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   1122篇
  免费   104篇
  国内免费   26篇
电工技术   20篇
综合类   46篇
化学工业   228篇
金属工艺   78篇
机械仪表   87篇
建筑科学   84篇
矿业工程   8篇
能源动力   57篇
轻工业   131篇
水利工程   20篇
石油天然气   16篇
武器工业   11篇
无线电   90篇
一般工业技术   129篇
冶金工业   92篇
原子能技术   7篇
自动化技术   148篇
  2023年   9篇
  2022年   18篇
  2021年   29篇
  2020年   33篇
  2019年   23篇
  2018年   21篇
  2017年   35篇
  2016年   48篇
  2015年   35篇
  2014年   45篇
  2013年   88篇
  2012年   55篇
  2011年   81篇
  2010年   56篇
  2009年   56篇
  2008年   55篇
  2007年   82篇
  2006年   62篇
  2005年   53篇
  2004年   64篇
  2003年   46篇
  2002年   33篇
  2001年   28篇
  2000年   21篇
  1999年   21篇
  1998年   17篇
  1997年   14篇
  1996年   18篇
  1995年   16篇
  1994年   5篇
  1993年   7篇
  1992年   8篇
  1991年   7篇
  1990年   5篇
  1989年   12篇
  1988年   6篇
  1987年   4篇
  1986年   5篇
  1985年   6篇
  1984年   5篇
  1983年   4篇
  1981年   2篇
  1979年   1篇
  1978年   1篇
  1972年   1篇
  1967年   2篇
  1965年   1篇
  1964年   2篇
  1959年   1篇
  1955年   2篇
排序方式: 共有1252条查询结果,搜索用时 14 毫秒
1.
奇异值分解方法在日负荷曲线降维聚类分析中的应用   总被引:1,自引:0,他引:1  
负荷曲线聚类对负荷预测、电网规划和需求侧响应等应用有重要意义,但是海量的历史负荷曲线为数据存储和计算效率带来了挑战。为此,提出一种基于奇异值分解的日负荷曲线降维聚类方法。首先利用奇异值分解将日负荷曲线数据旋转变换至新的坐标系中,求解出的奇异值反映了相应坐标轴的重要程度。然后,将负荷曲线在各坐标轴上的坐标作为降维指标,用以反映负荷曲线的主要特征,再依据奇异值下降趋势确定指标的数目。最后,以各坐标轴对应的奇异值作为指标权重,采用基于加权欧式距离的K-means算法对日负荷曲线进行聚类。算例结果表明所提方法运行时间短、鲁棒性好,可以提高负荷曲线聚类的准确性。  相似文献   
2.
Highway design which ensures that successive elements are coordinated in such a way as to produce harmonious and homogeneous driver performances along the road is considered consistent and safe. On the other hand, an alignment which requires drivers to handle high speed gradients and does not meet drivers' expectancy is considered inconsistent and produces higher crash frequency.  相似文献   
3.
There are practical situations in which the quality of a process or product can be better characterized by a functional relationship between a response variable and one or more explanatory variables, which is called profile. Such profiles frequently can be represented adequately using linear or nonlinear models. While there are several studies in monitoring profiles, there are few studies to evaluate the capability of a process with profile quality characteristic; specifically, there is no method in the literature to analyze process capability characterized by nonlinear profiles. In this paper, we propose two methods to measure the capability of these processes, based on the concept of functional depth. These methods do not have distributional assumptions and extend to functional data the Process Capability Indexes proposed by Clements 1 to measure the capability of a process characterized by a random variable. Performance of the proposed methods is evaluated through simulation studies. An example illustrates the applicability of these methods. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
4.
蔡玉强  孟欣 《流体机械》2015,(4):17-20,56
蒸汽压缩蒸馏装置是空间站中实现水的再生与闭路循环的关键。罗茨压缩机作为蒸汽压缩蒸馏装置中的核心设备对其工作性能起着至关重要的作用。查阅相关文献,对罗茨压缩机转子的型线进行改进,建立了罗茨压缩机二维有限元模型。运用动网格技术对罗茨压缩机内部瞬态流动进行了数值模拟,得出了罗茨压缩机流量、流速场、压力场随时间的变化规律。  相似文献   
5.
Expanded gamut printing is an approach in color reproduction that expands the color gamut of conventional CMYK printing processes via the use of additional colorants, such as Orange, Green, and Violet inks. This study evaluates the ability of commercial color management software to create an accurate solution for an expanded gamut printing system. In this study, two printing processes were used, an Epson SureColor P9000 inkjet printer/proofer and an HP Indigo 7900 digital production press, both with 7-color expanded gamut ink sets. Software solutions from Alwan, CGS ORIS, ColorLogic, GMG Color, Heidelberg, and Kodak were evaluated. The systems were tested to see how well they could reproduce the colors in the entire PANTONE+ Solid Coated spot color library. It is shown that the solutions are able to reproduce 89% to 94% of the spot colors on the Epson P9000 inkjet printer and 77% to 87% of the library on the Indigo 7900, both to less than two CIEDE2000 (a typical tolerance in label and packaging work). The number of color patches in expanded gamut characterization test charts was noted, as this is still an area of proprietary, nonstandardized working practice. There are many different colorant combinations that can make the same color in expanded gamut printing. The ink build created by the different software solutions was studied, as it relates to press stability through appropriate choice of colorants. Pantone and Adobe provide everyday commercial tools for expanded color workflows. The study identified some issues with products from these companies that could confuse a less-skilled user in a busy production environment. The conclusion of the study is that expanded gamut solutions for spot color printing produce totally acceptable results for digital printing processes; expanded gamut printing is ready, here and now. The findings show that expanded gamut printing can replace cumbersome conventional spot color workflows creating considerable savings and advantages, especially for label and packaging printers.  相似文献   
6.
To investigate the application of the multi-beam angle sensor (MBAS) to high-precision optical aspheric and freeform surfaces, which are critical components in optical systems, we present a method of using an MBAS to reconstruct an aspheric surface from angle data. The MBAS is based on a multi-autocollimator system with a microlens array, which can split the beam into several spots and can convert centroid detection of the light intensity into an angle measurement. The MBAS is designed to address the curvature-range problem via a circumferential scan better than other methods and automatically eliminates the tilt error caused by rotation of a workpiece. Using a tracking technique, the MBAS can automatically determine focal spot positions from the centroid measurement of the light intensity. This is directly related to the accuracy of the angular difference measurement. The experimental results confirm the feasibility of using an MBAS for 3D surface profile measurements of cylindrical surfaces.  相似文献   
7.
8.
9.
The ability to predict how far a drug will penetrate into the tumour microenvironment within its pharmacokinetic (PK) lifespan would provide valuable information about therapeutic response. As the PK profile is directly related to the route and schedule of drug administration, an in silico tool that can predict the drug administration schedule that results in optimal drug delivery to tumours would streamline clinical trial design. This paper investigates the application of mathematical and computational modelling techniques to help improve our understanding of the fundamental mechanisms underlying drug delivery, and compares the performance of a simple model with more complex approaches. Three models of drug transport are developed, all based on the same drug binding model and parametrized by bespoke in vitro experiments. Their predictions, compared for a ‘tumour cord’ geometry, are qualitatively and quantitatively similar. We assess the effect of varying the PK profile of the supplied drug, and the binding affinity of the drug to tumour cells, on the concentration of drug reaching cells and the accumulated exposure of cells to drug at arbitrary distances from a supplying blood vessel. This is a contribution towards developing a useful drug transport modelling tool for informing strategies for the treatment of tumour cells which are ‘pharmacokinetically resistant’ to chemotherapeutic strategies.  相似文献   
10.
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