全文获取类型
收费全文 | 2442篇 |
免费 | 105篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 34篇 |
综合类 | 17篇 |
化学工业 | 631篇 |
金属工艺 | 53篇 |
机械仪表 | 42篇 |
建筑科学 | 166篇 |
矿业工程 | 15篇 |
能源动力 | 35篇 |
轻工业 | 219篇 |
水利工程 | 12篇 |
石油天然气 | 5篇 |
无线电 | 179篇 |
一般工业技术 | 443篇 |
冶金工业 | 249篇 |
原子能技术 | 35篇 |
自动化技术 | 418篇 |
出版年
2023年 | 25篇 |
2022年 | 44篇 |
2021年 | 73篇 |
2020年 | 46篇 |
2019年 | 56篇 |
2018年 | 50篇 |
2017年 | 50篇 |
2016年 | 60篇 |
2015年 | 54篇 |
2014年 | 85篇 |
2013年 | 125篇 |
2012年 | 105篇 |
2011年 | 180篇 |
2010年 | 120篇 |
2009年 | 140篇 |
2008年 | 114篇 |
2007年 | 105篇 |
2006年 | 106篇 |
2005年 | 90篇 |
2004年 | 79篇 |
2003年 | 63篇 |
2002年 | 70篇 |
2001年 | 54篇 |
2000年 | 52篇 |
1999年 | 54篇 |
1998年 | 89篇 |
1997年 | 60篇 |
1996年 | 41篇 |
1995年 | 37篇 |
1994年 | 42篇 |
1993年 | 28篇 |
1992年 | 18篇 |
1991年 | 27篇 |
1990年 | 24篇 |
1989年 | 22篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 15篇 |
1983年 | 17篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 16篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1905年 | 3篇 |
1903年 | 3篇 |
排序方式: 共有2553条查询结果,搜索用时 62 毫秒
91.
Isabella Gallino Ralf Busch 《JOM Journal of the Minerals, Metals and Materials Society》2017,69(11):2171-2177
At temperatures below the glass transition temperature, physical properties of metallic glasses, such as density, viscosity, electrical resistivity or enthalpy, slowly evolve with time. This is the process of physical aging that occurs among all types of glasses and leads to structural changes at the microscopic level. Even though the relaxation pathways are ruled by thermodynamics as the glass attempts to re-attain thermodynamic equilibrium, they are steered by sluggish kinetics at the microscopic level. Understanding the structural and dynamic pathways of the relaxing glassy state is still one of the grand challenges in materials physics. We review some of the recent experimental advances made in understanding the nature of the relaxation phenomenon in metallic glasses and its implications to the macroscopic and microscopic properties changes of the relaxing glass. 相似文献
92.
P. Hofer E. Kaschnitz P. Schumacher 《JOM Journal of the Minerals, Metals and Materials Society》2014,66(9):1638-1646
Two individual high-pressure die casting geometries were developed to study the influence of process parameters and alloy composition on the distortion behavior of aluminum alloy castings. These geometries, a stress lattice and a V-shaped lid, tend to form residual stress due to a difference in wall thickness and a deliberate massive gating system. Castings were produced from two alloys: AlSi12(Fe) and AlSi10MnMg. In the experimental castings, the influence of important process parameters such as die temperature, ejection time, and cooling regime was examined. The time evolution of process temperatures was measured using thermal imaging. Subsequent to casting, distortion was measured by means of a tactile measuring device at ambient temperatures. The measured results were compared against a numerical process and stress simulations of the casting, ejection, and cooling process using the commercial finite element method software ANSYS Workbench. The heat transfer coefficients were adapted to the temperature distributions of the die, and the castings were observed by thermal imaging. A survey of the results of the comparison between simulation and experiment is given for both alloys. 相似文献
93.
Hinkel Georg Goldschmidt Thomas Burger Erik Reussner Ralf 《Software and Systems Modeling》2019,18(1):129-155
Software and Systems Modeling - Model-driven engineering (MDE) has proved to be a useful approach to cope with today’s ever-growing complexity in the development of software systems;... 相似文献
94.
95.
96.
Computational Economics - We present a new modeling approach for house price movements as a consequence of the trading behavior of market agents. In our modeling approach, all agents are assumed to... 相似文献
97.
Pietro Abate Roberto Di Cosmo Ralf Treinen Stefano Zacchiroli 《Journal of Systems and Software》2012,85(10):2228-2240
Maintenance of component-based software platforms often has to face rapid evolution of software components. Component dependencies, conflicts, and package managers with dependency solving capabilities are the key ingredients of prevalent software maintenance technologies that have been proposed to keep software installations synchronized with evolving component repositories. We review state-of-the-art package managers and their ability to keep up with evolution at the current growth rate of popular component-based platforms, and conclude that their dependency solving abilities are not up to the task.We show that the complexity of the underlying upgrade planning problem is NP-complete even for seemingly simple component models, and argue that the principal source of complexity lies in multiple available versions of components. We then discuss the need of expressive languages for user preferences, which makes the problem even more challenging.We propose to establish dependency solving as a separate concern from other upgrade aspects, and present CUDF as a formalism to describe upgrade scenarios. By analyzing the result of an international dependency solving competition, we provide evidence that the proposed approach is viable. 相似文献
98.
Photonic Nanostructures Patterned by Thermal Nanoimprint Directly into Organo‐Metal Halide Perovskites
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
99.
Oxidation Kinetics of an Amorphous Silicon Carbonitride Ceramic 总被引:4,自引:0,他引:4
Rishi Raj Linan An Sandeep Shah Ralf Riedel Claudia Fasel Hans-Joachim Kleebe 《Journal of the American Ceramic Society》2001,84(8):1803-1810
The oxidation kinetics of amorphous silicon carbonitride (SiCN) was measured at 1350°C in ambient air. Two types of specimens were studied: one in the form of thin disks, the other as a powder. Both specimens contained open nanoscale porosity. The disk specimens exhibited weight gain that saturated exponentially with time, analogous to the oxidation behavior of reaction-bonded Si3 N4 . The saturation value of the weight gain increased linearly with specimen volume, suggesting the nanoscale pore surfaces oxidized uniformly throughout the specimen. This interpretation was confirmed by high-resolution electron microscopy and secondary ion mass spectroscopy. Experiments with the powders (having a particle size much larger than the scale of the nanopores) were also consistent with measurements of the disks. However, the powder specimens, having a high surface-to-volume ratio, continued to show measurable weight gain due to oxidation of the exterior surface. The wide range of values for the surface-to-volume ratio, which included all specimens, permitted a separation of the rate of oxidation of the free surface and the oxidation of the internal surfaces of the nanopores. Surface oxidation data were used to obtain the rate constant for parabolic growth of the oxidation scale. The values for the rate constant obtained for SiCN lay at the lower end of the spectrum of oxidation rates reported in the literature for several Si3 N4 and SiC materials. Convergence in the behavior of SiCN and CVD-SiC is ascribed to the purity of both materials. Conversely, it is proposed that the high rates of oxidation of sintered polycrystalline silicon carbides and nitrides, as well as the high degree of variability of these rates, might be related to the impurities introduced by the sintering aids. 相似文献
100.
Benjamin Papendorf Emanuel Ionescu Hans‐Joachim Kleebe Christoph Linck Olivier Guillon Katharina Nonnenmacher Ralf Riedel 《Journal of the American Ceramic Society》2013,96(1):272-280
In this work, dense monolithic polymer‐derived ceramic nanocomposites (SiOC, SiZrOC, and SiHfOC) were synthesized via hot‐pressing techniques and were evaluated with respect to their compression creep behavior at temperatures beyond 1000°C. The creep rates, stress exponents as well as activation energies were determined. The high‐temperature creep in all materials has been shown to rely on viscous flow. In the quaternary materials (i.e., SiZrOC and SiHfOC), higher creep rates and activation energies were determined as compared to those of monolithic SiOC. The increase in the creep rates upon modification of SiOC with Zr/Hf relies on the significant decrease in the volume fraction of segregated carbon; whereas the increase of the activation energies corresponds to an increase of the size of the silica nanodomains upon Zr/Hf modification. Within this context, a model is proposed, which correlates the phase composition as well as network architecture of the investigated samples with their creep behavior and agrees well with the experimentally determined data. 相似文献