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   511篇
  免费   12篇
电工技术   5篇
综合类   1篇
化学工业   100篇
金属工艺   20篇
机械仪表   13篇
建筑科学   27篇
能源动力   7篇
轻工业   57篇
水利工程   1篇
石油天然气   4篇
无线电   24篇
一般工业技术   72篇
冶金工业   125篇
自动化技术   67篇
  2023年   4篇
  2021年   6篇
  2019年   11篇
  2018年   4篇
  2017年   6篇
  2016年   9篇
  2015年   8篇
  2014年   14篇
  2013年   10篇
  2012年   11篇
  2011年   24篇
  2010年   22篇
  2009年   13篇
  2008年   18篇
  2007年   17篇
  2006年   15篇
  2005年   14篇
  2004年   11篇
  2003年   17篇
  2002年   11篇
  2001年   10篇
  2000年   10篇
  1999年   11篇
  1998年   48篇
  1997年   22篇
  1996年   18篇
  1995年   17篇
  1994年   6篇
  1993年   10篇
  1992年   7篇
  1989年   4篇
  1988年   3篇
  1987年   3篇
  1985年   3篇
  1984年   4篇
  1983年   3篇
  1981年   3篇
  1980年   7篇
  1978年   8篇
  1977年   11篇
  1976年   12篇
  1972年   2篇
  1971年   2篇
  1970年   2篇
  1968年   4篇
  1966年   3篇
  1963年   4篇
  1956年   2篇
  1955年   5篇
  1954年   9篇
排序方式: 共有523条查询结果,搜索用时 15 毫秒
21.
Genome mining is a routine technique in microbes for discovering biosynthetic pathways. In plants, however, genomic information is not commonly used to identify novel biosynthesis genes. Here, we present the genome of the medicinal plant and oxindole monoterpene indole alkaloid (MIA) producer Gelsemium sempervirens (Gelsemiaceae). A gene cluster from Catharanthus roseus, which is utilized at least six enzymatic steps downstream from the last common intermediate shared between the two plant alkaloid types, is found in G. sempervirens, although the corresponding enzymes act on entirely different substrates. This study provides insights into the common genomic context of MIA pathways and is an important milestone in the further elucidation of the Gelsemium oxindole alkaloid pathway.  相似文献   
22.
23.
M3AlX (M = Ti/Zr/Hf, X = C/N) compounds are promising high‐temperature structural ceramics. However, their interesting polymorphism, thermomechanical stabilities, and thermal and mechanical properties were not fully understood. In this work, the polymorphisms of M3AX phases are investigated by combining first‐principles and lattice dynamics calculations. Only Ti3AlN shows polymorphic transition between the cubic and orthorhombic phases at around 1105 K; but other M3AlX phases do not display similar polymorphic phase transition. Furthermore, the temperature‐dependent heat capacity, thermal expansion, and elastic stiffness of Ti3AlN polymorphic phases are reported for the first time to explore the relationship between crystal structures, and mechanical and thermal properties. Ti3AlN polymorphs show anisotropic thermal expansion and elastic stiffness; and the orthorhombic Ti3AlN is suggested as a promising damage tolerant nitride, which has similar properties with the previously reported Zr3AlN and Hf3AlN.  相似文献   
24.
The aim of this study was to investigate the airflow distribution in a mixed-flow dryer (MFD) and to study the effect of different bed materials and air duct arrangements. The results were used to validate the numerical model developed in a previous work based on Computational Fluid Dynamics (CFD). A series of experiments have been conducted at a semi-technical MFD test dryer with horizontal and diagonal air duct arrangement. Wheat and rapeseed were used as bed materials. The experiments were performed under isothermal conditions. Two experimental methods were selected and adapted to the measuring problem—the measurement of the isobar distribution within the grain bed and the residence time analysis using the tracer gas pulse method. As could be shown, the isobar distributions measured for wheat and rapeseed agreed well with the model predictions. The numerical model could calculate the influence of the bed material with its different particle characteristics (e.g., particle shape, particle size, bed porosity). The results obtained from the residence time analysis confirmed the known quartering of the air stream flowing from one inlet air duct to the four surrounding outlet air ducts for the horizontal air duct arrangement; in the diagonal air duct arrangement, the air stream from one inlet air duct was nearly halved flowing to the two adjacent diagonal outlet air ducts. These results were confirmed by investigations of the air velocity distribution within the grain bulk. Further experiments are necessary to refine the model. The residence time and isobar measurements will be extended to study the influence of different air properties under real drying conditions, the effect of structural elements, and dryer designs.  相似文献   
25.
26.
A sensitive layer system of amorphous Teflon AF on silver has been coated on a glass substrate. With a monochromatic light source the reflectivity of the layer system as a function of the angle of incidence exhibits the surface-plasmon resonance as well as a set of leaky-mode resonances. These optical resonance phenomena are sensitive to small refractive-index changes that may be induced by diffusion of particles into the Teflon AF layer. On the basis of this effect, the aromatic vapors benzene; toluene; and o-, p-, and m-xylene have been investigated with different vapor concentrations. By selection of a distinct angle at a particular resonance, dynamic measurements can be performed. Assuming a diffusion process in accordance with Fick's law, the diffusion profile can be calculated as a function of time. As described by the Lorentz-Lorenz relation a refractive-index profile is induced that consequently interacts with the electromagnetic fields of the optical modes. With the function of the diffusion-induced refractive-index profile the shift of the resonance lines can be calculated from the measured reflectivity change as a function of time. The characteristic diffusion coefficients of the particular vapor allow for a distinction between the different types of aromate, even between the different xylenes.  相似文献   
27.
Quality control in orthopaedic diagnostics according to DIN EN ISO 9000ff requires methods of non-destructive process control, which do not harm the patient by radiation or by invasive examinations. To obtain an improvement in health economy, quality-controlled and non-destructive measurements have to be introduced into the diagnostics and therapy of human joints and bones. A non-invasive evaluation of the state of wear of human joints and of the cracking tendency of bones is, as of today's point of knowledge, not established. The analysis of acoustic emission signals allows the prediction of bone rupture far below the fracture load. The evaluation of dry and wet bone samples revealed that it is possible to conclude from crack initiation to the bone strength and thus to predict the probability of bone rupture.  相似文献   
28.
Integration of Product Design and Assembly Planning in the Digital Factory   总被引:1,自引:0,他引:1  
H. Bley  C. Franke 《CIRP Annals》2004,53(1):25-30
As assembly process planning fulfils the main function of connecting product design to production simulation and thus, the production system itself, a feasible software solution is needed to support this process. Thus, a novel concept is presented that aims at improving the integration of digital product design and assembly planning by introducing a consistent data structuring. This approach helps to reduce redundant tasks and supports the continuous data exchange. It is based on the use of assembly features, i.e. pre-defined geometry elements that contain additional technological information.The prototypical implementation of the concept focuses on the use of commercially available software tools, expanding them with additional functionality for the application of assembly features. The feature-based concept has been tested with a scenario from the automotive supplier industry. For the considered assembly, a comparison between the conventional and the feature-based planning approach is presented in the paper. It points out that the major advantages of the developed concept can be seen in an improved data consistency as well as a higher level of efficiency within the planning activities.  相似文献   
29.
30.
Under an artificial light:dark cycle, females of Lampronia capitella were observed calling, with extended terminal abdominal segments, during the first 2 hr of the photoperiod. Extracts of terminal abdominal segments from females elicited large electroantennographic responses from male antennae. Gas chromatography with electroantennographic detection revealed three active peaks. Based on comparison of retention times and mass spectra of synthetic standards, these compounds were identified as (Z,Z)-9,11-tetradecadienol and the corresponding acetate and aldehyde. The electroantennographic activity of the four geometric isomers of all three compounds was investigated, and the respective (Z,Z)-isomer was found to be the most active in all cases. Aldehydes generally elicited larger antennal responses than alcohols, whereas acetates were the least active compounds. A subtractive trapping assay in the field, based on a 13:26:100 micrograms mixture of (Z,Z)-9,11-tetradecadienal, (Z,Z)-9,11-tetradecadienyl acetate, and (Z,Z)-9,11-tetradecadienol confirmed that all three compounds are pheromone components. Subtraction of (Z,Z)-9,11-tetradecadienol from the blend completely eliminated its attractiveness, whereas the other two-component blends showed reduced activity. This is the first pheromone identification from the monotrysian superfamily Incurvarioidea, confirming that the common pheromones among ditrysian moths (long-chain fatty acid derivatives comprising alcohols, acetates, and aldehydes with one or more double bonds) is not an autapomorphy of Ditrysia, but a synapomorphy of the more advanced heteroneuran lineages.  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