全文获取类型
收费全文 | 14539篇 |
免费 | 1829篇 |
国内免费 | 924篇 |
专业分类
电工技术 | 213篇 |
综合类 | 1238篇 |
化学工业 | 3808篇 |
金属工艺 | 612篇 |
机械仪表 | 328篇 |
建筑科学 | 741篇 |
矿业工程 | 327篇 |
能源动力 | 1070篇 |
轻工业 | 580篇 |
水利工程 | 220篇 |
石油天然气 | 768篇 |
武器工业 | 62篇 |
无线电 | 1919篇 |
一般工业技术 | 2715篇 |
冶金工业 | 518篇 |
原子能技术 | 94篇 |
自动化技术 | 2079篇 |
出版年
2024年 | 86篇 |
2023年 | 397篇 |
2022年 | 451篇 |
2021年 | 676篇 |
2020年 | 685篇 |
2019年 | 568篇 |
2018年 | 546篇 |
2017年 | 637篇 |
2016年 | 671篇 |
2015年 | 615篇 |
2014年 | 809篇 |
2013年 | 989篇 |
2012年 | 908篇 |
2011年 | 988篇 |
2010年 | 726篇 |
2009年 | 890篇 |
2008年 | 717篇 |
2007年 | 902篇 |
2006年 | 855篇 |
2005年 | 740篇 |
2004年 | 581篇 |
2003年 | 563篇 |
2002年 | 413篇 |
2001年 | 360篇 |
2000年 | 356篇 |
1999年 | 233篇 |
1998年 | 187篇 |
1997年 | 130篇 |
1996年 | 120篇 |
1995年 | 104篇 |
1994年 | 76篇 |
1993年 | 55篇 |
1992年 | 55篇 |
1991年 | 29篇 |
1990年 | 28篇 |
1989年 | 33篇 |
1988年 | 26篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1958年 | 1篇 |
1957年 | 1篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Campaigns have increasingly resorted to Facebook because it has the highest number of users among social media platforms. The question as to whether Facebook is a more favorable choice of social media than a blog for political purposes must be addressed. In this comparative study, cross-sectional data collected in the 2009 and 2014 Taiwan local elections were used for exploring the differences among voter motivations, perceived credibility, and dependency between the use of political blogs and Facebook. In addition, the impact factors regarding the relationship between blogs and Facebook dependency were analyzed. The findings indicate that voter motivations, perceived credibility, and dependency were higher for political blogs than they were for Facebook, suggesting that in a political context, people prefer blogs to Facebook. The results of regression analyses indicate that the motivation for debating political topics was a significant predictor of the dependency on blogs, whereas motivations for general information and entertainment were related to Facebook use. The perceived credibility was not related to blog use; however, accuracy and information depth were significant factors for the use of Facebook. The reasons for the differences between peoples’ use of political blogs and Facebook are discussed in this paper. This study advances our understanding on the variations in people’s use of different social media platforms in a political context, and few studies have investigated this topic from a user-oriented perspective. 相似文献
152.
Hailong Qiu Tianyu Tang Muhammad Asif Xiaoxiao Huang Yanglong Hou 《Advanced functional materials》2019,29(19)
Lithium (Li) metal is the most ideal anode material for high‐energy density batteries. However, the high activity of Li metal, the large volume change, and Li dendrite formation during cycling hinder its practical application. Herein, 3D porous Cu synthesized through a simple time‐saving hydrogen bubble dynamic template method is used as a host for the improved performance Li metal anode. Contrary to the planar Cu foil, the synthesized 3D porous structure can reduce the local current density, suppress the mossy/dendritic Li growth, and buffer the volume change in the Li metal anode. Highly stable Coulombic efficiency is achieved at different specific current densities (0.5, 1, and 2 mA cm?2) with a capacity of 1.0 mAh cm?2. Moreover, symmetrical Li|Li‐3D Cu cells show more stable cyclic performance with a lower overpotential even at a high current density of 3 mA cm?2. 相似文献
153.
3D Graphene Films Enable Simultaneously High Sensitivity and Large Stretchability for Strain Sensors 下载免费PDF全文
Fei Pan Si‐Ming Chen Yuhan Li Zhuchen Tao Jianglin Ye Kun Ni Han Yu Bin Xiang Yibin Ren Faxiang Qin Shu‐Hong Yu Yanwu Zhu 《Advanced functional materials》2018,28(40)
Integration of 2D membranes into 3D macroscopic structures is essential to overcome the intrinsically low stretchability of graphene for the applications in flexible and wearable electronics. Herein, the synthesis of 3D graphene films (3D‐GFs) using chemical vapor deposition (CVD) is reported, in which a porous copper foil (PCF) is chosen as a template in the atmospheric‐pressure CVD preparation. When the 3D‐GF prepared at 1000 °C (noted as 3D‐GF‐1000) is transferred onto a polydimethylsiloxane (PDMS) membrane, the obtained 3D‐GF‐1000/PDMS hybrid film shows an electrical conductivity of 11.6 S cm?1 with good flexibility, indicated by small relative resistance changes (ΔR/R0) of 2.67 and 0.36 under a tensile strain of 50% and a bending radius of 1.6 mm, respectively. When the CVD temperature is reduced to 900 °C (generating a sample noted as 3D‐GF‐900), the 3D‐GF‐900/PDMS hybrid film exhibits an excellent strain‐sensing performance with a workable strain range of up to 187% and simultaneously a gauge factor of up to ≈1500. The 3D‐GF‐900/PDMS also shows a remarkable durability in resistance in repeated 5000 stretching‐releasing cycles. Kinetics studies show that the response of ΔR/R0 upon strain is related to the graphitization and conductivity of 3D‐GF which are sensitive to the CVD preparation temperature. 相似文献
154.
155.
156.
157.
Photo‐Induced Functionalization of Spherical and Planar Surfaces via Caged Thioaldehyde End‐Functional Polymers 下载免费PDF全文
Michael Kaupp Alexander S. Quick Cesar Rodriguez‐Emmenegger Alexander Welle Vanessa Trouillet Ognen Pop‐Georgievski Martin Wegener Christopher Barner‐Kowollik 《Advanced functional materials》2014,24(36):5649-5661
The synthesis and application of a novel reversible addition‐fragmentation chain transfer (RAFT) agent carrying a photocaged thioaldehyde moiety is described (λmax = 355 nm). RAFT polymerization of styrene, dimethylacrylamide and a glycomonomer is evidenced (3600 g mol?1 ≤ Mn ≤ 15 000 g mol?1; 1.07 ≤ ? ≤ 1.20) with excellent end‐group fidelity. The photogenerated thioaldehyde on the chain ends can undergo hetero Diels–Alder reactions with dienes as well as reactions with nucleophiles. The terminal photoreactive polymers are photografted to porous diene‐reactive polymeric microspheres. The grafted particles are in‐depth characterized via scanning electron microscopy, elemental analysis, X‐ray photoelectron spectroscopy, and high resolution FT‐IR microscopy, leading to a qualitative as well as quantitative image of the core–shell objects. Grafting densities up to 0.10 molecules nm?2 are reached. The versatility of the thioaldehyde ligation is evidenced by spatially resolved grafting of polystyrene onto nucleophilic groups present in poly (dopamine) (PDA)‐coated glass slides and silicon wafers via two‐photon direct laser writing (DLW) imaged by ToF‐SIMS. The combination of thioaldehyde ligation, RAFT polymerization, and DLW allows for the spatially resolved grafting of a vast range of polymers onto various substrates in any desired pattern with sub‐micrometer resolution. 相似文献
158.
159.
青海广播电视台为打造一个支持“全媒体、全业务、全流程、全覆盖、全扩展”适应未来发展需要的一体化平台.拟将新闻中心改造为高清采编基础上基于云计算技术的全媒体融合新闻平台.从系统规划、整体架构、关键技术等方面介绍了系统总体规划,从资源层、业务层、管理层三个方面分析了系统支撑云平台核心点设计. 相似文献
160.
Social influence is an important research topic in the technology acceptance literature, in particular for social media. Prior empirical studies have for the most part employed social influence theory to investigate user intentions to continue with social media, while culture driven theories have been neglected. Rather than using social influence theory, we introduced guanxi theory to explore how guanxi social mechanisms (or processes) influence Chinese users’ continuance intentions in WeChat. Specifically, we developed a model that examines the role of guanxi as manifested by renqing, mianzi and ganqing in perceived usefulness, perceived enjoyment and continuance intention in WeChat. A survey research method was adopted to test the proposed hypotheses. This study found that ganqing has a positive impact on perceived usefulness and continuance intention. Mianzi exerts a negative effect on continuance intention but exhibits a positive effect on perceived usefulness. Renqing was found to have no significant impact on perceived usefulness and continuance intention. Our study advances the Technology Acceptance Model (TAM) by introducing guanxi-based constructs in a Chinese mobile social-messaging application context. Our study also offers alternative insights on guanxi-based social influence processes in the Chinese technology acceptance literature. 相似文献