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   2793篇
  免费   123篇
  国内免费   101篇
电工技术   34篇
综合类   67篇
化学工业   213篇
金属工艺   51篇
机械仪表   204篇
建筑科学   116篇
矿业工程   27篇
能源动力   95篇
轻工业   76篇
水利工程   15篇
石油天然气   38篇
武器工业   15篇
无线电   314篇
一般工业技术   470篇
冶金工业   62篇
原子能技术   31篇
自动化技术   1189篇
  2024年   3篇
  2023年   21篇
  2022年   23篇
  2021年   37篇
  2020年   48篇
  2019年   43篇
  2018年   45篇
  2017年   62篇
  2016年   105篇
  2015年   121篇
  2014年   178篇
  2013年   233篇
  2012年   112篇
  2011年   196篇
  2010年   132篇
  2009年   156篇
  2008年   151篇
  2007年   169篇
  2006年   170篇
  2005年   152篇
  2004年   131篇
  2003年   123篇
  2002年   103篇
  2001年   56篇
  2000年   59篇
  1999年   59篇
  1998年   68篇
  1997年   37篇
  1996年   27篇
  1995年   27篇
  1994年   27篇
  1993年   24篇
  1992年   16篇
  1991年   21篇
  1990年   18篇
  1989年   17篇
  1988年   6篇
  1987年   4篇
  1986年   4篇
  1985年   5篇
  1984年   3篇
  1982年   4篇
  1981年   4篇
  1980年   2篇
  1979年   1篇
  1978年   6篇
  1977年   4篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
排序方式: 共有3017条查询结果,搜索用时 15 毫秒
1.
By leveraging the secret data coding using the remainder storage based exploiting modification direction (RSBEMD), and the pixel change operation recording based on multi-segment left and right histogram shifting, a novel reversible data hiding (RHD) scheme is proposed in this paper. The secret data are first encoded by some specific pixel change operations to the pixels in groups. After that, multi-segment left and right histogram shifting based on threshold manipulation is implemented for recording the pixel change operations. Furthermore, a multiple embedding policy based on chess board prediction (CBP) and threshold manipulation is put forward, and the threshold can be adjusted to achieve adaptive data hiding. Experimental results and analysis show that it is reversible and can achieve good performance in capacity and imperceptibility compared with the existing methods.  相似文献   
2.
An effective practical approach that allows not only a significant reduction in the scope of practical experiments in the course of studying suspension separation processes in hydrocyclones, but also makes it possible to assess the intensity of random components of the processes and define the interrelation between such components and hydrodynamics of flows in a hydrocyclone is presented. Within the frames of the developed probabilistic‐statistical model of suspension separation in hydrocyclones on the basis of statistical self‐similarity properties, a relationship was found between determined and random components of the processes. This allowed transitioning from three‐parameter probability density functions for suspension particles in hydrocyclones to two‐parameter functions; thus significantly improving the efficiency of practical application of the developed model.  相似文献   
3.
Eight datasets of 1-h black carbon (BC) concentrations measured in Warsaw agglomeration (Poland), at urban background and sub-urban sites, and in Racibórz, a small town in Upper Silesia district (regional background site) were analyzed to evaluate BC levels, daily profiles and statistical distributions of concentrations in Central-Eastern European region. The observed mean levels ranged from 1483 ng m−3 in suburban site during summer to 3358 ng m−3 in regional background site in winter. Observed diurnal patterns were bimodal in the locations dominated by traffic emissions, but unimodal, with elevated evening peak in individually heated residential area. Three theoretical frequency distributions were applied to fit analyzed datasets separately. The lognormal distribution was the most appropriate to represent the middle-range values, while the high concentrations were satisfactorily predicted by the type I two-parameter exponential distribution which was used to estimate the return periods of extreme concentrations for winter months.  相似文献   
4.
质量控制图系统的实现及在SMT中的应用   总被引:1,自引:0,他引:1  
张丹 《电子质量》2006,(4):39-41
本文将控制图理论与计算机技术相结合,开发了质量控制图系统.介绍了该系统的设计方案和关键技术问题,并以电子产品制造中监控SMT机的焊膏厚度为例说明了系统的应用.  相似文献   
5.
Three-dimensional models, or pharmacophores, describing Euclidean constraints on the location on small molecules of functional groups (like hydrophobic groups, hydrogen acceptors and donors, etc.), are often used in drug design to describe the medicinal activity of potential drugs (or ‘ligands’). This medicinal activity is produced by interaction of the functional groups on the ligand with a binding site on a target protein. In identifying structure-activity relations of this kind there are three principal issues: (1) It is often difficult to “align” the ligands in order to identify common structural properties that may be responsible for activity; (2) Ligands in solution can adopt different shapes (or `conformations’) arising from torsional rotations about bonds. The 3-D molecular substructure is typically sought on one or more low-energy conformers; and (3) Pharmacophore models must, ideally, predict medicinal activity on some quantitative scale. It has been shown that the logical representation adopted by Inductive Logic Programming (ILP) naturally resolves many of the difficulties associated with the alignment and multi-conformation issues. However, the predictions of models constructed by ILP have hitherto only been nominal, predicting medicinal activity to be present or absent. In this paper, we investigate the construction of two kinds of quantitative pharmacophoric models with ILP: (a) Models that predict the probability that a ligand is “active”; and (b) Models that predict the actual medicinal activity of a ligand. Quantitative predictions are obtained by the utilising the following statistical procedures as background knowledge: logistic regression and naive Bayes, for probability prediction; linear and kernel regression, for activity prediction. The multi-conformation issue and, more generally, the relational representation used by ILP results in some special difficulties in the use of any statistical procedure. We present the principal issues and some solutions. Specifically, using data on the inhibition of the protease Thermolysin, we demonstrate that it is possible for an ILP program to construct good quantitative structure-activity models. We also comment on the relationship of this work to other recent developments in statistical relational learning. Editors: Tamás Horváth and Akihiro Yamamoto  相似文献   
6.
采用了双极晶体管作为双极工艺的测试结构,将在线工艺的统计分析理论应用于双极工艺,研制了双极工艺的统计分析软件。最后给出了双极工艺的某些分析结果。  相似文献   
7.
一种新的加权最小二乘测距定位方法   总被引:8,自引:0,他引:8  
万群  彭应宁 《电子与信息学报》2002,24(12):1980-1984
三站二维定位问题是最小定位问题,一般只利用几何关系就能获得定位估计,但由于未利用距离测量的统计信息,定位精度较差。该文先将点到点的距离测量转化为点到线的距离估计,再在此基础上推导出一种新的加权几休定位方法,其中加权的确定利用了距离测量的统计信息。仿真实验表明,在测距误差较小时新方法具有更高的定位精度。  相似文献   
8.
Hock Chuan Chan   《Displays》2008,29(3):260-267
It is important to verify assumptions and methods of image retrieval against actual human behavior. A study was conducted to compare similarity methods of color histograms against human assessment of similarity. The similarity methods tested include basic histogram intersection, center histogram matching, locality histogram matching, and size-weighted histogram matching. 161 subjects participated in the empirical study. The findings, based on Spearman correlation analysis, showed that both the basic histogram intersection method and size-weighted histogram are very close to human assessment of similarity (Spearman correlation coefficient of 0.915). The other two are not close to human judgment on similarity. This study illustrates an alternative approach to evaluating matching algorithms. Unlike the usual measures of recall and precision, this approach emphasizes human validation. Fewer images are required with the use of statistical testing.  相似文献   
9.
10.
The three-parameter and two-parameter Weibull distributions are compared using 26 mechanical property data sets of fiber-reinforced polymeric (FRP) composite materials manufactured by the pultrusion process. Both strength and stiffness properties were examined. The probability distributions were compared on the basis of goodness of fit, nominal design values, and allowable load to achieve uniform reliability. It is recommended that the two-parameter Weibull distribution be used to characterize FRP composite material properties. The primary basis for this recommendation is small differences in nominal design values and small differences in allowable loads between the two-parameter and three-parameter Weibull distributions. Other supporting reasons for the recommendation are similar observed significance levels in distribution fitting, computational efficiency, and the fact that the location parameter of the three-parameter Weibull distribution is near the first order statistic.  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