively. The results for quantum-confined III–V compounds form a special case of our generalized analysis. The DMR has also been studied for QWs and QWWs of II–VI and IV–VI materials. Taking QWs and QWWs of CdGeAs2, InAs, CdS and PbSe as examples, it was found that the DMR increases with increasing carrier statistics and decreasing film thickness respectively in various oscillatory manners emphasizing the influence of dimensional quantizations and the energy band constants in different cases. An experimental method of determining the DMR in nanostructures with arbitrary dispersion laws has also been suggested and the present simplified analysis is in agreement with the suggested relationship. The well-known results for nanostructures with parabolic energy bands have also been obtained as special cases from this generalized analysis under certain limiting conditions. 相似文献
125.
When humans plan to execute a tool-use action, they can only specify the bodily movement parameters by taking into account the external target or goal of the tool-use action and the target-movement mapping implemented by the tool. In this study, the authors used the movement precuing method to investigate how people prepare for actions made with tools. More specifically, they asked whether people would be able to specify the spatial target and the target-movement mapping of the tool-use action independently of each other, and to what degree they would be able to prepare these components in advance. In 3 experiments, they precued either the target or the target-movement mapping of tool-use actions involving either a compatible or an incompatible target-movement mapping. Results indicate that participants benefit from partial advance information about the target-movement mapping, whereas no significant effects were found for precuing the spatial target of the action. These results occurred regardless of whether the target-movement mapping was compatible or incompatible and provide evidence for the notion that the target-movement mapping of a tool-use action is part of its cognitive representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
126.
Christos C. Agrafiotis Chrysoula Pagkoura Souzana Lorentzou Margaritis Kostoglou Athanasios G. Konstandopoulos 《Catalysis Today》2007,127(1-4):265-277
The present work summarizes the recent activities of our laboratory in the field of solar-aided hydrogen production with structured monolithic solar reactors. This reactor concept, “transferred” from the well-known automobile exhaust catalytic after-treatment systems, employs ceramic supports optimized to absorb effectively solar radiation and develop sufficiently high temperatures, that are coated with active materials capable to perform/catalyze a variety of “solar-aided” reactions for the production of hydrogen such as water splitting or natural gas reforming. Our work evolves in an integrated approach starting from the synthesis of active powders tailored to particular hydrogen production reactions, their deposition upon porous absorbers, testing of relevant properties of merit such as thermomechanical stability and hydrogen yield and finally to the design, operation simulation and performance optimization of structured monolithic solar hydrogen production reactors. This approach, among other things, has culminated to the world's first closed, solar-thermochemical cycle in operation that is capable of continuous hydrogen production employing entirely renewable and abundant energy sources and raw materials – solar energy and water, respectively – without any CO2 emissions and holds, thus, a significant potential for large-scale, emissions-free hydrogen production, particularly for regions of the world that lack indigenous resources but are endowed with ample solar energy. 相似文献
127.
128.
129.
《Materials and Manufacturing Processes》2007,22(1):5-8
The technological properties of the hot-work tool steels depend on their microstructural quality induced by the production process and the heat treatment. One of the frequently applied methods to improve microstructure is preheat treatment. The treatment of carbonitriding X37CrMoV5-1 steel has been investigated in fluidized bed furnaces. Thickness and phase composition have been conducted using optical microscopy Neophot 32 and scanning microscopy, JEOL 5400, after etching in nital. 相似文献
130.