全文获取类型
收费全文 | 21979篇 |
免费 | 2373篇 |
国内免费 | 663篇 |
专业分类
电工技术 | 130篇 |
综合类 | 1125篇 |
化学工业 | 6426篇 |
金属工艺 | 561篇 |
机械仪表 | 167篇 |
建筑科学 | 678篇 |
矿业工程 | 218篇 |
能源动力 | 461篇 |
轻工业 | 10823篇 |
水利工程 | 169篇 |
石油天然气 | 795篇 |
武器工业 | 23篇 |
无线电 | 349篇 |
一般工业技术 | 1146篇 |
冶金工业 | 799篇 |
原子能技术 | 256篇 |
自动化技术 | 889篇 |
出版年
2024年 | 119篇 |
2023年 | 490篇 |
2022年 | 800篇 |
2021年 | 1189篇 |
2020年 | 916篇 |
2019年 | 901篇 |
2018年 | 848篇 |
2017年 | 937篇 |
2016年 | 1018篇 |
2015年 | 918篇 |
2014年 | 1267篇 |
2013年 | 1616篇 |
2012年 | 1723篇 |
2011年 | 1827篇 |
2010年 | 1243篇 |
2009年 | 1184篇 |
2008年 | 1004篇 |
2007年 | 1257篇 |
2006年 | 1040篇 |
2005年 | 729篇 |
2004年 | 629篇 |
2003年 | 565篇 |
2002年 | 450篇 |
2001年 | 375篇 |
2000年 | 320篇 |
1999年 | 240篇 |
1998年 | 188篇 |
1997年 | 176篇 |
1996年 | 148篇 |
1995年 | 135篇 |
1994年 | 126篇 |
1993年 | 108篇 |
1992年 | 97篇 |
1991年 | 65篇 |
1990年 | 66篇 |
1989年 | 46篇 |
1988年 | 44篇 |
1987年 | 31篇 |
1986年 | 34篇 |
1985年 | 21篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1980年 | 21篇 |
1965年 | 5篇 |
1964年 | 5篇 |
1961年 | 5篇 |
1959年 | 7篇 |
1958年 | 5篇 |
1956年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Akihiko Sakurai Mina Masuda Mikio Sakakibara 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(9):952-958
The removal of phenol by peroxidase‐catalysed polymerization was examined using Coprinus cinereus peroxidase in the presence of surfactants. The non‐ionic surfactants with poly(oxyethene) residues, Triton X‐100, Triton X‐405 and Tween 20, enhanced the phenol removal efficiency at a level similar to high relative molecular mass poly(ethylene glycol) (relative molecular mass 3000). Although the improvement in the removal efficiency was less than that of Triton X‐100, Span 20, sodium lauryl sulfate (SDS) and lauryl trimethylammonium bromide (DTAB) also enhanced the removal efficiency. The requirement of the enzyme for almost 100% removal of 100 mg dm?3 phenol decreased to one‐fourth by the addition of 30 mg dm?3 Triton X‐100. Triton X‐100, Triton X‐405, Tween 20 and DTAB could reactivate the enzyme precipitated with the phenol polymer, leading to the restarting of the phenol removal reaction. Copyright © 2003 Society of Chemical Industry 相似文献
82.
咪唑封端扩链脲改性环氧树脂E-51/酸酐MTHPA体系性能研究 总被引:1,自引:0,他引:1
以端羟基聚环氧丙烷1000,甲苯二异氰酸酯(TDI),2-甲基咪唑为原料,合成了扩链脲TI,利用DSC,动态热机械分析仪DMA,冲击试验机及扫描电镜(SEM)等手段对TI改性的环氧树脂E-51/甲基四氢化邻苯二甲酸酐(MTHPA)固化体系的反应活性,动态力学行为,冲击性能,断裂面形态结构进行了系统研究,结果表明,改性后的E-51/MTHPA体系反应活性明显提高,固化反应峰顶温度较未改性体系降低160℃-200℃,固化反应的表观活化能由未改性体系的160.3kJ/mol降至63kJ/mol-87kJ/mol,同时与未改性体系相比,经过改性的环氧树脂固化体系冲击强度有较大的提高,在TI含量为5%时体系的玻璃化转变温度Ts达到最高,各改性体系冲击断面呈韧性断裂。 相似文献
83.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
84.
ABSTRACT: The absorbance of 2,2-diphenyl-1-picrylhydrazyl (DPPH) at 517 nm in methanol and acetone decreased by 20 and 35% for 120 min at 25 °C under light, respectively; in the dark it did not change significantly for 150 min. Decomposition of DPPH under 21% oxygen after 90 min under light was significantly higher than that under 1% oxygen. Absorbance of DPPH in pH 4 buffer solution in methanol, and in pH 10 buffer solution in acetone, decreased by 55 and 80%, respectively, under light for 120 min. The evaluation of antioxidant activity by the changes of DPPH absorbance should be carefully interpreted since the absorbance of DPPH at 517 nm is decreased by light, oxygen, pH, and type of solvent in addition to the antioxidant. 相似文献
85.
Safron Adam; Barch Bennett; Bailey J. Michael; Gitelman Darren R.; Parrish Todd B.; Reber Paul J. 《Canadian Metallurgical Quarterly》2007,121(2):237
Men exhibit much higher levels of genital and subjective arousal to sexual stimuli containing their preferred sex than they do to stimuli containing only the nonpreferred sex. This study used event-related functional magnetic resonance imaging to investigate how this category-specific pattern would be reflected in the brains of homosexual (n = 11) and heterosexual (n = 11) men. Comparisons of activation to preferred sexual stimuli, nonpreferred sexual stimuli, and sports stimuli revealed large networks correlated with sexual arousal, spanning multiple cortical and subcortical areas. Both homosexual and heterosexual men exhibited category-specific arousal in brain activity. Within the amygdala, greater preference-related activity was observed in homosexual men, but it is unclear whether this is a cause or a consequence of their sexuality. In a subsequent analysis of regions hypothesized to support arousal, both participant groups demonstrated widespread increases in evoked activity for preferred stimuli. Aggregate data from these regions produced significant differences between stimulus types in 16 out of 22 participants. Significant activational differences matched reported sexual orientation in 15 of these 16 participants, representing an advance in psychophysiological measures of arousal. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
86.
87.
模拟计算表明:采用活性趋于表层的分布,可以较明显地提高国产中温变换催化剂的内表面利用率,有效地节省催化剂用量,而对“热点”温度没有多大影响。 相似文献
88.
89.
本文在气相色谱仪联用微反应器装置上,研究了LaBO_3型催化剂中的B位元素对催化氧化活性的影响规律,并进行了程序升温脱附实验。另外,还对LaBO_3型载体催化剂进行了活性筛选,并在柴油机台架上与贵金属Pt/Al_2O_3进行了有害气体净化效果的对比实验。实验结果表明,LaBO_3氧化物中LaMnO_3对CO、CH_4的催化氧化活性最高,且CO、CH_4活性中心并不一致。LaMnO_3/γ-Al_2O_3浸渍微量助化剂后,能使CO在130℃完全氧化,CH_4的氧化温度在300~500℃范围内,LaMnO_3载体催化剂对柴油机有害排放物的净化率很低,浸渍微量助化剂后,净化率提高一倍以上,特别是LaMnO_3/堇青石蜂窝陶瓷,浸渍后的净化效果同贵金属Pt/Al_2O_3接近。 相似文献
90.
Post-harvest loss of resources to microbial competitors affects a number of species of animals, and many of them have evolved behaviors that reduce the likelihood of such loss. We previously described the inhibition ofBacillus psychrophilus by dogwood fruits (Cornus drummondii), which can comprise a significant portion of the winter food cache of the eastern woodrat (Neotoma floridana). The present study is a further investigation of the ability of dogwood fruits to inhibit growth ofB. psychrophilus. Additionally, we tested the antimicrobial activity of dogwood fruits onEscherichia coli andStaphlococcus aureus. Results of our study indicate that fresh fruits inhibit the growth ofB. psychrophilus andS. aureus but notE. coli. However, fruits taken from woodrat dens after four and six months storage inhibited growth of all three species of bacteria. Further, the strength of inhibition increased over the test period. We suggest the presence of an inhibitor allows woodrats to compete effectively for a valuable and limited food resource. 相似文献