全文获取类型
收费全文 | 20297篇 |
免费 | 2719篇 |
国内免费 | 1123篇 |
专业分类
电工技术 | 144篇 |
综合类 | 1154篇 |
化学工业 | 12615篇 |
金属工艺 | 1693篇 |
机械仪表 | 132篇 |
建筑科学 | 304篇 |
矿业工程 | 372篇 |
能源动力 | 763篇 |
轻工业 | 1803篇 |
水利工程 | 43篇 |
石油天然气 | 941篇 |
武器工业 | 153篇 |
无线电 | 441篇 |
一般工业技术 | 2226篇 |
冶金工业 | 904篇 |
原子能技术 | 290篇 |
自动化技术 | 161篇 |
出版年
2024年 | 63篇 |
2023年 | 340篇 |
2022年 | 479篇 |
2021年 | 663篇 |
2020年 | 646篇 |
2019年 | 636篇 |
2018年 | 669篇 |
2017年 | 765篇 |
2016年 | 847篇 |
2015年 | 788篇 |
2014年 | 1012篇 |
2013年 | 1490篇 |
2012年 | 1408篇 |
2011年 | 1305篇 |
2010年 | 1001篇 |
2009年 | 1114篇 |
2008年 | 917篇 |
2007年 | 1227篇 |
2006年 | 1206篇 |
2005年 | 880篇 |
2004年 | 902篇 |
2003年 | 820篇 |
2002年 | 682篇 |
2001年 | 593篇 |
2000年 | 530篇 |
1999年 | 413篇 |
1998年 | 353篇 |
1997年 | 338篇 |
1996年 | 275篇 |
1995年 | 228篇 |
1994年 | 243篇 |
1993年 | 194篇 |
1992年 | 196篇 |
1991年 | 192篇 |
1990年 | 138篇 |
1989年 | 101篇 |
1988年 | 57篇 |
1987年 | 54篇 |
1986年 | 39篇 |
1985年 | 84篇 |
1984年 | 71篇 |
1983年 | 47篇 |
1982年 | 52篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The objective of this work is to simulate the gas flow across a concrete wall of a nuclear power plant internal enclosure. In the laboratory, permeability measurements are generally made on cylindrical samples (15 cm diameter×5 cm height: ∅ 15×5 cm) with a steady-state experiment. To be able to predict structural behaviour, we studied size effect and steady-state time with a modified CEMBUREAU permeability test. A statistical approach showed that there is no size effect on concrete permeability. Laboratory results found on cylindrical samples can be applied to tests in situ, where concrete specimens are thicker. A model based on the mass balance relation provided times to reach steady state and reproduced experimental flow kinetics for uniform water content across specimens. 相似文献
102.
The kinetics of the transition metal-catalysed direct addition of amine NH bonds to carbon--carbon multiple bonds (hydroamination) has been explored by in situ spectroscopic techniques. From an open mass balance it was concluded that an intermediate species was formed during the cyclisation of 6-aminohex-1-yne. This species was identified as the enamine 2-methylene-piperidine, which is the primary hydroamination product. 相似文献
103.
Rates of Crystallization of Dried Lactose-sucrose Mixtures 总被引:1,自引:0,他引:1
The isothermal crystallization kinetics of glassy lactose/sucrose mixtures were studied at several storage temperatures (close to Tg and Tm). The kinetic parameters implicit in the Avrami equation were determined. Activation energies for transport (ED) and surface nucleation (W*) were also found and correlated to the molar composition of the lactose/sucrose mixtures. A monotonic increase in the half crystallization time (t1/z), Avrami index (n), % crystallization per day, activation energy for transport (ED) and surface nucleation energy (W*) and a decrease in the crystallization velocity constants (K) were related to the increase in the lactose content of lactose/sucrose mixtures. 相似文献
104.
105.
化学沉积Ni-P及Ni-Cu-P合金镀层晶化行为的比较 总被引:7,自引:1,他引:6
利用DSC和XRD对化学沉积Ni-P及Ni-Cu-P合金镀层的晶化行为进行了比较研究,结果表明:低磷Ni-P镀层直接转变为稳定相Ni3P,而低磷(高铜)Ni-Cu-P镀层则经生成亚稳中间相Ni5P2后再向稳定相Ni3P转变,高磷非晶态Ni-12.1%P(质量分数,下同)和Ni-17.96%Cu-9.29%P合金镀层均先形成亚稳中间相Ni5P2和Ni12P5后,再转变为稳定相Ni3P,但Ni-Cu-P合金镀层转变为亚稳相的温度比Ni-P镀层的高。 相似文献
106.
钙铁硅铁磁体微晶玻璃热处理制度的研究 总被引:4,自引:2,他引:2
使用XRD、DTA、VSM等分析测试手段对在还原气氛下含少量B2O3、P2O5钙铁硅微晶玻璃的热处理制度进行了较深入的研究。研究发展,预核化处理对于钙铁硅微晶玻璃的晶化无明显作用。900℃作为钙铁硅微晶玻璃的晶化温度较适宜,晶化时间宜8h以上。 相似文献
107.
研究了非晶Sm5Fe74.3Nb1.5Si11.7B4.5C2.5Cu0.5合金经400℃,保温10min预退火后的晶化动力学。结果表明;该合金的晶化相为α-Fe固溶体和Sm2Fe17Cx金属间化合物,两相的晶化表观激活能分别为557KJ/mol和514KJ/mol,当晶化体积分数为60%时,α-Fe相的晶化激活能达极大值;Sm2Fe17Cx相晶化激活能则随其晶化体积分数的增加而逐渐减小。 相似文献
108.
Sandra Aparecida de Assis Pedro Fernandes Bruno Sommer Ferreira Joaquim MS Cabral Olga Maria Mascarenhas Faria Oliveira 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2004,79(3):277-280
A partially purified extract of pectinmethylesterase (PME) from acerola fruit was immobilized on various supports: glass, celite, chrysotile, agarose, concanavalin A Sepharose 4B, egg shell, polyacrylamide and gelatin. In addition, reticulation with glutaraldehyde was assessed, as well as the use of gelatin in the presence of celite, glass and silica. The highest immobilization yields were obtained when the pectinmethylesterase was immobilized in concanavalin A Sepharose 4B (81.7%) and in gelatin‐water (78.0%). Copyright © 2004 Society of Chemical Industry 相似文献
109.
The methodology of response reactions (RERs) introduced earlier from thermodynamic and kinetic considerations is used in this work to develop a new algorithm for the classification and enumeration of unique/direct reaction routes (RRs) and overall reactions (ORs). According to the RERs approach, a unique set of both RRs and ORs may be generated starting from any conceivable set of linearly independent RRs and ORs. In particular, the direct ORs may be most conveniently enumerated starting from the formula matrix of the terminal species (reactants and products), i.e., without any relation to the elementary reactions comprising the detailed mechanism. Depending on the type of ORs produced by the RRs one can distinguish between two distinct types of direct RRs. Namely, one option is to define a direct RR by specifying the intermediate species that need to be eliminated. This type of RR is referred to as Milner RRs. The other option is to require the direct RRs to produce RERs, thus resulting in RRs referred to as Happel-Sellers RRs. 相似文献
110.
In this research, the biosorption of phenol using the fibres of a Mediterranean seagrass Posidonia oceanica (L.) was studied. Batch experimental procedures were made to investigate the ability of this novel marine biomass to remove phenol from aqueous phase. The influences of pH and contact time at different initial concentrations were evaluated. The results showed that biosorption capacity was enhanced using solution pH equal to 5.2. The modelling results showed that pseudo‐second‐order and Redlich‐Peterson models were found to be the most suitable to satisfactory describe the kinetic and equilibrium adsorption data, respectively. 相似文献