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   1375篇
  免费   20篇
电工技术   11篇
化学工业   558篇
金属工艺   12篇
机械仪表   27篇
建筑科学   39篇
矿业工程   1篇
能源动力   72篇
轻工业   213篇
水利工程   9篇
石油天然气   1篇
无线电   65篇
一般工业技术   220篇
冶金工业   58篇
原子能技术   6篇
自动化技术   103篇
  2024年   17篇
  2023年   36篇
  2022年   87篇
  2021年   105篇
  2020年   38篇
  2019年   52篇
  2018年   59篇
  2017年   50篇
  2016年   55篇
  2015年   46篇
  2014年   51篇
  2013年   73篇
  2012年   63篇
  2011年   90篇
  2010年   75篇
  2009年   53篇
  2008年   79篇
  2007年   65篇
  2006年   48篇
  2005年   27篇
  2004年   22篇
  2003年   28篇
  2002年   24篇
  2001年   15篇
  2000年   14篇
  1999年   13篇
  1998年   4篇
  1997年   8篇
  1996年   9篇
  1995年   7篇
  1994年   7篇
  1993年   6篇
  1992年   6篇
  1991年   6篇
  1990年   5篇
  1989年   4篇
  1988年   3篇
  1987年   3篇
  1986年   4篇
  1985年   4篇
  1984年   5篇
  1982年   3篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1977年   6篇
  1975年   4篇
  1974年   2篇
  1970年   2篇
  1966年   2篇
排序方式: 共有1395条查询结果,搜索用时 0 毫秒
991.
Summary Three types of a modified biopolymer based on the mycelium of Penicillium chrysogenum were evaluated as to their sorption characteristics for Hg2+, Pb2+, Cu2+ and Cd2+. Their useful and total sorption capacities were calculated from their respective breakthrough curves. The highest sorption capacity was recorded for Hg2+. Evidence is presented that the retained metals can be easily eluted with diluted mineral acids.  相似文献   
992.
    
This article aimed to evaluate the chemical, technological and sensory characteristics of gluten-free cakes made with teff (Eragrostis tef). Four cakes were evaluated: T1, 100% teff flour; T2, 75% teff flour, 12.5% rice flour, 12.5% cassava starch; T3, 50% teff flour, 25% rice flour, 25% cassava starch and T4, 25% teff flour, 37.5% rice flour, 37.5% cassava starch. Higher percentages of teff increased total ash. For apparent and specific volumes, T4 was the one with the highest mean. In sensory analysis, the attributes of appearance, colour and odour did not have significant difference among treatments. T1 received the lowest overall average for flavour (5.03). Regarding the purchase intention, the cakes did not show significant difference between T3 and T2 (3.25 and 3.08). T2, T3 and T4 obtained acceptance index higher than 70%. The use of teff flour in cakes can be promising in gluten free diet.  相似文献   
993.
A series of 37 benzolactam derivatives were synthesized, and their respective affinities for the dopamine D2 and D3 receptors evaluated. The relationships between structures and binding affinities were investigated using both ligand‐based (3D‐QSAR) and receptor‐based methods. The results revealed the importance of diverse structural features in explaining the differences in the observed affinities, such as the location of the benzolactam carbonyl oxygen, or the overall length of the compounds. The optimal values for such ligand properties are slightly different for the D2 and D3 receptors, even though the binding sites present a very high degree of homology. We explain these differences by the presence of a hydrogen bond network in the D2 receptor which is absent in the D3 receptor and limits the dimensions of the binding pocket, causing residues in helix 7 to become less accessible. The implications of these results for the design of more potent and selective benzolactam derivatives are presented and discussed.  相似文献   
994.
    
We report herein, a biomimetic approach for highly selective monodemethylation of N,N‐dimethyl anilines to generate secondary amines and subsequent coupling with α‐ketocarboxylic acids or alkynyl carboxylic acids to form α‐ketoamides or alkynamides respectively under visible light photoredox catalyst in a single operation. From the deuterium‐labeling experiment, it was probed that demethylation is the slowest step in this tandem process. Whereas, control experiments and spectroscopic studies revealed that photoredox catalyst is also involved in the subsequent amidation step. The reaction proceeds smoothly at room temperature providing moderate to excellent yield of the coupling products. The amides have also been converted to a series of biologically active spiro compounds.

  相似文献   

995.
    
Fire design of a historical structural steel column The old Lokhalle 21 in Brandenburg Wildau is soon filled with life again. In the historic industrial hall a flexible mixed use of sales, commercial and office areas as well as individual environments for artists is created. Due to the intended change of use of the building, any grandfather rights for the existing hall structure will be lost. The existing hall support structure consists of truss supports and truss roof. This article describes the fire protection design of a trussed column made of historical steel. The truss structure of the steel column is to be left without any fire protection coating or clothing. The report assesses the fire resistance of the column, based on a representative natural fire scenario, taking into account the material properties of the historical steel. Furthermore, measures for the trussed column are developed to fulfill the fire protection requirements.  相似文献   
996.
    
This paper investigates the feasibility of Fourier transform near-infrared (FT-NIR) spectroscopy, a fast and easy method based on chemometric methods to detect corn starch illegally added to turmeric powder. In this work, the pure turmeric powders were blended with corn starch to generate different concentrations (1–30%)(w/w) of starch-adulterated turmeric samples. The reflectance spectra of total of 224 samples were taken by FT-NIR spectroscopy. The exploratory data analysis was done by principal component analysis (PCA). The starch related peaks were selected by variable importance in projection (VIP) method and were explored by examination of original reflectance spectra, 1st derivative spectra, PCA loadings and β coefficients plot of the partial least square regression (PLSR) model. The coefficient of determination (R2) and root-mean-square error of partial least square regression (PLSR) models were found to be 0.91–0.99 and 0.23–1.3%, respectively, depending on the pre-processing techniques of spectral data. The figure of merit (FOM) of the model was found with the help of net analyte signal (NAS) theory.  相似文献   
997.
998.
    
ABSTRACT

As supervisor of the automation system during partially automated driving, it is essential for the driver to have a good awareness of the automation to fulfill this new task sufficiently. Therefore, feedback about intentions of the automation, for example lane changes, is crucial. So far, this feedback is mainly presented visually to the driver. Conversely, in this article, feedback for announcing lane changes is realized via active vehicle roll motions. Several designs are implemented in an automated test vehicle and are evaluated in four different driving scenarios on a test track. Totally, 39 participants rated the vehicle roll motions, for example, regarding the items roll direction, intensity, usefulness, and the predictability of the driving behavior. The results show that active roll motions as feedback for announcing automated lane changes should be clearly perceptible and are considered useful, not misleading, and support the drivers regarding their mode/system awareness.  相似文献   
999.
    
Multilevel inverter (MLI) generates stepped voltage with appropriate switching combination of power devices, thus restraining the requirement of filter circuit for an efficient power conversion. MLIs are attracting due to some of the major features like economic cost, installation space, bulkiness, complexity along with its enormous applications in industries like cement factory, ceramic industry, aerospace applications etc. In this paper, a single-phase generalised inverter based on five different algorithms is proposed that uses the minimum of overall power components. The presented topology can be used in low and medium voltage applications. To verify the simulation results obtained by MATLAB/Simulink, DS1103 controller is used to generate the corresponding experimental results by developing a prototype model in the laboratory. Nevertheless, a comparative assessment for the different required components of the proposed topology is carried out with some recently developed topologies. Reduction in power switches, driver circuits and DC voltage sources reduces the size, cost, complexity and enhances the overall performance. In addition, level per switch ratio is added in this paper to decide the effectiveness of the proposed topology.  相似文献   
1000.
    
The present work deals with the thermodynamic analysis of a solar-powered triple combined power cycle to generate emission-free power. The triple combined cycle comprises one topping cycle as Brayton cycle and two bottoming cycles, namely, steam Rankine cycle (SRC) and organic Rankine cycle (ORC). The Brayton cycle employs double-stage compression with intercooling. During intercooling, heat energy rejected by the compressed air was further utilized in the ORC. The energy carried away after the turbine exit was used in the SRC. The proposed cycle performance is investigated for three working fluids to use with the bottoming ORC. Results showed that the maximum overall thermal efficiency and work output of solar energy-based triple combined cycle are found 21.89% and 218.98 kJ/kg air, respectively, for organic fluid R245fa at the topping cycle pressure ratio of 31.  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