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   1585篇
  免费   57篇
  国内免费   5篇
电工技术   28篇
综合类   1篇
化学工业   315篇
金属工艺   45篇
机械仪表   37篇
建筑科学   23篇
矿业工程   5篇
能源动力   65篇
轻工业   87篇
水利工程   10篇
石油天然气   1篇
无线电   190篇
一般工业技术   356篇
冶金工业   255篇
原子能技术   7篇
自动化技术   222篇
  2023年   10篇
  2022年   24篇
  2021年   50篇
  2020年   37篇
  2019年   36篇
  2018年   48篇
  2017年   49篇
  2016年   48篇
  2015年   42篇
  2014年   46篇
  2013年   110篇
  2012年   52篇
  2011年   78篇
  2010年   53篇
  2009年   61篇
  2008年   87篇
  2007年   65篇
  2006年   42篇
  2005年   55篇
  2004年   38篇
  2003年   27篇
  2002年   28篇
  2001年   18篇
  2000年   19篇
  1999年   21篇
  1998年   59篇
  1997年   41篇
  1996年   46篇
  1995年   28篇
  1994年   28篇
  1993年   27篇
  1992年   24篇
  1991年   22篇
  1990年   18篇
  1989年   14篇
  1988年   13篇
  1987年   13篇
  1986年   11篇
  1985年   10篇
  1984年   16篇
  1983年   19篇
  1982年   7篇
  1981年   9篇
  1979年   8篇
  1978年   10篇
  1977年   13篇
  1976年   14篇
  1974年   9篇
  1973年   8篇
  1972年   6篇
排序方式: 共有1647条查询结果,搜索用时 15 毫秒
61.
Abstract: Recent evidence has demonstrated that nitrites play an important role in the cardiovascular system. Fennel (Foneiculum vulgare) seeds are often used as mouth fresheners after a meal in both the Indian sub‐continent and around the world. The present study aims to quantify the nitrite and nitrates in fennel seeds as well as elucidating the effect of fennel derived‐nitrites on vascular functions. Results from our study show that fennel seeds contain significantly higher amount of nitrites when compared to other commonly used post‐meal seeds. Furthermore our study confirmed the functional effects of fennel derived‐nitrites using in vitro and ex vivo models that describe the promotion of angiogenesis, cell migration, and vasorelaxation. We also showed that chewing fennel seeds enhanced nitrite content of saliva. Thus our study indicates the potential role of fennel derived‐nitrites on the vascular system. Practical Application: This study is focused on determining the effect of fennel‐derived nitrites on angiogenesis (the formation of new blood vessels from pre‐existing ones), cell migration, and vasorelaxation (dilation of blood vessels) thereby preserving cardiovascular health.  相似文献   
62.
A 2D model for the potential distribution in silicon film is derived for a symmetrical double gate MOSFET in weak inversion. This 2D potential distribution model is used to analytically derive an expression for the subthreshold slope and threshold voltage. A drain current model for lightly doped symmetrical DG MOSFETs is then presented by considering weak and strong inversion regions including short channel effects, series source to drain resistance and channel length modulation parameters. These derived models are compared with the simulation results of the SILVACO (Atlas) tool for different channel lengths and silicon film thicknesses. Lastly, the effect of the fixed oxide charge on the drain current model has been studied through simulation. It is observed that the obtained analytical models of symmetrical double gate MOSFETs are in good agreement with the simulated results for a channel length to silicon film thickness ratio greater than or equal to 2.  相似文献   
63.
Quarrying of basalt stone in the Early Cretaceous Rajmahal Trap region of eastern India is increasing at an alarming pace. The quarries have created an extensive ugly landscape of pits and overburden dumps. The stone workshops continuously emit dust. These quarries generate year‐round employment in an impoverished terrain. The workforce mostly comprises the socio‐economically deprived indigenous tribal population. They are an important source of income to the State Governments of Jharkhand and West Bengal. While the need for building stone cannot be denied in a region that is rapidly industrialising and urbanising, issues of land degradation and health cannot be ignored. The paper offers measures to contain environmental degradation and generate alternative sources of income with bio‐fuel crops such as Jatropha curcas.  相似文献   
64.
65.
ABSTRACT

The life-of-mine optimization of open pit mine production scheduling under geological uncertainty is a computationally intensive process. Production scheduling determines the optimal extraction sequence by maximizing net present value (NPV). In this paper, an algorithm is proposed to schedule an open pit mine under geological uncertainty, where instead of solving the whole problem at once, the production schedule is generated by sequentially solving sub-problems. The sub-gradient method is used to generate the upper bound solution of a Lagrangian relaxed sub-problem. If the upper bound relaxed solution is infeasible, a mixed integer programming is applied to the latter solution. The algorithm is validated by solving six problems and is compared to the linear relaxation of the original production scheduling problem. The results show that the proposed algorithm generates a solution that is very close to optimal, with less than a 3% optimality gap. An application at a copper mine, where geological uncertainty is quantified with geostatistical simulations of the related orebody, shows that all constraints are satisfied and an 11% higher NPV is generated when compared to the corresponding deterministic equivalent of the proposed approach, while a 26% higher NPV is generated compared to a common conventional industry approach.  相似文献   
66.
Das  Soham  Guha  Spandan  Ghadai  Ranjan  Sharma  Ashis  Chatterjee  Saikat 《SILICON》2022,14(1):183-199
Silicon - Titanium Nitride (TiN) thin films were deposited by thermal chemical vapor deposition process (CVD) over Si (100) substrate under different substrate temperatures. Morphological,...  相似文献   
67.

Titanium alloys are processed to develop a wide range of microstructure configurations and therefore material properties. While these properties are typically measured experimentally, a framework for property prediction could greatly enhance alloy design and manufacturing. Here a microstructure-sensitive framework is presented for the prediction of strength and ductility as well as estimates of the bounds in variability for these properties. The framework explicitly considers distributions of microstructure via new approaches for instantiation of structure in synthetic samples. The parametric evaluation strategy, including the finite element simulation package FEpX, is used to create and test virtual polycrystalline samples to evaluate the variability bounds of mechanical properties in Ti-6Al-4V. Critical parameters for the property evaluation framework are provided by measurements of single crystal properties and advanced characterization of microstructure and slip system strengths in 2D and 3D. Property distributions for yield strength and ductility are presented, along with the validation and verification steps undertaken. Comparisons between strain localization and slip activity in virtual samples and in experimental grain-scale strain measurements are also discussed.

  相似文献   
68.
Adsorption has been found to be significant in ultrafiltration by mixed matrix membrane. Removal of very low molecular weight solutes compared to the molecular weight cut off of the membrane is facilitated by adsorption. The modeling of the adsorption coupled with concentration polarization is presented based on the mathematical approach developed by Gekas et al. (Gekas et al. Chem Eng Sci. 1993;48:2753–2765), from the first principles. However, extensive modifications were included in theoretical development including those suggested by Ruiz‐Bevia et al. (Ruiz‐Bevia et al. Chem Eng Sci. 1997;52:2343–2352). The developed model captured the rejection dynamics with the help of retention factor. The model equations were solved under the framework of boundary layer analysis, using the integral approach. Effects of the adsorption isotherm and the different parameters affecting the system performance were also investigated. Further, experimental validation of the model results with two different mixed matrix ultrafiltration studies was also elucidated. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2354–2364, 2014  相似文献   
69.
This article describes a subgradient-based near-optimal heuristic algorithm designed for minimizing the search of links that need to be added to an existing telecommunications network to enhance the survivability and routability of the network.  相似文献   
70.
Forty three metameric pairs were obtained by comparison, shade-adjustment, and redyeing of 660 self shades dyed with direct, azoic, vat, and reactive dyes. The pairs were regrouped shadewise and ranked visually in increasing order of metamerism. Spearman's rank correlation coefficients were calculated between 11 measures of metamerism and the visual metameric ranking under three illuminants A, D65, and TL84 in pairs. The illuminant-independent general indices included the indices based on reflectance differences (Bridgeman), weighted reflectance differences (Nimeroff and Yurow), Cohen-Kappauf's residual differences (proposed) obtained from the spectral decompositions of the reflectance spectra of the metameric pair. Illuminant-specific special indices included color-differences under test illuminant, addition, subtraction, division, and multiplication of color-differences under test and reference illuminants, indices based on ΔL*, Δa*, Δb* differences under two illuminants, based on chromatic adapted ΔL*, Δa*, Δb* differences with multiplicative corrections for tristimulus differences under reference illuminant (Berns-Billmeyer), differences of the color constancy indices. The present work showed that indices based on ΔL*, Δa*, Δb* differences under two illuminants, both unmodified and modified by Berns-Billmeyer performed best among the existing indices. The differences of color constancy indices showed good correlation with the degree of metamerism in some cases, and this may be utilized for developing newer indices of metamerism. © 1996 John Wiley & Sons, Inc.  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