全文获取类型
收费全文 | 6468篇 |
免费 | 633篇 |
国内免费 | 513篇 |
专业分类
电工技术 | 142篇 |
综合类 | 356篇 |
化学工业 | 2701篇 |
金属工艺 | 713篇 |
机械仪表 | 86篇 |
建筑科学 | 133篇 |
矿业工程 | 303篇 |
能源动力 | 241篇 |
轻工业 | 347篇 |
水利工程 | 16篇 |
石油天然气 | 199篇 |
武器工业 | 46篇 |
无线电 | 269篇 |
一般工业技术 | 807篇 |
冶金工业 | 535篇 |
原子能技术 | 453篇 |
自动化技术 | 267篇 |
出版年
2024年 | 29篇 |
2023年 | 112篇 |
2022年 | 202篇 |
2021年 | 295篇 |
2020年 | 249篇 |
2019年 | 203篇 |
2018年 | 184篇 |
2017年 | 231篇 |
2016年 | 271篇 |
2015年 | 231篇 |
2014年 | 297篇 |
2013年 | 405篇 |
2012年 | 409篇 |
2011年 | 427篇 |
2010年 | 324篇 |
2009年 | 364篇 |
2008年 | 320篇 |
2007年 | 419篇 |
2006年 | 352篇 |
2005年 | 320篇 |
2004年 | 278篇 |
2003年 | 244篇 |
2002年 | 208篇 |
2001年 | 170篇 |
2000年 | 166篇 |
1999年 | 125篇 |
1998年 | 109篇 |
1997年 | 89篇 |
1996年 | 95篇 |
1995年 | 66篇 |
1994年 | 67篇 |
1993年 | 62篇 |
1992年 | 38篇 |
1991年 | 56篇 |
1990年 | 38篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1959年 | 1篇 |
1951年 | 7篇 |
排序方式: 共有7614条查询结果,搜索用时 31 毫秒
141.
Acrylonitrile–ammonium itaconate copolymers were prepared by H2O/dimethyl formamide suspension polymerization technique. Differential scanning calorimetry results of the degradation of acrylonitrile–ammonium itaconate copolymers in air are presented. The apparent activation energy of degradation of the copolymer was calculated using the Kissinger method. Effects of copolymerization conditions on the apparent activation energy of copolymer were studied. Increasing the dimethyl formamide concentration in the solvent mixture leads to a rapid increase in the degradation apparent activation energy of acrylonitrile–ammonium itaconate copolymer. The value of the degradation apparent activation energy of the copolymer synthesized in dimethyl formamide solvent increases up to 168.3 kJ mol?1. The apparent activation energy decreases quickly along with an increase in ammonium itaconate concentration, and this change becomes less prominent as the weight ratio of ammonium itaconate/acrylonitrile goes beyond 6/94, ΔEa = 89.4 ± 2.0 kJ mol?1. The apparent activation energy shows a trend of increase with increasing copolymerization temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1708–1711, 2005 相似文献
142.
Mercier Gustavo A. Jr; Osman Roman; Weinstein Harel 《Protein engineering, design & selection : PEDS》1988,2(4):261-270
A proton transfer triggered by a ligand interacting with thereceptor had been suggested as the initial step in the activationof a receptor for the neurotransmitter serotonin (5-hydroxy-tryptamine;5-HT). To evaluate the role of the receptor macromolecule inmodulating the primary molecular event in ligand-mediated activation,the process of proton transfer was analysed in the environmentof a protein model for the 5-HT receptor. In the absence ofa detailed receptor structure, the enzyme actinidin was chosenas the model for the receptor based on criteria obtained fromstructure-activity considerations on the ligands. The firstsimulation of a mechanism for receptor activation was performedon this model using methods of theoretical chemistry to studythe effect of specific structural elements. The premise is thatthe role of the elements of secondary structure of soluble proteins(e.g. actinidin) in determining structure-function relationsin these macromolecules is maintained when these elements arepart of membrane-bound receptor proteins. Results from the calculationsof the effects of the six alpha helices of actinidin on theproton transfer process from the imidazolium side chain of His162 to the thiol side chain of Cys 25 in the protein show thatthe helices contribute in different ways to modulate the energyof proton transfer. The largest helix, Al, opposes the protontransfer through the effect of the helix dipole. The chargedresidues (primary structure) in helix A3 favor the proton transfer,and mask the effect of its helix dipole (secondary structure)which opposes the transfer. The direction of the proton transfersimulated for the activation mechanism is opposite to that assumedin the catalytic process of the thiol protease, and the entireprotein environment opposes the transfer. This supports thespecific role of the ligand in triggering the proton transferas a response to its binding. 相似文献
143.
144.
以不同软化点的乙烯裂解焦油调制的各向同性沥青为原料。通过热失重和差热分析,得到不同沥青的DTA和TG曲线,并通过计算机拟合逼近处理,求出沥青样品的氧化活化能和反应级数等数据。不同软化点调制的沥青,其氧化级数均为一级反应,而软化点与氧化反应活化能间没有明显规律性关系,但升温速率对氧化反应的影响有明显规律。说明通过热分析可以预测不同沥青的预氧化碳化处理性能。 相似文献
145.
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
146.
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
147.
陈若莉 《徐州工程学院学报》2010,(4):53-57
在粉煤灰理化特性分析的基础上,对粉煤灰进行了物理激发和化学激发.研究结果表明:物理激发和化学激发均能提高粉煤灰的吸附活性.化学激发方法在反应温度为90℃、反应时间为12h、灰钙比为5、水固比为15时,粉煤灰的吸附活性提高最大. 相似文献
148.
采用无钯活化粉体化学镀技术制备了银包碳酸钙导电粉体.探讨了表面处理和PH值对沉积效果的影响,以及复合粒子的结合强度.通过扫描电镜(SEM),X射线能量色散谱仪(EDS)和X射线衍射(XRD)对复合粉体进行表面形貌分析和成分测试.结果表明:碳酸钙粉体经WD-50表面处理后,生成的银粒子粒径较小,对碳酸钙粒子的包覆均匀致密.随着镀液pH值的升高,银的析出量增大,粉体表观颜色变浅.调节镀液pH至13.0,得到了镀层结合强度高的银包碳酸钙复合粉体. 相似文献
149.
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
150.
Kuo-Chih Chou 《北京科技大学学报(英文版)》2009,16(5):500-504
Electrical conductivity of molten slag is an important physicochemical property for designing the refining process in electric smelting furnaces.Though conductivities of many slag systems have been measured,the quantitative relationships of conductivity with slag composition and temperature are still very limited.In this article,the Arrhenius law was used to describe the experimental data of conductivities for CaO-MgO-Al2O3-SiO2,CaO-Al2O3-SiO2,CaO-MnO-Al2O3-SiO2,as well as CaO-MgO-MnO-Al2O3-SiO2 systems,and... 相似文献