全文获取类型
收费全文 | 690298篇 |
免费 | 7354篇 |
国内免费 | 1178篇 |
专业分类
电工技术 | 12336篇 |
综合类 | 528篇 |
化学工业 | 109534篇 |
金属工艺 | 30542篇 |
机械仪表 | 22507篇 |
建筑科学 | 15189篇 |
矿业工程 | 6010篇 |
能源动力 | 16887篇 |
轻工业 | 51735篇 |
水利工程 | 9040篇 |
石油天然气 | 20030篇 |
武器工业 | 48篇 |
无线电 | 70241篇 |
一般工业技术 | 146764篇 |
冶金工业 | 112409篇 |
原子能技术 | 18913篇 |
自动化技术 | 56117篇 |
出版年
2021年 | 6631篇 |
2019年 | 6299篇 |
2018年 | 11245篇 |
2017年 | 11417篇 |
2016年 | 11966篇 |
2015年 | 7337篇 |
2014年 | 12503篇 |
2013年 | 31253篇 |
2012年 | 19021篇 |
2011年 | 25302篇 |
2010年 | 20318篇 |
2009年 | 22712篇 |
2008年 | 23015篇 |
2007年 | 22578篇 |
2006年 | 19411篇 |
2005年 | 17505篇 |
2004年 | 16783篇 |
2003年 | 16450篇 |
2002年 | 15921篇 |
2001年 | 15381篇 |
2000年 | 14816篇 |
1999年 | 14335篇 |
1998年 | 32103篇 |
1997年 | 23526篇 |
1996年 | 18299篇 |
1995年 | 14148篇 |
1994年 | 12958篇 |
1993年 | 12687篇 |
1992年 | 9987篇 |
1991年 | 9816篇 |
1990年 | 9684篇 |
1989年 | 9379篇 |
1988年 | 9028篇 |
1987年 | 8335篇 |
1986年 | 8066篇 |
1985年 | 9024篇 |
1984年 | 8298篇 |
1983年 | 8027篇 |
1982年 | 7287篇 |
1981年 | 7440篇 |
1980年 | 7187篇 |
1979年 | 7406篇 |
1978年 | 7385篇 |
1977年 | 8043篇 |
1976年 | 9718篇 |
1975年 | 6669篇 |
1974年 | 6579篇 |
1973年 | 6646篇 |
1972年 | 5820篇 |
1971年 | 5399篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Epoxy novolac/anhydride cure kinetics has been studied by differential scanning calorimetry under isothermal conditions. The system used in this study was an epoxy novolac resin (DEN431), with nadic methyl anhydride as hardener and benzyldimethylamine as accelerator. Kinetic parameters including the reaction order, activation energy and kinetic rate constants, were investigated. The cure reaction was described with the catalyst concentration, and a normalized kinetic model developed for it. It is shown that the cure reaction is dependent on the cure temperature and catalyst concentration, and that it proceeds through an autocatalytic kinetic mechanism. The curing kinetic constants and the cure activation energies were obtained using the Arrhenius kinetic model. A suggested kinetic model with a diffusion term was successfully used to describe and predict the cure kinetics of epoxy novolac resin compositions as a function of the catalyst content and temperature. Copyright © 2003 Society of Chemical Industry 相似文献
12.
A set of poly[N‐oligo(ethylene oxide)yl 4‐vinylpyridinium tosylate] (P4VOEOOTs) has been prepared by spontaneous polymerization of 4‐vinylpyridine. This method gives a grafted polyelectrolyte having a positive charge on every backbone pyridinic moiety. The P4VP15Ts, P4VP164Ts, P4VP350Ts and P4VP750Ts aqueous solution conductivities were determined in the concentration range from 6 × 10?4 to 10?2 M at 25 °C. The variation of the conductivity versus concentration of the investigated system exhibits typical polyelectrolyte behaviour. The polyelectrolyte mobility was found to be dependent on the oligo(ethylene oxide) (OEO) side‐chain length. Manning's rod‐like model fails to describe these results. A simple steric effect is proposed to explain the influence of the OEO length. Copyright © 2003 Society of Chemical Industry 相似文献
13.
The activation of safety valves causes the development of flow reaction forces that have to be transferred in an adequate way via the piping to the steel structure or via the connected vessel into the foundation. If the safety valve outlet piping is connected to a blowdown system or, in case of blowing off into the atmosphere, are equipped with a T‐piece at the outlet, the stationary reaction forces are compensated completely. The transient opening process, however, develops flow reaction forces which culminate in peaks of short duration. In this article, a simple method will be proposed for the estimation of the resulting reaction forces as a function of the length of the pipe at the safety valve outlet. CFD calculations and blowdown tests executed with a full‐lift safety valve have confirmed this method on principle. Special importance is attributed to the short duration of the effect of the reaction forces which seems to have only a negligible impact on the supporting steel structure. 相似文献
14.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit. 相似文献
15.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
16.
Two types of photo heterojunction bipolar transistor (HBT) to directly down-convert optical signals to electronic signals have been reported in the literature: a conventional photo-HBT in which light penetrates through the area of the base-collector junction and an HBT where light shines through the base-collector edge for higher conversion efficiency. Although the performance in relation to bias conditions has been published, the detailed analyses for identifying the parameters and bias conditions that provide optimum direct down-conversion have not been examined. This paper provides a full explanation of the operation of the down-conversion for both HBT configurations based on low-frequency analyses. Such information is useful for both understanding the nonlinear mechanisms involved and designing for maximum efficiency. In addition, a new circuit has been developed from the basic HBT down-conversion circuit that provides improved performance. 相似文献
17.
Thomy V. Dubois L. Vanoverschelde C. Sozanski J.P. Pribetich J. 《IEEE sensors journal》2004,4(6):772-778
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented. 相似文献
18.
19.
Nobel A.B. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(1):83-98
This paper considers several aspects of the sequential prediction problem for unbounded, nonstationary processes under pth power loss /spl lscr//sub p/(u,v)=|u-v|/sup p/, 1
相似文献
20.
为了分析多水库系统中两座水库之间灌溉用水的分配问题,建立了基到动态规划的神经网络模型。为了研究从一座上游水库取水在下游两座之库之间进行水量分配的问题,提出了3个状态变量和4个决策变量的改进的动态规划算法。采用神经网络模型,用3个状态变量动态规划算法得出调度原则,就所研究的多水库系统实例来说,新的动态规划神经网络模型的性能很好,将该模型的性能与临时凑合的标准调度原则和以前推荐使用的约束动态规划神经网络模型进行了比较。 相似文献