全文获取类型
收费全文 | 221380篇 |
免费 | 20149篇 |
国内免费 | 11333篇 |
专业分类
电工技术 | 12584篇 |
技术理论 | 2篇 |
综合类 | 21637篇 |
化学工业 | 51222篇 |
金属工艺 | 8478篇 |
机械仪表 | 11200篇 |
建筑科学 | 19393篇 |
矿业工程 | 8017篇 |
能源动力 | 6893篇 |
轻工业 | 27881篇 |
水利工程 | 6735篇 |
石油天然气 | 13037篇 |
武器工业 | 2124篇 |
无线电 | 11030篇 |
一般工业技术 | 23440篇 |
冶金工业 | 9460篇 |
原子能技术 | 2957篇 |
自动化技术 | 16772篇 |
出版年
2024年 | 937篇 |
2023年 | 3005篇 |
2022年 | 5559篇 |
2021年 | 6628篇 |
2020年 | 6876篇 |
2019年 | 6206篇 |
2018年 | 5785篇 |
2017年 | 7239篇 |
2016年 | 7913篇 |
2015年 | 7971篇 |
2014年 | 12648篇 |
2013年 | 12903篇 |
2012年 | 16287篇 |
2011年 | 16549篇 |
2010年 | 12557篇 |
2009年 | 12971篇 |
2008年 | 11740篇 |
2007年 | 14729篇 |
2006年 | 13252篇 |
2005年 | 11190篇 |
2004年 | 9389篇 |
2003年 | 8174篇 |
2002年 | 6860篇 |
2001年 | 5865篇 |
2000年 | 5189篇 |
1999年 | 4481篇 |
1998年 | 3567篇 |
1997年 | 2964篇 |
1996年 | 2540篇 |
1995年 | 2183篇 |
1994年 | 1850篇 |
1993年 | 1427篇 |
1992年 | 1243篇 |
1991年 | 896篇 |
1990年 | 709篇 |
1989年 | 629篇 |
1988年 | 455篇 |
1987年 | 306篇 |
1986年 | 251篇 |
1985年 | 169篇 |
1984年 | 170篇 |
1983年 | 85篇 |
1982年 | 76篇 |
1981年 | 78篇 |
1980年 | 66篇 |
1979年 | 49篇 |
1978年 | 29篇 |
1977年 | 27篇 |
1959年 | 29篇 |
1951年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Huseyin Selcuk Jeosadaque J Sene Marc A Anderson 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(9):979-984
This study addresses the removal of humic acid (HA) dissolved in an aqueous medium by a photoelectrocatalytic process. UV254 removal and the degradation of color (Vis400) followed pseudo‐first order kinetics. Rate constants were 1.1 × 10?1 min?1, 8.3 × 10?2 min?1 and 2.49 × 10?2 min?1 (R2 > 0.97) for UV254 degradation and 1.7 × 10?1 min?1, 6.5 × 10?2 min?1 and 2.0 × 10?2 min?1 for color removal from 5 mg dm?3, 10 mg dm?3 and 25 mg dm?3 HA respectively. Following a 2 h irradiation time, 96% of the color, 98% of the humic acid and 85% of the total organic carbon (TOC) was removed from an initial 25 mg dm?3 HA solution in the photoanode cell. Photocatalytic removal on the same photoanode was also studied in order to compare the two methods of degradation. Results showed that the photoelectrocatalytic method was much more effective than the photocatalytic method especially at high pH values and with respect to UV254 removal. The effect of other important reaction variables, eg pH, external potential and electrolyte concentration, on the photoelectrocatalytic HA degradation was also studied. Copyright © 2003 Society of Chemical Industry 相似文献
52.
本文通过焊接试验对奥氏体不锈钢绕带容器环板与绕带焊接工艺进行了研究分析,并得出了合理的焊接方法和工艺参数。 相似文献
53.
Power devices with high capability have been developed. 8‐kV/3.5‐kA‐class light‐triggered thyristors have the highest capability among power devices. These devices are used in the Kii Channel HVDC transmission system in Japan. In this paper, we report the extracted problems of conventional testing methods of 8‐kV/3.5‐kA‐class light‐triggered thyristors among manufacturers, and the proposed unified testing methods on the basis of element characteristics and operating conditions in the Kii Channel HVDC system. Furthermore, we propose a figure of merit for power devices for the practical use, and try to extract elements used at the Kii Channel HVDC system with small margins and low withstand capabilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 61–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10024 相似文献
54.
氧浓度对近临界水中纤维素分解的影响 总被引:3,自引:0,他引:3
研究了不同初始氧浓度对纤维素在近临界水中分解的影响,实验结果表明,氧浓度显著地影响产物总碳收支平衡,液相不同组分的收率、气体的产量以及气相产物的组成,微量氧对产物总碳收支平衡影响不大,而对液相不同组分的收率有一定的影响。从实验结果可以看出,离子型反应机理在纤维素水解的第一步中起主导作用。而单糖的进一步分解是一个以自由基反应机理为主的过程。 相似文献
55.
56.
The precise integration and differential quadrature methods are two new unconditionally stable numerical schemes to approximate
time derivative with more than the second order accuracy. Recent studies showed that compared with the Houbolt and Newmark
methods, they produced more accurate solutions with large time step for the problems where response is primarily dominated
by low and intermediate frequency modes. This paper aims to investigate these time schemes in the context of the dual reciprocity
BEM (DRBEM) formulation of various shock-excited scalar elastic wave problems, where high modes have important affect on traction
response. The Houbolt method was widely recommended in many literatures for such DRBEM dynamic formulations. However, this
study found that the damped Newmark algorithm was the most efficient and accurate for impact traction analysis in conjunction
with the DRBEM. The precise integration and differential quadrature methods are shown inapplicable for such shock-excited
problems due to the absence of numerical damping. On the other hand, we also found that to achieve the same order of accuracy,
the differential quadrature method required much less computing effort than the precise integration method due to the use
of the Bartels–Stewart algorithm solving the resulting Lyapunov matrix analogization equation.
Received 6 November 2000 相似文献
57.
58.
Tatsuro Kijima Kouji Ohshima Hideo Kise 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(1):61-65
Racemic amino acid esters were optically resolved via hydrolysis in organic solvents by the catalysis of an industrial alkaline protease, “Alcalase”. The products which were composed mainly of L-amino acids were insoluble and easily separated by filtration. The activity of the enzyme and enantiomeric excess of the products were significantly dependent on the nature of solvent and the water content in the reaction media. Generally, high values of enantiomeric excess were obtained at low water contents. Many natural and unnatural amino acids were resolved by this method. 相似文献
59.
文章介绍了选择过一硫酸合成的最佳条件及进行生产的可行性。介绍了过一硫酸用于含铀煌斑岩、辉绿岩、花岗岩及炭板岩矿石提取铀时,与常规酸浸方法对比,有很好的经济效益和对环境的保护价值。 相似文献
60.
《Drying Technology》2007,25(7):1193-1201
This work describes how probiotic bacteria can be dried at low temperature in two steps, combining spray drying and vacuum drying, in order to enhance their survival during storage. A sufficient number of dried probiotics survived storage for more than 3 months at 30°C, if an appropriate combination of protein and carbohydrate was selected as carrier and storage conditions were maintained optimal. The use of soy protein and maltodextrin or skim milk and arabic gum resulted in the best survival rates of probiotics during storage. No evident difference was found between different spray dryer configurations, although a cocurrent flow was preferred. 相似文献