全文获取类型
收费全文 | 6937篇 |
免费 | 923篇 |
国内免费 | 261篇 |
专业分类
电工技术 | 861篇 |
综合类 | 496篇 |
化学工业 | 989篇 |
金属工艺 | 492篇 |
机械仪表 | 372篇 |
建筑科学 | 817篇 |
矿业工程 | 306篇 |
能源动力 | 241篇 |
轻工业 | 549篇 |
水利工程 | 258篇 |
石油天然气 | 169篇 |
武器工业 | 39篇 |
无线电 | 846篇 |
一般工业技术 | 751篇 |
冶金工业 | 319篇 |
原子能技术 | 33篇 |
自动化技术 | 583篇 |
出版年
2024年 | 22篇 |
2023年 | 103篇 |
2022年 | 160篇 |
2021年 | 229篇 |
2020年 | 262篇 |
2019年 | 193篇 |
2018年 | 201篇 |
2017年 | 240篇 |
2016年 | 283篇 |
2015年 | 263篇 |
2014年 | 466篇 |
2013年 | 420篇 |
2012年 | 557篇 |
2011年 | 582篇 |
2010年 | 440篇 |
2009年 | 463篇 |
2008年 | 447篇 |
2007年 | 449篇 |
2006年 | 388篇 |
2005年 | 350篇 |
2004年 | 283篇 |
2003年 | 267篇 |
2002年 | 199篇 |
2001年 | 178篇 |
2000年 | 127篇 |
1999年 | 136篇 |
1998年 | 84篇 |
1997年 | 52篇 |
1996年 | 52篇 |
1995年 | 31篇 |
1994年 | 44篇 |
1993年 | 27篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有8121条查询结果,搜索用时 15 毫秒
991.
这里研究了基于虚拟企业进行机电产品协同开发的过程,开发了一个支持虚拟企业组建、运行与解体的异地并行设计与制造系统,介绍了系统的基本框架与实现方法。 相似文献
992.
993.
通过引入2-丙烯酰胺-2-甲基丙磺酸(AMPS)和甲基丙烯酰氧乙基三甲基氯化铵(DMC)两种小单体,并采用相对分子量较大的甲基烯丙基聚氧乙烯醚(HPEG)大单体,合成了一种两性聚羧酸减水剂ZQ-3,使用红外光谱对其结构进行了确证.将该减水剂与另外三种聚羧酸减水剂进行了性能对比研究.水泥净浆实验结果表明:减水剂ZQ-3具有良好的分散性及分散性经时保持性能,对净浆的凝结时间影响不大;混凝土实验及XRD分析表明:减水剂ZQ-3能够促进水泥的早期水化,明显提高混凝土蒸养脱模强度和早期强度. 相似文献
994.
Lumber size control is an essential element in maximising yield and productivity because a small reduction in rough green target size could lead to substantial savings in wood fibre. One of the key components of rough green target size is sawing variation. In this study, the optimum side clearance of band saw teeth leading to a minimum saw teeth deflection and minimum lumber thickness variation of stellite-tipped and swage-set saws when processing Triplochiton scleroxylon a tropical hardwood were examined. It was observed that the accuracy of kerf width was best with stellite-tipped saws. However, Analysis of variance (ANOVA) at 5% level of significance indicates that there was no significant difference between the accuracy of kerf width of stellite-tipped saws and swage-set saws. It also was observed that at 5% level of significance, the mean kerf width of stellite-tipped saws, which was 4.2 mm, was significantly greater than the mean kerf width of 3.06 mm of the swage-set saws. Sawing variation as indicated by standard deviation of lumber thickness was best for the swage-set saws. A quadratic relationship between sawing variation and side clearance of stellite-tipped saws was established. As the side clearance of the saw increases, the sawing variation decreases until it reaches a minimum value and thereafter, further increase in side clearance of the saw teeth results in an increase in sawing variation. It was observed that an optimum side clearance of 0.69 mm under a saw blade thickness of 1.3 mm was required to produce on the average, a minimum value of 0.42 mm for within-board standard deviation, and 0.59 mm for the total standard deviation. An error margin of less than 1% was achieved when the experimental results for the optimum side clearance was compared with a theoretical assertion. 相似文献
995.
设计了一种新的基于需求侧响应的电力数据采集系统,包括底层的终端电表、中间层的采集服务器和平台层的需求侧管理平台.该系统通过分析用户的负荷情况将需要的数据点采集到采集服务器,再通过无线4G网络发送至需求侧管理平台,以实现电能的实时采集. 相似文献
996.
Host Exciton Confinement for Enhanced Förster‐Transfer‐Blend Gain Media Yielding Highly Efficient Yellow‐Green Lasers
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Qi Zhang Jingguan Liu Qi Wei Xiangru Guo Yan Xu Ruidong Xia Linghai Xie Yan Qian Chen Sun Larry Lüer Juan Cabanillas‐Gonzalez Donal D. C. Bradley Wei Huang 《Advanced functional materials》2018,28(17)
This paper reports state‐of‐the‐art fluorene‐based yellow‐green conjugated polymer blend gain media using Förster resonant‐energy‐transfer from novel blue‐emitting hosts to yield low threshold (≤7 kW cm?2) lasers operating between 540 and 590 nm. For poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) (15 wt%) blended with the newly synthesized 3,6‐bis(2,7‐di([1,1′‐biphenyl]‐4‐yl)‐9‐phenyl‐9H‐fluoren‐9‐yl)‐9‐octyl‐9H–carbazole (DBPhFCz) a highly desirable more than four times increase (relative to F8BT) in net optical gain to 90 cm?1 and 34 times reduction in amplified spontaneous emission threshold to 3 µJ cm?2 is achieved. Detailed transient absorption studies confirm effective exciton confinement with consequent diffusion‐limited polaron‐pair generation for DBPhFCz. This delays formation of host photoinduced absorption long enough to enable build‐up of the spectrally overlapped, guest optical gain, and resolves a longstanding issue for conjugated polymer photonics. The comprehensive study further establishes that limiting host conjugation length is a key factor therein, with 9,9‐dialkylfluorene trimers also suitable hosts for F8BT but not pentamers, heptamers, or polymers. It is additionally demonstrated that the host highest occupied and lowest unoccupied molecular orbitals can be tuned independently from the guest gain properties. This provides the tantalizing prospect of enhanced electron and hole injection and transport without endangering efficient optical gain; a scenario of great interest for electrically pumped amplifiers and lasers. 相似文献
997.
Room‐Temperature‐Operated Ultrasensitive Broadband Photodetectors by Perovskite Incorporated with Conjugated Polymer and Single‐Wall Carbon Nanotubes
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wenzhan Xu Yikun Guo Xiaotao Zhang Luyao Zheng Tao Zhu Dahui Zhao Wenping Hu Xiong Gong 《Advanced functional materials》2018,28(7)
In this work, room‐temperature‐operated ultrasensitive solution‐processed perovskite photodetectors (PDs) with near infrared (NIR) photoresponse are reported. In order to enable perovskite PDs possessing extended NIR photoresponse, novel n‐type low bandgap conjugated polymer, poly[(N,N′‐bis(2‐octyldodecyl)‐1,4,5,8‐naphthalene diimide‐2,6‐diyl) (2,5‐dioctyl‐3,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione‐5,5′‐diyl)] (NDI‐DPP), which has strong absorption in the NIR region, is developed and then employed in perovskite PDs. By the formation of type II band alignment between NDI‐DPP with single‐wall carbon nanotubes (SWCNTs), the NIR absorption of NDI‐DPP is exploited, which contributes to the NIR photoresponse for the perovskite PDs, where perovskite is incorporated with NDI‐DPP and SWCNTs as well. In addition, SWCNTs incorporated with perovskite active layer can offer the percolation pathways for high charge‐carrier mobility, which tremendously boosts the charge transfer in the photoactive layer, and consequently improves the photocurrent in the visible region. As a result, the perovskite PDs exhibit the responsivities of ≈400 and ≈150 mA W?1 and the detectivities of over 6 × 1012 Jones (1 Jones = 1 cm Hz1/2 W?1) and over 2 × 1012 Jones in the visible and NIR regions, respectively. This work reports the development of perovskite PDs with NIR photoresponse, which is terrifically beneficial for the practical applications of perovskite PDs. 相似文献
998.
Fluorinated and Alkylthiolated Polymeric Donors Enable both Efficient Fullerene and Nonfullerene Polymer Solar Cells
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Guangjun Zhang Xiaopeng Xu Zhaozhao Bi Wei Ma Dongsheng Tang Ying Li Qiang Peng 《Advanced functional materials》2018,28(10)
In this work, four donor (D)–acceptor (A) copolymers based on benzodithiophene (BDT) and benzothiadiazole (BT) with different alkylthiolated and/or fluorinated side chains are developed for efficient fullerene and nonfullerene polymer solar cells (PSCs). The synergistic effect of sulfuration and fluorination on the optical absorption, energy level, crystallinity, carrier mobility, blend morphology, and photovoltaic performance is investigated systematically. By incorporating sulfur atoms onto the side chains, a little blueshifted but significantly increased absorption can be obtained for PBDTS‐FBT compared to PBDT‐FBT . On the other side, a little more blueshifted but much stronger absorption and much lower‐lying highest occupied molecular orbital (HOMO) level can be realized for PBDTF‐FBT when introducing fluorine atoms instead of sulfur atoms. With the combination of both fluorination and sulfuration strategies, PBDTS‐FBT exhibits the best absorption ability, lowest HOMO energy level, and highest crystallinity, which make PBDTSF‐FBT devices show the highest power conversion efficiency (PCE) of 10.69% in fullerene PSCs and 11.66% in nonfullerene PSCs. The PCE of 11.66% is the best value for PSCs based on BT‐containing copolymer donors reported so far. The results indicate that fluorination and sulfuration have a synergistically positive effect on the performance of D–A photovoltaic copolymers and their solar cell devices. 相似文献
999.
Effect of side‐chain functionality on the organic field‐effect transistor performance of oligo(p‐phenylenevinylene) derivatives
下载免费PDF全文
![点击此处可从《应用聚合物科学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In order to observe the effects of the substitution of electronegative flourine with aromatic groups in oligo(p ‐phenylenevinylene) compounds on their packing, morphology, and charge carrier mobility, we have synthesized napthol‐substituted oligo(p ‐phenylenevinylene) compounds and examined their solubility, redox properties, thin film morphologies, and charge carrier properties. To date, very few examples of conjugated oligomers bearing napthol side groups have been reported in the literature. After annealing at 150 °C, the mobility of S1, S2, and S3 was 4.0 × 10?2 cm2 V?1 s?1, 1.2 × 10?2 cm2 V?1 s?1, and 2.6 × 10?3 cm2 V?1 s?1, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44825. 相似文献
1000.
Kwang Myung Jeon Su Yeon Park Chan Jun Chun Nam In Park Hong Kook Kim 《ETRI Journal》2017,39(3):398-405
In this paper, an artificial stereo extension method that creates stereophonic sound from a mono sound source is proposed. The proposed method first trains deep neural networks (DNNs) that model the nonlinear relationship between the dominant and residual signals of the stereo channel. In the training stage, the band‐wise log spectral magnitude and unwrapped phase of both the dominant and residual signals are utilized to model the nonlinearities of each sub‐band through deep architecture. From that point, stereo extension is conducted by estimating the residual signal that corresponds to the input mono channel signal with the trained DNN model in a sub‐band domain. The performance of the proposed method was evaluated using a log spectral distortion (LSD) measure and multiple stimuli with a hidden reference and anchor (MUSHRA) test. The results showed that the proposed method provided a lower LSD and higher MUSHRA score than conventional methods that use hidden Markov models and DNN with full‐band processing. 相似文献