全文获取类型
收费全文 | 2849篇 |
免费 | 213篇 |
国内免费 | 45篇 |
专业分类
电工技术 | 13篇 |
综合类 | 51篇 |
化学工业 | 1457篇 |
金属工艺 | 192篇 |
机械仪表 | 46篇 |
建筑科学 | 41篇 |
矿业工程 | 15篇 |
能源动力 | 148篇 |
轻工业 | 111篇 |
水利工程 | 6篇 |
石油天然气 | 49篇 |
武器工业 | 3篇 |
无线电 | 203篇 |
一般工业技术 | 363篇 |
冶金工业 | 193篇 |
原子能技术 | 116篇 |
自动化技术 | 100篇 |
出版年
2024年 | 14篇 |
2023年 | 147篇 |
2022年 | 55篇 |
2021年 | 87篇 |
2020年 | 73篇 |
2019年 | 78篇 |
2018年 | 73篇 |
2017年 | 75篇 |
2016年 | 111篇 |
2015年 | 73篇 |
2014年 | 122篇 |
2013年 | 243篇 |
2012年 | 111篇 |
2011年 | 229篇 |
2010年 | 113篇 |
2009年 | 141篇 |
2008年 | 133篇 |
2007年 | 118篇 |
2006年 | 112篇 |
2005年 | 97篇 |
2004年 | 81篇 |
2003年 | 107篇 |
2002年 | 95篇 |
2001年 | 75篇 |
2000年 | 57篇 |
1999年 | 62篇 |
1998年 | 53篇 |
1997年 | 44篇 |
1996年 | 30篇 |
1995年 | 25篇 |
1994年 | 25篇 |
1993年 | 24篇 |
1992年 | 27篇 |
1991年 | 19篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 24篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1974年 | 3篇 |
1964年 | 4篇 |
1961年 | 3篇 |
1959年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有3107条查询结果,搜索用时 15 毫秒
1.
有机化学是化学化工、材料、制药、食品等多个专业的基础课程,在其教学过程中,教师可以根据课程的内容及特点,分别以有机化学发展中的重大历史事件、有机化物的性质及有机反应为引导,开展学生的思想品德教育,加强课程思政建设。 相似文献
2.
Jeongchan Lee Dr. Joonwon Kim Hyun Kim Eun-Jung Kim Prof. Dr. Hee-Jin Jeong Prof. Dr. Kwon-Young Choi Prof. Dr. Byung-Gee Kim 《Chembiochem : a European journal of chemical biology》2020,21(10):1446-1452
Tryptophan halogenases are found in diverse organisms and catalyze regiospecific halogenation. They play an important role in the biosynthesis of halogenated indole alkaloids, which are biologically active and of therapeutic importance. Here, a tryptophan 6-halogenase (SatH) from Streptomyces albus was characterized by using a whole-cell reaction system in Escherichia coli. SatH showed substrate specificity for chloride and bromide ions, leading to regiospecific halogenation at the C6-position of l -tryptophan. In addition, SatH exhibited higher performance in bromination than that of previously reported tryptophan halogenases in the whole-cell reaction system. Through structure-based protein mutagenesis, it has been revealed that two consecutive residues, A78/V79 in SatH and G77/I78 in PyrH, are key determinants in the regioselectivity difference between tryptophan 6- and 5-halogenases. Substituting the AV with GI residues switched the regioselectivity of SatH by moving the orientation of tryptophan. These data contribute to an understanding of the key residues that determine the regioselectivity of tryptophan halogenases. 相似文献
3.
4.
Antonio Camarano Javier Narciso Donatella Giuranno 《Journal of the European Ceramic Society》2019,39(14):3959-3970
Reactivity between SiC and Ir as a function of SiC-crystallinity was investigated by diffusion bonding technique under a vacuum and over the temperature range of 1200–1450 °C. As reaction products, various Ir-silicides and free unreacted-C were detected. Reactivity is strongly affected by the temperature and SiC-crystallinity involving a series of interactions, from “no reaction” to “massive exothermic reactions”. In particular, interfacial phenomena are more pronounced by the presence of defects and grain boundaries.Solid state reactions result in formation of fine C-precipitates rearranged in a quasi-periodic microstructure. On the contrary, clustering of highly ordered C-precipitates (C-graphitized) occurs after “massive reactions” take place.A relationship between the degree of graphitization (from 1 to multi-layers of graphene), temperature and SiC crystallinity was found by Raman spectroscopy. 2D-layering phenomenon is enhanced in polycrystalline SiC at high temperature. 相似文献
5.
《Cement and Concrete Research》2003,33(4):517-524
The kinetics of the pozzolanic reaction between lime (calcium hydroxide) and sugar cane straw ash (SCSA) with 20% and 30% of clay burned at 800 and 1000 °C is studied. A simple experimental technique was used in which the conductivity is the experimental variable. For correlating the conductivity with the concentration of calcium hydroxide (CH), a calibration curve was established. We elaborated a mathematical model that allows us to describe the process in either kinetic or kinetic-diffusive regimes. The fitting of the model by computerized methods enables us determine the parameters that characterize the process: i.e. the diffusion coefficient and reaction rate constant. The pozzolanic activity is evaluated according to the obtained values of the reaction rate constant. The results show that SCSA has a good pozzolanic activity comparable to that of the rice husk ash (RHA). 相似文献
6.
本文阐述了通过Friedel-Crafts反应合成邻-(4-乙基苯甲酰基)苯甲酸的方法.研究了影响产物质量的因素,提出了适宜的工艺条件. 相似文献
7.
The In-Sn-Ni alloys of various compositions were prepared and annealed at 160°C and 240°C. No ternary compounds were found;
however, most of the binary compounds had extensive ternary solubility. There was a continuous solid solution between the
Ni3Sn phase and Ni3In phase. The Sn-In/Ni couples, made of Sn-In alloys with various compositions, were reacted at 160°C and 240°C and formed
only one compound for all the Sn-In alloys/Ni couples reacted up to 8 h. At 240°C, Ni28In72 phase formed in the couples made with pure indium, In-10at.%Sn and In-11at.%Sn alloys, while Ni3Sn4 phase formed in the couples made of alloys with compositions varied from pure Sn to In-12at.%Sn. At 160°C, except in the
In/Ni couple, Ni3Sn4 formed by interfacial reaction. 相似文献
8.
9.
Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (Tg). melting points (Tm) and crystallisation temperatures (Tc) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in Tg, Tm and Tc. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation. 相似文献
10.
Photoluminescence features in a commercial grade cured DGEBA-based epoxy resin have been investigated with as objective to determine which of the material compounds are responsible for cured resin emissions. The origin of the bands has been approached by considering photoluminescence of base resin and hardener taken separately, of their mixture, and in the course of curing. Most of the bands observed in the cured resin could be interpreted based on those found in the components taken separately. Fluorescence of the cured resin appears dominated by two broad bands that are characteristic of the hardener and exhibits a blue shift by up to 30 nm in the course of curing which could be used for cure monitoring purpose of the investigated system. Fluorescence of the base resin is clearly detected in the resin cured with tertiary amine as catalyser. However, it is very weak if the catalyser is not added. Two phosphorescence processes have been isolated in the cured resin, one of them being related to the base resin. Finally, a chemiluminescence spectrum has been recorded in the course of curing, which has been related to either curing-related reactions or to an oxidation process. 相似文献