全文获取类型
收费全文 | 742篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 9篇 |
化学工业 | 117篇 |
金属工艺 | 19篇 |
机械仪表 | 33篇 |
建筑科学 | 11篇 |
能源动力 | 51篇 |
轻工业 | 61篇 |
水利工程 | 6篇 |
石油天然气 | 1篇 |
无线电 | 63篇 |
一般工业技术 | 208篇 |
冶金工业 | 111篇 |
原子能技术 | 4篇 |
自动化技术 | 70篇 |
出版年
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 19篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 24篇 |
2017年 | 26篇 |
2016年 | 11篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 28篇 |
2012年 | 18篇 |
2011年 | 36篇 |
2010年 | 23篇 |
2009年 | 24篇 |
2008年 | 19篇 |
2007年 | 25篇 |
2006年 | 17篇 |
2005年 | 15篇 |
2004年 | 24篇 |
2003年 | 13篇 |
2002年 | 11篇 |
1999年 | 9篇 |
1998年 | 30篇 |
1997年 | 20篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 14篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 12篇 |
1976年 | 17篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1970年 | 6篇 |
排序方式: 共有764条查询结果,搜索用时 187 毫秒
1.
2.
3.
4.
5.
6.
Electrical conduction in non-metallic rare-earth solids 总被引:1,自引:0,他引:1
Schematic energy band diagrams for the genesis of charge carriers in non-metallic rare-earth solids have been presented. It has been shown that positions of 4f bands have significant effect on the genesis and nature of charge carriers, their conduction mechanism and magnitude of electrical conductivity () and Seebeck coefficient (S) of the solid. Relevant relations have been given for both and S in different situations. Experimental data on rare-earth sesquioxides (R2O3), rare-earth tungstates [R2(WO4)3] and rare-earth molybdates [R2(MoO4)3] in the intrinsic range have been explained as examples for the validity of energy band diagrams. 相似文献
7.
Mohd Akram Hira Lal Mohammad Osama Farah Ansari Sana Anwar Kabir-ud-Din Ajaz Ahmad Samreen Naved Azum Hadi M. Marwani Abdullah M. Asiri 《Journal of surfactants and detergents》2021,24(1):35-49
In this study, we prepared a novel series of diester-functionalized cationic gemini surfactants (Cm-E2O2-Cm) containing ethylene oxide as a spacer with varying alkyl chain lengths and characterized by 1H NMR, FT-IR, elemental analysis, and ESI-MS. The physicochemical properties of the geminis were explored by tensiometry, fluorescence, dye solubilization, and Krafft point. These geminis acquire superior surface activity than the conventional surfactants. Fluorescence spectroscopy analysis affirmed that the micropolarity and aggregation number of micelles diminished with increase in the alkyl chain length. These geminis represent a new group of amphiphiles of considerably high biodegradability, better cleavability, and low toxicity as assessed by BOD test, FT-IR analysis, and HC50 analysis, respectively. They also showed significant level of antimicrobial activity toward some specified bacterial strains of Gram-positive and Gram-negative by using agar well diffusion method. Furthermore, the thermogravimetric analysis provided information regarding thermal stabilities of the newly synthesized gemini surfactants. 相似文献
8.
The thermal degradation of cellulose and its phosphorylated products (phosphates, diethylphosphate, and diphenylphosphate) were studied in air and nitrogen by differential thermal analysis and dynamic thermogravimetry from ambient temperature to 750°C. From the resulting data various thermodynamic parameters were obtained following the methods of Broido and Freeman and Carroll. The values of Ea for decomposition for phosphorylated cellulose were found to be in the range 55–138 kJ mol?1 in air and 85–152 kJ mol?1 in nitrogen and depended upon the percent of phosphorus contents in the samples. The mass spectrum of cellobiose phosphate indicated the absence of the molecular ion, indicating that the compound was thermally unstable. The IR spectra of the pyrolysis residues of cellulose phosphate gave indication of formation of a compound having C?O and P?O groups. A fire retardancy mechanism for the thermal degradation of cellulose phosphate has been proposed. 相似文献
9.
Huifen Nie Minghai Li Rama Bansil estmír Kok Martin Helmstedt Jyotsana Lal 《Polymer》2004,45(26):8791-8799
We have examined solutions of a polystyrene-polybutadiene pentablock copolymer in n-heptane, a strongly selective solvent for polybutadiene. Small angle neutron scattering from 7 to 15% samples reveals domains about 10 nm in radius formed by the association of 200 polystyrene blocks. Dynamic light scattering measurements on 8 and 9% samples showed three modes: a fast diffusive mode related to the collective diffusion in semidilute solutions/gels; a relaxational mode related to the local dynamics of polystyrene domains trapped in the gel formed by bridging the domains with the polybutadiene chains; and a very slow diffusive mode. The relaxational dynamics persisted over the entire temperature range, becoming faster with increasing temperature, indicating a decreased microviscosity at higher temperatures. The slow dynamics seems to be connected with heterogeneities in the physical gel due to microsyneresis and almost disappeared above 50 °C. Macroscopic phase separation into two liquid phases was observed in a dilute solution of the un-associated copolymer, and into a liquid and gel phase at higher concentrations. The absence of flower-like micelles in dilute solutions and the macroscopic phase seperation suggest that the gels in the pentablock are formed by random association of multiplet domains and not by bridging of micellar domains. 相似文献
10.