全文获取类型
收费全文 | 1852篇 |
免费 | 25篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 128篇 |
综合类 | 1篇 |
化学工业 | 410篇 |
金属工艺 | 50篇 |
机械仪表 | 35篇 |
建筑科学 | 50篇 |
能源动力 | 53篇 |
轻工业 | 131篇 |
水利工程 | 2篇 |
石油天然气 | 4篇 |
无线电 | 170篇 |
一般工业技术 | 268篇 |
冶金工业 | 398篇 |
原子能技术 | 45篇 |
自动化技术 | 135篇 |
出版年
2022年 | 19篇 |
2021年 | 28篇 |
2020年 | 15篇 |
2019年 | 14篇 |
2017年 | 21篇 |
2016年 | 20篇 |
2015年 | 18篇 |
2014年 | 37篇 |
2013年 | 77篇 |
2012年 | 62篇 |
2011年 | 81篇 |
2010年 | 58篇 |
2009年 | 57篇 |
2008年 | 74篇 |
2007年 | 71篇 |
2006年 | 56篇 |
2005年 | 50篇 |
2004年 | 49篇 |
2003年 | 59篇 |
2002年 | 41篇 |
2001年 | 33篇 |
2000年 | 30篇 |
1999年 | 48篇 |
1998年 | 158篇 |
1997年 | 101篇 |
1996年 | 65篇 |
1995年 | 49篇 |
1994年 | 51篇 |
1993年 | 43篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 14篇 |
1989年 | 25篇 |
1988年 | 20篇 |
1987年 | 10篇 |
1986年 | 27篇 |
1985年 | 28篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1979年 | 24篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 24篇 |
1975年 | 10篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有1880条查询结果,搜索用时 15 毫秒
31.
The influence of the cis/trans ratio of 1,4-polybutadienes on the volatile products formed during temperature-programmed thermal degradation to 15% weight loss has been investigated using a mass chromatograph (a gas chromatograph which directly provides mass numbers of resolved components of a mixture) and an “on the fly” vapor-phase infrared spectrophotometer. In order of amounts, major volatile products were 4-vinyl-1-cyclohexene (dimer), 1,3-butadiene (monomer), cyclopentene, and 1,3-cyclohexadiene. With increasing trans content, the relative quantities of 4-vinyl-1-cyclohexene decreased strongly, cyclopentene increased strongly, 1,3-butadiene decreased moderately, and 1,3-cyclohexadiene increased moderately. For a high-trans polybutadiene, increasing the heating rate produced relatively more monomer and dimer but less cyclopentene. Mass chromatograms from 1,4-polybutadienes which had been heated to 15% weight loss in their prehistory were similar to those obtained from 1,2-polybutadiene, indicating that 1,4-polybutadiene undergoes isomerization prior to degradation. Mechanisms for the formation of the main volatile products of decomposition are discussed. 相似文献
32.
Imoto Taiji; Ueda Tadashi; Tamura Tomohiro; Isakari Yoshimasa; Abe Yoshito; Inoue Makoto; Miki Takeyoshi; Kawano Keiichi; Yamada Hidenori 《Protein engineering, design & selection : PEDS》1994,7(6):743-748
Mutations around His15 which lie far away from the active site,stimulated glycol chitin activity of lysozyme at physiologicaltemperature. Del-Argl4Hisl5 lysozyme, a mutant lysozyme whoseArgl4 and Hisl5 were deleted together, and has the highest activityamong these mutant lysozymes, had a similar binding abilityto a trimer of N-acetyl-glucosamine, a substrate analogue, relativeto native lysozyme. This suggests that the increased activitywas due to an increased kcat in the catalysis reaction. TheH-D exchange rate of the N-1 proton in the Trp63 which is locatedin the active site cleft, was enhanced in the Del-Argl4Hisl5lysozyme, while 2-D proton NMR analysis revealed no conformationalchange around Trp63. We conclude that some sort of fluctuationat the active site might be required for the manifestation ofactivity. This theory is supported by the finding that the Del-Argl4Hisl5lysozyme showed a shift in temperature dependency of activityto lower temperatures compared with that of native lysozyme. 相似文献
33.
Keiichi Tomishige Tomohisa Miyazawa Takeo Kimura Kimio Kunimori Naoto Koizumi Muneyoshi Yamada 《Applied catalysis. B, Environmental》2005,60(3-4):299-307
In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H2S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO2/SiO2 using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H2S. Steam reforming Ni catalyst was effective for the tar removal without H2S addition, however, the addition of H2S deactivated drastically. In contrast, Rh/CeO2/SiO2 exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H2S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO2/SiO2, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis. 相似文献
34.
Eighteen sterols were isolated from the aerial parts ofKalanchoe pinnata (Crassulaceae) including four novel sterols,viz. (24R)-stigmasta-5,25-dien-3β-ol (24-epiclerosterol), (24R)-5α-stigmasta-7,25-dien-3β-ol, 5α-stigmast-24-en-3β-ol, and 25-methyl-5α-ergost-24(28)-en-3β-ol. 24-Epiclerosterol and its
Δ7-analog occur together with their 24S/β-epimers in the same plant making this the first report of the isolation of both C-24 epimers of Δ25-unsaturated 24-alkylsterols from a non-marine organism. Iodine-catalyzed isomerization of stigmasta-5,24-dien-3β-ol (24-ethyldesmosterol),
the main sterol ofK. pinnata, yielded 24-epiclerosterol among other products. 相似文献
35.
Unique deterioration with a periodical striped pattern on the injection moldings of polypropylene/rubber blends is reported. After exposure to ultraviolet irradiation with a sunshine fade meter, striped patterns appeared on the injection moldings along the flow direction of the molten resin during the filling process of injection molding, even though the initial specimen showed no sign of any stripe pattern on its surface. The stripe was carefully observed with ultrasonic echo imaging, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. As a result, a number of microvoids were observed inside the injected body at a depth of 50–100 μm from the surface. It became clear that the difference in the number of voids along the flow direction formed the stripe pattern. Surprisingly, these voids occurred in domains comprising a rubber phase. The distribution of voids in depth indicated the existence of a trace of a snakelike flow caused inside the injected body during the injection‐molding process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
36.
T. Itoh K. Yoshida T. Yatsu T. Tamura T. Matsumoto G. F. Spencer 《Journal of the American Oil Chemists' Society》1981,58(4):545-550
Nine Spanish olive oils, including three each of virgin (pressed oil), refined virgin, and B-residue (solvent-extracted pomace
oil) oils from different commercial sources, have been analyzed for their unsaponifiable matter (USM). Four sterolic fractions
separated from the oils have been analyzed by preparative thin-layer chromatography (TLC); these fractions are triterpene
alcohols, 4-methylsterols, sterols and triterpene dialcohols. The compositions of the four sterolic fractions were determined
as their acetates by gas-liquid chromatography (GLC) on an OV-17 glass capillary column. Identification of each component
was carried out by argentation TLC, GLC and combined gas chromatography-mass spectrometry (GC-MS); 44 components were identified,
of which four: 24-methylene-31-nor-9(11)-lanostenol, 24-methyl-31-nor-E-23-dehydrocycloartanol, 24-ethyl-E-23-dehydrolophenol
and 5,E-23-stigmastadienol, were considered to be new sterols from natural sources. Several characteristics, including the
content of triteterpene dialcohols in the USM and that of C-24(28) unsaturated sterols in each of the four sterolic fractions,
which can be used to distinguish between virgin and B-residue olive oils, were observed. 相似文献
37.
Melt viscosity and flow birefringence of bisphenol A-type polycarbonate were measured and analyzed by the application of rubber-like photoelastic theory. The melt viscosity in the Newtonian flow region increased with the molecular weight to the power of 3.4. In polycarbonate, the shear stress of the Newtonian flow region was to 106 dyn/cm2, whereas in PMMA it was at most 3 = 105 dyn/cm2. The flow birefringence δn has a linear relation with shear stress S, that is δn = 5.7 × 10?10 S. The principal polarization difference of flow unit α1 – α2 was 1.62 × 10?23 cm3, which was obtained by the application of the rubber-like elastic theory. In PMMA, it was 3.9 = 10?25 cm3; about 1/40 of that was polycarbonate. The anisotropy of polarizability of the flow unit of polycarbonate was also about 40 times larger than that of PMMA. So the anisotropy reflected the large flow birefringence of the polycarbonate. 相似文献
38.
Masami Fujiwara Takamitsu Tamura Yasuhiro Akabane 《Journal of the American Oil Chemists' Society》1995,72(1):97-103
The reaction of N-chloro-4-hydroxy-2,2,6,6-tetramethylpiperidine (TMP-Cl) with sodium perborate (PB) was investigated with
special reference to the generation of singlet oxygen and the possible application to a new oxidative bleaching process. Generation
of the singlet oxygen (1O2), the hydroxyl radical (HO·) and superoxide anion radical (O2·−) in the PB/TMP-Cl mixed solution was confirmed by the trapping reagent method. From the results of another experiment, in
which the bleaching abilities of each active oxygen species were confirmed, the main active oxygen species contributing to
the bleaching of purpurogallin, the skeleton of black tea pigment, in the PB/TMP-Cl system was concluded to be1O2. 相似文献
39.
Keiichi Honda 《Journal of chemical ecology》1981,7(6):1089-1113
The larval osmeterial secretions of sixPapilio species examined displayed a remarkable qualitative change at the fourth larval ecdysis. The secretions of 4th (penultimate) instar larvae ofP. machaon, P. memnon, P. helenus, P. bianor, andP. maackii principally comprised mono- and/or sesquiterpenoids. The compounds identified from these species included -pinene, sabinene, -myrcene, limonene, -phellandrene, (Z)--ocimene, (E)--ocimene, -elemene, -caryophyllene, (E)--farnesene, -selinene, (E,E)--farnesene, germacrene-A, germacrene-B, caryophyllene oxide, methyl 3-hydroxy-n-butyrate, and acetic acid. In contrast, the secretion of 4th larval instar ofP. xuthus, although containing similar terpenic compounds, was accompanied by large amounts of aliphatic acids and their esters: isobutyric acid, 2-methylbutyric acid, methyl isobutyrate and methyl 2-methylbutyrate. On the other hand, the osmeterial secretions of 5th (last) instar larvae varied little in quality among the six species, and the identified compounds consisted of isobutyric acid, 2-methylbutyric acid, methyl isobutyrate, ethyl isobutyrate, methyl 2-methylbutyrate, ethyl 2-methylbutyrate, and isovaleric acid, the last of which was specific toP. bianor andP. maackii. The chemical alteration of osmeterial exudate synchronized at the final larval ecdysis with the larval morphological change (particularly in body coloration) that appears to be of defensive significance against predators. 相似文献
40.
Keiichi Tomishige Shogo Kanazawa Motoki Sato Kenji Ikushima Kimio Kunimori 《Catalysis Letters》2002,84(1-2):69-74
Pt(0.3)/Ni(10)/Al2O3, prepared by a sequential impregnation method, exhibited a more excellent performance in methane reforming with CO2 and O2 in terms of the catalytic activity and the temperature profile of the catalyst bed than Pt(0.3) + Ni(10)/Al2O3 prepared by a coimpregnation method, Ni(10)/Al2O3, Pt(0.3)/Al2O3, and Pt(10)/Al2O3. It is thought that this is because the surface Pt atoms on Ni catalyst can contribute to the enhancement of the catalyst reducibility. 相似文献