全文获取类型
收费全文 | 7458篇 |
免费 | 655篇 |
国内免费 | 542篇 |
专业分类
电工技术 | 174篇 |
综合类 | 400篇 |
化学工业 | 2832篇 |
金属工艺 | 739篇 |
机械仪表 | 125篇 |
建筑科学 | 246篇 |
矿业工程 | 341篇 |
能源动力 | 258篇 |
轻工业 | 421篇 |
水利工程 | 43篇 |
石油天然气 | 219篇 |
武器工业 | 49篇 |
无线电 | 312篇 |
一般工业技术 | 882篇 |
冶金工业 | 695篇 |
原子能技术 | 467篇 |
自动化技术 | 452篇 |
出版年
2024年 | 43篇 |
2023年 | 129篇 |
2022年 | 283篇 |
2021年 | 309篇 |
2020年 | 279篇 |
2019年 | 211篇 |
2018年 | 199篇 |
2017年 | 244篇 |
2016年 | 290篇 |
2015年 | 255篇 |
2014年 | 329篇 |
2013年 | 486篇 |
2012年 | 445篇 |
2011年 | 484篇 |
2010年 | 382篇 |
2009年 | 417篇 |
2008年 | 376篇 |
2007年 | 486篇 |
2006年 | 395篇 |
2005年 | 355篇 |
2004年 | 309篇 |
2003年 | 281篇 |
2002年 | 235篇 |
2001年 | 192篇 |
2000年 | 180篇 |
1999年 | 135篇 |
1998年 | 119篇 |
1997年 | 95篇 |
1996年 | 108篇 |
1995年 | 72篇 |
1994年 | 76篇 |
1993年 | 72篇 |
1992年 | 42篇 |
1991年 | 64篇 |
1990年 | 43篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 29篇 |
1986年 | 14篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 9篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1975年 | 4篇 |
1965年 | 5篇 |
1959年 | 4篇 |
1951年 | 7篇 |
排序方式: 共有8655条查询结果,搜索用时 15 毫秒
71.
可发泡性酚醛树脂的合成研究 总被引:8,自引:1,他引:8
考查了可发泡性酚醛树脂的合成条件,如反应时间、温度和催化剂用量等对树脂活性、物理以及酚醛泡沫塑料容重和表观品质的影响,结果表明:催化剂用量越大,树脂粘度越大,泡沫固化时间越长;反应时间介于65~95min,泡沫塑料容重和表观品质较好;用加热板测定了合成的可发泡性树脂的固化速度,并求出固化反应活化能。 相似文献
72.
Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were conducted on two common types of rye straws (Danko and Kustro) at a heating rate of 20°C/min in an oxidizing atmosphere (15% oxygen and 85% nitrogen, by volume) between ambient temperature and 700°C. The two step nature of the TGA curves and the dual peak characteristics of the DTA curves showed that rye straw had two distinct reaction zones. The initial degradation temperatures, the residual mass at 700°C, the thermal degradation rates in the first and second reaction zones and the kinetic parameters of each reaction zone (order of reaction, activation energy and pre-exponential factor) were determined. Higher thermal degradation rates were observed in the first reaction zone as compared to those in the second reaction zone. 相似文献
73.
The electrochemical behaviour of Al, Al—In and Al–Ga–In alloys in 0.6 m NaCl solutions with and without Zn2+ was investigated. The study was performed by means of open circuit potential, potentiodynamic polarization, potentiostatic current-time and electrochemical impedance spectroscopy measurements as well as by SEM-EDAX examination. It was found that the Al—In alloy exhibits the highest negative open circuit potential in 0.6 m NaCl and the corrosion resistance of the tested electrodes decreases in the following order: Al > Al–Ga–In > Al—In. The greater activity of the Al—In alloy was interpreted on the basis of the autocatalytic attack by indium. The potentiostatic current–time measurements in Zn2+ containing electrolyte at potentials above the pitting potential revealed that Zn2+ has an insignificant influence on the Al electrode, while it enhances the corrosion of the Al–Ga–In alloy and improves the attack morphology of the Al—In alloy. Furthermore, the impedance spectra recorded under open circuit conditions showed a decrease in the polarization resistance of Al—In and Al–Ga–In alloys in presence of Zn2+ indicating the activating effect of Zn2+ ions. 相似文献
74.
臭氧氧化法除地表水有机物试验研究 总被引:9,自引:0,他引:9
本文阐述臭氧化法除地表水有机物的重要意义,实验结果表明:臭氧氧化有机物的总氧化速率受活化控制,影响氧化率的最高显著因素是温度,其次是pH,接触时间等,臭氧很容易氧化腐植酸,在30℃,pH9.0~10.0,7min内,COD去除率可达60%以上,对邯郸热电厂生产处理也取得良好效果,35℃,pH7.4~7.6,10min内,COD去除率可达67%,可望将臭氧化水处理工艺应用于电厂水处理。 相似文献
75.
Nonisothermal crystallization of poly(N‐methyldodecano‐12‐lactam) (MPA) was investigated using DSC method at cooling rates of 2–40 K/min. With increasing cooling rate, crystallization exotherms decreased in magnitude and shifted toward lower temperatures. Subsequent heating runs (10 K/min) showed an exotherm just above Tg, which increased in magnitude with the rate of preceding cooling run, corresponding to the continuation of primary crystallization interrupted as the system crossed Tg on cooling. Kinetic evaluation by the Avrami method gave values of exponent n close to 2.0, suggesting two‐dimensional crystal growth combined with heterogeneous nucleation. The Tobin method, covering the intermediate range of relative crystallinities, provided n ? 2.20, suggesting possible partial involvement of homogeneous nucleation at later stages of nonisothermal crystallization. The crystallization rate parameter k1/n showed a linear dependency on cooling rate for both methods, the Tobin values being slightly higher. The Ozawa approach failed to provide reasonable values of the kinetic exponent m of MPA. The Augis–Bennet method was used to determine the effective activation energy of the entire nonisothermal crystallization process of MPA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 564–572, 2005 相似文献
76.
Effectiveness of microwave heating in an activation treatment of zeolites was studied and utilization of zeolites for reusable desiccant was examined. X zeolite was chosen as a target material for its large adsorption capacity. Na-X zeolite easily caused a thermal runaway by microwave radiation of 500 W but Ca contained X zeolite merely reached ca. 573 K under the same conditions. Mixtures of Na-X and Ca-X with suitably mixed ratios did not cause the thermal runaway and their heating temperatures were controlled (>573 K) at will. Under the most suitable conditions, the mixture reached a dehydration degree of 92%. A degradation degree of adsorptive capacity of the mixture for water was examined after three treatments. The average degradation degree was 1.5% per treatment. The heating method is promising as a quick and easy technique to activate zeolite. By applying the method, the zeolites with suitable mixing ratios are usable as a reusable desiccant for home use. 相似文献
77.
78.
Dmitri V. Besedin Leila Yu. Ustynyuk Yuri A. Ustynyuk Valerij V. Lunin 《Topics in Catalysis》2005,32(1-2):47-60
The model reactions of ethylene polymerization and hydrogenolysis of linear alkanes (propane, n-butane, and n-pentane) on the silica-supported zirconium hydrides (Si–O)3ZrIVH, (Si–O)2ZrIVH2, and (Si–O)2ZrIIIH were studied using the DFT approach. Catalytic processes under study were shown to occur involving different surface hydrides. The ethylene polymerization was found to proceed at comparable rates on the zirconium monohydrides, (Si–O)3ZrH, and dihydrides, (Si–O)2ZrH2. Cleavage of linear alkanes on the monohydrides (Si–O)3ZrH is thermodynamically unfavorable; however, the dihydrides (Si–O)2ZrH2 can act as catalysts of the process under mild conditions. Hydrides of the trivalent zirconium, (Si–O)2ZrIIIH, can also contribute to the hydrogenolysis reaction. A feature of all the systems studied is low regioselectivity of the corresponding processes. 相似文献
79.
The structure of benzoxazines is similar to that of phenolic resin through thermal self‐curing of the heterocyclic ring opening reaction that neither requires catalyst nor releases any condensation byproduct. These polybenzoxazine resins have several outstanding properties such as high thermal stability and high glass transition temperature. To better understand the curing kinetics of this copolybenzoxazine thermosetting resin, dynamic and isothermal differential scanning calorimetry measurements were performed. Three models, the Kissinger method, the Flynn–Wall–Osawa method, and the Kamal method, were used to describe the curing process. Dynamic kinetic activation energies based on Kissinger and Flynn–Wall–Osawa methods are 72.11 and 84.06 KJ/mol, respectively. The Kamal method based on an autocatalytic model results in a total order of reaction between 2.66 and 3.03, depending on curing temperature. Its activation energy and Arrhenius preexponential are 50.3 KJ/mol and 7959, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 730–737, 2005 相似文献
80.
Based on the steady-state strain measured by single-pass hot compression tests, the method by a double-pass hot compression
testing was developed to measure the metadynamic-recrystallization kinetics. The metadynamic recrystallization behavior of
low-alloy steel Q345B during hot compression deformation was investigated in the temperature range of 1 000–1 100 °C, the
strain rate range of 0.01–0.10 s−1 and the interpass time range of 0.5–50 s on a Gleeble-3500 thermo-simulation machine. The results show that metadynamic recrystallization
during the interpass time can be observed. As the deformation temperature and strain rate increase, softening caused by metadynamic
recrystallization is obvious. According to the data of thermo-simulation, the metadynamic recrystallization activation energy
is obtained to be Q
md=100.674 kJ/mol and metadynamic recrystallization kinetics model is set up. Finally, the error analysis of metadynamic recrystallization
kinetics model proves that the model has high accuracy (correlation coefficient R=0.988 6). 相似文献