首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1322篇
  免费   33篇
  国内免费   4篇
电工技术   73篇
综合类   5篇
化学工业   317篇
金属工艺   26篇
机械仪表   22篇
建筑科学   21篇
矿业工程   1篇
能源动力   42篇
轻工业   122篇
水利工程   6篇
无线电   137篇
一般工业技术   200篇
冶金工业   242篇
原子能技术   42篇
自动化技术   103篇
  2023年   4篇
  2022年   16篇
  2021年   9篇
  2020年   9篇
  2019年   19篇
  2018年   26篇
  2017年   16篇
  2016年   18篇
  2015年   17篇
  2014年   28篇
  2013年   83篇
  2012年   48篇
  2011年   56篇
  2010年   48篇
  2009年   53篇
  2008年   59篇
  2007年   39篇
  2006年   40篇
  2005年   61篇
  2004年   34篇
  2003年   36篇
  2002年   40篇
  2001年   35篇
  2000年   18篇
  1999年   31篇
  1998年   92篇
  1997年   54篇
  1996年   46篇
  1995年   39篇
  1994年   32篇
  1993年   34篇
  1992年   26篇
  1991年   9篇
  1990年   17篇
  1989年   12篇
  1988年   13篇
  1987年   7篇
  1986年   9篇
  1985年   15篇
  1984年   13篇
  1983年   16篇
  1982年   12篇
  1981年   11篇
  1980年   15篇
  1979年   5篇
  1978年   9篇
  1977年   8篇
  1976年   11篇
  1970年   2篇
  1932年   2篇
排序方式: 共有1359条查询结果,搜索用时 15 毫秒
61.
Volatiles were extracted from rice plants of various growth stages with solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS) to identify attractants that cause invasion of the rice leaf bug Trigonotylus caelestialium (Kirkaldy) into paddy fields. The composition of volatile blends produced by rice plants changed with rice development. In addition, volatile blend compositions differed between the panicles and the stems and leaves. The relative geranyl acetone content was high in all plant structures analyzed. In volatiles from whole plants in the fourth-leaf stage and panicles in the full-ripe stage, the relative content of green leaf volatiles (GLVs) was higher than that found in other rice plant structures. In contrast, relative terpene levels emitted from whole plants in the panicle-formation stage and by panicles and stems and leaves in the flowering stage were higher than those of other rice plant structures. However, the type of terpenes found differed between the panicles and the stems and leaves. Relative levels of β-caryophyllene in whole plants in the panicle-formation stage and panicles in the flowering stage were much higher than that in stems and leaves in the flowering stage. Our previous studies demonstrated that the odor from whole plants in the panicle-formation stage and panicles in the flowering stage is attractive to rice leaf bugs. Here, the attractiveness of β-caryophyllene to adult bugs was investigated in olfactometer assays. Adult females were attracted to β-caryophyllene at a concentration of 0.001%, which is approximately equivalent to the concentration produced by flowering rice panicles. However, β-caryophyllene also was present in the odor of whole plants in the fourth-leaf stage and in stems and leaves in the flowering stage. Furthermore, the amounts of this compound emitted from these structures were similar. Therefore, we suggest that the relative abundance of this compound in a volatile blend is important for attractance of the bugs.  相似文献   
62.
To examine dioxin contamination in commercial baby foods in Japan, congener analyses of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) were performed on 102 varieties of baby foods obtained from supermarkets in 2001-2002. The toxic equivalent quantity (TEQ) levels for dioxins in samples ranged from < 0.001 to 0.135 pg-TEQ/g wet weight when undetected or trace levels of congeners were taken as zero. Among 102 samples tested, 26 samples exceeded 0.010 pg-TEQ/g. The highest TEQ value was for "sardine, vegetables" (0.135 pg-TEQ/g), followed by "Japanese radish (daikon), sardine" (0.080 pg-TEQ/g). Thus, dioxins were detected at low levels in baby foods containing animal products such as fishes and/or dairy products.  相似文献   
63.
We have developed an analytical method for terpene resins in chewing gum. The fraction including terpene resins was prepared by means of hexane extraction and two silica gel column chromatography treatments (hexane and ethyl acetate) from chewing gum. The terpene resin fraction was analyzed with LC/MS and IR. The terpene resins are mixtures of polymeric pinene and/or limonene, which have a monomer molecular weight of 136. The MS spectrum of the terpene resin peak on the LC/MS total ion chromatogram showed protonated molecular ion (M + H)+ peaks at intervals of m/z 136, characteristic of a complex mixture of polyterpenes. IR spectroscopy is a suitable technique to identify the terpene resin type, ie., pinene or limonene. When the method was applied to imported chewing gum sold in Japan, terpene resins were clearly detected.  相似文献   
64.
The effects of foods and chemicals related to food hygiene on degranulation were evaluated using a method for assaying the enzyme activity of beta-hexosaminidase as an index of chemical mediator release from RBL-2H3 cells in vitro. Using a previously developed assay system, we had found a large number of inhibitors and promoters of degranulation of RBL-2H3 cells. In the present study, we examined the inhibitory effect of zinc chloride on the degranulation (beta-hexosaminidase release) from RBL-2H3 cells with or without antigen in the presence of the degranulation-promotive chemicals, namely, 4 food additives, 7 pesticides and 2 veterinary drugs. These promotive chemicals were classified into two types on the basis of inhibitory profile by zinc chloride: 1) those which showed marked degranulation-inhibitory action when the cells were stimulated with antigen, such as butylhydroxyanisole, dibutylhydroxytoluene, EPN, cis- and trans-permethrin, prothiofos, pyridaben, terbufos, 2) those which showed marked degranulation-inhibitory action whether the cells were stimulated with antigen or not, such as butyl p-hydroxybenzoate, o-phenylphenol, bitertanol, salinomycin. In conclusion, zinc had a dramatic inhibitory effect on enhanced degranulation induced by synthetic chemicals in vitro.  相似文献   
65.
The effect of the addition of CeO2 or La2O3 on the surface properties and catalytic behaviors of Al2O3-supported Pd catalysts was studied in the steam reforming of methane. The FTIR spectroscopy of adsorbed CO and the Pd dispersion suggest the partial coverage of Pd0 by ceria or lanthana species. This could lead to the formation of an adduct MPd x O (M = Ce or La) at the surface of the metal crystallites. The addition of ceria or lanthana resulted in an increase of the turnover rate and specific rate for steam reforming of methane. One possible explanation if that the Pd0*Pdδ+O–M interfacial species (M = Ce or La) are oxidized by H2O or CO2, promoting the O* transfer to the metal surface. This could facilitate the removal of C* species from the metal surface, resulting in the increase of specific reaction rate and increase of the accessibility of CH4 to metal active sites.  相似文献   
66.
1 Introduction  MEMS (MicroElectroMechanicalSystem )basedonsemiconductormicrofabricationplaysim portantrolesforexampleinthe peripheryofITsystems.NEMS (NanoElectroMechanicalSys tem)containsnano_scalestructures.Sophisticatedandhighperformancesystemsbasedonth…  相似文献   
67.
We prepared polycrystalline pellets of (U,Y)O2, containing YO1.5 up to 11 mol.%. We performed indentation tests on the pellets, and evaluated the Young’s modulus and hardness. We measured the heat capacity and the thermal diffusivity, and evaluated the thermal conductivity. We succeeded in evaluating the effect of Y content on the thermophysical properties of (U,Y)O2. We revealed that the Young’s modulus, hardness, and thermal conductivity of (U,Y)O2 decreased with increasing the Y content.  相似文献   
68.
69.
70.
The effect of thermal treatment to improve the metal adhesion into poly-(p-phenylene terephthalamide) (PPTA), e.g. aramid fiber, has been investigated. After palladium(II)-hexafluoroacetylacetonate metal complex, Pd(hfac)2, seeding into the fiber using supercritical fluid carbon dioxide, scCO2, a post-thermal treatment was conducted. As a result, after carrying out electroless copper plating, the adhesive strength between polymer substrate and copper layer greatly increased. Also, in order to have a better comprehension on decomposition reactions of Pd(hfac)2 under supercritical conditions, remains of metal complex were analyzed using electron ionization mass spectrometry technique (EI-MS). EI-MS mass spectra derived from Pd(hfac)2 gave us useful information about its dissociation reactions and reaction temperature under supercritical conditions. Additionally, to verify the Pd particles seeding in the fiber surface, X-ray photoelectron spectrometry (XPS) analyses were performed. The results confirmed that post-thermal treatment induced Pd particles diffusion and deeper penetration of Pd complex and its fragments into the fiber.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号