全文获取类型
收费全文 | 84563篇 |
免费 | 11619篇 |
国内免费 | 4227篇 |
专业分类
电工技术 | 4876篇 |
技术理论 | 3篇 |
综合类 | 4980篇 |
化学工业 | 18002篇 |
金属工艺 | 3217篇 |
机械仪表 | 4798篇 |
建筑科学 | 5869篇 |
矿业工程 | 2545篇 |
能源动力 | 1848篇 |
轻工业 | 8471篇 |
水利工程 | 2226篇 |
石油天然气 | 4146篇 |
武器工业 | 1012篇 |
无线电 | 13282篇 |
一般工业技术 | 12261篇 |
冶金工业 | 3058篇 |
原子能技术 | 1440篇 |
自动化技术 | 8375篇 |
出版年
2024年 | 439篇 |
2023年 | 1767篇 |
2022年 | 4861篇 |
2021年 | 5229篇 |
2020年 | 3018篇 |
2019年 | 2931篇 |
2018年 | 3087篇 |
2017年 | 3799篇 |
2016年 | 5049篇 |
2015年 | 5523篇 |
2014年 | 6131篇 |
2013年 | 6083篇 |
2012年 | 5216篇 |
2011年 | 4682篇 |
2010年 | 3731篇 |
2009年 | 3826篇 |
2008年 | 3505篇 |
2007年 | 4925篇 |
2006年 | 4984篇 |
2005年 | 4099篇 |
2004年 | 2969篇 |
2003年 | 2791篇 |
2002年 | 2084篇 |
2001年 | 1551篇 |
2000年 | 1478篇 |
1999年 | 1099篇 |
1998年 | 784篇 |
1997年 | 680篇 |
1996年 | 661篇 |
1995年 | 494篇 |
1994年 | 478篇 |
1993年 | 401篇 |
1992年 | 313篇 |
1991年 | 248篇 |
1990年 | 252篇 |
1989年 | 199篇 |
1988年 | 124篇 |
1987年 | 92篇 |
1986年 | 85篇 |
1985年 | 85篇 |
1984年 | 93篇 |
1983年 | 56篇 |
1982年 | 53篇 |
1981年 | 42篇 |
1980年 | 51篇 |
1966年 | 25篇 |
1964年 | 34篇 |
1962年 | 64篇 |
1959年 | 24篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
103.
The exact magnetization pattern of magnetic films close to a spin-reorientation transition is difficult to analyze due to the intrinsically three-dimensional (3d) variation of the orientation of the local magnetization. We present a technique how this can be performed, based on the analysis of high quality 2d polarization maps from a single scanning electron microscope with polarization analysis (SEMPA) measurement with tilted sample. The key tool is the statistical distribution of all occurring polarization doublets, visualized in a 2d histogram plot. From the shape of the distribution the type of transition—canted-phase, or coexisting phases—can be inferred. For the canted-phase state, the canting angle can be accurately determined from geometrical considerations. With help of the histogram the image data can be analyzed and the three components of the magnetization can be calculated for most points of the image. For a Co/Pt multilayer film we found a cone state. The magnetization forms a complex pattern consisting of out-of-plane domains while the in-plane magnetization shows a maze pattern. 相似文献
104.
András Ványolos Balázs Dóra Attila Virosztek 《Journal of Superconductivity and Novel Magnetism》2007,20(7-8):643-645
We report of a theoretical study on quasi-one dimensional unconventional charge density wave (UCDW) driven by electron–phonon
interaction. Within mean field theory, we find that the wavevector dependence of the coupling leads to a momentum dependent
single particle gap on the Fermi surface. The presence of small energy single particle excitations around the gap nodes significantly
changes the optical conductivity compared to the conventional CDW result. In addition to that, the collective phase excitation
arising from fluctuation of the order parameter leads to further qualitative changes of the conductivity and results in an
effective mass that is nonmonotonic in temperature.
相似文献
105.
This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important. 相似文献
106.
The fabrication and characterization of two‐photon polymerized features written within and outside of colloidal crystals is presented. Two‐photon polymerization (TPP) response diagrams are introduced and developed to map the polymerization and damage thresholds for features written via modulated beam rastering. The use of tris[4‐(7‐benzothiazol‐2‐yl‐9,9‐diethylfluoren‐2‐yl)phenyl]amine (AF‐350) as an initiator for TPP is demonstrated for the first time and TPP response diagrams illustrate the polymerization window. These diagrams also demonstrate that the polymerization behavior within and outside of colloidal crystals is similar and electron microscopy reveals nearly identical resolution. Fluorescence confocal microscopy further enables visualization of non‐self‐supporting, three‐dimensional TPP features within self‐assembled photonic crystals. Finally, microspot spectroscopy is collected from a two‐photon feature written within a colloidal crystal and this is compared with simulation. 相似文献
107.
Sante Camo 《Canadian Metallurgical Quarterly》2003,8(5):297-311
Cable reliability analysis involves the combined evaluation of cable capacity and cable load in a probabilistic manner. Assessment of cable capacity is only possible through visual inspections of the wires, field sampling, laboratory analysis of the degraded wire populations, and analytical techniques. In addition to a brief presentation of cable mechanics and deterministic models that approximate cable strength, this paper discusses inspection methodologies and statistical methods of estimation of the sizes of the degraded wire populations, and wire properties, leading to cable capacities. These capacities are described by probability distributions. The paper also discusses fundamentals of reliability analysis as they apply to bridge cables. Load criteria of present standard specifications (such as AASHTO or other international codes) are not applicable to long-span suspension bridges. The paper discusses criteria of bridge loading and reliability indices for bridge cables. More work is needed in the evaluation of loading for long-span bridges. 相似文献
108.
A. J. Slifka T. Hall E. S. Boltz 《Journal of research of the National Institute of Standards and Technology》2003,108(2):151-156
A simple measurement system is described for evaluating damage to graphite-epoxy panels, such as those used in high-performance aircraft. The system uses a heating laser and infrared imaging system to measure thermal performance. Thermal conductivity or diffusivity is a sensitive indicator of damage in materials, allowing this thermal measurement to show various degrees of damage in graphite-epoxy composites. Our measurements track well with heat-flux damage to graphite epoxy panels. This measurement system, including analysis software, could easily be used in the field, such as on the deck of an aircraft carrier or at remote air strips. 相似文献
109.
Ganesh Thiagarajan 《Canadian Metallurgical Quarterly》2003,7(1):64-72
This paper presents the results of an experimental and analytical comparison of a study on the flexural behavior of concrete beams reinforced with sandblasted carbon fiber-based composite rods. Twelve beams, including three control beams reinforced with steel, were tested for strength, deformation, and failure characteristics. Analytical comparisons included the generation of the theoretical strength and moment curvature relations. Experimental data from pullout tests indicated that bonding of sandblasted rods is not a major concern. However, excessive deformation in achieving the predicted moment capacity could be a limiting factor in the design of these beams. 相似文献
110.
J. Lub W.P.M. Nijssen R.T. Wegh J.P.A. Vogels A. Ferrer 《Advanced functional materials》2005,15(12):1961-1972
This paper describes the synthesis of photoisomerizable derivatives of isosorbide. These derivatives contain a stilbene or cinnamate moiety and can therefore be used as photoisomerizable chiral compounds in cholesteric liquid‐crystalline mixtures. The reflection wavelength of cholesteric layers made from these mixtures is increased by UV irradiation due to the fact that the Z‐isomers of these derivatives exhibit a lower helical twisting power than the corresponding E‐isomers. The cinnamate derivatives are very suitable for use in cholesteric color filters that find application in liquid‐crystal displays. 相似文献