全文获取类型
收费全文 | 128555篇 |
免费 | 11479篇 |
国内免费 | 6035篇 |
专业分类
电工技术 | 7449篇 |
技术理论 | 11篇 |
综合类 | 8482篇 |
化学工业 | 21235篇 |
金属工艺 | 7357篇 |
机械仪表 | 8485篇 |
建筑科学 | 10930篇 |
矿业工程 | 3852篇 |
能源动力 | 3648篇 |
轻工业 | 8344篇 |
水利工程 | 2477篇 |
石油天然气 | 7360篇 |
武器工业 | 1141篇 |
无线电 | 15507篇 |
一般工业技术 | 15337篇 |
冶金工业 | 6197篇 |
原子能技术 | 1477篇 |
自动化技术 | 16780篇 |
出版年
2024年 | 539篇 |
2023年 | 2193篇 |
2022年 | 3975篇 |
2021年 | 5320篇 |
2020年 | 4141篇 |
2019年 | 3421篇 |
2018年 | 3662篇 |
2017年 | 4316篇 |
2016年 | 3857篇 |
2015年 | 5371篇 |
2014年 | 6631篇 |
2013年 | 7905篇 |
2012年 | 8548篇 |
2011年 | 9267篇 |
2010年 | 8112篇 |
2009年 | 7799篇 |
2008年 | 7633篇 |
2007年 | 7155篇 |
2006年 | 7048篇 |
2005年 | 5929篇 |
2004年 | 3952篇 |
2003年 | 3323篇 |
2002年 | 3168篇 |
2001年 | 2868篇 |
2000年 | 2704篇 |
1999年 | 2959篇 |
1998年 | 2577篇 |
1997年 | 2119篇 |
1996年 | 2022篇 |
1995年 | 1625篇 |
1994年 | 1456篇 |
1993年 | 1065篇 |
1992年 | 786篇 |
1991年 | 653篇 |
1990年 | 473篇 |
1989年 | 377篇 |
1988年 | 332篇 |
1987年 | 205篇 |
1986年 | 157篇 |
1985年 | 112篇 |
1984年 | 61篇 |
1983年 | 62篇 |
1982年 | 61篇 |
1981年 | 38篇 |
1980年 | 35篇 |
1979年 | 17篇 |
1976年 | 5篇 |
1967年 | 3篇 |
1959年 | 5篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
41.
To realize joint optimization of spatial diversity and equalization combining in the intersymbol interference (ISI) channel, an iterative equalization combining algorithm is proposed. The proposed algorithm uses the coefficients of Turbo equalization to calculate the combination weights without estimating the signal to noise ratio in each diversity branch. The equalized symbols from different diversity branches are combined, and the extrinsic information output from the decoder is fed back to the equalizers, so as to exchange soft information between the equalizers and the decoder. The performance of the proposed algorithm is analyzed using the extrinsic information transfer (EXIT) chart and verified by simulations. Results show that our approach fully exploits time domain information from the multipath channel and spatial domain information from multi receiving antennas, which efficiently improve the performance of the receiver in the severe ISI channel. 相似文献
42.
43.
Kang Zhang Rong‐rong Wang Kai‐rui Zhang Fei Cheng Yu Tian Yi Lin Mi Zhou Pu‐xin Zhu 《Polymer International》2020,69(3):274-279
A series of hyperbranched poly(citric polyethylene glycol) (PCPEG) materials with varied polyethylene glycol (PEG) chain lengths as plasticizers were mixed with maize starch (MS) via cooking and film‐forming. The structure, pasting property, plasticization, aging property, moisture absorption and compatibility of plasticized starches were studied by means of Fourier transform infrared spectroscopy, X‐ray diffraction, rapid viscosity analysis, tension testing, moisture absorption measurements and scanning electron microscopy. Compared with PEG and citric acid, PCPEG was more effective in promoting starch chain movement and inhibiting the retrogradation of starch film. Also, PCPEG/MS had smaller moisture content. The longer the plasticizer chain, the better were the aging resistance and moisture resistance of starch. But with an increase of PEG chain length, mechanical properties of PCPEG/MS deteriorated and the compatibility between PCPEG and MS decreased. The hyperbranched derivative of PEG with longer chain exhibited improved plasticization and compatibility with starch. © 2019 Society of Chemical Industry 相似文献
44.
针对现有技术中输送系统控制不稳定、控制能力低下等问题,本文提出基于工业CAN总线的输送系统集成化控制.在控制系统CAN通信节点利用代码进行数据的转化,通过emit关键字将数据绘制成显示曲线,由输入的代码不断对系统数据进行刷新,实现了输送系统的实时监控,提高了系统运行的安全性.通过时间同步技术将SAEAS6802时钟同步协议与时钟修正算法相结合,有效地对数据处理时间和接收时间进行校正,减少了数据接收误差,提高了时间同步精度.实验结果表明,本文研究方法提高了输送控制系统的运行安全性和可靠性. 相似文献
45.
Spinel LiSr0·1Cr0·1Mn1·8O4 was synthesised by high temperature solid state method in order to enhance the electrochemical performance. The LiSr0·1Cr0·1Mn1·8O4 (LSCMO) materials were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The XRD and SEM studies confirm that LSCMO had spinel crystal structure with a space group of Fd3m, and the particle of LSCMO shows irregular shape. The cyclic voltammetry data illustrated that the heavy current charge–discharge performance of LMO was improved by Sr2+ and Cr3+ doping. The galvanostatic charge–discharge of LSCMO cathode materials was measured at 1, 5, 10 and 20 C. The results indicated that LSCMO improved the capacity retention. 相似文献
46.
47.
Energy transfer from photo-excited electrons in a metal thin film to the dielectric substrate is important for understanding the ultrafast heat transfer process across the two materials. Substantial research has been conducted to investigate heat transfer in a metal-dielectric structure. In this work, a two-temperature model in metal was used to analyze the interface electron and dielectric substrate coupling. An improved temperature and wavelength-dependent Drude–Lorentz model was implemented to interpret the signals obtained in optical measurements. Ultrafast pump-and-probe measurements on Au-Si samples were carried out, where the probe photon energy was chosen to be close to the interband transition threshold of gold to minimize the influence of non-equilibrium electrons on the optical response and maximize the thermal modulation to the optical reflectance. Electron-substrate interface thermal conductance at different pump laser fluences was obtained, and was found to increase with the interface temperature. 相似文献
48.
Weiguo Cao Wenjuan Li Liang Zhang Jianfa Chen Shuo Yu Zhuanghong Zhou Yun Zhang Xiaobo Shen Yingxin Tan 《International Journal of Hydrogen Energy》2021,46(52):26693-26707
The explosion venting duct can effectively reduce the hazard degree of a gas explosion and conduct the venting energy to the safe area. To investigate the flame quantitative propagation law of explosion venting with a duct, the effects of hydrogen fraction and explosion venting duct length on jet flame propagation characteristics of premixed H2-air mixtures were analyzed through experiment and simulation. The experiment results under initial conditions of room temperature and 1 atm show that when hydrogen fraction was high enough, part of the unburned hydrogen was mixed with air again to reach an ignitable concentration, resulting in the secondary combustion was easier produced and the duration of the secondary flame increased. With the increase of venting duct length, the flame front distance and propagation velocity increased. Meanwhile, the spatial distribution of pressure field and temperature field, and the propagation process and mechanism of the flame venting with a duct were analyzed using FLUENT software. The variation of the pressure wave and the pressure reflection oscillation law in the explosion venting duct was captured. Therefore, in the industrial explosion venting design with a duct, the hazard caused by the coupling of venting pressure and venting flame under different fractions should be considered comprehensively. 相似文献
49.
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
50.
Wei-Li Xie Xiao-Dong Zhang Wen-Hui Liu Qi Xie Guang-Wu Wen Xiao-Xiao Huang Jian-Dong Zhu Fei-Xiang Ma 《稀有金属(英文版)》2019,(3)
SiC nano wires were fabricated on the silicon substrate dipped with a layer of Ni catalyst at 900 ℃ by gas pressure annealing processing. The morphologies and crystal structures were determined by scanning electron microscopy(SEM), transmission electron microscopy(TEM)and X-ray diffraction(XRD). The results show that the assynthesized nanowires are β-SiC single crystalline with diameter range of 50-100 nm, and length of tens of micron by directly annealing at 900 ℃. The SiC nano wires grow along the [111] direction with highly uniform morphology. And the possible growth mechanism of SiC nano wires is proposed.The present work provides an efficient strategy for the production of high-quality SiC nano wires. 相似文献