全文获取类型
收费全文 | 5285篇 |
免费 | 327篇 |
国内免费 | 45篇 |
专业分类
电工技术 | 117篇 |
综合类 | 51篇 |
化学工业 | 1298篇 |
金属工艺 | 156篇 |
机械仪表 | 150篇 |
建筑科学 | 264篇 |
矿业工程 | 34篇 |
能源动力 | 341篇 |
轻工业 | 773篇 |
水利工程 | 43篇 |
石油天然气 | 79篇 |
武器工业 | 12篇 |
无线电 | 227篇 |
一般工业技术 | 798篇 |
冶金工业 | 508篇 |
原子能技术 | 48篇 |
自动化技术 | 758篇 |
出版年
2024年 | 18篇 |
2023年 | 45篇 |
2022年 | 133篇 |
2021年 | 196篇 |
2020年 | 137篇 |
2019年 | 150篇 |
2018年 | 206篇 |
2017年 | 218篇 |
2016年 | 216篇 |
2015年 | 193篇 |
2014年 | 245篇 |
2013年 | 506篇 |
2012年 | 283篇 |
2011年 | 347篇 |
2010年 | 313篇 |
2009年 | 253篇 |
2008年 | 243篇 |
2007年 | 224篇 |
2006年 | 154篇 |
2005年 | 104篇 |
2004年 | 138篇 |
2003年 | 135篇 |
2002年 | 161篇 |
2001年 | 97篇 |
2000年 | 82篇 |
1999年 | 70篇 |
1998年 | 145篇 |
1997年 | 100篇 |
1996年 | 56篇 |
1995年 | 46篇 |
1994年 | 60篇 |
1993年 | 47篇 |
1992年 | 25篇 |
1991年 | 16篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 26篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 20篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1977年 | 12篇 |
1976年 | 23篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 6篇 |
排序方式: 共有5657条查询结果,搜索用时 31 毫秒
31.
北电网络提供的Contivity解决方案不仅可以使用户建立各种类型的VPN,而且还可以把这些VPN集成到未来的融合话音和数据的网络中。该方案已实现了安全路由选择;可通过多种技术支持鉴权功能,从而实现安全接入;允许用户使用其各自的安全性配置文件设置;其设计中没有“后门”,重点介绍了Contivity 2700网关的主要特征及其优势。 相似文献
32.
Celso M. F. Lapa Cludio M. N. A. Pereira Paulo F. Frutuoso e Melo 《Reliability Engineering & System Safety》2003,81(1):103-109
In order to maximize systems average availability during a given period of time, it has recently been developed a non-periodic surveillance test optimization methodology based on genetic algorithms (GA). The fact of allowing non-periodic tests turns the solution space much more flexible and schedules can be better adjusted, providing gains in the overall system average availability, when compared to those obtained by an optimized periodic test scheme. This approach, however, turns the optimization problem more complex. Hence, the use of a powerful optimization technique, such as GA, is required.Considering that some particular features of certain systems can turn it advisable to introduce other specific constraints in the optimization problem, this work investigates the application of seasonal constraints for the set of the Emergency Diesel Generation of a typical four-loop pressurized water reactor in order to planning and optimizing its surveillance test policy. In this analysis, the growth of the blackout accident probability during summer, due to electrical power demand increases, was considered. Here, the used model penalizes surveillance test interventions when the blackout probability is higher.Results demonstrate the ability of the method in adapting the surveillance test policy to seasonal constraints. The knowledge acquired by the GA during the searching process has lead to test schedules that drastically minimize test interventions at periods of high blackout probability. It is compensated by more frequent redistributed tests through the periods of low blackout probability in order to improve on the overall average availability at the system level. 相似文献
33.
José Luiz Antunes de Oliveira e Sousa Ravindra Gettu 《Canadian Metallurgical Quarterly》2006,132(2):141-148
The determination of the fundamental stress versus crack opening (σ-w) response of concrete under uniaxial tension is performed in this study through inverse analysis using data from notched beam tests. The procedure used for optimizing the parameters of the σ-w relation using the load versus crack mouth opening displacement response of the notched beam is described. Satisfactory comparisons have been obtained between the σ-w curves obtained through the inverse analysis and those directly measured in uniaxial tension tests. The use of weighting functions in the inverse analysis may be necessary when large crack widths are to be considered. 相似文献
34.
This research focused on the syllable as a processing unit in handwriting. Participants wrote, in uppercase letters, words that had been visually presented. The interletter intervals provide information on the timing of motor production. In Experiment 1, French participants wrote words that shared the initial letters but had different syllable boundaries. In Experiment 2, French- and Spanish-speaking participants wrote cognates and pseudowords with a letter sequence that was always intrasyllabic in French and intersyllabic in Spanish. In Experiment 3, French-Spanish bilinguals wrote the cognates and pseudowords with the same type of sequences. In the 3 experiments, the critical interletter intervals were longer between syllables than within syllables, indicating that word syllable structure constrains motor production both in French and Spanish. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
35.
Amorphous SiNx:H films were prepared by the rf glow-discharge decomposition of ammonia/silane gas mixture with varying nitrogen content. The steady-state photoconductivity and its dependence on light intensity have been investigated in a-SiNx:H as a function of temperature between 100 and 420 K. The electron drift mobility of a set of SiNx:H samples has been determined from their steady-state photoconductivity and response time measurements. The results suggest that electron drift mobility of the samples was nearly unchanged for a low nitrogen content. Two samples containing lowest nitrogen showed higher photoconductivity than that of unalloyed sample within a temperature range including the room temperature. 相似文献
36.
37.
A novel and efficient way of producing of aldonic acids is reported. The selective catalytic oxidation of monosaccharides (arabinose, ribose, xylose, lyxose, mannose, rhamnose, glucose, galactose, N-acetyl-glucosamine) and disaccharides (lactose, maltose, cellobiose, melibiose) on Au, Pd and Pt catalysts was investigated. By using the gold catalyst, a total selectivity with respect to aldonic acids and a high catalytic activity for all investigated sugars was found. The reaction conditions for the production of maltobionic and lactobionic acids via oxidation on gold catalysts were optimised. A high long-term stability of two different gold catalysts for the oxidation of maltose and lactose, respectively, was found. 相似文献
38.
A Ruiz Pérez M Santana A?e B Villaverde A?e F Bandera Tirado N Santana Santos 《Canadian Metallurgical Quarterly》1995,47(3):219-220
Patients who have a unicornuate uterus with a noncommunicating rudimentary horn that contains an endometrial cavity are at risk for endometriosis and obstetric complications. As in this case, resection of the rudimentary horn can be performed laparoscopically without increased risk to the patient and with some potential benefit. 相似文献
39.
海洋丝状真菌转化石油烃的研究 总被引:8,自引:0,他引:8
研究从湄洲湾海域分离的4株丝状真菌MF1,MF2,MF3,MF4的生长特性及去除油污的过程,观察在温度26℃,初始油浓度在3g/l,培养12d的过程中培养液的变化,分析培养液的pH值及原油的去除率与时间的关系,结果表明,丝状真菌去除原油的[过程是生物吸附与生物降解相结合的生物转化过程,比较革兰氏阴性细菌与丝状真菌细胞壁组成,结构,得出海洋微生物的脱油作用与其细胞壁有直接的关系。 相似文献
40.
A 0.3% Au/Al2O3 catalyst prepared by the incipient wetness (IW) method was investigated in the continuous-flow liquid-phase glucose oxidation. Therefore, a continuous stirred tank reactor (CSTR) system equipped with an ultrasonic separator was used. The continuous-flow glucose oxidation was carried out at 40 °C, pH 9 and 1 bar oxygen partial pressure. Residence time and glucose concentration were varied. The IW gold catalyst showed very high activity and selectivity to gluconic acid within its 110 days of operation and, thus, an excellent long-term stability. Even after severe microbial contaminations of the catalyst, its activity could be completely restored by in situ regeneration with 2-propanol. 相似文献