全文获取类型
收费全文 | 206032篇 |
免费 | 15421篇 |
国内免费 | 7842篇 |
专业分类
电工技术 | 11267篇 |
技术理论 | 14篇 |
综合类 | 11224篇 |
化学工业 | 35756篇 |
金属工艺 | 10558篇 |
机械仪表 | 12024篇 |
建筑科学 | 16433篇 |
矿业工程 | 4974篇 |
能源动力 | 5857篇 |
轻工业 | 12698篇 |
水利工程 | 3220篇 |
石油天然气 | 11089篇 |
武器工业 | 1345篇 |
无线电 | 25530篇 |
一般工业技术 | 26760篇 |
冶金工业 | 10950篇 |
原子能技术 | 2123篇 |
自动化技术 | 27473篇 |
出版年
2024年 | 885篇 |
2023年 | 3272篇 |
2022年 | 5859篇 |
2021年 | 7967篇 |
2020年 | 5824篇 |
2019年 | 5022篇 |
2018年 | 5430篇 |
2017年 | 6207篇 |
2016年 | 5703篇 |
2015年 | 7301篇 |
2014年 | 9547篇 |
2013年 | 12291篇 |
2012年 | 12250篇 |
2011年 | 13896篇 |
2010年 | 11630篇 |
2009年 | 11482篇 |
2008年 | 10892篇 |
2007年 | 10477篇 |
2006年 | 10866篇 |
2005年 | 9634篇 |
2004年 | 6568篇 |
2003年 | 5778篇 |
2002年 | 5258篇 |
2001年 | 4726篇 |
2000年 | 4871篇 |
1999年 | 5639篇 |
1998年 | 5284篇 |
1997年 | 4354篇 |
1996年 | 3958篇 |
1995年 | 3311篇 |
1994年 | 2768篇 |
1993年 | 2188篇 |
1992年 | 1700篇 |
1991年 | 1277篇 |
1990年 | 1018篇 |
1989年 | 877篇 |
1988年 | 681篇 |
1987年 | 496篇 |
1986年 | 394篇 |
1985年 | 334篇 |
1984年 | 212篇 |
1983年 | 198篇 |
1982年 | 163篇 |
1981年 | 145篇 |
1980年 | 131篇 |
1979年 | 97篇 |
1978年 | 63篇 |
1977年 | 63篇 |
1976年 | 77篇 |
1975年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
eCRM (electronic Customer Relationship Management) systems focus on using the web-site as the main interaction channel for businesses to simulate an old fashioned one-to-one direct relationship—high touch—with customers. In this research two distinct but related concepts, media richness from the Human Computer Interaction and Computer Mediated Communication fields and perceived interactivity from the Marketing and MIS fields, are disentangled and their unique impacts on technology acceptance variables are examined in the eCRM Acceptance Model. The present study contributes in extending the Technology Acceptance Model for the eCRM context and in establishing media richness and perceived interactivity as antecedents to perceived usefulness and perceived ease of use. Our research model integrates system perception (e.g., perceived usefulness and perceived ease of use) and subjective outcome measures (e.g., decision satisfaction) in a single model to fully understand the impact of eCRM “touch” design perceived by e-customers on their intention to return after the initial visit. An experimental survey of two culture groups (independent vs. interdependent self-construal) of technology savvy, young college students reveals that culture value-orientation (e.g., self-construal) moderates the effect of decision satisfaction on behavior intention to return in our eCRM Acceptance model. Findings of this research thus have significant theoretical and managerial implications. 相似文献
152.
153.
Yi‐Hung Chen Ching‐Yuan Chang Wei‐Ling Su Chun‐Yu Chiu Yue‐Hwa Yu Pen‐Chi Chiang Chiung‐Fen Chang Je‐Lueng Shie Chyow‐San Chiou Sally IM Chiang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(1):68-75
This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry 相似文献
154.
Xi-Ren Cao Han-Fu Chen 《Automatic Control, IEEE Transactions on》1997,42(10):1382-1393
Two fundamental concepts and quantities, realization factors and performance potentials, are introduced for Markov processes. The relations among these two quantities and the group inverse of the infinitesimal generator are studied. It is shown that the sensitivity of the steady-state performance with respect to the change of the infinitesimal generator can be easily calculated by using either of these three quantities and that these quantities can be estimated by analyzing a single sample path of a Markov process. Based on these results, algorithms for estimating performance sensitivities on a single sample path of a Markov process can be proposed. The potentials in this paper are defined through realization factors and are shown to be the same as those defined by Poisson equations. The results provide a uniform framework of perturbation realization for infinitesimal perturbation analysis (IPA) and non-IPA approaches to the sensitivity analysis of steady-state performance; they also provide a theoretical background for the PA algorithms developed in recent years 相似文献
155.
156.
Let Ψ be any adaptive sampling algorithm that can run in real time on a tapeless multichannel electrocardiogram (ECG) Holter system. Simple methods which can significantly improve Ψ's fidelity are described and their results are compared in this paper. It is shown that by adding some simple tests to Ψ, the signals reconstructed by Ψ can be improved as much as 5.45 dB. It is also shown that under the same data rate, a good data compressor with slowly sampled input ECG is preferable to a bad data compressor with highly sampled input ECG 相似文献
157.
Jenghwa Chang Graber H.L. Ping Chen Koo Aronson R. Barbour S.-L.S. Barbour R.L. 《IEEE transactions on medical imaging》1997,16(1):68-77
Presents a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed 相似文献
158.
本文在条状屏彩色显象管校正透镜设计的基础上,提出了蹼状屏彩色显示管校正透镜的优化设计方法并给出了设计实例,通过计算机模拟电子束轨迹和光线追迹,分析了校正透镜面型修正程序的精度。 相似文献
159.
基于SDL的通信软件维护模型SMM 总被引:1,自引:0,他引:1
软件维护是软件生存周期的一个重要且花费很大的阶段,维护工作的自动化是软件行业十分迫切的需要。本文提出了一个基于ITU-TSDL语言的通信软件维护模型SMM。在此模型中,软件维护被分成三个部分:建立面向维护的数据库,制定维护规范和基于功能转换的自动维护。该模型将有助于软件维护支撑环境的建立 相似文献
160.
RT-AGVS是物流管理中十分重要的课题,车辆位置监测网是其重要的组成部分。本文详细介绍了一个基于单片机系统的车辆位置实时监测网,本监测网设计先进,性能价格比高,它的设计方法和技术对其他许多领域有借鉴作用。 相似文献