全文获取类型
收费全文 | 121979篇 |
免费 | 20396篇 |
国内免费 | 5074篇 |
专业分类
电工技术 | 6686篇 |
技术理论 | 6篇 |
综合类 | 7005篇 |
化学工业 | 28898篇 |
金属工艺 | 5201篇 |
机械仪表 | 5906篇 |
建筑科学 | 7972篇 |
矿业工程 | 2399篇 |
能源动力 | 3049篇 |
轻工业 | 16221篇 |
水利工程 | 2201篇 |
石油天然气 | 3662篇 |
武器工业 | 910篇 |
无线电 | 16047篇 |
一般工业技术 | 19602篇 |
冶金工业 | 4234篇 |
原子能技术 | 999篇 |
自动化技术 | 16451篇 |
出版年
2024年 | 406篇 |
2023年 | 1315篇 |
2022年 | 2747篇 |
2021年 | 3637篇 |
2020年 | 3965篇 |
2019年 | 5046篇 |
2018年 | 5295篇 |
2017年 | 5957篇 |
2016年 | 6205篇 |
2015年 | 7432篇 |
2014年 | 8257篇 |
2013年 | 10370篇 |
2012年 | 8956篇 |
2011年 | 9223篇 |
2010年 | 8859篇 |
2009年 | 8500篇 |
2008年 | 8122篇 |
2007年 | 7452篇 |
2006年 | 6617篇 |
2005年 | 5397篇 |
2004年 | 4307篇 |
2003年 | 3784篇 |
2002年 | 3669篇 |
2001年 | 3151篇 |
2000年 | 2540篇 |
1999年 | 1593篇 |
1998年 | 901篇 |
1997年 | 731篇 |
1996年 | 596篇 |
1995年 | 479篇 |
1994年 | 396篇 |
1993年 | 303篇 |
1992年 | 225篇 |
1991年 | 192篇 |
1990年 | 154篇 |
1989年 | 105篇 |
1988年 | 87篇 |
1987年 | 59篇 |
1986年 | 60篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 21篇 |
1982年 | 26篇 |
1981年 | 22篇 |
1980年 | 36篇 |
1979年 | 32篇 |
1978年 | 16篇 |
1977年 | 18篇 |
1976年 | 20篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
This paper presents the current understanding of the flame retardant mechanism of Casico?. The study includes the flame retardant effect of each individual component: ethylene–acrylate copolymer, chalk and silicone elastomer, as well as the formation of an intumescent structure during heating. The flame retardant properties were investigated by cone calorimetry and oxygen index tests. To obtain insight into the flame retardant mechanism, heat treatment under different conditions has also been performed. The results indicate that the flame retardant mechanism of Casico is complex and is related to a number of reactions, e.g. ester pyrolysis of acrylate groups, formation of carbon dioxide by reaction between carboxylic acid and chalk, ionomer formation and formation of an intumescent structure stabilized by a protecting char. Special emphasis is given to the formation of the intumescent structure and its molecular structure as evaluated from 13C MAS‐NMR and 29Si MAS‐NMR, ESCA and XRD analysis. After treatment at 500°C the intumescent structure consists mainly of silicon oxides and calcium carbonate and after treatment at 1000°C the intumescent structure consists of calcium silicate, calcium oxide and calcium hydroxide. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
102.
Frdric Boschet Catherine Branger Andr Margaillan Thieo E Hogen‐Esch 《Polymer International》2005,54(1):90-95
The synthesis of 2,2,3,3‐tetrahydro‐perfluoroundecanoyl end‐functionalized polystyrene–poly(ethylene oxide) block (PS‐block‐PEO‐RF) copolymers and their matching PS‐block‐PEO diblock copolymers was carried out by sequential anionic polymerization. Viscometry and 19F NMR studies show that the PS‐block‐PEO copolymers, in contrast to their matching PS‐block‐PEO‐RF copolymers, exhibit a micellar rather than the associative behavior seen for the latter. However, the presence of an excess of fluorinated acid, used for end‐functionalization, produces a reduction of the associative behavior above the overlap concentration, with the fluorinated acid acting like a surfactant. A competition may also occur between PS—and RF—mediated micellization. Copyright © 2004 Society of Chemical Industry 相似文献
103.
Expanded polytetrafluoroethylene (ePTFE) membranes were modified by graft copolymerization with methacryloxyethyl phosphate (MOEP) in methanol and 2‐butanone (methyl ethyl ketone (MEK)) at ambient temperature using gamma irradiation. The effect of dose rate (0.46 and 4.6 kGy h?1), monomer concentration (1–40 %) and solvent were studied and the modified membranes were characterized by weight increase, X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XPS was used to determine the % degree of surface coverage using the C? F (ePTFE membrane) and the C? C (MOEP graft copolymer) peaks. Grafting yield, as well as surface coverage, were found to increase with increasing monomer concentration and were significantly higher for samples grafted in MEK than in methanol solution. SEM images showed distinctly different surface morphologies for the membranes grafted in methanol (smooth) and MEK (globular), hence indicating phase separation of the homopolymer in MEK. We propose that in our system, the non‐solvent properties of MEK for the homopolymer play a more important role than solvent chain transfer reactions in determining grafting outcomes. Copyright © 2005 Society of Chemical Industry 相似文献
104.
105.
J. Gegner Priv.‐Doz. Dr. W. Nierlich M. Brückner 《Materialwissenschaft und Werkstofftechnik》2007,38(8):613-623
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology. 相似文献
106.
107.
108.
随着深亚微米集成电路技术的发展,集成电路的规模越来越大,工作频率越来越高,并正朝着系统集成的方向发展,因而在模拟速度,模拟精度和可模拟的电路规模等各个方面对电路仿真技术提出了新的要求。近年来,各种新的电路仿真方法和仿真系统用相继脱颖百出,并将取代那些传统的,已经无法适应深亚微米技术发展的电路仿真器。 相似文献
109.
This paper investigates the issue of building software in the Internet environment, where local area network (LAN) based
systems are interconnected by links with different bandwidth and do not share file systems. The software is modeled as a directed
acyclic graph. Each node in the graph represents a logical step in processing the software while the edges describe the order
of execution. The problem is to construct the software at a particular LAN with minimum Internet communication cost. An optimal
polynomial algorithm, SOFTCON, with time complexity is presented, where and are the number of nodes and edges in the graph describing the software respectively, is the number of LANs in the Internet environment, and is the time complexity of the network flow algorithm on the flow network with nodes and edges transformed from the directed acyclic graph of the software.
Received: 6 December 1995 / 1 May 1996 相似文献
110.
In this paper, we study a manufacturing system consisting of two machines separated by two intermediate buffers, and capable of producing two different products. Each product requires a constant processing time on each of the machines. Each machine requires a constant non-negligible setup change time from one product to the other. The demand rate for each product is considered to be piecewise constant. Each machine undergoes failure and repair. The time-to-failure and time-to-repair are exponentially distributed random variables. The setup change and processing operations are resumable. We model our system as a continuous time, continuous flow process. An optimal control problem is formulated for the system to minimize the total expected discounted cost over an infinite horizon. To determine the optimal control policy structure, a discrete version of the problem is solved numerically using a dynamic programming formulation with a piecewise linear penalty function. A real-time control algorithm is then developed with the objective of maintaining low work-in-process inventory and keeping the production close to the demand. The algorithm uses a hierarchical control structure to generate the loading times for each product on each machine in real time and to respond to random disruptions in the system. The system is simulated using this algorithm to study its performance. The performance of the algorithm is also compared to alternative policies. 相似文献