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   1025篇
  免费   28篇
  国内免费   3篇
电工技术   83篇
综合类   6篇
化学工业   312篇
金属工艺   40篇
机械仪表   26篇
建筑科学   34篇
矿业工程   2篇
能源动力   46篇
轻工业   66篇
水利工程   3篇
石油天然气   3篇
无线电   60篇
一般工业技术   155篇
冶金工业   85篇
原子能技术   54篇
自动化技术   81篇
  2022年   14篇
  2021年   21篇
  2020年   4篇
  2019年   13篇
  2018年   11篇
  2017年   12篇
  2016年   22篇
  2015年   15篇
  2014年   35篇
  2013年   67篇
  2012年   34篇
  2011年   69篇
  2010年   52篇
  2009年   40篇
  2008年   43篇
  2007年   58篇
  2006年   42篇
  2005年   44篇
  2004年   29篇
  2003年   39篇
  2002年   27篇
  2001年   21篇
  2000年   13篇
  1999年   27篇
  1998年   45篇
  1997年   22篇
  1996年   21篇
  1995年   17篇
  1994年   17篇
  1993年   11篇
  1992年   10篇
  1991年   7篇
  1990年   11篇
  1989年   10篇
  1988年   4篇
  1987年   5篇
  1986年   7篇
  1985年   13篇
  1984年   9篇
  1983年   14篇
  1982年   11篇
  1981年   11篇
  1980年   9篇
  1979年   8篇
  1978年   9篇
  1977年   8篇
  1976年   8篇
  1974年   3篇
  1973年   2篇
  1972年   4篇
排序方式: 共有1056条查询结果,搜索用时 15 毫秒
81.
82.
83.
Eight strains of bacteria which could not grow under aerobic conditions, were isolated from Japanese spiny lobster. All the strains were Gram-positive, non-sporeforming cocci, and grew well under anaerobic conditions. The strains required a decreased oxygen tension rather than an increased CO2 tension. Catalase, oxidase, nitrate reductase and urease were not produced. The strains fermented glucose, cellobiose, trehalose and levulose. Indole and H2S were not produced. Macromolecule substances including starch, esculin, casein, gelatin and chitin were not hydrolyzed. Lactic acid was the sole product from peptone-yeast extract-Fildes solution-glucose broth. Fermentable carbohydrates were not required. The strains could grow at 20 to 37°C, and required NaCl for growth. From the above results, the strains were identified as anaerobic (aerotolerant) Streptococcus sp.  相似文献   
84.
This paper is concerned with systematic developments of the Fraunhofer-diffraction method for studies of plasma density fluctuations in high-temperature plasmas using infrared lasers, namely (i) development of the general theory of the Fraunhofer-diffraction method, (ii) measurements of fluctuations propagating in an azimuthal direction, (iii) measurements of fluctuation intensities, and (iv) application in measurements on high-temperature plasmas.  相似文献   
85.
86.
Summary Poly(proline) and random copolypeptide composed of Pro and Ala residues were synthesized, and their solution properties and molecular conformation were investigated. Aqueous solutions of the polypeptide were irradiated with γ-rays above the transition temperature. It was shown that the transition temperature of the aqueous solution of the copolypeptide is influenced by Ala-residue content and γ-ray irradiation.  相似文献   
87.
Summary Phenolic resins containing alkylenediamine in the main chain could be prepared by the co-condensation reaction of phenol, formaldehyde and alkylenediamines such as ethylenediamine and hexamethylenediamine. The molecular structures were determined by1H-NMR spectra, IR spectra and nitrogen content. The molecular conformation of these resins in THF solution were studied from the viscosity measurements, and it became clear that the molecules were considerably compact compared with linear vinyl polymers. To clarify the reason of this phenomenon, the resins whose degrees of branching were different from each other and the resins whose phenolic hydroxyl groups were acetylated were prepared. From viscosity data, it was pointed out that the intramolecular hydrogen bonding contributes to the compaction of the phenolic resins containing alkylenediamine in the main chain more strongly than the branching does.  相似文献   
88.
Chiral amino acids are important intermediates for the pharmaceutical industry. We have developed a novel one‐pot enzymatic method for D ‐amino acid synthesis by the dynamic kinetic resolution of N‐succinyl‐dl ‐amino acids using D ‐succinylase (DSA) and N‐succinylamino acid racemase (NSAR, EC 4.2.1.113). The DSA from Cupriavidus sp. P4‐10‐C, which hydrolyzes N‐succinyl‐D ‐amino acids enantioselectively to their corresponding D ‐amino acids, was identified for the first time by screening soil microorganisms. Subsequently, the DSA gene was cloned and overexpressed in Escherichia coli. DSA was shown to comprise two subunits with molecular masses of 26 kDa and 60 kDa. Additionally, the NSAR gene from Geobacillus stearothermphilus NCA1503, which racemizes N‐succinylamino acids, was also cloned and overexpressed in E. coli. The highly purified DSA and NSAR prepared from each recombinant E. coli were characterized and used for D ‐amino acid synthesis. A one‐pot enzymatic method converted 100 mM N‐succinyl‐dl ‐phenylalanine to D ‐phenylalanine in 91.1% conversion with 86.7% ee. This novel enzymatic method may be useful for the industrial production of many D ‐amino acids.

  相似文献   

89.
Concrete filled double skin tubular (CFDST in abbreviation) stub columns consist of double concentric thin steel tubes and filled concrete between them. Their mechanical behaviors under axial compression were investigated experimentally. Two testing parameters considered were inner-to-outer diameters ratio and diameter-to-thickness ratio. Observed failure modes were controlled by the local buckling of both the tubes associated with shearing failure of the filled concrete. Main discussion is given on confinement effect by the outer tube to the filled concrete strength. Equations to estimate their ultimate strengths under compression were proposed based upon the yielding strengths of the tubes and the filled concrete cylinder strength.  相似文献   
90.
In this study, the experiment of the extrusion lamination process using high‐pressure process low‐density polyethylene (LDPE) was performed. The nonisothermal viscoelastic simulation of the extrusion lamination experiment was also carried out. The simulation results were in good agreement with the experimental data within wide range of take up velocity and air gap length. We developed the theoretical model based on force balance and deformation type of a film to predict the neck‐in behavior in the extrusion lamination or cast film process. It was suggested from the neck‐in model that the neck‐in correlates with the ratio of planar to uniaxial elongational viscosity. It was confirmed that the neck‐in model could predict the film edge shape and neck‐in properly for conventional LDPE. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers  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