全文获取类型
收费全文 | 2465篇 |
免费 | 26篇 |
专业分类
电工技术 | 17篇 |
化学工业 | 202篇 |
金属工艺 | 70篇 |
机械仪表 | 19篇 |
建筑科学 | 61篇 |
能源动力 | 44篇 |
轻工业 | 126篇 |
水利工程 | 4篇 |
石油天然气 | 4篇 |
无线电 | 148篇 |
一般工业技术 | 228篇 |
冶金工业 | 1397篇 |
原子能技术 | 5篇 |
自动化技术 | 166篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 22篇 |
2016年 | 20篇 |
2015年 | 32篇 |
2014年 | 30篇 |
2013年 | 58篇 |
2012年 | 42篇 |
2011年 | 66篇 |
2010年 | 52篇 |
2009年 | 53篇 |
2008年 | 55篇 |
2007年 | 58篇 |
2006年 | 40篇 |
2005年 | 46篇 |
2004年 | 43篇 |
2003年 | 44篇 |
2002年 | 43篇 |
2001年 | 30篇 |
2000年 | 26篇 |
1999年 | 74篇 |
1998年 | 444篇 |
1997年 | 230篇 |
1996年 | 198篇 |
1995年 | 122篇 |
1994年 | 114篇 |
1993年 | 100篇 |
1992年 | 20篇 |
1991年 | 28篇 |
1990年 | 31篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 43篇 |
1976年 | 72篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1971年 | 3篇 |
排序方式: 共有2491条查询结果,搜索用时 468 毫秒
91.
Song Lu Qing-Miao Hu Erna Krisztina Delczeg-Czirjak Börje Johansson Levente Vitos 《Acta Materialia》2012,60(11):4506-4513
Although the stacking fault energy (SFE) is a fundamental variable determining the minimum grain size (dmin) obtainable in severe plastic deformation (SPD) processes, its accurate measurement is difficult. Here we establish the SFEs of binary Pd–Ag, Pd–Cu, Pt–Cu and Ni–Cu solid solutions using the axial interaction model and the supercell model in combination with first-principles theory. The two models yield consistent formation energies. For Pd–Ag, Pd–Cu and Ni–Cu, the theoretical SFEs agree well with those from the experimental measurements. For Pt–Cu no experimental results are available, and thus our calculated SFEs represent the first reasonable predictions. We discuss the correlation of the SFE and dmin in SPD experiments and show that the dmin values can be evaluated from first-principles calculations. 相似文献
92.
Jieqiang Wei Bart Besselink Junfeng Wu Henrik Sandberg Karl H. Johansson 《控制理论与应用(英文版)》2020,18(4):419-430
A finite-time consensus protocol is proposed for multi-dimensional multi-agent systems, using direction-preserving signum controls. Filippov solutions and nonsmooth analysis techniques are adopted to handle discontinuities. Sufficient and necessary conditions are provided to guarantee infinite-time convergence and boundedness of the solutions. It turns out that the number of agents which have continuous control law plays an essential role in finite-time convergence. In addition, it is shown that the unit balls introduced by ?p norms, where p∈[1,∞], are invariant for the closed loop. 相似文献
93.
This paper focuses on the design of materials supply systems in product development projects. In order to design the materials supply system in parallel with the product, product data must be available to the materials supply systems designers. The aim of this paper is to analyse the information quality of the required product data and to indicate how this information quality can be increased. Empirical data have been gathered through case studies conducted within the manufacturing industry. The empirical data show that it is possible to identify the product data required for materials supply systems design. It is also shown that there is an information gap between design engineering and materials supply systems design. The information quality of the required product data for the materials supply systems design has many imperfections, mainly in terms of accessibility, ease of operation, timeliness, understandability, interpretability, relevancy, and completeness. The information quality can be improved by the use of PDM systems, which are especially useful for facilitating an increase in accessibility, ease of operation, and timeliness. 相似文献
94.
A method is developed to generate a top of the atmosphere clear reflectance from the Global Vegetation Index (GVI) product. Our goal is to use this dataset as a threshold to be applied to the forthcoming POLDER observations, for operational cloud detection. The method is based on the hypothesis that clouds add a high frequency signal to the slow variations of the surface reflectance in clear conditions. The validity of our algorithm is verified through an analysis of the temporal profile of the reflectance that it generates. We show that these profiles are better than those resulting from the simpler Maximum Value Composite (MVC) method. The method is applied to five years of GVI products and the results are used to derive a reference database which accounts for the interannual variability of the surface reflectance. 相似文献
95.
96.
The naturally occurring mineral ilmenite, FeTiO3, has been examined as oxygen carrier for chemical-looping combustion. NiO-based particles have been used as an additive, in order to examine if it is possible to utilize the catalytic properties of metallic Ni to facilitate decomposition of hydrocarbons into more reactive combustion intermediates such as CO and H2. Firstly, ilmenite was examined by oxidation and reduction experiments in a batch fluidized-bed reactor. These experiments indicated moderate reactivity between ilmenite and CH4, which was used as reducing gas. However, adding 5 wt.% of NiO-based particles to the ilmenite improved the conversion of CH4 greatly, resulting in an increase in combustion efficiency with a factor of 3. Secondly, 83 h of chemical-looping combustion experiments were conducted in a small circulating fluidized-bed reactor, using ilmenite as oxygen carrier and natural gas as fuel. A wide range of process parameters and different levels of NiO addition were examined. Occasionally, there were problems with the circulation of solids between the air reactor and fuel reactor, but most of the time the experiments worked well. The products were mostly CO2, H2O and unconverted CH4. Adding small amounts of NiO-based particles to the reactor increased the conversion of the fuel considerably. For the base case conducted at 900°, the combustion efficiency was 76% for pure ilmenite and 90% for the corresponding experiments with 1 wt.% NiO-based particles added to the reactor. The properties of ilmenite were found to change considerably during operation. Used particles had lower density, were more reactive and more porous than fresh particles. These changes appear to have been physical, and no unexpected chemical phases could be identified. 相似文献
97.
98.
The Effect of processing on the content and composition of free sterols and sterol esters in soybean oil 总被引:1,自引:0,他引:1
The content and composition of free sterols and sterol esters in crude soybean oil and in oils from different stages of two
continuous refining systems were determined. The sterols were isolated by preparative thin layer chromatography and analyzed
by gas chromatography with cholesterol as an internal standard. The free sterols in one of the degummed oils amounted to 3.1
mg/g and were diminished to 1.8 mg/g oil by the De Laval Short-Mix refining process. The content of free sterols of the other
degummed oil was reduced from 3.4 to 1.6 mg/g oil by the Zenith process. The greatest reduction of sterol content was caused
by the treatment with bleaching earth. The sterol esters accounted for 0.6 mg/g of the degummed oil, and only very small changes
were observed during the processes. However, changes in the composition of fatty acids of the sterol esters were found. These
changes might indicate a selective deacylation of sterol esters or an interesterification during the refining processes. The
composition of sterols in free and esterified form were different. Campesterol, stigmasterol and sitosterol were obtained
in both free and esterified form, but Δ7 stigmasterol was only found in esterified form. Only small changes in the percentage
distribution of the sterols occurred during the processes.
Present adress Food Technology Division, ALFA-LAVAL,S-14700 Tumba, Sweden 相似文献
99.
Liang Li Anders Rasmuson Andy Ingram Mats Johansson Johan Remmelgas Christian von Corswant Staffan Folestad 《American Institute of Chemical Engineers》2015,61(3):756-768
Particle cycle and residence time distributions are critical factors in determining the coating quality in the Wurster process. Positron emission particle tracking experiments are performed to determine the cycle and residence times of particles in different regions of a Wurster fluid bed. The results show that particles tend to recirculate in and sneak out below from the Wurster tube. The experiments also show that a larger batch size leads to a shorter cycle time and a narrower cycle time distribution (CTD). It is possible to avoid recirculations and obtain a shorter cycle time and a narrower CTD by selecting the operating conditions appropriately or via equipment design. Experiments using binary mixtures of particles with a diameter ratio of 1.5 show that large particles have a longer cycle time than small particles and that the cycle time is shorter for mixtures with approximately equal amounts of small and large particles. © 2014 American Institute of Chemical Engineers AIChE J, 61: 756–768, 2015 相似文献
100.