全文获取类型
收费全文 | 5104篇 |
免费 | 654篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 79篇 |
综合类 | 2篇 |
化学工业 | 1523篇 |
金属工艺 | 153篇 |
机械仪表 | 287篇 |
建筑科学 | 52篇 |
能源动力 | 297篇 |
轻工业 | 597篇 |
水利工程 | 10篇 |
石油天然气 | 3篇 |
无线电 | 842篇 |
一般工业技术 | 1284篇 |
冶金工业 | 161篇 |
原子能技术 | 75篇 |
自动化技术 | 402篇 |
出版年
2024年 | 2篇 |
2023年 | 63篇 |
2022年 | 97篇 |
2021年 | 182篇 |
2020年 | 140篇 |
2019年 | 208篇 |
2018年 | 208篇 |
2017年 | 227篇 |
2016年 | 301篇 |
2015年 | 238篇 |
2014年 | 332篇 |
2013年 | 391篇 |
2012年 | 414篇 |
2011年 | 497篇 |
2010年 | 335篇 |
2009年 | 322篇 |
2008年 | 253篇 |
2007年 | 233篇 |
2006年 | 192篇 |
2005年 | 139篇 |
2004年 | 147篇 |
2003年 | 126篇 |
2002年 | 118篇 |
2001年 | 116篇 |
2000年 | 103篇 |
1999年 | 86篇 |
1998年 | 78篇 |
1997年 | 39篇 |
1996年 | 35篇 |
1995年 | 31篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 16篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有5767条查询结果,搜索用时 15 毫秒
991.
In this work, the performance of a hydrogen generation system with an electroless-deposited Co–P/Ni foam catalyst for NaBH4 hydrolysis was evaluated. The performance of a hydrogen generator using a combination of Co/γ-Al2O3 and Co–P/Ni foam catalysts was also evaluated in order to address the shortcomings with the individual catalysts. The generator had high conversion efficiency, fast response characteristics, and strong catalyst durability. Hydrogen generation tests were performed to investigate the effect of the composition of the NaBH4 solution on the hydrogen generation properties. The generator's conversion efficiency decreased with an increase in the amount of solute dissolved in NaBH4 solution because of the accumulation of precipitates on the catalyst, and NaOH concentration had a greater effect on the hydrogen generation properties than did NaBH4 concentration. According to these results, the hydrogen generation system with the Co–P/Ni foam catalyst is suitable as a hydrogen supplier for proton exchange membrane fuel cells owing to the strong durability and inexpensive cost of the catalyst. 相似文献
992.
N. Nambi Krishnan Dirk Henkensmeier Jong Hyun Jang Hyoung-Juhn Kim Heung Yong Ha Suk Woo Nam 《International Journal of Hydrogen Energy》2013
A new alkyl chain modified sulfonated poly(ether sulfone) (mPES) was synthesized and formed into membranes. The MEAs were tested in the PEMFC and evaluated systematically in the DMFC by varying the methanol concentration from 0.5 to 5.0 M at 60 °C and 70 °C. The synthesized mPES copolymer has been characterized by nuclear magnetic resonance spectroscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. The proton conductivity of the resulting membrane is higher than the threshold value of 10−2 S cm−1 at room temperature for practical PEM fuel cells. The membrane is insoluble in boiling water, thermally stable until 250 °C and shows low methanol permeability. In the H2/air PEMFC at 70 °C, a current density of 600 mA cm−2 leads to a potential of 637 mV and 658 mV for 50 μm thick mPES 60 and Nafion NRE 212, respectively. In the DMFC, mPES 60's methanol crossover current density is 4 times lower than that for Nafion NRE 212, leading to higher OCV values and peak power densities. Among all investigated conditions and materials, the highest peak power density of 120 mW cm−2 was obtained with an mPES 60 based MEA at 70 °C and a methanol feed of 2 M. 相似文献
993.
Hyun Sik Yoon Jae Hwan Jung Yong Gap Park 《Numerical Heat Transfer, Part A: Applications》2013,63(9):701-721
This study investigates natural convection in a cooled square enclosure with two inner heated circular cylinders with the same diameter. The centers of two equidiameter cylinders are placed at those of the lower and upper half of the enclosure, respectively. The immersed boundary method (IBM) to model the inner circular cylinders based on the finite volume method is used to study a two-dimensional natural convection for different Rayleigh numbers varying in the range of 103 ≤ Ra ≤ 105. The effect of the radius of inner circular cylinders in an enclosure on heat transfer and fluid flow at different Rayleigh numbers has been examined. As the Rayleigh number increases, the horizontal symmetry is broken and the asymmetry occurred from the smaller radius. As the radius decreases, the dependence of the convection on the Rayleigh number is considerable. The dependence of the Nusselt number on the radius and the Rayleigh number is presented. 相似文献
994.
Dong Woo Suh Joo Hyun Ryu Min Sung Joo Hong Seok Yang Kyooyoung Lee H. K. D. H. Bhadeshia 《Metallurgical and Materials Transactions A》2013,44(1):286-293
The manganese concentration of steels which rely on transformation-induced plasticity is generally less than 2 wt pct. Recent work has highlighted the potential for strong and ductile alloys containing some 6 wt pct of manganese, but with aluminum additions in order to permit heat treatments which are amenable to rapid production. However, large concentrations of aluminum also cause difficulties during continuous casting. Alloy design calculations have been carried out in an effort to balance these conflicting requirements, while maintaining the amount of retained austenite and transformation kinetics. The results indicate that it is possible by adjusting the carbon and manganese concentrations to reduce the aluminum concentration, without compromising the mechanical properties or transformation kinetics. The deformation-induced transformation of retained austenite is explained quantitatively, for a range of alloys, in terms of a driving force which takes into account the very fine state of the retained austenite. 相似文献
995.
Jung Ho Heo Byung-Su Kim Joo Hyun Park 《Metallurgical and Materials Transactions B》2013,44(6):1352-1363
We investigated the effect of flux (lime) addition on the reduction behavior of iron oxide in copper slag by solid carbon at 1773 K (1500 °C). In particular, we quantified the recovery of iron by performing typical kinetic analysis and considering slag foaming, which is strongly affected by the thermophysical properties of slags. The iron oxide in the copper slag was consistently reduced by solid carbon over time. In the kinetic analysis, we determined mass transfer coefficients with and without considering slag foaming using a gas holdup factor. The mass transfer of FeO was not significantly changed by CaO addition when slag foaming was ignored, whereas the mass transfer of FeO when slag foaming was considered was at a minimum in the 20 mass pct CaO system. Iron recovery, defined as the ratio of the amount of iron clearly transferred to the base metal ingot to the initial amount of iron in the slag phase before reduction, was maximal (about 90 pct) in the 20 mass pct CaO system. Various types of solid compounds, including Mg2SiO4 and Ca2SiO4, were precipitated in slags during the FeO reduction process, and these compounds strongly affected the reduction kinetics of FeO as well as iron recovery. Iron recovery was the greatest in the 20 mass pct CaO system because no solid compounds formed in this system, resulting in a highly fluid slag. This fluid slag allowed iron droplets to fall rapidly with high terminal velocity to the bottom of the crucible. A linear relationship between the mass transfer coefficient of FeO considering slag foaming and foam stability was obtained, from which we concluded that the mass transfer of FeO in slag was effectively promoted not only by gas evolution due to reduction reactions but also by foamy slag containing solid compounds. However, the reduced iron droplets were finely dispersed in foamy and viscous slags, making actual iron recovery a challenge. 相似文献
996.
A series of allenic quinazolines were synthesized as receptor tyrosine kinase inhibitors by using a simple protocol for palladium-catalyzed allene transformation. Among the compounds synthesized, two allenic 4-anilinoquinazolines selectively suppressed epidermal growth factor receptor (EGFR) tyrosine kinase activity in vitro. According to immunoblot analysis, the allenic quinazolines inhibited the EGF-mediated phosphorylation of EGFR and its downstream kinases in A431 cells. Furthermore, one of these allenic quinazolines decreased the proliferation of A431 cells through the induction of cell-cycle arrest and apoptosis. 相似文献
997.
Jae Song Cho Byung Soo Kim Hoon Hyun Moon Suk Kim Jae Hoon Ko Gilson Khang 《Polymer》2008,49(7):1777-1782
The polymerization of trimethylene carbonate (TMC) in the presence of HCl·Et2O via activated monomer mechanism was performed to synthesize 4a-PEG-b-PTMC star block copolymers composed of poly(ethylene glycol) (PEG) and poly(trimethylene carbonate) (PTMC) using four-arm (4a) PEG as an initiator. The TMC conversion and molecular weight of PTMC increased linearly with the polymerization time or the feed ratios of the TMC to 4a-PEG in the presence of HCl·Et2O in CH2Cl2 at 25 °C. The obtained PTMC had molecular weights close to the theoretical value calculated from TMC to PEG molar ratio and exhibited monomodal GPC curve. We prepared successfully 4a-PEG-b-PTMC star block copolymers without metal catalyst at room temperature via living ring-opening polymerization (ROP) of TMC from 4a-PEG as an initiator in the presence of HCl·Et2O as a monomer activator. The CMCs of the 4a-PEG-b-PTMC star block copolymers determined from fluorescence measurements. The CMCs of the 4a-PEG-b-PTMC star block copolymers decreased in the order of the increase in the PTMC segment. The partition equilibrium constant, Kv, which is an indicator of the hydrophobicity of the micelles of the 4a-PEG-b-PTMC star block copolymers in aqueous media, increased with the increase in the PTMC segment. In conclusion, we confirmed that the 4a-PEG-b-PTMC star block copolymers form micelles and hence may be potential hydrophobic-drug delivery vehicles. 相似文献
998.
Sung Ho Ha Sang Hyun Lee Dung Thanh Dang Min Sik Kwon Woo-Jin Chang Yong Jae Yu Il Suk Byun Yoon-Mo Koo 《Korean Journal of Chemical Engineering》2008,25(2):291-294
The activity and stability of lipase from Candida antarctica were investigated in the kinetic resolution of (R,S)-1-phenylethanol with vinyl acetate using ionic liquids (ILs) as reaction media. Among ILs tested, the highest activity of
lipase was observed in [Edmim][Tf2N]. In hydrophobic ILs such as [Edmim][Tf2N], [Emim][Tf2N] and [Pmim] [PF6], lipase could retain its activity after 5 times reuse, while the activity of lipase in hydrophilic ILs and organic solvents
was drastically decreased. The activities of lipase in [Edmim][Tf2N], [Emim][Tf2N] and [Pmim][PF6] were also well maintained after 1 day incubation at 80 °C. The lipase suspended in [Edmim][Tf2N] could be successfully reused 6 times without loss of activity. 相似文献
999.
Min-Soo Hyun Sang-Kyung Kim Byungrock Lee Donghyun Peck Yonggun Shul Doohwan Jung 《Catalysis Today》2008,132(1-4):138-145
PtRu/C catalysts were prepared using an aqueous co-impregnation method with NaBH4 as a reducing agent. In order to investigate the effect of the reducing agent concentration, metal ions were reduced in different NaBH4 concentrations for which the molar ratios of NaBH4 to metal ions were controlled to 1, 2, 5, 15, 50, and 250. The electrochemical properties were studied by cyclic voltammetry in a 0.5 M H2SO4 solution. The surface compositions and oxidation states of the catalysts were observed by X-ray photoelectron spectroscopy (XPS). According to the X-ray diffraction (XRD) results, Pt (fcc) peak shifts were observed and crystal sizes were calculated. The electro-catalytic activities of the prepared catalysts for methanol electro-oxidation were estimated using linear sweep voltammetry. Unit cell tests were carried out to compare the direct methanol fuel cell performances. The NaBH4 concentration was found to affect the dispersion and the surface composition of the prepared PtRu particles. Optimum molar ratios of NaBH4 to metal ions were 5 and 15 for methanol electro-oxidation. 相似文献
1000.
In this study, the chemical composition and anti-inflammatory activities of hydrodistilled essential oil from Farfugium japonicum were investigated for the first time. The chemical constituents of the essential oil were further analyzed by GC-MS and included 1-undecene (22.43%), 1-nonene (19.83%), beta-caryophyllene (12.26%), alpha-copaene (3.70%), gamma-curcumene (2.86%), germacrene D (2.69%), and 1-decene (2.08%). The effects of the essential oil on nitric oxide (NO) and prostaglandin E2 (PGE(2)) production in lipopolysaccharide (LPS)-activated RAW 264.7 macrophages were also examined. The results indicate that the F. japonicum essential oil is an effective inhibitor of LPS-induced NO and PGE(2) production in RAW 264.7 cells. These inhibitory effects of the F. japonicum essential oil were accompanied by dose-dependent decreases in the iNOS and COX-2 mRNA expression. In order to determine whether F. japonicum essential oil can safely be applied to human skin, the cytotoxic effects of F. japonicum essential oil were determined by colorimetric MTT assays in human dermal fibroblast and keratinocyte HaCaT cells. F. japonicum essential oil exhibited low cytotoxicity at 100 mug/mL. Based on these results, we suggest that F. japonicum essential oil may be considered a potential anti-inflammatory candidate for topical application. 相似文献