全文获取类型
| 收费全文 | 75296篇 |
| 免费 | 8726篇 |
| 国内免费 | 2546篇 |
专业分类
| 电工技术 | 1101篇 |
| 技术理论 | 1篇 |
| 综合类 | 3158篇 |
| 化学工业 | 27576篇 |
| 金属工艺 | 10626篇 |
| 机械仪表 | 1437篇 |
| 建筑科学 | 2101篇 |
| 矿业工程 | 1132篇 |
| 能源动力 | 1394篇 |
| 轻工业 | 11414篇 |
| 水利工程 | 386篇 |
| 石油天然气 | 1374篇 |
| 武器工业 | 371篇 |
| 无线电 | 2862篇 |
| 一般工业技术 | 17204篇 |
| 冶金工业 | 3240篇 |
| 原子能技术 | 273篇 |
| 自动化技术 | 918篇 |
出版年
| 2025年 | 127篇 |
| 2024年 | 2085篇 |
| 2023年 | 2101篇 |
| 2022年 | 2623篇 |
| 2021年 | 3641篇 |
| 2020年 | 3576篇 |
| 2019年 | 2881篇 |
| 2018年 | 3080篇 |
| 2017年 | 3434篇 |
| 2016年 | 3418篇 |
| 2015年 | 3510篇 |
| 2014年 | 4078篇 |
| 2013年 | 5204篇 |
| 2012年 | 4750篇 |
| 2011年 | 5612篇 |
| 2010年 | 3774篇 |
| 2009年 | 4084篇 |
| 2008年 | 3423篇 |
| 2007年 | 3741篇 |
| 2006年 | 3558篇 |
| 2005年 | 2816篇 |
| 2004年 | 2744篇 |
| 2003年 | 2342篇 |
| 2002年 | 1918篇 |
| 2001年 | 1329篇 |
| 2000年 | 1189篇 |
| 1999年 | 916篇 |
| 1998年 | 823篇 |
| 1997年 | 701篇 |
| 1996年 | 537篇 |
| 1995年 | 470篇 |
| 1994年 | 346篇 |
| 1993年 | 257篇 |
| 1992年 | 266篇 |
| 1991年 | 214篇 |
| 1990年 | 246篇 |
| 1989年 | 239篇 |
| 1988年 | 85篇 |
| 1987年 | 57篇 |
| 1986年 | 60篇 |
| 1985年 | 69篇 |
| 1984年 | 67篇 |
| 1983年 | 33篇 |
| 1982年 | 55篇 |
| 1981年 | 7篇 |
| 1980年 | 35篇 |
| 1979年 | 7篇 |
| 1978年 | 6篇 |
| 1975年 | 6篇 |
| 1974年 | 6篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
991.
《Materials and Manufacturing Processes》2012,27(3):315-317
Cetylpyridinium chloride (CPC)-stabilized gold organosol in toluene has been prepared by using a two-phase (water-toluene) extraction of AuCl4 − followed by its reduction with sodium borohydride in the presence of the surfactant, CPC. The surfactant-stabilized gold nanoparticles were exploited to examine their optical properties when exposed to various solvent systems by measuring the changes in the localized surface plasmon resonance (LSPR) spectrum. 相似文献
992.
《Materials and Manufacturing Processes》2012,27(5):573-578
The effects of precooling on the structural conditions of the heat affected zone (HAZ) of high manganese and high carbon content steel were studied. The steel samples were welded, homogenized at 1100°C for 45 minutes, and quenched in water. These samples were precooled to temperatures of 0°, − 30°, and − 60°C. Carbides, microfissures, cracks, or fractures in grain boundary were not found after the welding process. In the case of the homogenized samples with and without any precooling treatment, voids and microvoids were found at the grain boundary. No variations were observed in form and size of voids and microvoids in all samples. A significant increase in the hardness of the grain and grain boundaries located next to the fusion line of the heat affected zone of the precooled steel samples was found in relation to the homogenized samples. X-ray diffraction was used to study the evolution of the crystalline quality of the homogenized and precooled samples. It was found that the lattice parameter decreased and the crystalline quality increased as a result of the precooled conditions and welding process. 相似文献
993.
994.
《Materials and Manufacturing Processes》2012,27(2):198-208
Artificial neural networks are parameterized nonlinear models used for empirical regression and classification modelling. Their flexibility enables them to discover very complex relationships among large number of variables with complex interdependencies. Hence it is a very appropriate technique for developing predictive models in the short term. This article discusses the development of neural network models based on a Bayesian framework and some applications of the same. These examples include: (i) prediction of yield and tensile strengths of hot-rolled low-carbon ferrite-pearlite steel plates as a function of composition and rolling parameters, (ii) estimation of bainite plate thickness, (iii) estimation of retained austenite as a function of process parameters in Transformation Induced Plasticity aided (TRIP-aided) steels, and (iv) analysis of strain-induced transformation behavior of retained austenite during uniaxial tensile testing of TRIP-aided steels. While examples (i), (ii), and (iv) provide an overview of the work reported earlier, example (iii) is reported here in open literature for the first time. In all these four cases, it has been shown that the results are consistent with the established physical metallurgy principles. 相似文献
995.
27SiMn液压支架管经过调质热处理来实现其良好的综合力学性能.采用四因素三水平的热处理正交试验,研究了不同热处理工艺参数（淬火温度、淬火保温时间、回火温度和回火保温时间）对力学性能的影响,并确定了最优热处理工艺制度为930℃,40 min淬火和480℃,50 min回火.经最优热处理工艺处理后,其力学性能为：屈服强度895 MPa,抗拉强度1030MPa,伸长率15%,断面收缩率54%,冲击功53.3 J,满足了GB/T 17396—1998标准中对27SiMn钢的性能要求. 相似文献
996.
《Materials and Manufacturing Processes》2012,27(1):102-106
Typical friction welds are made by holding a non-rotating sample in contact with a rotating sample under constant or gradually increasing pressure until the interface reaches the welding temperature and then stopping pressure rotating to complete the weld. This process requires additional time and is labor intensive. Recently, several control systems have been introduced to the industry for improving the welding process such as conventional automatic control, microcontroller control, and Programmable Logic Controller (PLC). However, these processes have limitations either on materials selection or on visualization. In this study, continuous monitoring, control and recording are implemented. Computer-controlled platform for the simulation and control of mechanisms is based on a Microsoft Visual Basic environment. Welding parameters such as friction time, forge time and breaking time are entered with a keyboard and can be saved and used again. To show the feasibility and versatility of the study, the evaluation is used for sample joining. It has been observed that this system works successfully and gives good performance. 相似文献
997.
《Materials and Manufacturing Processes》2012,27(5):489-493
Powders of K0.5Na0.5NbO3 (KNN) were prepared by the Polymerized Complex Method (PC method), based on the Pechini-type reaction route. The crystallization process of KNN during the calcination of an amorphous precursor was observed, using TG-DSC analysis and X-ray powder diffraction. After calcination the powders were ball milled, pressed into pellets, and sintered at 1100°C, which is lower than the sintered temperature of the conventional solid-state method. Using this procedure, we achieved relatively high-density and very homogeneous KNN ceramics. The electric properties of the ceramics were investigated. The results showed that these values are superior to those of sintered KNN ceramic counterparts made by the conventional solid-state method. 相似文献
998.
《Materials and Manufacturing Processes》2012,27(4):369-376
Cryogenic treatment is an inexpensive supplementary process to conventional heat treatment, which improves the tribological properties of steels. A study has been made on the effect of cryogenic treatment on En 31 steels done at different stages of heat treatment. It is observed that through cryogenic treatment the wear can be decreased by a maximum of 75% depending on the service conditions. Scanning electron microscopy (SEM) study was also conducted to identify the possible mechanism which augments the improvement in wear resistance (WR) in cryogenically treated En 31 steels. Based on the study it is also confirmed that the cryogenic treatment should be done before tempering immediately after quench hardening to obtain maximum benefits. 相似文献
999.
《Materials and Manufacturing Processes》2012,27(3):251-260
AA6061 aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio and good corrosion resistance. Compared to many of the fusion welding processes that are routinely used for joining structural aluminium alloys, the Friction Stir Welding (FSW) process is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a nonconsumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, axial force, etc., and tool pin profile play a major role in deciding the joint properties. In this investigation, an attempt has been made to study the effect of rotational speed and tool pin profile on mechanical properties of AA6061 aluminium alloy. Five different tool pin profiles (straight cylindrical, tapered cylindrical, threaded cylindrical, triangular, and square) have been used to fabricate the joints at five different tool rotational speeds (800–1600 RPM). Tensile properties, microhardness, and microstructure of the joints have been evaluated. From this investigation it is found that the joints fabricated using square pin profiled tool with a tool rotational speed of 1200 RPM exhibited superior mechanical properties compared to other joints. 相似文献
1000.
《Materials and Manufacturing Processes》2012,27(8):809-815
Ammonium dihydrogen orthophosphate (ADP) crystal continues to be an interesting nonlinear optical and dielectric material. In order to understand the effect of NaCl as an impurity on the electrical properties of ADP, we have grown from aqueous solutions pure and NaCl added single crystals and electrically characterized. Density and atomic absorption spectroscopic measurements indicate that the impurity molecules have entered into the crystal matrix of ADP. DC and AC electrical measurements were carried out at various temperatures ranging between 40–150°C along both a- and c-directions. Results indicate an increase of the electrical parameters, viz σdc, ϵ r , tanδ, and σac with the increase of temperature which can be attributed mainly to the increase of thermally generated hydrogen bond vacancies (L-defects). Also, the present study indicates that NaCl addition leads to nonlinear variation of electrical parameters of ADP single crystals with impurity concentration. Activation energies were also estimated. 相似文献