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   4417篇
  免费   188篇
  国内免费   5篇
电工技术   22篇
综合类   8篇
化学工业   1148篇
金属工艺   46篇
机械仪表   48篇
建筑科学   187篇
矿业工程   14篇
能源动力   75篇
轻工业   742篇
水利工程   27篇
石油天然气   9篇
无线电   131篇
一般工业技术   497篇
冶金工业   1106篇
原子能技术   24篇
自动化技术   526篇
  2023年   20篇
  2022年   138篇
  2021年   205篇
  2020年   93篇
  2019年   99篇
  2018年   108篇
  2017年   85篇
  2016年   100篇
  2015年   95篇
  2014年   135篇
  2013年   260篇
  2012年   174篇
  2011年   229篇
  2010年   195篇
  2009年   161篇
  2008年   218篇
  2007年   194篇
  2006年   149篇
  2005年   136篇
  2004年   121篇
  2003年   99篇
  2002年   124篇
  2001年   74篇
  2000年   67篇
  1999年   85篇
  1998年   89篇
  1997年   58篇
  1996年   77篇
  1995年   53篇
  1994年   56篇
  1993年   54篇
  1992年   67篇
  1991年   18篇
  1990年   49篇
  1989年   69篇
  1988年   46篇
  1987年   52篇
  1986年   56篇
  1985年   53篇
  1984年   60篇
  1983年   46篇
  1982年   32篇
  1981年   47篇
  1980年   26篇
  1979年   23篇
  1978年   22篇
  1977年   23篇
  1976年   30篇
  1975年   27篇
  1970年   17篇
排序方式: 共有4610条查询结果,搜索用时 31 毫秒
131.
Cleaning before coating — the last step of the manufacturing process Before coating the surface of the component which shall be coated is cleaned. Several machines and chemicals can be used. After the cleaning the surface must be ready for coating. The influence of the machining parameters on the surface of a component is shown. The effectiveness of the cleaning processes prior to coating is discussed, and put in context to the whole manufacturing process. A classification of the manufacturing process should not be based on the different locations where it takes place. All the machining steps which influence the properties and the coat ability of the metal surface should be considered as connected. All these treatment steps are ideally tuned in a way that the surface can be coated flawlessly.  相似文献   
132.
Thin sheet anode and cathode materials made in composite structures constitute some of the most important components of a Li-ion battery. These materials are currently cut by punching technology, which shows degrading behaviour as the tool wears out. A viable option for Li-ion battery electrode manufacturing is the use of remote laser cutting. However, the operation requires fulfilling both productivity and quality aspects to substitute the conventional production method. One of the most critical aspects in quality is the clearance width, which is defined as the extent of the exposed middle layer of the sandwich at the laser cut kerf. This work investigates the quality aspects of laser cutting of Li-ion electrodes when a green fibre laser source (λ?=?532 nm, τ?=?1 ns) is used rather than the more traditional infrared (IR) fibre laser source (λ?=?1,064 nm, τ?=?250 ns). The processing conditions were investigated to reveal the technological feasibility zones. Clearance width was studied within the technological feasibility zones for all the material-laser combinations. Results showed that high productivity criterion is met by the IR system, since cutting speed could reach 30 m/min with 54 W average laser power on both anode and cathode. On the other hand, the green laser provided clearance width below 20 μm. In the best case, the clearance on anode could be eliminated with the green laser system. Although the maximum cutting speed was 4.5 m/min, upscaling of green laser power can provide required productivity.  相似文献   
133.
134.
儿童总是喜爱玩耍的,神秘的洞穴更是对他们有着无穷的吸引力。在孩子的眼中,色彩是丰富世界的一个缩影。因此,迫庆一郎先生在设计巴塞罗那儿童品牌Imaginarium旗舰店时,就以洞穴·彩虹作为了设计的主题。  相似文献   
135.
136.
Carbon foams are non-toxic, highly porous, light materials which demonstrate a wide range of properties. That fact allows carbon foams to be applied in many areas of life, ranging from electronics industry, through machinery, car and construction industry, to environmental protection. The properties of carbon foams are closely connected with their density, and its value is especially influenced by their internal structure, i.e. mainly size and number of pores, pore wall thickness and structural order of solid matrix. That is why it is possible to design the properties of carbon foams by controlling their growth. The main control factors are selecting the suitable raw material, the process parameters (temperature and pressure) and the suitable production method. Additionally, the properties of carbon foams may be modified by doping them with carbon or mineral fillers. The second method is the enrichment of carbon matrix with heteroatoms, mainly of boron and nitrogen. This paper presents the review of the possibilities of tailoring the structure and properties of carbon foams, based on the current level of knowledge available in the literature.  相似文献   
137.
Based on the information needs of stakeholders (from animal feed to consumers, including the authorities and organizations involved) an integrated IT-system without structural fractures and barriers shall be developed. It will be designed to enable the merging, internal exchange and utilization of relevant data and parameters. Subprojects of the interdisciplinary research consortium cover the entire supply chain and also address cross-section issues, such as logistics, costs and benefits, veterinarian services, quality assurance systems, a comprehensive IT-solution including data format standards (agroXML), and requirements for sustainability. Substantial added value has been generated from intensive interdisciplinary co-operation. The interdisciplinary research project IT FoodTrace () aims at achieving traceability and quality assurance along the food chain of “meat and meat products”. The aim of this paper is the presentation of (a) the complexity of underlying problems, (b) the project structure, (c) available results from selected sub-projects and (d) the added values from interdisciplinary co-operation. Selected findings include an optimized single animal data collection and information management in livestock systems, benefits gained by linking animal-health-related information to an integrated animal-health system, requirements and features of an integrated IT-System, including consequences for data protection and security, and findings from a Delphi-based cost–benefit-analysis of an integrated quality assurance and traceability system.  相似文献   
138.
139.
Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains.  相似文献   
140.
Current developments in cement chemistry increasingly rely on predictive thermodynamic modeling of the phase composition in cementitious composites with the aim of linking the performance of the material with the phase composition of the material. This approach requires identification of the cement phases that form in hydrating cementitious materials using standard techniques, such as X‐ray diffraction (XRD) and thermal analysis (DTA, TGA), but also state‐of‐the‐art synchrotron‐based techniques, in particular for those cases in which the signals of solid solutions overlap in XRD and TGA measurements. In this study, two ordinary Portland cements, with different chemical compositions and subject to different hydration times (~10, ~50 yr), were investigated aiming at identifying the most stable Fe‐containing cement phase in the cement pastes. The Fe‐containing cement phases and their solid solutions with the Al analogues in the complex cement matrix were analyzed with X‐ray absorption spectroscopy, indicating the formation of a mixed Fe–Al siliceous hydrogarnet as the major Fe‐containing phase. The presence of this phase after long hydration periods and upon selective dissolution of the pastes further indicates that, independent of the chemical compositions of cements, formation of the mixed Fe–Al siliceous hydrogarnet is thermodynamically favored in aged pastes, which is supported by published thermodynamic calculations.  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