全文获取类型
收费全文 | 63795篇 |
免费 | 6106篇 |
国内免费 | 3854篇 |
专业分类
电工技术 | 2625篇 |
技术理论 | 1篇 |
综合类 | 4961篇 |
化学工业 | 16224篇 |
金属工艺 | 7289篇 |
机械仪表 | 2068篇 |
建筑科学 | 3505篇 |
矿业工程 | 2333篇 |
能源动力 | 3201篇 |
轻工业 | 5762篇 |
水利工程 | 1314篇 |
石油天然气 | 3793篇 |
武器工业 | 665篇 |
无线电 | 4579篇 |
一般工业技术 | 6498篇 |
冶金工业 | 3932篇 |
原子能技术 | 1224篇 |
自动化技术 | 3781篇 |
出版年
2024年 | 129篇 |
2023年 | 996篇 |
2022年 | 1630篇 |
2021年 | 2029篇 |
2020年 | 2200篇 |
2019年 | 1974篇 |
2018年 | 1889篇 |
2017年 | 2325篇 |
2016年 | 2382篇 |
2015年 | 2371篇 |
2014年 | 3660篇 |
2013年 | 4088篇 |
2012年 | 4500篇 |
2011年 | 4874篇 |
2010年 | 3615篇 |
2009年 | 3792篇 |
2008年 | 3356篇 |
2007年 | 4144篇 |
2006年 | 3572篇 |
2005年 | 3080篇 |
2004年 | 2636篇 |
2003年 | 2304篇 |
2002年 | 1943篇 |
2001年 | 1703篇 |
2000年 | 1445篇 |
1999年 | 1074篇 |
1998年 | 961篇 |
1997年 | 788篇 |
1996年 | 775篇 |
1995年 | 617篇 |
1994年 | 500篇 |
1993年 | 422篇 |
1992年 | 386篇 |
1991年 | 319篇 |
1990年 | 276篇 |
1989年 | 175篇 |
1988年 | 123篇 |
1987年 | 97篇 |
1986年 | 92篇 |
1985年 | 83篇 |
1984年 | 78篇 |
1983年 | 38篇 |
1982年 | 58篇 |
1981年 | 49篇 |
1980年 | 47篇 |
1979年 | 22篇 |
1978年 | 29篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This study investigated the oxidation kinetics of silicon-containing steel at 1150–1300 °C using a Simultaneous Thermal Analyzer under atmospheric conditions similar to that of an industry reheating furnace. There is a critical time point for the oxidation kinetics at an oxygen concentration of 4·0 vol.-%., following which the oxidation rate constant increases with the increasing oxidation temperature. The model coefficient A in the kinetic oxidation equation was found to be constant. However, before the critical time point, the oxidation rate constant remained unchanged; the model coefficient A decreased with the increasing temperature. Therefore, the kinetic model of silicon-containing steel for isothermal oxidation was observed to be a modified one on the basis of the experimental data. In addition, the critical time point was prolonged with the increasing isothermal oxidation temperature. Moreover, the oxidation activation energy of the tested silicon-containing steel was 366·16 kJ mol?1. 相似文献
62.
63.
64.
对盐穴储气库系统密封性的测试与评价方法进行了详细介绍。测试方法选取原则、测试相关计算方法以及测试标准为储气库密封性测试的工程设计提供了详实的理论基础。 相似文献
65.
Naoya Miyahara Shuhei Miwa Naoki Horiguchi Isamu Sato Osaka Masahiko 《Journal of Nuclear Science and Technology》2019,56(2):228-240
In order to improve LWR source term under severe accident conditions, the first version of a fission product chemistry database named ‘ECUME’ was developed. The ECUME is intended to include several datasets of major chemical reactions and their effective kinetic constants for representative severe accident sequences. It is expected that the ECUME can serve as a fundamental basis from which fission product chemical models can be elaborated for use in the severe accident analysis codes. The implemented chemical reactions in the first version were those for representative gas species in Cs-I-B-Mo-O-H system from 300 to 3000 K. The chemical reaction kinetic constants were evaluated from either literature data or calculated values using ab-initio calculations. The sample chemical reaction calculation using the presently constructed dataset showed meaningful kinetics effects at 1000 K. Comparison of the chemical equilibrium compositions by using the dataset with those by chemical equilibrium calculations has shown rather good consistency for the representative Cs-I-B-Mo-O-H species. From these results, it was concluded that the present dataset should be useful to evaluate fission product chemistry in Cs-I-B-Mo-O-H system under LWR severe accident conditions, where kinetics effects should be considered. 相似文献
66.
Relations between asphaltene content,viscosity reduction rate of heavy oil and ultrasonic parameters
Ultrasonic treatment could decrease the viscosity of heavy oil and previous study on had focused on one heavy oil sample and involved less on the influence of asphaltene content. This study examined the effect of asphaltene content on viscosity reduction rate by ultrasonication. A comparison on samples with various asphaltene content and vibration parameter was made. The results showed that the optimal vibration frequency might decrease as the asphaltene content increased, whereas the optimal vibration intensity and the optimal treatment time were suggested to be enlarged. A semi-quantitative correlation was matched, which helped for numerical simulation about ultrasonic treatment. 相似文献
67.
During present investigations, an attempt was made to understand the effect of mean stress and oxidation on low cycle fatigue (LCF) behaviour of CM 247 DS LC alloy at T?=?850°C. A significant reduction in fatigue life was observed during LCF tests conducted at strain ratio (R) of 0 as compared to R?=??1. Reduction in fatigue life is attributed to the synergistic effect of mean stress, oxidation and the expanding precipitates within the grain boundaries which imparts high stresses at the grain boundary leading to the intergranular cracking. Additionally, to account the effect of mean stress on fatigue life of the alloy CM 247 DS LC empirical relations developed by Smith–Watson–Topper (SWT) and Morrow were used. 相似文献
68.
69.
智能交通的出现使得车辆自组织网络受到越来越多的关注。车辆自组织网络的动态拓扑结构变化非常剧烈,这对网络的吞吐率、传输速率等性能提出了很高的要求。提出1种具有握手机制协议的自适应多通道双时钟NP-CSMA随机多址接入协议。该协议首先区分2种P-CSMA协议,握手机制成功解决了隐藏的终端问题,双时钟机制减少了平均空闲时间,多通道机制增加通道数量和划分用户优先级的同时提高了系统吞吐率,自适应机制能够使系统在高负载下保持稳定吞吐率。还对该协议的传输速率进行了分析,得出该协议的传输速率相对较高的结论。通过平均周期方法推导吞吐率和传输速率的计算公式,仿真结果与理论推导一致。 相似文献
70.
Ozone (O3) chemistry is thought to dominate the oxidation of indoor surfaces. We consider the hypothesis that reactions taking place within indoor boundary layers result in greater than anticipated hydroxyl radical (OH) deposition rates. We develop models that account for boundary layer mass‐transfer phenomena, O3‐terpene chemistry and OH formation, removal, and deposition; we solve these analytically and by applying numerical methods. For an O3‐limonene system, we find that OH flux to a surface with an O3 reaction probability of 10?8 is 4.3 × 10?5 molec/(cm2 s) which is about 10 times greater than predicted by a traditional boundary layer theory. At very low air exchange rates the OH surface flux can be as much as 10% of that for O3. This effect becomes less pronounced for more O3‐reactive surfaces. Turbulence intensity does not strongly influence the OH concentration gradient except for surfaces with an O3 reaction probability >10?4. Although the O3 flux dominates OH flux under most conditions, OH flux can be responsible for as much as 10% of total oxidant uptake to otherwise low‐reactivity surfaces. Further, OH chemistry differs from that for ozone; therefore, its deposition is important in understanding the chemical evolution of some indoor surfaces and surface films. 相似文献