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   47968篇
  免费   5079篇
  国内免费   3007篇
电工技术   1661篇
技术理论   2篇
综合类   4260篇
化学工业   4211篇
金属工艺   2677篇
机械仪表   3572篇
建筑科学   1296篇
矿业工程   1679篇
能源动力   523篇
轻工业   5497篇
水利工程   467篇
石油天然气   1531篇
武器工业   923篇
无线电   7782篇
一般工业技术   3877篇
冶金工业   1992篇
原子能技术   395篇
自动化技术   13709篇
  2024年   119篇
  2023年   691篇
  2022年   1100篇
  2021年   1458篇
  2020年   1387篇
  2019年   1108篇
  2018年   1019篇
  2017年   1362篇
  2016年   1476篇
  2015年   1857篇
  2014年   2607篇
  2013年   2629篇
  2012年   3242篇
  2011年   3661篇
  2010年   2723篇
  2009年   2785篇
  2008年   2871篇
  2007年   3347篇
  2006年   2986篇
  2005年   2645篇
  2004年   2234篇
  2003年   2037篇
  2002年   1640篇
  2001年   1344篇
  2000年   1264篇
  1999年   950篇
  1998年   856篇
  1997年   769篇
  1996年   648篇
  1995年   531篇
  1994年   494篇
  1993年   415篇
  1992年   323篇
  1991年   258篇
  1990年   241篇
  1989年   204篇
  1988年   148篇
  1987年   81篇
  1986年   71篇
  1985年   85篇
  1984年   64篇
  1983年   80篇
  1982年   58篇
  1981年   40篇
  1980年   32篇
  1979年   29篇
  1978年   19篇
  1977年   24篇
  1976年   13篇
  1973年   8篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
An engineered variant of the yeast Pichia pastoris was used to produce the potential malaria vaccine D1M1. This paper describes the implementation of an expanded bed adsorption chromatography step into a sequential cultivation process of the yeast in order to link protein expression, cell release, and product capture of the secreted protein in a fully automated plant. The process is operated with a semi-continuous strategy for an integrated production. Process improvements have been achieved using design of experiments. Resulting purities of product achieved up to 87% with recoveries of 51% in a single downstream operation. Furthermore, a multivariate analysis of historical batch data was used to develop a golden batch model for process monitoring.  相似文献   
42.
We present a data-driven method for monitoring machine status in manufacturing processes. Audio and vibration data from precision machining are used for inference in two operating scenarios: (a) variable machine health states (anomaly detection); and (b) settings of machine operation (state estimation). Audio and vibration signals are first processed through Fast Fourier Transform and Principal Component Analysis to extract transformed and informative features. These features are then used in the training of classification and regression models for machine state monitoring. Specifically, three classifiers (K-nearest neighbors, convolutional neural networks and support vector machines) and two regressors (support vector regression and neural network regression) were explored, in terms of their accuracy in machine state prediction. It is shown that the audio and vibration signals are sufficiently rich in information about the machine that 100% state classification accuracy could be accomplished. Data fusion was also explored, showing overall superior accuracy of data-driven regression models.  相似文献   
43.
This paper summarizes the basics of pulsed thermal nondestructive testing (TNDT) including theoretical solutions, data processing algorithms and practical implementation. Typical defects are discussed along with 1D analytical and multi-dimensional numerical solutions. Special emphasis is focused on defect characterization by the use of inverse solutions. A list of TNDT terms is provided. Applications of active TNDT, mainly in the aerospace industry, are discussed briefly, and some trends in the further development of this technique are described.  相似文献   
44.
关键词:双相不锈钢; 流变曲线; 本构方程; 热加工图  相似文献   
45.
As a decisive attribute, flavour could be influenced by HP treatments through multiple physical and chemical pathways within the high pressure (HP)-assisted meat curing process. This investigation aimed to identify the major pathway influencing volatile flavour patterns of two representative vinasse-cured duck (VCD) products with HP treatments (150–300 MPa/15 min), including wet and dry types, by employing headspace fingerprinting as an untargeted approach. Results suggested that HP treatments greatly lowered moisture contents and increased Warner-Bratzler shear force and thiobarbituric acid reactive substances of the cured samples. According to multivariate models, the volatile flavour patterns of the HP-processed VCD could be clearly separated from the unprocessed samples, but the VCD pressurised at different intensities represented similar volatile fingerprinting, which was validated by e-nose analysis. The discriminant analysis (OPLS-DA) model outlined vinasse-derived ethanol, acetic acid, 3-methyl-1-butanol, 2-methyl-1-butanol, phenethyl alcohol and 2-methyl-3-octanone as the major discriminant aromas across the unpressurised and pressurised samples.  相似文献   
46.
Modern refractory castables contain between 3.5 and 5?wt.-% water that is necessary for sufficient flow during emplacement and for the formation of hydrate phases, necessary for the green strength of the material. Prior to the high temperature use of this material, it must be dried very carefully to avoid explosive spalling.This paper will demonstrate that beside conventional drying of pre-shaped materials in resistance furnaces microwave radiation is an energy saving and rapid method to remove pore water as well as hydrate bond water from the castable. In comparison to resistance furnaces, the use of microwave radiation does not affect the castable properties as there are mechanical strength (MOR, CCS), open porosity and pore size distribution. This study proved microwave radiation as valuable alternative with a series of tabular alumina based low cement castables (LLC) in which the water-to-cement-ratio (wcr = 0.64, 0.75, 0.82 and 1.13) was systematically altered by changing the cement concentration at constant mixing water concentration of 4.5%.  相似文献   
47.
Biological information is stored in DNA, RNA and protein sequences, which can be understood as genotypes that are translated into phenotypes. The properties of genotype–phenotype (GP) maps have been studied in great detail for RNA secondary structure. These include a highly biased distribution of genotypes per phenotype, negative correlation of genotypic robustness and evolvability, positive correlation of phenotypic robustness and evolvability, shape-space covering, and a roughly logarithmic scaling of phenotypic robustness with phenotypic frequency. More recently similar properties have been discovered in other GP maps, suggesting that they may be fundamental to biological GP maps, in general, rather than specific to the RNA secondary structure map. Here we propose that the above properties arise from the fundamental organization of biological information into ‘constrained'' and ‘unconstrained'' sequences, in the broadest possible sense. As ‘constrained'' we describe sequences that affect the phenotype more immediately, and are therefore more sensitive to mutations, such as, e.g. protein-coding DNA or the stems in RNA secondary structure. ‘Unconstrained'' sequences, on the other hand, can mutate more freely without affecting the phenotype, such as, e.g. intronic or intergenic DNA or the loops in RNA secondary structure. To test our hypothesis we consider a highly simplified GP map that has genotypes with ‘coding'' and ‘non-coding'' parts. We term this the Fibonacci GP map, as it is equivalent to the Fibonacci code in information theory. Despite its simplicity the Fibonacci GP map exhibits all the above properties of much more complex and biologically realistic GP maps. These properties are therefore likely to be fundamental to many biological GP maps.  相似文献   
48.
张银萍 《煤矿机械》2020,41(3):23-25
介绍了煤矿地面轨道运输矿车自动避障技术。首先介绍了基于雷达的矿车前方障碍物检测技术及其相关算法,然后详细介绍了基于机器视觉的矿车前方障碍物检测系统和常用的图像处理方法以及相关的算法,最后介绍了雷达和机器视觉融合的障碍物检测技术在煤矿地面轨道运输矿车自动避障过程中的应用。  相似文献   
49.
煤矿开采过程中会产生大量的废弃矿井水,不仅造成水资源的大量浪费,而且还威胁着矿区生态环境。本文综述了我国常见矿井水的常规处理方法,以及将矿井水视为水资源的可持续矿井水水处理与资源化技术,首次提出以“时间维度和空间维度”对矿井水进行全时空处理,并着重阐述了矿井水分级处理、分质利用技术,反渗透浓水处理与资源化技术,煤泥处理与资源化技术,以及重金属回收与利用技术等,对煤矿区矿井水处理与资源化利用具有指导意义。  相似文献   
50.
《Ceramics International》2020,46(5):5602-5609
SiC fibers can be obtained by the spinning, curing, and heat treatment of polycarbosilane (PCS); however, the properties of the PCS precursor must be considered to set the correct spinning conditions. Although many studies have focused on the synthesis conditions, the characterization (in particular, the structural characteristics) of PCS fibers, and the polymer itself has limitations. In this study, PCS was prepared in two steps, and the growth of the polymer with respect to the reaction conditions was analyzed. We found that PCS is formed and grown by the rearrangement and subsequent condensation reactions of polydimethylsilane (PDMS). Further, fiber formation was affected by the reaction temperature, time, and pressure. Three types of PCS were obtained under different synthetic conditions, and they were all characterized. Regardless of the structural similarity of the PCS fibers (based on the spectroscopic analysis), the polymers showed different thermal and rheological properties. Our findings will be important in improving the production of PCS fibers (and subsequent SiC fibers) with finely controlled properties.  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