全文获取类型
收费全文 | 61450篇 |
免费 | 5009篇 |
国内免费 | 2689篇 |
学科分类
工业技术 | 69148篇 |
出版年
2024年 | 101篇 |
2023年 | 963篇 |
2022年 | 1424篇 |
2021年 | 2354篇 |
2020年 | 1825篇 |
2019年 | 1633篇 |
2018年 | 1864篇 |
2017年 | 2051篇 |
2016年 | 1831篇 |
2015年 | 2377篇 |
2014年 | 3027篇 |
2013年 | 3484篇 |
2012年 | 3692篇 |
2011年 | 4065篇 |
2010年 | 3722篇 |
2009年 | 3344篇 |
2008年 | 3300篇 |
2007年 | 3246篇 |
2006年 | 3207篇 |
2005年 | 2789篇 |
2004年 | 2054篇 |
2003年 | 2163篇 |
2002年 | 2490篇 |
2001年 | 2086篇 |
2000年 | 1597篇 |
1999年 | 1680篇 |
1998年 | 1234篇 |
1997年 | 1053篇 |
1996年 | 1094篇 |
1995年 | 841篇 |
1994年 | 627篇 |
1993年 | 467篇 |
1992年 | 362篇 |
1991年 | 271篇 |
1990年 | 203篇 |
1989年 | 165篇 |
1988年 | 151篇 |
1987年 | 86篇 |
1986年 | 69篇 |
1985年 | 37篇 |
1984年 | 30篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Qinghua Zhang Sandong Guo Binghui Ge Peng Chen Yuan Yao Lijuan Wang Lin Gu Yanguo Wang Xiaofeng Duan Changqing Jin Banggui Liu Richeng Yu 《Journal of the American Ceramic Society》2014,97(4):1264-1268
Manganese oxides are good candidates of strongly correlated electron materials due to the uniqueness of electronic structure of manganese and the mobility of oxygen among lattice sites under external impacts. Here, we used electron beam as the excitation source to explore the structural evolution of YMnO3 and identified a new phase under the radiation of electron beam in the transmission electron microscope. Analyses of the electron energy‐loss spectra reveal that this phase originates from ordered oxygen vacancy. We applied the first principles calculation to pick out the optimized stable structure with a lower polarization, and verified its correctness by electron diffraction and image simulations. Analyses of density of states indicate that weak Y–O covalence is favorable for the existence of ferroelectricity, supporting the electrostatic nature of ferroelectricity in the YMnO3. 相似文献
992.
Jin‐Feng Wang Zheng Li Xi‐Jun Xu Zheng‐Bin Gu Guo‐Liang Yuan Shan‐Tao Zhang 《Journal of the American Ceramic Society》2014,97(4):1137-1142
Sr2FeMoO6 ceramics with different Fe/Mo antisite defect (ASD) concentrations and grain‐boundary (GB) properties were prepared. The competitive and combining effects of GB and Fe/Mo ASD on the transport and magnetoresistance were discussed. The GB properties, that is, intergrain coupling strength, positively related with resistivity value, is extremely sensitive to the total flux of reducing gas, in general, lower total gas flux leads to larger resistivity, thus stronger intergrain coupling strength, and then the contributions of GB effect to low‐field magnetoresistance (LFMR) increase appreciably regardless of the amount of ASD. In detail, when ASD concentration is less than 26%, LFMR is dominantly controlled by the GB effect. However, the suppressed ASD effect on LFMR behavior comes to play when the ASD content is larger than or equal to 26%, where the GB and ASD effects contribute together to the LFMR. 相似文献
993.
Xiaoqiang Zou Jianhua Huang Qingzhe Jin Zheng Guo Lingzhi Cheong Xuebing Xu Xingguo Wang 《Journal of the American Oil Chemists' Society》2014,91(12):1987-1998
Human milk fat substitutes (HMFSs) with triacylglycerol profiles highly similar to those of human milk fat (HMF) were prepared from lard by physical blending followed by enzymatic interesterification. Based on the fatty acid profiles of HMF, different vegetable and single‐cell oils were selected and added to the lard. Blend ratios were calculated based on established physical blending models. The blended oils were then enzymatically interesterified using a 1,3‐regiospecific lipase, Lipozyme RM IM (RML from Rhizomucor miehei immobilized on Duolite ES562; Novozymes A/S, Bagsværd, Denmark), to approximate HMF triacylglycerol (TAG) profiles, particularly with respect to the distribution of palmitic acid in the sn?2 position. The optimized blending ratios were determined to be: lard:sunflower oil:canola oil:palm kernel oil:palm oil:algal oil:microbial oil = 1.00:0.10:0.50:0.13:0.12:0.02:0.02. The optimized reaction conditions were determined to be: enzyme load of 11 wt%, temperature of 60 °C, water content of 3.5 wt%, and reaction time of 3 hours. The resulting product was evaluated for total and sn?2 fatty acids, polyunsaturated fatty acids, and TAG composition. A high degree of similarity was obtained, indicating the great potential of the product as a fat alternative for use in infant formulas. 相似文献
994.
Silicon oxycarbide (SiOC) fibers with different chemical compositions were successfully fabricated by electrospinning a mixture of polyvinylpyrrolidone (PVP) and commercially available polymethylsilsesquioxane (MK) or polymethylphenylsilsesquioxane (H44) preceramic polymers, followed by cross‐linking and pyrolysis at 1000°C in Argon. The influence of the processing procedure (solvent selection, cross‐linking catalyst and additives) on the morphology of the produced fibers was investigated. For the MK/isopropanol system, the introduction of 20 vol% N,N‐dimethylformamide (DMF) enabled to decrease the diameter of the as‐spun fibers from 2.72 ± 0.12 μm to 1.65 ± 0.09 μm. For the H44/DMF systems, beads‐free fibers were obtained by adding 50 vol% choloroform. After pyrolysis, the resultant SiOC fibers derived from MK and H44 resins possessed uniform morphology, with an average diameter of 0.97 ± 0.07 μm and 1.07 ± 0.08 μm, respectively. Due to their different chemical compositions, the MK‐derived and H44‐derived SiOC ceramic fibers could find different potential applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39836. 相似文献
995.
Structure and mechanical properties of crosslinked glycidyl azide polymers via click chemistry as potential binder of solid propellant 下载免费PDF全文
Depending upon the advantages of high efficiency, insensitivity to humidity and so on, the reaction of azide groups in glycidyl azide polymers (GAP) with alkynyl compounds has been used as a substitute of the urethane curing strategy to develop GAP‐based binder for solid propellant. In this work, an alkynyl compound of dimethyl 2,2‐di(prop‐2‐ynyl)malonate (DDPM) reacted with GAP to produce new crosslinked materials under the catalysis of Cu(I)Cl at ambient temperature, and showed great potential as a binder in composite propellant. As the feeding molar ratio of DDPM vs. GAP increased from 1 : 1 to 5 : 1, the crosslinking densities of as‐prepared materials gradually increased, together with simultaneous enhancement of Young's modulus and tensile strength. The breaking elongation showed the maximum value of ca. 82% when the feeding molar ratio of DDPM vs. GAP was 3 : 1. In addition, with an increase of the crosslinking densities, the glass transition temperatures of as‐prepared materials significantly increased from ?43.9°C to ?5.1°C while the mechanical loss peaks also gradually broadened and shifted up to high temperature, and even presented two peaks at the feeding molar ratio of DDPM vs. GAP higher than 4 : 1. It indicated that the formation of triazole‐based network resulted in structural heterogeneity in the as‐prepared materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40636. 相似文献
996.
Char barrier effect of graphene nanoplatelets on the flame retardancy and thermal stability of high‐density polyethylene flame‐retarded by brominated polystyrene 下载免费PDF全文
Graphene nanoplatelets (GNPs) with the char barrier effect were combined with brominated polystyrene (BPS) and antimony trioxide (Sb2O3) to improve the flame retardancy and thermal stability of high‐density polyethylene. Thermogravimetric analysis, limited oxygen index (LOI) testing, and vertical burning testing (UL‐94) showed that the presence of GNPs led to enhanced thermal oxidation stability and significantly reduced the flammability. The addition of 1 wt % GNPs to polyethylene/BPS–Sb (mass ratio = 92/6/2) led to UL‐94 grades from NG (first burning time > 30 s) to V‐2 (total burning time = 14 s), and the LOI value increased from 23.4 to 24.1%. The results of the pyrolysis products provided evidence that the GNPs restricted volatilization. The morphology of the chars also proved the formation of the char layer, which could act as a barrier to isolate the material from the flame and retard the vaporization of flammable gases via a tortuous pathway. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40520. 相似文献
997.
Dan Wang Zhongling Zhao Lina Yu Kejin Zhang Hui Na Shanqiang Ying Dechao Xu Guo Zhang 《应用聚合物科学杂志》2014,131(15)
The modified polypropylene (PP) separators with self‐polymerization of dopamine on the surfaces are prepared by a simple solution‐immersion method to improve the interfacial hydrophilic and discharge performance. The contact angle test and the liquid electrolyte uptake capacity test results show that the wettability and the electrolyte‐retention ability of polydopamine‐modified separator are improved significantly. The robust and thin polydopamine layer on the surface also enhances thermal performance and tensile strength of the modified PP separator certified by DSC and tensile strength tests. The ionic conductivity of the modified PP separator is up to 3.08 mS·cm?1, ~2.5 times of the bare separator. Good discharge capacity retention and C‐rate discharge performance are demonstrated by a 2025 coin half‐cell with the liquid electrolyte‐soaked polydopamine modified PP separator sandwiched between lithium metal anode and LiFePO4 cathode. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40543. 相似文献
998.
In this contribution, random copolymers of p(styrene‐co‐acrylonitrile) via initiators for continuous activator regeneration (ICAR) in atom transfer radical polymerization (ATRP) (ICAR ATRP) of styrene and acrylonitrile (SAN) were synthesized at 90°C in low molecular weight polyethylene glycol (PEG‐400) using CCl4 as initiator, FeCl3·6H2O as catalyst, succinic acid as ligand and thermal radical initiator azobisisobutyronitrile (AIBN) as thermal free radical initiator. In this system, well‐defined copolymer of SAN was achieved. The kinetics results showed that the copolymerization rate obeyed first‐order kinetics model with respect to the monomer concentration, and a linear increase of the molecular weights with the increasing of monomer conversion with narrow molecular weight distribution was observed in the range of 1.1–1.5. The conversion decreased with increasing the amount of FeCl3·6H2O and increased with increasing the molar ratio of [St]0/[AN]0/[CCl4]0 and temperature. AIBN has a profound effect on the polymerization. The activation energy was 55.67 kJ mol?1. The living character of copolymerization was confirmed by chain extension experiment. The resultant random copolymer was characterized by 1H‐NMR and GPC. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40135. 相似文献
999.
Silicones are widely used for electrical insulation owing to their high dielectric strength and thermal stability. However, recent studies revealed insufficient stability of silicone for high‐temperature applications. To study the effect of Al2O3 fiber on silicone stability, we measured the dielectric strength of unfilled silicone and Al2O3/silicone composites as a function of aging time at 250°C in air and analyzed data by Weibull probability distribution to determine characteristic dielectric strength (E0) and shape parameter (β). Prior to aging, unfilled silicone and composites had similar behavior, with E0 at about 20 kV/mm and β > 15. During aging, unfilled silicone developed both micro‐ and macrocracks, with β dropped below five in 240 h and E0 decreased significantly. Composites developed microcracks, with β dropped below 5 in longer time and E0 remained almost constant. Addition of Al2O3 slowed down crack growth in silicone matrix, resulting in longer lasting high‐temperature dielectric materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41170. 相似文献
1000.