全文获取类型
收费全文 | 16158篇 |
免费 | 1438篇 |
国内免费 | 1205篇 |
专业分类
电工技术 | 298篇 |
综合类 | 1314篇 |
化学工业 | 2244篇 |
金属工艺 | 806篇 |
机械仪表 | 567篇 |
建筑科学 | 656篇 |
矿业工程 | 686篇 |
能源动力 | 503篇 |
轻工业 | 714篇 |
水利工程 | 225篇 |
石油天然气 | 4347篇 |
武器工业 | 226篇 |
无线电 | 708篇 |
一般工业技术 | 1040篇 |
冶金工业 | 1297篇 |
原子能技术 | 126篇 |
自动化技术 | 3044篇 |
出版年
2024年 | 32篇 |
2023年 | 234篇 |
2022年 | 407篇 |
2021年 | 468篇 |
2020年 | 509篇 |
2019年 | 387篇 |
2018年 | 372篇 |
2017年 | 468篇 |
2016年 | 510篇 |
2015年 | 497篇 |
2014年 | 830篇 |
2013年 | 1060篇 |
2012年 | 1074篇 |
2011年 | 1151篇 |
2010年 | 903篇 |
2009年 | 930篇 |
2008年 | 846篇 |
2007年 | 983篇 |
2006年 | 992篇 |
2005年 | 899篇 |
2004年 | 766篇 |
2003年 | 701篇 |
2002年 | 630篇 |
2001年 | 558篇 |
2000年 | 411篇 |
1999年 | 372篇 |
1998年 | 309篇 |
1997年 | 255篇 |
1996年 | 228篇 |
1995年 | 192篇 |
1994年 | 128篇 |
1993年 | 95篇 |
1992年 | 76篇 |
1991年 | 70篇 |
1990年 | 79篇 |
1989年 | 56篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 29篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1980年 | 10篇 |
1966年 | 11篇 |
1964年 | 21篇 |
1963年 | 18篇 |
1961年 | 10篇 |
1959年 | 13篇 |
1956年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(79):33765-33780
This work investigates selective Ni locations over Ni/CeZrOx–Al2O3 catalysts at different Ni loading contents and their influences on reaction pathways in ethanol steam reforming (ESR). Depending on the Ni loading contents, the added Ni selectively interacts with CeZrOx–Al2O3, resulting in the stepwise locations of Ni over CeZrOx–Al2O3. This behavior induces a remarkable difference in hydrogen production and coke formation in ESR. The selective interaction between Ni and CeZrOx for 10-wt.% Ni generates more oxygen vacancies in the CeZrOx lattice. The Ni sites near the oxygen vacancies enhance reforming via steam activation, resulting in the highest hydrogen production rate of 1863.0 μmol/gcat·min. In contrast, for 15 and 20-wt.% Ni, excessive Ni is additionally deposited on Al2O3 after the saturation of Ni–CeZrOx interactions. These Ni sites on Al2O3 accelerate coking from the ethylene produced on the acidic sites, resulting in a high coke amount of 19.1 mgc/gcat·h (20Ni/CZ-Al). 相似文献
2.
Sehar Tasleem Muhammad Tahir Wesam Alsayeh Khalifa 《International Journal of Hydrogen Energy》2021,46(27):14148-14189
Photocatalytic H2 generation using semiconductor photocatalysts is considered as a cost-effective and eco-friendly technology for solar to energy conversion; however, the present photocatalysts have been recognized to depict low efficiency. Currently, porous coordination polymers known as metal-organic frameworks (MOFs) constituting flexible and modifiable porous structure and having excess active sites are considered to be appropriate for photocatalytic H2 production. This review highlights current progress in structural development of MOF materials along with modification strategies for enhanced photoactivity. Initially, the review discusses the photocatalytic H2 production mechanism with the concepts of thermodynamics and mass transfer with particular focus on MOFs. Elaboration of the structural categories of MOFs into Type I, Type II, Type III and classification of MOFs for H2 generation into transition metal based, post-transition metal based, noble-metal based and hetero-metal based has been systematically discussed. The review also critically deliberate various modification approaches of band engineering, improvement of charge separation, efficient irradiation utilization and overall efficiency of MOFs including metal modification, heterojunction formation, Z-scheme formation, by introducing electron mediator, and dye based composites. Also, the MOF synthesized derivatives for photocatalytic H2 generation are elaborated. Finally, future perspectives of MOFs for H2 generation and approaches for efficiency improvement have been suggested. 相似文献
3.
针对云计算应用于无线传感器网络(Wireless Sensor Network,WSN)时延敏感型业务时存在的高传输时延问题,提出了一种WSN低功耗低时延路径式协同计算方法。该方法基于一种云雾网络架构开展研究,该架构利用汇聚节点组成雾计算层;在数据传输过程中基于雾计算层的计算能力分步骤完成任务计算,降低任务处理时延;由于汇聚节点计算能力较弱,时延降低将导致能耗增加,WSN工作寿命减短,为此提出能耗约束下的任务映射策略,并利用离散二进制粒子群优化(Binary Particle Swarm Optimization,BPSO)算法解决能耗约束下的时延优化问题。仿真结果表明,在相同的能耗约束下,对比其他算法,基于BPSO算法得出的映射方案能有效降低业务处理时延,满足时延敏感型业务的需求。 相似文献
4.
《Journal of the European Ceramic Society》2021,41(15):7868-7877
In this work, 0.5TRPO•0.5Gd2Zr2O7 ceramic with an average grain size of only ∼15 nm was prepared by a high pressure (5 GPa/520 °C) sintering method. Phase evolutions and microstructure changes of the as-fabricated super nano and micron-grained ceramics under a high-dose displacement damage induced by 300 keV Kr2+ ions were investigated. The results show that the super nano-grained ceramic has low degree of amorphization, obvious grain growth (2–3 times in grain size) and big Kr bubbles (10–68 nm) formation after irradiation. The micron-grained ceramic was severely amorphized after irradiation and many microcracks were formed parallel to its surface. The formation mechanism of Kr bubbles in the super nano-grained ceramic is on account of grain boundary diffusion and migration induced by the accumulation of the injecting Kr ions and irradiation defects. Nevertheless, microcracks formed in the micron-grained sample are caused by the accumulation of Kr atoms. 相似文献
5.
6.
Ivonne Sgura Amos S. Lawless Benedetto Bozzini 《Inverse Problems in Science & Engineering》2019,27(5):618-647
The process of electrodeposition can be described in terms of a reaction-diffusion partial differential equation (PDE) system that models the dynamics of the morphology profile and the chemical composition. Here we fit such a model to the different patterns present in a range of electrodeposited and electrochemically modified alloys using PDE constrained optimization. Experiments with simulated data show how the parameter space of the model can be divided into zones corresponding to the different physical patterns by examining the structure of an appropriate cost function. We then use real data to demonstrate how numerical optimization of the cost function can allow the model to fit the rich variety of patterns arising in experiments. The computational technique developed provides a potential tool for tuning experimental parameters to produce desired patterns. 相似文献
7.
Journal of Computer Science and Technology - DOACROSS loops are significant parts in many important scientific and engineering applications, which are generally exploited pipeline/wave-front... 相似文献
8.
9.
This study explored adolescents’ opinions about how Internet use supports the achievement of their developmental tasks. Qualitative data were collected in focus groups interviews with 127 Italian Internet users (11–20) attending middle and high schools. Discussions were recorded, transcribed and analyzed using content analysis. Results showed that the Internet plays important functions in identity formation, personal autonomy, and relationships outside the family. It allows teens to develop their own interests, to identify with others and, at the same time, differentiate from others. The Internet is also an arena in which adolescents develop and practice autonomy. The Internet can be a source of conflict with parents, because of parents’ concerns about Internet use. However, the Internet can also be a meeting ground with parents. Finally, participants indicated the Internet is used to form close relationships with peers. Gender and age differences are discussed. Although the study is cross-sectional and relies only on adolescent report, findings illustrate how the conceptual framework of developmental goals may be helpful for understanding how the Internet can affect adolescents’ lives. 相似文献
10.
V.I. Popkov O.V. Almjasheva V.N. Nevedomskiy V.V. Panchuk V.G. Semenov V.V. Gusarov 《Ceramics International》2018,44(17):20906-20912
Formation and structural transformations of yttrium orthoferrite crystals have been studied using X-ray diffractometry, Mössbauer spectroscopy and transmission electron microscopy combined with electron microdiffraction. Said processes have been studied under heat treatment of glycine-nitrate combustion products. There have been identified formations of three structural yttrium orthoferrite modifications – amorphized hexagonal <h1>-YFeO3 (P63cm) and nanocrystalline hexagonal h2-YFeO3 (P63/mmc), as well as nanocrystalline orthorhombic o-YFeO3 (Pbnm), which are selectively formed depending on available three-dimensional confinements. Based on the analysis of changes in the fluid and size composition formulation, it has been proposed mechanism for formation and transformation of YFeO3 nanocrystals, including growth stage of h2-YFeO3 crystals due to amorphized phase of <h1>-YFeO3 up to critical size of about 15?nm and their subsequent transformation into orthorhombic form o-YFeO3. 相似文献