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   2195篇
  免费   53篇
  国内免费   3篇
电工技术   58篇
综合类   6篇
化学工业   545篇
金属工艺   32篇
机械仪表   39篇
建筑科学   215篇
矿业工程   6篇
能源动力   36篇
轻工业   231篇
水利工程   14篇
石油天然气   2篇
无线电   129篇
一般工业技术   319篇
冶金工业   301篇
原子能技术   17篇
自动化技术   301篇
  2023年   13篇
  2022年   37篇
  2021年   49篇
  2020年   22篇
  2019年   30篇
  2018年   27篇
  2017年   18篇
  2016年   57篇
  2015年   64篇
  2014年   64篇
  2013年   112篇
  2012年   82篇
  2011年   120篇
  2010年   59篇
  2009年   89篇
  2008年   99篇
  2007年   83篇
  2006年   74篇
  2005年   71篇
  2004年   63篇
  2003年   37篇
  2002年   47篇
  2001年   30篇
  2000年   23篇
  1999年   41篇
  1998年   74篇
  1997年   55篇
  1996年   49篇
  1995年   30篇
  1994年   25篇
  1993年   29篇
  1992年   27篇
  1991年   22篇
  1990年   20篇
  1987年   24篇
  1986年   21篇
  1985年   21篇
  1984年   27篇
  1983年   25篇
  1982年   17篇
  1981年   20篇
  1980年   25篇
  1976年   19篇
  1975年   23篇
  1971年   14篇
  1970年   16篇
  1969年   15篇
  1968年   12篇
  1967年   16篇
  1966年   18篇
排序方式: 共有2251条查询结果,搜索用时 0 毫秒
51.
We propose a new current conveyor terminology and explain how these terms are coined. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
52.
统计不相关最佳鉴别矢量集的本质研究   总被引:6,自引:0,他引:6  
对统计不相关最佳鉴别矢量集的本质进行研究,在基于总体散布矩阵特征分解的基础上,构造了一种白化变换,使得变换后的样本空间中的总体散布矩阵为单位矩阵,这样使得传统的最佳鉴别矢量集算法得到的均是具有统计不相关的最佳鉴别矢量集,从而揭示了统计不相关最佳鉴别变换的本质——白化变换加普通的线性鉴别变换。该方法的最大优点在于所获得的最优鉴别矢量同时具有正交性和统计不相关性。该方法对代数特征抽取具有普遍适用性。用ORL人脸数据库的数值实验,验证了该方法的有效性。  相似文献   
53.
Materials Data for Fatigue Life Calculation of Steel Sheet Structures for Automotive Engineering Within a joint project of the steel and automotive industry 17 steel sheet materials for automotive engineering in various delivery and forming conditions at temperatures of –40 °C, 22 °C and 100 °C were investigated. In the course of 37 test series strain controlled fatigue curves to crack initiation and stress‐strain‐curves under monotonic and cyclic loading were determined. All experimental data, hysteresis loops and determined cyclic properties are available in a database. A correlation between the mechanical properties from tensile tests and the properties from strain controlled cyclic experiments seems to be possible.  相似文献   
54.
Based on the solidification theory for metal alloys, a simple recipe for the controlled processing of globular microstructures without external stirring is presented: Firstly, small solidification nuclei must be distributed homogeneously throughout a melt. In New Rheocasting (NRC) these nuclei are formed by forced homogeneous nucleation due to partial quenching of the melt, while in Super Rheocasting (SRC) the nuclei are “second phase particles” in specially designed alloys, which are grown in a controlled fashion in a certain temperature range. Potential alloy compositions for SRC are provided. Secondly, given these melts with small particles in them, globular growth can be assured by utilizing the Gibbs‐Thomson “self healing effect” and slow further cooling to allow diffusion in the melt and to suppress constitutional supercooling. This simple recipe is applicable to various ferrous and non‐ferrous alloys. If an SRC alloy is cooled more rapidly than necessary for globular growth of the primary phase, but is held sufficiently long in the SRC range for dispersoid formation, these dispersoids can act as potent grain refiners and possibly enhance elevated temperature properties. A combination of both processes by using SRC alloys in the NRC equipment may lead to pressure tight castings with low porosity and finer grain structure than can be achieved with NRC on its own, and consequently, better mechanical properties.  相似文献   
55.
It is argued that Kirton's theory of styles of creativity is conceptually and methodologically unsound. A solution to the conceptual and methodological dilemmas is offered by way of making a clear‐cut distinction between novelty on the stimulus and novelty on the response side. This distinction is used as a platform for the development of a new taxonomy of different kinds of creativity and intelligent behaviour. A major feature of this new model is the distinction made between proactive and reactive creativity. The implications of this distinction for opening new avenues for a more differentiated assessment of creativity, as well as for the development of a conceptually firmer and more differentiated platform for developing new practical training programmes in creativity are suggested.  相似文献   
56.
Intestinal epithelial cells (IEC) can exist as polarized cells and are capable of secreting interleukin-6 (IL-6), yet it has not been determined if this IL-6 is secreted in a polarized fashion. Using the non-transformed rat IEC-6 intestinal epithelial cell line grown on microporous membrane inserts, we have determined that these cells were capable of secreting IL-6 preferentially to the basal surface when stimulated basally with IL-1 beta. In contrast, stimulation of the cells with TNF-alpha resulted in an equal level of IL-6 secretion to the apical and basal surfaces, regardless of whether the cells were stimulated by the apical or basal route. Experiments designed to test the permeability of the IEC-6 cell layer to apically added sodium fluorescein confirmed that neither IL-1 beta nor TNF-alpha altered the integrity of the cell layer after three days. These results suggest that IEC may have the capacity to secret IL-6 in different patterns depending upon the stimulation received. This would allow communication between the IEC and lamina propria cells via basal secretion and rapid communication between IEC via apical secretion.  相似文献   
57.
The knowledge of interactions between different molecules is undoubtedly the driving force of all contemporary biomedical and biological sciences. Chemical biology/biological chemistry has become an important multidisciplinary bridge connecting the perspectives of chemistry and biology to the study of small molecules/peptidomimetics and their interactions in biological systems. Advances in structural biology research, in particular linking atomic structure to molecular properties and cellular context, are essential for the sophisticated design of new medicines that exhibit a high degree of druggability and very importantly, druglikeness. The authors of this contribution are outstanding scientists in the field who provided a brief overview of their work, which is arranged from in silico investigation through the characterization of interactions of compounds with biomolecules to bioactive materials.  相似文献   
58.
A comparative study of the purification of betanin   总被引:3,自引:0,他引:3  
Betanin is a natural pigment with antioxidant properties used as a food colourant. This work describes the spectrophotometric and chromatographic quantification of betanin (2S/15S) and its epimer isobetanin (2S/15R) in fresh beetroot juice, food-grade beetroot powder and betanin standard diluted in dextrin. Absorption spectra of all three samples were deconvoluted using a mixed three-function model. Food-grade beetroot powder has the largest amount of violet-red impurities, probably formed during processing. The purification of betanin from these complex matrices was carried out by seven different methods. Ion exchange chromatography was the most efficient method for the purification of betanin from all samples; however, fractions contain high amounts of salt. Reversed-phase HPLC as well as reversed-phase column chromatography also produced good results at a much faster rate. The longer retention time of isobetanin when compared to betanin in reversed-phase conditions has been investigated by means of quantum-mechanical methods.  相似文献   
59.
目的:探究人乳N-链寡糖组(human milk N-glycome,HMN)与牛乳N-链寡糖组(bovine milk N-glycome,BMN)对小鼠肠道菌群的影响.方法:以C57BL/6J雄性小鼠为对象,首先在体外测定粪便菌群中与N-链寡糖相关的糖苷酶活性,并模拟粪便菌群对HMN与BMN的利用;然后将小鼠随机分...  相似文献   
60.
Learning comprehensive spatiotemporal features is crucial for human action recognition.Existing methods tend to model the spatiotemporal feature blocks in an in...  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