全文获取类型
收费全文 | 3854篇 |
免费 | 66篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 161篇 |
综合类 | 4篇 |
化学工业 | 751篇 |
金属工艺 | 82篇 |
机械仪表 | 84篇 |
建筑科学 | 54篇 |
矿业工程 | 1篇 |
能源动力 | 144篇 |
轻工业 | 334篇 |
水利工程 | 9篇 |
石油天然气 | 16篇 |
无线电 | 403篇 |
一般工业技术 | 617篇 |
冶金工业 | 958篇 |
原子能技术 | 92篇 |
自动化技术 | 219篇 |
出版年
2023年 | 18篇 |
2022年 | 29篇 |
2021年 | 47篇 |
2020年 | 27篇 |
2019年 | 28篇 |
2018年 | 38篇 |
2017年 | 48篇 |
2016年 | 53篇 |
2015年 | 37篇 |
2014年 | 71篇 |
2013年 | 155篇 |
2012年 | 128篇 |
2011年 | 146篇 |
2010年 | 135篇 |
2009年 | 125篇 |
2008年 | 135篇 |
2007年 | 131篇 |
2006年 | 114篇 |
2005年 | 98篇 |
2004年 | 91篇 |
2003年 | 113篇 |
2002年 | 77篇 |
2001年 | 85篇 |
2000年 | 88篇 |
1999年 | 139篇 |
1998年 | 393篇 |
1997年 | 214篇 |
1996年 | 170篇 |
1995年 | 106篇 |
1994年 | 113篇 |
1993年 | 114篇 |
1992年 | 65篇 |
1991年 | 50篇 |
1990年 | 45篇 |
1989年 | 31篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 39篇 |
1984年 | 32篇 |
1983年 | 36篇 |
1982年 | 28篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 22篇 |
1978年 | 26篇 |
1977年 | 24篇 |
1976年 | 51篇 |
1975年 | 11篇 |
1972年 | 10篇 |
排序方式: 共有3929条查询结果,搜索用时 10 毫秒
141.
Hiromi Nabeshi Tomoaki Yoshikawa Akihiro Arimori Tokuyuki Yoshida Saeko Tochigi Toshiro Hirai Takanori Akase Kazuya Nagano Yasuhiro Abe Haruhiko Kamada Shin-ichi Tsunoda Norio Itoh Yasuo Yoshioka Yasuo Tsutsumi 《Nanoscale research letters》2011,6(1):1-6
In this study, complexes composed of poly-l-tyrosine (pLT) and single-walled carbon nanotubes (SWCNTs) were produced and the dispersibility of the pLT/SWCNT complexes in water by measuring the ζ potential of the complexes and the turbidity of the solution were investigated. It is found that the absolute value of the ζ potential of the pLT/SWCNT complexes is as high as that of SWCNTs modified with double-stranded DNA (dsDNA) and that the complexes remain stably dispersed in the water at least for two weeks. Thermogravimetry analysis (TGA) and visualization of the surface structures of pLT/SWCNT complexes using an atomic force microscope (AFM) were also carried out. 相似文献
142.
143.
Cristiane Aparecida da Silva Márcia Maria Favaro Inez Valéria Pagotto Yoshida Maria do Carmo Gonçalves 《应用聚合物科学杂志》2011,121(5):2559-2566
Highly branched alkoxysilane (HB) units were prepared in situ via a Michael‐type reaction between pentaerythrithol triacrylate and aminopropyltriethoxysilane. These units were used as an inorganic component for the modification of cellulose acetate (CA) films using the sol–gel process. The thermal and dynamic‐mechanical behaviors, the morphology, and the dimensional stability of the modified CA films were analyzed. The siloxane‐modified CA films showed thermal stability similar to pure CA, but the residue content at 900°C increased with the addition of HB units. The morphology of these films was characterized by siloxane nanodomains dispersed in the CA matrix, with good interfacial adhesion between the phases. Moreover, the CA/siloxane nanocomposite films showed improved dimensional stability in comparison with CA, i.e., in the presence of HB, the dimensional change was reduced to around 50% of the value observed for pure CA. Finally, a complex dynamic‐mechanical behavior was obtained for the nanocomposite films, as a consequence of the heterogeneous morphology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
144.
Yasunori Yoshida Takashi Nakano Hidetsugu Tanaka Terunori Fujita 《Israel journal of chemistry》2002,42(4):353-359
This contribution reports the catalytic behavior of bis(pyrrolide-imine)Ti complexes 1 and 2 , [2-(RNCH)-C4H3N]2TiCl2 ( 1 , R = Ph; 2 , R = cyclohexyl), and bis(phenoxy-imine)Ti complex 3 , [2-(Ph-NCH)-3-t Bu-C6H3O]2TiCl2 for the copolymerization of ethylene with propylene, 1-hexene, or norbornene. An inspection of the X-ray structures of complexes 1–3 suggested that complexes 1 and 2 with pyrrolide-imine ligands would provide more space for olefin polymerization than complex 3 with phenoxy-imine ligands. In addition, DFT calculations also showed that active species derived from complexes 1 and 2 possess higher electrophilicity of the Ti center compared to that from complex 3 . Complexes 1 and 2 on activation with methylalumoxane (MAO) had higher affinity for propylene and 1-hexene and incorporated higher amounts of propylene ( 1 ; 30.5 mol%, 2 ; 23.4 mol%) and 1-hexene ( 1 ; 1.9 mol%, 2 ; 1.7 mol%) than complex 3 (propylene; 4.5 mol%, 1-hexene; 0.4 mol%). The incorporation levels of propylene and 1-hexene displayed by complexes 1 and 2 were lower than those for Cp2TiCl2 (propylene; 41.6 mol%, 1-hexene; 5.1 mol%) under identical conditions. In contrast, complexes 1 and 2 exhibited higher incorporation ability for norbornene and produced copolymers with much higher norbornene contents ( 1 ; 32.0 mol%, 2 ; 26.5 mol%) than Cp2TiCl2 (1.2 mol%) under the same conditions. Additionally, complex 3 also promoted higher norbornene incorporation (4.3 mol%) than Cp2TiCl2 and provided a copolymer with extremely narrow molecular weight distribution (Mw/Mn 1.14). A correlation exists between electrophilicity of the Ti center in active species and norbornene incorporation. 相似文献
145.
Hiromi Yoshida Yuki Hirakawa Sayaka Abe Yoshiyuki Mizushina 《European Journal of Lipid Science and Technology》2002,104(2):116-122
Sunflower seeds ((Helianthus annuus were roasted for 6, 12, 20 or 30 min at a frequency of 2450 MHz using a domestic microwave oven. After the kernels were separated from the sunflower seeds, the quality characteristics and the compositions of the oils were investigated in relation to their tocopherol distributions, and they were further evaluated as compared with an unroasted oil sample. Only minor increases (p < 0.05) in chemical and physical changes of the oils, such as the carbonyl value, the p‐anisidine value and the color development, occurred at a prolonged roasting period. Significant decrease (p < 0.05) was observed in the amounts of phospholipids in the oils after microwave roasting. Nevertheless, compared to the original level, more than 92 wt‐% tocopherols still remained after 30 min of roasting. With a few exceptions, these results indicate that the exposure of sunflower seeds to microwaves for 12 min caused no significant (p < 0.05) loss or change in the content of tocopherols and polyunsaturated fatty acids in the kernels. 相似文献
146.
Mikio Inoue Yuki Bisaiji Kohei Yoshida Nobuyuki Takagi Takao Fukuma 《Topics in Catalysis》2013,56(1-8):3-6
The detailed reaction mechanism of Di-Air, which showed the unprecedented high deNOx performance at high temperature conditions, was studied in this work. Since the Di-Air phenomenon occurs with continuous short pulse injections of hydrocarbons over NSR (NOx storage and reduction) catalyst, this study focused on the specific function of HC as an effective reductant for NOx reduction reaction. As a first step, the deNOx performance was compared with three different reductant gases including CO, H2 and C3H6 in a modified synthetic gas bench equipped with a gas injector which enables continuous small amount of injections. At inlet gas temperature of 450 °C C3H6 showed the best deNOx performance whereas H2 was the best at 150 °C. Moreover the result of temperature programmed desorption showed that intermediate species represented by –NCO (isocyanates) produced from C3H6 was thermally more stable than that produced from CO. These results confirmed that the injected HC reacts with adsorbed NOx on NSR catalyst generating thermally stable intermediates, which could contribute the high deNOx performance at high temperature conditions. 相似文献
147.
Male Sprague-Dawley rats were fed a cholesterol-free (Exp. 1) or cholesterol-supplemented (Exp. 2) diet containing 20% casein
(control group) or 15% defatted squid and 5% casein (defatted squid group), as protein, for 14 d. Serum and hepatic cholesterol
concentrations were lower in rats fed defatted squid than in those fed casein in both cholesterol-free (−20%, P<0.05 and −15%, P<0.05, respectively) and cholesterol-supplemented (−25%, P<0.05 and −15%, P<0.05, respectively) diets. Hepatic triglyceride concentration was lower in the defatted squid than in the control groups
in both cholesterol-free (−51%, P<0.05) and cholesterol-supplemented diets (−38%, P<0.01). The activities of cytosolic fatty acid synthase and the NADPH-generating enzymes, malic enzyme and glucose-6-phosphate
dehydrogenase, in the liver were lower in the defatted squid than in the control groups in both cholesterol-free (−21%, P<0.01, −33%, P<0.05, and −33%, P<0.01, respectively) and cholesterol-supplemented diets (−34%, P<0.05, −57%, P<0.05, and −67%, P<0.05, respectively). The activity of mitochondrial carnitine palmitoyltransferase in the liver was comparable between the
control and defatted squid groups. The activity of Mg2+-dependent phosphatidate phosphohydrolase in the liver cytosol was lower in the defatted squid (−9%, P<0.05) than in the control groups only in the cholesterol-free diet. Fecal excretion of total steroids was stimulated by the
feeding of defatted squid in both cholesterol-free (+77%, P<0.005) and cholesterol-supplemented diets (+29%, P<0.01). These results suggest that the nonlipid fraction of squid exerts a hypocholesterolemic effect by increasing the excretion
of total steroids in feces. The fraction also induces a triglyceride-lowering activity in the liver by decreasing hepatic
lipogenesis. 相似文献
148.
Yoko Watanabe Masaharu Nakajima Tsutomu Hoshino Koda Jayasimhulu Elwood E. Brooks Edna S. Kaneshiro 《Lipids》2001,36(5):513-519
Members of the bacterial genus Bdellovibrio include strains that are free-living whereas others are known to invade and parasitize larger Gram-negative bacteria. The bacterium can synthesize several sphingophospholipid compounds including those with phosphoryl bonds as well as phosphonyl bonds. In the present study, the dominant sphingophosphonolipid component was isolated by column chromatography, and the long-chain bases, fatty acids, and polar head groups were identified by thin-layer and gas-liquid chromatographic procedures. The definitive structural identity of the sphingolipid was established by nuclear magnetic resonance and mass spectrometry of hydrolysis products and the intact compound. The compound was identified as N-2′-hydroxypentadecanoyl-2-amino-3,4-dihydroxyheptadecan-1-phosphono-(1-hydroxy-2-aminoethane). 相似文献
149.
Keisuke Yoshida Kenji Mishiro Yoshihiro Ueda Takashi Shigeta Takumi Furuta Takeo Kawabata 《Advanced Synthesis \u0026amp; Catalysis》2012,354(17):3291-3298
A highly geometry‐selective organocatalytic acylation of tri‐ and tetra‐substituted 2‐alkylidene‐1,3‐propanediols has been developed. The highly E‐selective acylation of various tetrasubstituted 2‐alkylidene‐1,3‐propanediols was achieved in 96 to >99% selectivity for the first time by a non‐enzymatic protocol. 相似文献
150.
Tomoya Nagira Hideyuki Yasuda Takumi Sakimura Kentarou Yoshida 《Journal of the European Ceramic Society》2012,32(10):2137-2143
It has been reported that solidification of the Al2O3–YAG equilibrium eutectic structure follows melting of the Al2O3–YAP metastable eutectic structure. Since the exothermic heat due to solidification was consumed by the endothermic heat due to melting, a fine and uniform eutectic structure was obtained. However, the composition of the Al2O3–YAG eutectic structure is restricted to the metastable eutectic composition. In this paper, Al2O3–YAG eutectic compacts with an off-metastable eutectic composition were prepared by the addition of Al2O3 particles to Al2O3–YAP eutectic particles with diameters less than 20 μm. In compositions ranging from 18.5 mol%Y2O3 to 13.5 mol%Y2O3, dense Al2O3–YAG eutectic compacts were formed without any Al2O3 segregation. The flexural strength and the fracture toughness remained almost unchanged with the increase in the Al2O3 phase. The addition of Al2O3 particles to the Al2O3–YAP eutectic particles enabled the matrix phase to change from the YAG phase to the Al2O3 phase. 相似文献