全文获取类型
收费全文 | 114753篇 |
免费 | 12777篇 |
国内免费 | 5772篇 |
专业分类
电工技术 | 5111篇 |
技术理论 | 1篇 |
综合类 | 6683篇 |
化学工业 | 35116篇 |
金属工艺 | 13846篇 |
机械仪表 | 3364篇 |
建筑科学 | 6222篇 |
矿业工程 | 1793篇 |
能源动力 | 5336篇 |
轻工业 | 11764篇 |
水利工程 | 1202篇 |
石油天然气 | 3529篇 |
武器工业 | 1383篇 |
无线电 | 6748篇 |
一般工业技术 | 22643篇 |
冶金工业 | 5030篇 |
原子能技术 | 1019篇 |
自动化技术 | 2512篇 |
出版年
2024年 | 413篇 |
2023年 | 2497篇 |
2022年 | 3612篇 |
2021年 | 4797篇 |
2020年 | 4788篇 |
2019年 | 4110篇 |
2018年 | 4150篇 |
2017年 | 4918篇 |
2016年 | 5036篇 |
2015年 | 5166篇 |
2014年 | 6676篇 |
2013年 | 8069篇 |
2012年 | 7661篇 |
2011年 | 8820篇 |
2010年 | 6184篇 |
2009年 | 6607篇 |
2008年 | 5536篇 |
2007年 | 6570篇 |
2006年 | 6271篇 |
2005年 | 4965篇 |
2004年 | 4513篇 |
2003年 | 3783篇 |
2002年 | 3273篇 |
2001年 | 2485篇 |
2000年 | 2197篇 |
1999年 | 1700篇 |
1998年 | 1458篇 |
1997年 | 1289篇 |
1996年 | 933篇 |
1995年 | 848篇 |
1994年 | 638篇 |
1993年 | 518篇 |
1992年 | 507篇 |
1991年 | 420篇 |
1990年 | 419篇 |
1989年 | 377篇 |
1988年 | 193篇 |
1987年 | 128篇 |
1986年 | 117篇 |
1985年 | 142篇 |
1984年 | 133篇 |
1983年 | 81篇 |
1982年 | 104篇 |
1981年 | 35篇 |
1980年 | 53篇 |
1979年 | 16篇 |
1975年 | 10篇 |
1974年 | 10篇 |
1959年 | 9篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 309 毫秒
61.
AbstractDifferent drying methods (spray drying (SD), vacuum drying (VD), microwave vacuum drying (MVD), and infrared vacuum drying (IFVD)) were applied in order to compare the hygroscopicity behavior of chicken powders. The hygroscopicity curves and glass transition temperature were used to evaluate the influence of ambient humidity and temperature on moisture absorption of powders. The results showed that the chicken powder dried by MVD had the lowest moisture absorption, followed by IFVD, VD, and SD. The hygroscopicity of SD chicken powders was different from other three kinds of chicken powders due to the physical properties of particles and the changes of protein secondary structure as detected by the Fourier transform-infrared spectrometer. For the three vacuum drying methods, the difference of protein secondary structure was the main reason of differences in hygroscopicity. Although MVD chicken powders were slightly inferior to SD chicken powders in taste, MVD chicken powders were the best in terms of smell and color as suggested by instrumental sensory parameter evaluations. It was found that MVD had a positive effect on reducing moisture absorption and maintaining sensory quality of chicken powders. 相似文献
62.
《Ceramics International》2020,46(7):9240-9248
The effects of Sr2+ substitution for Ba2+ on phase structure, microstructure, dielectric and electric properties for Ba4-xSrxSmFe0.5Nb9.5O30 (x = 0, 1, 2, 3 and 4) ceramics were systematically researched. X-ray diffraction patterns show that Ba4-xSrxSmFe0.5Nb9.5O30 (x = 0, 1, 2 and 3) ceramics are tetragonal tungsten bronze compound with a space group of P4bm, while the sample for x = 4 is an orthorhombic structure compound. The result can be corroborated by the analysis of Raman spectroscopy. As the Sr2+ contents increase from 0 to 3, the full width at half maximum of Raman lines of all samples increase gradually, indicating that the degree of lattice distortion increase. All tetragonal tungsten bronze ceramics exhibited a broad permittivity peaks, accompanied by frequency dispersion, indicating all samples are relaxor. The electrical properties of BSSFN ceramics were further studied by complex impedance spectroscopy. XPS spectrum shows that Fe2+ and Fe3+ coexist in Ba4-xSrxSmFe0.5Nb9.5O30 ceramics, and their proportion varies with the concentration of Sr2+. 相似文献
63.
Rong Zhang Hailong Hu Hai Chen Siqi Li Cheng Ying Shuai Huang Qingting Liu Xudong Fu Shengfei Hu Ching-Ping Wong 《应用聚合物科学杂志》2020,137(39):49186
Recently, thermal interface materials (TIMs) are in great demands for modern electronics. For mechanically mixed polymer composite TIMs, the thermal conductivity and the mechanical properties are generally lower than expected values due to the sharply increased viscosity and poor filler dispersion. This work shows that addition of a small amount of polyester-based hyperbranched polymer (HBP) avoided the trade-off in mechanically mixed ABS/hexagonal boron nitride (h-BN) composites. After adding 0.5 wt% HBP, the maximum h-BN content in the composites increased from 50 to 60 wt%. The out-of-plane, in-plane thermal conductivity, and tensile strength of ABS/h-BN with 50 wt% h-BN were 0.408, 0.517 W/mK, and 18 MPa, respectively, and were increased to 0.729, 0.847 W/mK, and 32 MPa by adding 0.5 wt% HBP, while 0.972, 1.12 W/mK, and 29.5 MPa were achieved for ABS/h-BN/HBP with 60 wt% h-BN. The morphological and rheological results proved that these enhancements are due to the improved h-BN dispersion by decreasing viscosity of composites during mixing. Theoretical modeling based on the modified effective medium theory confirmed such results and showed that the interfacial thermal resistance also decreased slightly. Thus, this work demonstrates a facile and scalable method for simultaneously improving the thermal conductivity and mechanical properties of thermoplastic-based TIMs. 相似文献
64.
Mohammad Afshari Amir-Reza Rouhani Isfahani Saeed Hasani Fatemeh Davar Khadijeh Jahanbani Ardakani 《International Journal of Applied Ceramic Technology》2019,16(4):1612-1621
In the present study, spinel structure CoFe2O4 nanoparticles were successfully synthesized by the sol-gel auto-combustion technique. The effect of apple cider vinegar (ACV) addition as an organic biocompatible agent on the size, morphology, and magnetic properties of CoFe2O4 nanoparticles was investigated in detail. The phase evolution, particle size, and lattice parameter changes of the synthesized phase have been estimated by using Rietveld structure refinement analysis of X-ray powder diffraction data. Also, Fourier transform infrared spectra (FT-IR) of the samples verified the presence of two expected bands correspond to tetrahedral and octahedral metal-oxygen complexes within the spinel structure. Furthermore, microstructural observations revealed that ultrafine particles have a semi-spherical morphology. It was shown that the particles size decreased from ~45 to ~17 nm with an increase in the amount of ACV. Magnetic properties were carried out by vibrating sample magnetometer (VSM) at room temperature. Both the saturation magnetization (Ms) and coercivity (Hc) were found to be significantly dependent on the crystallite size and the amount of ACV. 相似文献
65.
热电厂的短期热负荷预测在城市集中供暖中起着至关重要的作用,直接影响热电厂的经济效益和热能利用率。电厂的短期热负荷一般采用神经网络预测模型进行预测,而BP神经网络应用最为广泛。Elman神经网络算法在BP神经网络基础上加入了承接层,作为一步延时算子,实现记忆能力,使系统具备适应时变能力,增强系统全局稳定性。但Elman神经网络算法模型的构造依然需要大量样本的支撑,而且输入层的变量多,导致预测时间依然很长,收敛速度慢。该文在Elman神经网络预测前,进行了相关系数预处理和对样本中异常值的平均化预处理,通过数据归一化运算,使Elman神经网络输入层变量大幅减少。仿真实验表明,改进的Elman神经网络算法使预测模型快速寻优,减少预测时间的同时明显提高预测精度。 相似文献
66.
Robert Bertuzzi 《岩石力学与岩土工程学报(英文版)》2019,11(3):494-510
This paper presents the results of ongoing research carried out by the author exploring methods to provide a more robust estimate of rock mass properties specifically for use in tunnel design. Data from various large-scale rock mass failures are introduced, including coal pillars. The damage-initiation,spalling-limit approach is compared to the coal pillar database. New comparisons of estimating the geological strength index(GSI) and relationships to estimate the Hoeke Brown failure criterion parameters, mb, s and a, are presented. 相似文献
67.
Various methods have been developed to monitor the health and strain state of carbon fiber reinforced polymers, each with a unique set of pros and cons. This research assesses the use of piezoresistive sensors for in situ strain measurement of carbon fiber and other composite structures in multidirectional laminates. The piezoresistive sensor material and the embedded circuitry are both evaluated. For the piezoresistive sensor, a conductive nickel nanocomposite sensor is compared with the piezoresistivity of the carbon fiber itself. For the circuit, the use of carbon fibers already present in the structure is compared with the use of nickel coated carbon fiber. Successful localized strain sensing is demonstrated for several sensor and circuitry configurations. Numerous engineering applications are possible in the ever-growing field of carbon-composites. 相似文献
68.
《Ceramics International》2019,45(15):18501-18508
The modification and tuning features of nanostructured films are of great interest because of controllable and distinctive inherent properties in these materials. Here, nanocrystalline MoS2 films were fabricated on the stainless steels by a radio frequency magnetron sputtering at ambient temperature. X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Raman scattering spectroscopy were used to study the chemical state, chemical composition, crystal structure and vibrational properties of the fabricated MoS2 films. The bias voltage dependent structural evolution and its influence on the optical properties of MoS2 nanocrystalline films were systematically investigated. Besides, the residual stresses of MoS2 nanocrystalline films were explored by employing sin2ψ approach. X-ray diffraction demonstrates that the nanocrystalline MoS2 films have single-phase hexagonal crystal structure. All MoS2 films are polycrystalline in nature. The bandgap values are found to be intensively dependent on bias voltage. Our findings show that the nanocrystalline MoS2 films with different physical properties and intense quantum confinement effect can be realized through adjusting bias voltages. This work may provide deep insight for realizing transitional metal dichalcogenide-based nanostructured film optoelectronic devices with tunable physical properties through a traditional, very cost-effective, and large-scale fabrication method. 相似文献
69.
有机化学是化学化工、材料、制药、食品等多个专业的基础课程,在其教学过程中,教师可以根据课程的内容及特点,分别以有机化学发展中的重大历史事件、有机化物的性质及有机反应为引导,开展学生的思想品德教育,加强课程思政建设。 相似文献
70.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided. 相似文献