全文获取类型
收费全文 | 6202篇 |
免费 | 207篇 |
国内免费 | 29篇 |
专业分类
电工技术 | 336篇 |
综合类 | 20篇 |
化学工业 | 1718篇 |
金属工艺 | 219篇 |
机械仪表 | 192篇 |
建筑科学 | 139篇 |
矿业工程 | 6篇 |
能源动力 | 248篇 |
轻工业 | 498篇 |
水利工程 | 20篇 |
石油天然气 | 6篇 |
无线电 | 507篇 |
一般工业技术 | 1153篇 |
冶金工业 | 724篇 |
原子能技术 | 164篇 |
自动化技术 | 488篇 |
出版年
2023年 | 37篇 |
2022年 | 43篇 |
2021年 | 155篇 |
2020年 | 66篇 |
2019年 | 84篇 |
2018年 | 106篇 |
2017年 | 72篇 |
2016年 | 133篇 |
2015年 | 103篇 |
2014年 | 151篇 |
2013年 | 312篇 |
2012年 | 288篇 |
2011年 | 352篇 |
2010年 | 292篇 |
2009年 | 328篇 |
2008年 | 349篇 |
2007年 | 271篇 |
2006年 | 251篇 |
2005年 | 194篇 |
2004年 | 194篇 |
2003年 | 211篇 |
2002年 | 196篇 |
2001年 | 128篇 |
2000年 | 119篇 |
1999年 | 120篇 |
1998年 | 284篇 |
1997年 | 216篇 |
1996年 | 172篇 |
1995年 | 123篇 |
1994年 | 105篇 |
1993年 | 114篇 |
1992年 | 84篇 |
1991年 | 74篇 |
1990年 | 54篇 |
1989年 | 64篇 |
1988年 | 32篇 |
1987年 | 55篇 |
1986年 | 30篇 |
1985年 | 53篇 |
1984年 | 35篇 |
1983年 | 39篇 |
1982年 | 52篇 |
1981年 | 45篇 |
1980年 | 36篇 |
1979年 | 44篇 |
1978年 | 29篇 |
1977年 | 34篇 |
1976年 | 44篇 |
1975年 | 18篇 |
1974年 | 10篇 |
排序方式: 共有6438条查询结果,搜索用时 78 毫秒
981.
The alumina–carbon composite fibers were obtained from poly[(acyloxy)aloxane] (PAA) with 3-ethoxypropanoic (EPA) and m-anisic acids (m-AA) legands. This preceramic polymer can be dissolved in p-xylene-methanol-EPA mixed solvent, and the concentrated solution exhibited an excellent spinnability. During the pyrolysis and sintering processes, aliphatic carboxylate in the side groups was easily decomposed and eliminated. The aromatic carboxylate, however, seems to be converted and migrated to a carbon domain in the alumina matrix into which aloxane repetition was converted. The fibers pyrolyzed up to 800 and 1000°C have electrical conductivities that monotonically increase with increasing temperature. The fiber pyrolyzed up to 1200°C showed the electrical conductivity in a rather complicated manner. 相似文献
982.
The photocatalytic oxidation of CO into CO2 with oxidants such as NO, N2O and O2 proceeded efficiently on a Mo/SiO2 with high Mo dispersion under UV light irradiation. It was found that the reaction rate greatly depended on the kind and concentration of the oxidant. Photoluminescence investigations reveal the close relationship between the reaction rate and the relative concentration of the photo-excited Mo6+-oxide species, i.e. charge transfer–excited–triplet state (Mo5+–O−)*, under steady-state reaction conditions. Moreover, the photocatalytic oxidation of CO with O2 in excess H2 was carried out to test suitability for applications to supplying pure H2. This reaction was seen to proceed efficiently on Mo/SiO2 with a high CO conversion of 100% and CO selectivity of 99% after 180 min under UV light irradiation, showing higher photocatalytic performance than TiO2 (P-25) photocatalyst. UV–vis, XAFS, photoluminescence and FT-IR investigations revealed that the high reactivity of the charge transfer–excited–triplet state (Mo5+–O−)*, with CO as well as the high reactivity of the photoreduced Mo-oxide species (Mo4+-species) with O2 to produce the original Mo-oxide species (Mo6+O2−), played a crucial role in the reactions. 相似文献
983.
Synchronous fluorescence spectra of model polycondensed aromatic hydrocarbon molecules were recorded and used to identify the number of condensed rings in the aromatic molecules. A coal-derived liquid from Yubarishinko coal was initially separated into fractions having different number of condensed aromatic rings, and each fraction was further divided into narrow fractions having different numbers of carbon atoms. These fractions were studied using synchronous fluorescence spectroscopy. Results indicate the potential usefulness of synchronous fluorescence spectroscopy as a method of analysis of complex mixtures as coal-derived liquids despite the limitation of the method that some molecules give only weak peaks. Several components in some fractions were identified by a combination of synchronous fluorescence spectra and conventional excitation and emission fluorescence spectra. 相似文献
984.
Reactive blending has been usually utilized to stabilize morphology and to improve the properties of multi-component polymer blends by generating copolymers in situ at the interface. However, the present study on blends composed of poly(butylene terephthalate) (PBT) and functionalized styrene-acrylonitrile random copolymer (SAN) demonstrates another possibility for this method, i.e. tailoring morphology and thereby controlling the properties of polymer blends. By varying reaction conditions it was demonstrated that blends could be formed having the same ratio of [PBT]/[SAN] but which possessed completely different microstructural forms: a sea-island morphology with and without micelles, a corded dispersed phase morphology, and a highly oriented, layer-like morphology. 相似文献
985.
Preparation and properties of poly(methylmethacrylate)-silica hybrid materials incorporating reactive silica nanoparticles 总被引:1,自引:0,他引:1
In this study, poly(methylmethacrylate) (PMMA)-based hybrid materials were prepared from reactive silica nanoparticles. These nanoparticles were obtained by the reaction of 2-(methacryloyloxy)ethyl isocyanate with colloidal silica dispersed in ethyl acetate, and they were copolymerized in various ratios with methyl methacrylate. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and visible spectrometry were performed to evaluate the physical properties of the resulting hybrid materials. The PMMA-silica hybrid copolymers maintained high transparency, and their storage elastic modulus and surface hardness increased with increasing silica content. Moreover, in comparison with PMMA, the hybrid copolymers had greater heat resistance and lower volume contraction. 相似文献
986.
Yutaka Shinoda Michiyuki Yoshida Takashi Akatsu Fumihiro Wakai 《Journal of the American Ceramic Society》2004,87(10):1919-1926
The deformation behavior of boron- and carbon-doped β-silicon carbide (B,C-SiC) with an average grain size of 260 ± 18 nm containing 1 wt% boron was investigated by compression testing at elevated temperatures. Extensive grain growth during deformation was observed. The stress–strain curves were compensated for grain growth by assuming power-law type of dependence on grain size and strain rate. The stress exponent n was ∼1.3 and the grain size exponent p was ∼2.7 at temperatures ranging from 1593° to 1758°C. The apparent activation energy of deformation Q d was ∼760 kJ/mol, which was lower than the activation energy for lattice diffusion of silicon and carbon in SiC and higher than that for grain-boundary diffusion of carbon in SiC. These results suggest that the deformation mechanism of the fine-grained B,C-SiC is grain-boundary sliding accommodated by the grain-boundary diffusion. 相似文献
987.
Mikihito Takenaka Shotaro Nishitsuji Masataka Yamaguchi Takeji Hashimoto 《Polymer》2006,47(22):7846-7852
We investigated the shear-induced phase separation and/or concentration fluctuation phenomena in semidilute polymer solution by using computer simulation in 3-dimensional space with Doi-Onuki theory. The enhancement of the concentration fluctuations occurs under shear flow and the scattering function in qx-qz plane exhibits the so-called butterfly pattern as observed experimentally, where qx and qz are the components of the scattering vector for flow direction and neutral direction, respectively. The time changes in the peak position and the intensity at peak position in the scattering function in qx-qz plane can be divided into two regions: the peak position becomes smaller and the peak intensity increases with t, and then the peak position and intensity become constant and the system reaches its steady state. These agree with the experimental results qualitatively. However, the computer simulation results indicate that the peak position at the steady state is almost independent of the shear rate, while the decrease in the peak position at steady state with shear rate has been observed experimentally. This disagreement originates from the use of the simplest constitutive equation in the computer simulation. 相似文献
988.
Hiroko Kosugi Takashi Kojima Kiyomi Kikugawa 《Journal of the American Oil Chemists' Society》1991,68(1):51-55
The thiobarbituric acid (TBA) reactivity of oxidized methyl linoleate, soybean oil, sesame oil, lard, chicken oil and sardine
oil was characterized by using four different methods with 0.01% butylated hydroxytoluene (BHT). Optimal pH for the reactivity
of most of the oxidized samples was 3–4, and that of some samples was above 5. Introduction of 2 mMt-butyl hydroperoxide (t-Bu00H) or 0.2 mM ferric ion in the reaction markedly enhanced the reactivity. Introduction of 0.2 mM ethylenediamine tetraacetic
acid suppressed the reactivity. The characteristics of the TBA-reactivity of the samples were similar to those of alkadienals
or alkenals. The most preferable method for the estimation of the TBA-reactive substances of the oxidized fats and oils was
that using solvents at pH 3.5 with introduction of BHT, andt-Bu00H or ferric ion. 相似文献
989.
Prevention of catalyst deactivation in carbon monoxide methanation on a highly active Ni-based composite catalyst has been investigated. The composite catalyst, Ni-La2O3-Ru supported on silica, has greater activity than that of a Ni catalyst, but the decrease of the catalyst activity with reaction time is greater than that of the Ni catalyst, especially when the CO conversion is low. The reason for this behaviour is found in the relation between the amount of surface-carbon species and the degree of deactivation. When the CO methanation reaction is operated at above the temperature of complete CO conversion, catalyst deactivation is avoided. At such high temperatures the amount of surface-carbon species is small. The catalyst deactivation is considerably suppressed with a low concentration, e.g. 1–3 kPa, of additional CO2 or CO2 + H2O. The cause of this suppression is considered to be the renewal of the covered surface with the carbon-species by the competitive adsorption of these additives. 相似文献
990.
Multiple melting behavior of poly(butylene-2,6-naphthalate) (PBN) was studied with X-ray analysis and differential scanning calorimetry (DSC). Double endothermic peaks L and H attributed to the α-form crystal modification, a small peak attributed to the β-form crystal modification, and a new shoulder peak S at a lower temperature of peak H appeared in the DSC melting curves. Wide-angle X-ray diffraction patterns of the samples isothermally crystallized at 200 and 220 °C were obtained at a heating rate of 1 K min−1, successively. In this heating process, change of crystal structure and increase of quantity of the β-form crystallites could not be observed up to the final melting. With increasing temperature, the diffraction intensity decreased gradually and then increased distinctly before a steep decrease due to the final melting. The X-ray analysis clearly proved the melt-recrystallization during heating. The β-form crystal modification was formed during slow heating process in the high temperature region. 相似文献