全文获取类型
收费全文 | 4942篇 |
免费 | 198篇 |
国内免费 | 39篇 |
专业分类
电工技术 | 89篇 |
综合类 | 77篇 |
化学工业 | 854篇 |
金属工艺 | 63篇 |
机械仪表 | 84篇 |
建筑科学 | 226篇 |
矿业工程 | 14篇 |
能源动力 | 60篇 |
轻工业 | 1937篇 |
水利工程 | 34篇 |
石油天然气 | 43篇 |
武器工业 | 5篇 |
无线电 | 299篇 |
一般工业技术 | 744篇 |
冶金工业 | 178篇 |
原子能技术 | 22篇 |
自动化技术 | 450篇 |
出版年
2023年 | 50篇 |
2022年 | 92篇 |
2021年 | 139篇 |
2020年 | 97篇 |
2019年 | 73篇 |
2018年 | 91篇 |
2017年 | 80篇 |
2016年 | 84篇 |
2015年 | 87篇 |
2014年 | 148篇 |
2013年 | 178篇 |
2012年 | 193篇 |
2011年 | 237篇 |
2010年 | 166篇 |
2009年 | 151篇 |
2008年 | 183篇 |
2007年 | 158篇 |
2006年 | 136篇 |
2005年 | 104篇 |
2004年 | 104篇 |
2003年 | 105篇 |
2002年 | 105篇 |
2001年 | 61篇 |
2000年 | 62篇 |
1999年 | 58篇 |
1998年 | 67篇 |
1997年 | 44篇 |
1996年 | 49篇 |
1995年 | 53篇 |
1994年 | 58篇 |
1993年 | 36篇 |
1921年 | 34篇 |
1919年 | 35篇 |
1917年 | 48篇 |
1916年 | 78篇 |
1915年 | 88篇 |
1914年 | 54篇 |
1913年 | 61篇 |
1912年 | 82篇 |
1911年 | 84篇 |
1910年 | 94篇 |
1909年 | 97篇 |
1908年 | 102篇 |
1907年 | 101篇 |
1906年 | 94篇 |
1905年 | 118篇 |
1904年 | 150篇 |
1903年 | 94篇 |
1902年 | 65篇 |
1901年 | 74篇 |
排序方式: 共有5179条查询结果,搜索用时 15 毫秒
1.
Ajit Sharma Doan Van Thuan Thanh-Dong Pham Mai Hung Thanh Tung Nguyen Thi Thanh Truc Dai-Viet N. Vo 《化学工程与技术》2020,43(4):752-761
FeO-doped TiO2 nanoparticle photocatalysts were immobilized onto the surface of fibrous activated carbon (ACF) via a sol-gel process. As an adsorbent and photocatalyst, FeO-TiO2 on immobilized ACFs (FeO-TiO2/ACF) greatly improved the photocatalysis rate of hydrogen production as compared with pure TiO2 and ACF-TiO2 under UV irradiation and visible light. The addition of ACFs surface significantly reduced the photogenerated pairs of electrons-hole recombination, thereby promoting the photocatalysis action of doped photo-metal oxides of FeO-TiO2. Co-doping of FeO onto the lattice of the TiO2 approach can improve the absorption activity of visible light through photo-metal oxide of TiO2 and further enhance hydrogen production under visible light. The photocatalytic fabrics (FeO-TiO2/ACF) were effortlessly split out from the experimental solution for re-utilization and exhibited high stability even after five complete regeneration cycles. 相似文献
2.
3.
一、SQL简介 如果说七十年代关系数据库还处于研制实验阶段,那么到了八十年代大量关系数据库商用产品的面市几乎占据了整个数据库市场,其中的原因在于它们使用了统一的语言界面,那就是,SQL成为了关系数据库的通用语言。 1974年.IBM公司San Jose研究实验室的D.D.Chamberlin在开发SEQUEL-XRM原型时提出了SE-QUEL(Structured English Query Language),1976年又修改成为SEQUEL/2.也就是目前的SQL(StructuredQuer Language)。SEQUEL/2主要成形于IBM的Sys-tem R原型中[2],并在原有基础上大加扩展,其后逐渐完善并最终成为一种完备的结构化数据库查询语言。 相似文献
4.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained. 相似文献
5.
We determine the exact power of two-prover interactive proof systems introduced by Ben-Or, Goldwasser, Kilian, and Wigderson (1988). In this system, two all-powerful noncommunicating provers convince a randomizing polynomial time verifier in polynomial time that the inputx belongs to the languageL. We show that the class of languages having tow-prover interactive proof systems is nondeterministic exponential time.We also show that to prove membership in languages inEXP, the honest provers need the power ofEXP only.The first part of the proof of the main result extends recent techniques of polynomial extrapolation used in the single prover case by Lund, Fortnow, Karloff, Nisan, and Shamir.The second part is averification scheme for multilinearity of a function in several variables held by an oracle and can be viewed as an independent result onprogram verification. Its proof rests on combinatorial techniques employing a simple isoperimetric inequality for certain graphs: 相似文献
6.
中国珠宝销售的可持续发展 总被引:2,自引:1,他引:1
通过对改革开放20多年来中国珠宝业发展的回顾与分析, 认为在激烈的市场竞争中, 珠宝业要达到可持续发展必须具备6个要素: (1)敬业精神; (2)信用意识; (3)创新意识和创新能力; (4)激励机制和团队精神; (5)资本营运和资源整合能力; (6)关系营销技巧. 相似文献
7.
8.
Molecular dynamics simulations are used to investigate polymer networks made by either end-linking or randomly crosslinking a melt of linear precursor chains. The resulting network structures are very different, since end-linking leads to nearly ideal monodisperse networks, while random crosslinking leads to polydisperse networks, characterized by an exponential strand length distribution. Networks with average strand length 20 and 100 were generated. These networks were used to study the effects of disorder in the network connectivity on observables averaged either over the entire network or selected sub-structures. Heterogeneities in the randomly crosslinked networks cause significant differences in the localization of monomers, however, neither the localization of crosslinks nor the microscopic strain response are significantly affected. Compared to end-linked networks, randomly crosslinked networks have a slightly increased tube diameter, and as a result a slightly decreased shear modulus, but otherwise identical stress-strain behavior. For the investigated systems, we conclude that the microscopic strain response, tube diameter, and stress-strain relation are all insensitive to the heterogeneities due to the linking process by which the network were made. 相似文献
9.
Shiqi He Qianchu Liu Yiu-Wing Mai Roland Bryant 《Journal of materials science. Materials in medicine》1996,7(10):611-616
Abrasive wear is a major problem in the application of dental composite resins. In this study the friction and wear behaviours of two types of dental composites: one containing relatively coarse filler particles and some microfillers (Estilux) and another containing only microfiller particles (Durafill), have been investigated by using a scratch testing machine. Experimental results show that the coefficients of friction in both composites are essentially constant for applied loads up to 20 N. The wear resistance of Durafill is better than Estilux. Under the same testing conditions, the size, shape and distribution of the filler particles are more important variables than applied load and sliding speed in controlling the wear mechanism. It is shown that for Estilux, plastic ploughing by the diamond indenter is the predominant mechanism. For Durafill, however, the formation and propagation of tensile cracks on the worn surface is the main wear mechanism. The effects of two different indenters, diamond and enamel, on the basic wear mechanisms are also discussed. 相似文献
10.
This study provides a meta-analysis of research on the associations between relationship conflict, task conflict, team performance, and team member satisfaction. Consistent with past theorizing, results revealed strong and negative correlations between relationship conflict, team performance, and team member satisfaction. In contrast to what has been suggested in both academic research and introductory textbooks, however, results also revealed strong and negative (instead of the predicted positive) correlations between task conflict, team performance, and team member satisfaction. As predicted, conflict had stronger negative relations with team performance in highly complex (decision making, project, mixed) than in less complex (production) tasks. Finally, task conflict was less negatively related to team performance when task conflict and relationship conflict were weakly, rather than strongly, correlated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献