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   2820篇
  免费   121篇
  国内免费   89篇
化学   457篇
晶体学   1篇
力学   22篇
综合类   11篇
数学   325篇
物理学   206篇
无线电   2008篇
  2024年   6篇
  2023年   33篇
  2022年   43篇
  2021年   35篇
  2020年   50篇
  2019年   40篇
  2018年   37篇
  2017年   55篇
  2016年   60篇
  2015年   78篇
  2014年   139篇
  2013年   156篇
  2012年   139篇
  2011年   125篇
  2010年   138篇
  2009年   130篇
  2008年   149篇
  2007年   181篇
  2006年   175篇
  2005年   149篇
  2004年   145篇
  2003年   112篇
  2002年   119篇
  2001年   86篇
  2000年   90篇
  1999年   69篇
  1998年   78篇
  1997年   51篇
  1996年   80篇
  1995年   67篇
  1994年   37篇
  1993年   27篇
  1992年   51篇
  1991年   15篇
  1990年   42篇
  1989年   11篇
  1988年   14篇
  1987年   2篇
  1986年   1篇
  1985年   2篇
  1984年   3篇
  1983年   1篇
  1982年   4篇
  1981年   2篇
  1980年   1篇
  1978年   2篇
排序方式: 共有3030条查询结果,搜索用时 15 毫秒
71.
基于CMOS多功能数字芯片的ESD保护电路设计   总被引:1,自引:0,他引:1  
基于CSMC 2P2M 0.6 μm CMOS工艺设计了一种ESD保护电路。整体电路采用Hspice和CSMC 2P2M 的0.6 μm CMOS工艺的工艺库(06mixddct02v24)仿真,基于CSMC 2P2M 0.6 μm CMOS工艺完成版图设计,并在一款多功能数字芯片上使用,版图面积为1 mm×1 mm,参与MPW(多项目晶圆)计划流片,流片测试结果表明,芯片满足设计目标。  相似文献   
72.
于凌宇  冯玉萍 《电子质量》2002,(10):164-168
该文对中国与世界IC产业的发展进行了历史回顾,重点阐述了产业现状与发展方向,并对新世纪的前景进行了科学预测。  相似文献   
73.
SOC时代低功耗设计的研究与进展   总被引:10,自引:1,他引:10  
王祚栋  魏少军 《微电子学》2005,35(2):174-179
在片上系统(SOC)时代,芯片内核的超高功耗密度以及移动应用市场对低功耗的无止境需求,使低功耗设计变得日益重要.文章全面系统地介绍了低功耗设计的相关内容,包括背景、原理和不同层次的功耗优化技术,着重介绍了面向SOC的系统级功耗优化技术.通过对已有研究成果按设计抽象层次和系统功能的分析,指出了其优化的全局性不够充分.提出了基于软硬件协同设计的系统功耗优化思路和设计流程,展望了SOC低功耗设计的发展方向.  相似文献   
74.
基于非接触式IC卡的信息管理系统   总被引:1,自引:0,他引:1  
基于非接触式IC卡的信息管理系统由软硬件组成。硬件主要包括3部分,读写部分,读出或写入射频卡中的数据,其功能主要由SHC1702读写模块完成;显示部分,使用TMl2232A显示芯片以点阵显示代替LED段显示;串口通信部分:负责计算机和刷卡装置之间的通信,使用MAX485芯片以保证足够的通信距离;此外采用的X5043芯片带有4kB的闪存,能在单片机“死机”或掉电的情况下,及时保存重要数据,并尽快使之恢复正常工作状态。软件部分包括单片机的下位机程序,PC机的上位机程序,数据库,实现通信、管理等工作。  相似文献   
75.
This paper discusses how gamma irradiation plants are putting the latest advances in computer and information technology to use for better process control, cost savings, and strategic advantages.

Some irradiator operations are gaining significant benefits by integrating computer technology and robotics with real-time information processing, multi-user databases, and communication networks. The paper reports on several irradiation facilities that are making good use of client/server LANs, user-friendly graphics interfaces, supervisory control and data acquisition (SCADA) systems, distributed I/O with real-time sensor devices, trending analysis, real-time product tracking, dynamic product scheduling, and automated dosimetry reading. These plants are lowering costs by fast and reliable reconciliation of dosimetry data, easier validation to GMP requirements, optimizing production flow, and faster release of sterilized products to market.

There is a trend in the manufacturing sector towards total automation using “predictive process control”. Real-time verification of process parameters “on-the-run” allows control parameters to be adjusted appropriately, before the process strays out of limits. Applying this technology to the gamma radiation process, control will be based on monitoring the key parameters such as time, and making adjustments during the process to optimize quality and throughput. Dosimetry results will be used as a quality control measurement rather than as a final monitor for the release of the product. Results are correlated with the irradiation process data to quickly and confidently reconcile variations. Ultimately, a parametric process control system utilizing responsive control, feedback and verification will not only increase productivity and process efficiency, but can also result in operating within tighter dose control set points.  相似文献   

76.
Modeling the behavior of air plasma spray (APS) process, one of the challenges nowadays is to identify the parameter interdependencies, correlations and individual effects on coating properties, characteristics and influences on the in-service properties. APS modeling requires a global approach which considers the relationships between coating characteristics/ in-service properties and process parameters. Such an approach permits to reduce the development costs. This is why a robust methodology is needed to study these interrelated effects. Artificial intelligence based on fuzzy logic and artificial neural network concepts offers the possibility to develop a global approach to predict the coating characteristics so as to reach the required operating parameters. The model considered coating properties (porosity) and established the relationships with power process parameters (arc current intensity, total plasma gas flow rate, hydrogen content) on the basis of artificial intelligence rules. Consequently, the role and the effects of each power process parameter were discriminated. The specific case of the deposition of alumina–titania (Al2O3–TiO2, 13% by weight) by APS was considered.  相似文献   
77.
In quantitative on-line/in-line monitoring of chemical and bio-chemical processes using spectroscopic instruments, multivariate calibration models are indispensable for the extraction of chemical information from complex spectroscopic measurements. The development of reliable multivariate calibration models is generally time-consuming and costly. Therefore, once a reliable multivariate calibration model is established, it is expected to be used for an extended period. However, any change in the instrumental response or variations in the measurement conditions can render a multivariate calibration model invalid. In this contribution, a new method, spectral space transformation (SST), has been developed to maintain the predictive abilities of multivariate calibration models when the spectrometer or measurement conditions are altered. SST tries to eliminate the spectral differences induced by the changes in instruments or measurement conditions through the transformation between two spectral spaces spanned by the corresponding spectra of a subset of standardization samples measured on two instruments or under two sets of experimental conditions. The performance of the method has been tested on two data sets comprising NIR and MIR spectra. The experimental results show that SST can achieve satisfactory analyte predictions from spectroscopic measurements subject to spectrometer/probe alteration, when only a few standardization samples are used. Compared with the existing popular methods designed for the same purpose, i.e. global PLS, univariate slope and bias correction (SBC) and piecewise direct standardization (PDS), SST has the advantages of implementation simplicity, wider applicability and better performance in terms of predictive accuracy.  相似文献   
78.
K. Jones 《Chromatographia》1988,25(7):577-581
Summary The flexibility of process scale high performance liquid chromatography is demonstrated by three examples of reversed-phase separations (a) a standard purification (b) isolation of trace compounds, and (c) recovery from crystallisation mother liquors. It was shown that a material, thought to be acceptably pure, contained a toxic impurity, and a remaining impurity, a previously unseen component of potential therapeutic interest. Favourable cost data were indicated for example (3). This work was conducted in the Chemical Technology Unit, University of Manchester Institute of Science and Technology, PO Box 88, Manchester M6O 1OD, UK.  相似文献   
79.
Reaction optimisation and understanding is fundamental for process development and is achieved using a variety of techniques. This paper explores the use of self-optimisation and experimental design as a tandem approach to reaction optimisation. A Claisen-Schmidt condensation was optimised using a branch and fit minimising algorithm, with the resulting data being used to fit a response surface model. The model was then applied to find new responses for different metrics, highlighting the most important for process development purposes.  相似文献   
80.
许竞早  彭振磊  张育红  王川  金国杰 《色谱》2018,36(4):376-380
建立了阀切换-离子色谱法测定1,2-环氧丁烷(1,2-BO)产品中有机酸(甲酸、乙酸和丙酸)的方法。样品经乙醇稀释后,通过阀切换技术,有机酸被IonPac TAC-ULP1捕集柱捕集,然后进入IonPac AS11分析柱分离,并由电导检测器检测。结果表明:甲酸、乙酸和丙酸均能实现较好地分离,在各自的范围内其色谱峰面积呈现良好的线性关系。实际样品的加标回收率为92.5%~111.8%,相对标准偏差小于5.6%(n=3),检出限为0.60~4.80 μg/L。该方法具有前处理简单、快速、准确等特点,适用于不溶于水的有机体系中有机酸的分析。  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