全文获取类型
收费全文 | 1507篇 |
免费 | 38篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 143篇 |
综合类 | 4篇 |
化学工业 | 403篇 |
金属工艺 | 77篇 |
机械仪表 | 38篇 |
建筑科学 | 26篇 |
矿业工程 | 5篇 |
能源动力 | 27篇 |
轻工业 | 97篇 |
水利工程 | 8篇 |
石油天然气 | 7篇 |
无线电 | 109篇 |
一般工业技术 | 280篇 |
冶金工业 | 150篇 |
原子能技术 | 45篇 |
自动化技术 | 134篇 |
出版年
2022年 | 12篇 |
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 17篇 |
2018年 | 22篇 |
2017年 | 17篇 |
2016年 | 17篇 |
2015年 | 28篇 |
2014年 | 39篇 |
2013年 | 90篇 |
2012年 | 48篇 |
2011年 | 61篇 |
2010年 | 63篇 |
2009年 | 62篇 |
2008年 | 91篇 |
2007年 | 62篇 |
2006年 | 54篇 |
2005年 | 48篇 |
2004年 | 46篇 |
2003年 | 40篇 |
2002年 | 39篇 |
2001年 | 41篇 |
2000年 | 27篇 |
1999年 | 30篇 |
1998年 | 70篇 |
1997年 | 48篇 |
1996年 | 48篇 |
1995年 | 23篇 |
1994年 | 30篇 |
1993年 | 34篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 20篇 |
1983年 | 23篇 |
1982年 | 25篇 |
1981年 | 22篇 |
1980年 | 21篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1974年 | 5篇 |
1971年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有1553条查询结果,搜索用时 15 毫秒
51.
Production of eicosapentaenoic acid by a recombinant marine cyanobacterium, Synechococcus sp. 总被引:1,自引:0,他引:1
The eicosapentaenoic acid (EPA) synthesis gene cluster from an EPA-producing bacterium, Shewanella sp. SCRC-2738, was cloned into a broad-host range vector, pJRD215, and then introduced into a marine cyanobacterium, Synechococcus sp. NKBG15041c, by conjugation. The transconjugant cyanobacteria produced 3.7±0.2% (2.24±0.13 mg/L) EPA (n-3) and 2.5 ±0.2%
(1.49±0.06 mg/L) eicosatetraenoic acid (n-3) of the total fatty acids when the cells were cultured at 23°C at a light intensity
of 1,000–1,500 Lux. The EPA and eico-satetraenoic acid contents of the cells were increased to 4.6±0.6% (3.86±1.11 mg/L) and
4.7±0.3% (3.86±0.82 mg/L), and 7.5±0.3% (1.76±0.10 mg/L) and 5.1±0.2% (1.19±0.06 mg/L) when they were cultured at low temperature
(18°C) and at lower light intensity (40 Lux), respectively. 相似文献
52.
Tomoharu Suzuki Shigeru Oshio Mari Iwata Hisayo Saburi Takashi Odagiri Tadashi Udagawa Isamu Sugawara Masakazu Umezawa Ken Takeda 《Particle and fibre toxicology》2010,7(1):1-8
Background
Epidemiological studies suggest that inhalation of carbonaceous particulate matter from biomass combustion increases susceptibility to bacterial pneumonia. In vitro studies report that phagocytosis of carbon black by alveolar macrophages (AM) impairs killing of Streptococcus pneumoniae. We have previously reported high levels of black carbon in AM from biomass smoke-exposed children and adults. We therefore aimed to use a mouse model to test the hypothesis that high levels of carbon loading of AM in vivo increases susceptibility to pneumococcal pneumonia.Methods
Female outbred mice were treated with either intranasal phosphate buffered saline (PBS) or ultrafine carbon black (UF-CB in PBS; 500 μg on day 1 and day 4), and then infected with S. pneumoniae strain D39 on day 5. Survival was assessed over 72 h. The effect of UF-CB on AM carbon loading, airway inflammation, and a urinary marker of pulmonary oxidative stress was assessed in uninfected animals.Results
Instillation of UF-CB in mice resulted a pattern of AM carbon loading similar to that of biomass-smoke exposed humans. In uninfected animals, UF-CB treated animals had increased urinary 8-oxodG (P = 0.055), and an increased airway neutrophil differential count (P < 0.01). All PBS-treated mice died within 72 h after infection with S. pneumoniae, whereas morbidity and mortality after infection was reduced in UF-CB treated animals (median survival 48 h vs. 30 h, P < 0.001). At 24 hr post-infection, UF-CB treated mice had lower lung and the blood S. pneumoniae colony forming unit counts, and lower airway levels of keratinocyte-derived chemokine/growth-related oncogene (KC/GRO), and interferon gamma.Conclusion
Acute high level loading of AM with ultrafine carbon black particles per se does not increase the susceptibility of mice to pneumococcal infection in vivo. 相似文献53.
Thermosensitive 4VP‐NIPAAm‐4G copolymer beads containing pyridyl groups were first prepared by suspension copolymerization of 4‐vinylpyridine (4VP), N‐isopropylacrylamide(NIPAAm), and tetraethylene glycol dimethacrylate (4G; crosslinking reagent) in a saturated Na2SO4 aqueous solution in the presence of surfactant and MgCO3 as dispersants. Then the copolymer beads containing pyridinium groups were obtained by the quaternization of the copolymer beads with various alkyl iodides (CH3I, C4H9I, C8H17I) in N,N‐dimethylformamide. The 4VP‐NIPAAm‐4G (15 : 97 : 3) copolymer bead and the 4VP‐NIPAAm‐4G copolymer beads quaternized with butyl iodide exhibited high thermosensitivity in water, although the 4VP‐NIPAAm‐4G copolymer beads quaternized with methyl iodide or octyl iodide hardly exhibited thermosensitivity. All the quaternized copolymer beads exhibited antibacterial activity against Escherichia coli (E. coli), although the 4VP‐NIPAAm‐4G copolymer bead did not. In particular, the copolymer bead quaternized with butyl iodide exhibited the highest antibacterial activity against E. coli at 30°C. It was also found that the antibacterial activity of the quaternized 4VP‐NIPAAm‐4G copolymer beads was greatly affected by not only chain length of alkyl groups in alkyl iodides, with which the 4VP‐NIPAAm‐4G copolymer beads were quaternized, but also by temperature of the solutions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
54.
Mamoru Ishida Takeo Uehara Toshio Arai Hideki Takeda Tadashi Yamaguchi Takeshi Taniguchi Tetsuya Katsumi Masayuki Kobayashi Hitoshi Ofune 《Intermetallics》2002,10(11-12)
The performance of MU/SC conversion sleeve produced by bulk metallic glass (Zr55Al10Ni5Cu30) was examined. A precision die-casting method was applied to improve size accuracy. The size accuracy of the conversion sleeve produced by the precision die-casting method was ±1 μm, and optical insertion loss (Li) was less than 0.3 dB for a standard value. The wear resistance of metallic glass is improved by surface oxidation treatment in air at 673 K. The MU/SC conversion sleeve produced from bulk metallic glass has superior characteristics for optical parts. 相似文献
55.
Shinya Inai Yuji Hiruma Muneyasu Suzuki Hajime Nagata Tadashi Takenaka 《Ceramics International》2008,34(4):741-744
The temperature dependence of the piezoelectric properties of vanadium substituted strontium bismuth niobate, SrBi2Nb1.95V0.05O9 (SBNV) ceramics, were investigated in various vibration modes. The effects of grain orientation in SBNV ceramics on the piezoelectric properties were also studied by the hot-forging (HF) method. The anisotropy of the piezoelectric properties of each vibration mode was confirmed by observing the grain orientation. In particular, HF-SBNV ceramics of the (33) and (15) modes showed excellent piezoelectric properties with relatively high mechanical quality factors, Qm (2200, 4600), and high electrical quality factors, Qe max (66.0, 21.6), respectively. In addition, HF-SBNV ceramics showed low temperature coefficients of resonance frequency TC-fr (−16.5, −27.0). HF-SBNV ceramics are considered to be superior candidates for the lead-free piezoelectric application of ceramic resonators. 相似文献
56.
Yoshihisa Matsushita Nobuko Ohba Tadashi Suzuki Teijiro Ichimura 《Catalysis Today》2008,132(1-4):153-158
A photocatalytic microreaction system was developed and photocatalytic N-alkylation process of benzylamine, aniline, and piperidine was examined. The reaction proceeded quite rapidly in the microreactors with immobilized Pt-free TiO2 as well as Pt-loaded TiO2, while it has been reported that the N-alkylation did not occur by the irradiation of Pt-free TiO2 in conventional batch reactors. It was revealed that by using the unique features of the continuous-flow microreactor, for instance spatial illumination homogeneity and precise control of flow and irradiation conditions, one can control the selectivity of N-alkylation and N,N-dialkylation processes. These results suggest the possibilities of a photocatalytic microreaction system on organic synthetic reactions. 相似文献
57.
Tomiko M. Suzuki Tadashi Nakamura Eiichi Sudo Yusuke Akimoto Kazuhisa Yano 《Microporous and mesoporous materials》2008,111(1-3):350-358
A new type of sulfonic acid-functionalized monodispersed mesoporous silica spheres (MMSS) were synthesized directly by co-condensation and subsequent oxidation. By changing the methanol ratio, sulfonic acid-functionalized MMSS with different particle diameters (390–830 nm) and the same mesopore sizes were successfully synthesized. TEM observations revealed that the mesopores were aligned radially from the center towards the outside of the spheres, even in the sulfonic acid-functionalized MMSS. The catalytic activities of the sulfonic acid-functionalized MMSS were studied in condensation reactions between 2-methylfuran and acetone, and it was found that their catalytic activities are highly dependent on the particle diameters. In addition, the catalytic activity of MMSS was much higher than that of other forms of mesoporous silica due to its radially-aligned mesopores. 相似文献
58.
Rheological properties in a molten state are studied extensively for poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), PHB‐HV, with a small amount of crosslinked poly(epichlorohydrin), PECH, having low density of crosslink points. It is found that adding 2 wt % of xPECH greatly enhances the melt elasticity of PHB‐HV, one of the serious defects of microbial PHB, whereas it has no effect on the shear viscosity. As a result, viscoelastic nature, and thus processability, of PHB‐HV can be controlled by blending the crosslinked PECH. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
59.
R. Subramanian M. Nakajima A. Yasui H. Nabetani T. Kimura T. Maekawa 《Journal of the American Oil Chemists' Society》1999,76(10):1247-1253
The first step in the process of vegetable oil refining is degumming, in which phospholipids and mucilaginous gums are removed
that otherwise result in a low-grade oil. A membrane process is remarkably simple yet potentially offers many advantages in
degumming. Studies were conducted on surfactant-aided membrane degumming with soybean and rapeseed oils in a magnetically
stirred flat membrane batch cell with different types of microfiltration membranes. The reduction of phospholipids in soybean
oil was in the range of 85.8–92.8% during the membrane process. The phosphorus content of membrane permeates of soybean oil
was in the range of 20–58 mg/kg. Crude rapeseed oil contained higher amount of nonhydratable phospholipids and hence resulted
in lower reduction in phospholipids, in the range of 66.4–83.2%. Addition of hydratable phospholipids could improve the efficiency
of degumming in the membrane process without using any electrolyte, resulting in improvement of quality as well as quantity
of the phospholipids. 相似文献
60.
Yusuke Kitamura Yoshiaki Morisada Hidetoshi Fujii Tadashi Mizuno Genryuu Abe 《Welding International》2017,31(4):278-283
(The microstructural refinement of cobalt-based alloy (Stellite No. 6) by laser cladding and friction stir processing (FSP) was studied. A nanometer-sized microstructure consisting of fine carbide (particle size: 100–200 nm) and a grain (grain size: 150–250 nm) was successfully fabricated by the FSP on the laser clad cobalt-based alloy. The nanostructured cobalt-based alloy (Stellite No. 6) had an extremely high hardness of about 750 HV. 相似文献