全文获取类型
收费全文 | 5301篇 |
免费 | 184篇 |
国内免费 | 70篇 |
专业分类
电工技术 | 21篇 |
综合类 | 26篇 |
化学工业 | 1446篇 |
金属工艺 | 781篇 |
机械仪表 | 133篇 |
建筑科学 | 40篇 |
矿业工程 | 16篇 |
能源动力 | 490篇 |
轻工业 | 11篇 |
水利工程 | 4篇 |
石油天然气 | 7篇 |
武器工业 | 11篇 |
无线电 | 168篇 |
一般工业技术 | 1884篇 |
冶金工业 | 301篇 |
原子能技术 | 46篇 |
自动化技术 | 170篇 |
出版年
2024年 | 7篇 |
2023年 | 257篇 |
2022年 | 193篇 |
2021年 | 123篇 |
2020年 | 266篇 |
2019年 | 227篇 |
2018年 | 97篇 |
2017年 | 256篇 |
2016年 | 285篇 |
2015年 | 382篇 |
2014年 | 378篇 |
2013年 | 335篇 |
2012年 | 290篇 |
2011年 | 162篇 |
2010年 | 241篇 |
2009年 | 258篇 |
2008年 | 90篇 |
2007年 | 185篇 |
2006年 | 185篇 |
2005年 | 102篇 |
2004年 | 77篇 |
2003年 | 109篇 |
2002年 | 122篇 |
2001年 | 118篇 |
2000年 | 103篇 |
1999年 | 95篇 |
1998年 | 30篇 |
1997年 | 24篇 |
1996年 | 24篇 |
1995年 | 43篇 |
1994年 | 39篇 |
1993年 | 32篇 |
1992年 | 32篇 |
1991年 | 27篇 |
1990年 | 30篇 |
1989年 | 18篇 |
1988年 | 41篇 |
1987年 | 75篇 |
1986年 | 83篇 |
1985年 | 25篇 |
1984年 | 21篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1975年 | 2篇 |
排序方式: 共有5555条查询结果,搜索用时 15 毫秒
61.
62.
3D Mesostructures: Fabrication and Deformation of 3D Multilayered Kirigami Microstructures (Small 11/2018)
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
63.
In this communication, the crystal structure of Cr_4AlB_4, a new MAB phase compound(where M is a transition metal, A is Al or Si, B is boron) discovered in Cr-Al-B system is reported. This new MAB phase was synthesized from a mixture of CrB and Al powders at 1000?C and its crystal structure was determined by a combination of X-ray diffraction, first-principles calculations and energy dispersive X-ray spectroscopy(EDS). Cr_4AlB_4 crystallizes in an orthorhombic structure with Immm space group. The lattice constants are a = 2.9343(6) ?, b = 18.8911(0) ?, c = 2.9733(7) ?, and the atomic positions are Cr1 at 4 g(0, 0.2936(5),0), Cr2 at 4 h(0.5, 0.5859(7), 0), Al at 2 b(0, 0.5, 0.5), B1 at 4 h(0, 0.3839(8), 0.5) and B2 at 4 g(0.5, 0.6646(2),0.5). 相似文献
64.
《材料科学技术学报》2019,35(6):1017-1026
In this study, Cu was added into the high-pressure die-casting Al-5.5Mg-0.7Mn (wt%) alloy to improve the tensile properties. The effects of Cu addition on the microstructures, mechanical properties of the Al-5.5Mg-0.7Mn alloys under both as-cast and T5 treatment conditions have been investigated. Additions of 0.5 wt%, 0.8 wt% and 1.5 wt% Cu can lead to the formation of irregular-shaped Al2CuMg particles distributed along the grain boundaries in the as-cast alloys. Furthermore, the rest of Cu can dissolve into the matrixes. The lath-shaped Al2CuMg precipitates with a size of 15–20 nm × 2–4 nm were generated in the T5-treated Al-5.5Mg-0.7Mn-xCu (x = 0.5, 0.8, 1.5 wt%) alloys. The room temperature tensile and yield strengths of alloys increase with increasing the content of Cu. Increasing Cu content results in more Al2CuMg phase formation along the grain boundaries, which causes more cracks during tensile deformation and lower ductility. Al-5.5Mg-0.7Mn-0.8Cu alloy exhibits excellent comprehensive tensile properties under both as-cast and T5-treated conditions. The yield strength of 179 MPa, the ultimate tensile strength of 303 MPa and the elongation of 8.7% were achieved in the as-cast Al-5.5Mg-0.7Mn-0.8Cu alloy, while the yield strength significantly was improved to 198 MPa after T5 treatment. 相似文献
65.
66.
In this paper, an intelligent diagnosis for fault gear identification and classification based on vibration signal using discrete wavelet transform and adaptive neuro-fuzzy inference system (ANFIS) is presented. The discrete wavelet transform (DWT) technique plays one of the important roles for signal feature extraction in the proposed system. The abnormal transient signals will show in different decomposition levels and can be used to recognize the various faults by the DWT figure. However, many fault conditions are hard to inspect accurately by the naked eye. In the present study, the feature extraction method based on discrete wavelet transform with energy spectrum is proposed. The different order wavelets are considered to identify fault features accurately. The database is established by feature vectors of energy spectrum which are used as input pattern in the training and identification process. Furthermore, the ANFIS is proposed to identify and classify the fault gear positions and the gear fault conditions in the fault diagnosis system. The proposed ANFIS includes both the fuzzy logic qualitative approximation and the adaptive neural network capability. The experimental results verified that the proposed ANFIS has more possibilities in fault gear identification. The ANFIS achieved an accuracy identification rate which was more satisfactory than traditional vision inspection in the proposed system. 相似文献
67.
Mohammed Moumnassi Salim Belouettar Éric Béchet Stéphane P.A. Bordas Didier Quoirin Michel Potier-Ferry 《Computer Methods in Applied Mechanics and Engineering》2011,200(5-8):774-796
In this paper, we present some novel results and ideas for robust and accurate implicit representation of geometric surfaces in finite element analysis. The novel contributions of this paper are threefold: (1) describe and validate a method to represent arbitrary parametric surfaces implicitly; (2) represent arbitrary solids implicitly, including sharp features using level sets and boolean operations; (3) impose arbitrary Dirichlet and Neumann boundary conditions on the resulting implicitly defined boundaries. The methods proposed do not require local refinement of the finite element mesh in regions of high curvature, ensure the independence of the domain’s volume on the mesh, do not rely on boundary regularization, and are well suited to methods based on fixed grids such as the extended finite element method (XFEM). Numerical examples are presented to demonstrate the robustness and effectiveness of the proposed approach and show that it is possible to achieve optimal convergence rates using a fully implicit representation of object boundaries. This approach is one step in the desired direction of tying numerical simulations to computer aided design (CAD), similarly to the isogeometric analysis paradigm. 相似文献
68.
Ohmic contacts were obtained to p-type Hg0.3Cd0.7Te crystals by metalorganic chemical vapour deposition (MOCVD) of HgTe as an interface material between the crystals and the contacting metal. Deposition at a reduced temperature of 350C did not lead to an obvious change in the material performance. Electronic-transport data are given. Two acceptor levels, at 4.8 and 60 meV above the valence-band edge, were found. 相似文献
69.
A. R. Khodabandeh M. Jahazi S. Yue S. T. Aghdashi 《Materials and Manufacturing Processes》2006,21(1):105-110
The influences of various reheating and forging temperatures as well as cooling rates on the microstructure and mechanical properties, particularly impact energy, during the forging of a Nb-V microalloyed steel to be used for automotive safety parts were investigated. Increasing the prior austenite grain size increased the volume percent of acicular ferrite and reduced pearlite content in the microstructure even for very low post-forging cooling rates, resulting in improved toughness and tensile strength values. Increasing the cooling rate enhanced the acicular ferrite content, thereby increasing the impact energy properties. At lower reheating temperatures the yield strength and impact energy levels are determined by the percentage of pearlite present in the microstructure; while as the cooling rate is increased the amount of acicular ferrite and retained austenite are increased, improving the toughness and tensile strength of the forged part. This effect is more pronounced for the parts solutionized at 1250°C and is related to the presence of very fine carbonitride precipitates under these conditions, which contributes to improved yield strength, particularly at higher cooling rates. An optimized forging process was determined and adapted to a 25 MN production forging press to validate the experimental results on semi-industrial production scale. By adequate control of the above parameters, high-strength, high-toughness parts (T.S. = 800 MPa, CVN = 35 J) were forged and optimum mechanical properties were achieved without the need for any additional heat treatment. 相似文献
70.
《Materials Research Bulletin》2006,41(2):376-386
The utilization of single-source molecular precursor approach to obtain II–VI and IV–VI semiconductors encapsulated in porous Vycor glass (PVG) is described. The procedure is based on the impregnation of cadmium and lead(II) diethyl-dithiocarbamate complexes, Cd(S2CNEt2)2 and Pb(S2CNEt2)2, inside the porous environment of PVG followed by a thermal treatment of the glass. The pyrolysis of the impregnated precursor gives rise to binary semiconductors CdS and PbS, respectively. The impregnation step is driven by interactions between the precursors and active sites located at glass pore surfaces. After completing the impregnation–decomposition cycle, it was found that the active glass sites were regenerated, making new cycles possible. The amount of encapsulated semiconductor increases linearly as a function of the number of cycles. Nanocomposites obtained after 1–10 cycles were prepared and characterized by optical spectroscopy, X-ray diffraction powder and transmission electron microscopy. 相似文献