全文获取类型
收费全文 | 58806篇 |
免费 | 4233篇 |
国内免费 | 1558篇 |
专业分类
电工技术 | 3671篇 |
综合类 | 5686篇 |
化学工业 | 4066篇 |
金属工艺 | 1891篇 |
机械仪表 | 2251篇 |
建筑科学 | 11327篇 |
矿业工程 | 1543篇 |
能源动力 | 942篇 |
轻工业 | 13631篇 |
水利工程 | 3242篇 |
石油天然气 | 1812篇 |
武器工业 | 222篇 |
无线电 | 3153篇 |
一般工业技术 | 2965篇 |
冶金工业 | 3285篇 |
原子能技术 | 185篇 |
自动化技术 | 4725篇 |
出版年
2024年 | 323篇 |
2023年 | 829篇 |
2022年 | 1357篇 |
2021年 | 1776篇 |
2020年 | 1813篇 |
2019年 | 1479篇 |
2018年 | 1338篇 |
2017年 | 1611篇 |
2016年 | 1696篇 |
2015年 | 1921篇 |
2014年 | 4237篇 |
2013年 | 3312篇 |
2012年 | 4188篇 |
2011年 | 4423篇 |
2010年 | 3473篇 |
2009年 | 3723篇 |
2008年 | 3309篇 |
2007年 | 3930篇 |
2006年 | 3552篇 |
2005年 | 2874篇 |
2004年 | 2520篇 |
2003年 | 2271篇 |
2002年 | 2003篇 |
2001年 | 1452篇 |
2000年 | 1193篇 |
1999年 | 932篇 |
1998年 | 611篇 |
1997年 | 478篇 |
1996年 | 414篇 |
1995年 | 348篇 |
1994年 | 259篇 |
1993年 | 193篇 |
1992年 | 169篇 |
1991年 | 114篇 |
1990年 | 81篇 |
1989年 | 81篇 |
1988年 | 60篇 |
1987年 | 57篇 |
1986年 | 30篇 |
1985年 | 35篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 20篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1964年 | 3篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
基于自适应四叉树分形图像编码的数字水印技术 总被引:1,自引:0,他引:1
提出了一种基于自适应四叉树分形编码的数字水印技术。对原始图像进行四叉树分形编码后,通过给定子块在不同的寻找区域中搜索其最佳匹配父块来嵌入水印。实验结果表明,本方法在嵌入水印编码时间、图像质量和鲁棒性方面均比传统的方法有较大的改进。 相似文献
142.
建设工程质量保证体系存在的问题及对策 总被引:13,自引:2,他引:11
结合建筑业市场管理体制的改革及其发展态势,就建筑工程质量保证体系存在的问题作了阐述,从加强勘察设计资格的管理,完善监理法规等方面,提出了健全和完善质保体系的措施。 相似文献
143.
对照IS0 9001质量管理体系标推的要求,结合石化销售企业质量管理工作中存在的主要问题,提出质量管理工作创新的建议。 相似文献
144.
145.
146.
Intelligent methods for automatic protection and restoration are critical in optical transport mesh networks. This paper discusses the problem of quality-of-service (QoS)-based protection in terms of the protection-switching time and availability for end-to-end lightpaths in a WDM mesh network. We analyze the backup lightpath-sharing problem in such networks and study the correlation of the working lightpaths and the impact of the correlation on the sharing of the backup lightpaths. We present a multi-protocol-label-switching (MPLS) control-based fully distributed algorithm to solve the protection problem. The proposed algorithm includes intelligent and automatic procedures to set up, take down, activate, restore, and manage backup lightpaths. It greatly reduces the required resources for protection by allowing the sharing of network resources by multiple backup lightpaths. At the same time, it guarantees, if possible, to satisfy the availability requirement even with resource sharing by taking the correlation of working lightpaths into consideration. A simple analysis of the proposed algorithm in terms of computation time and message complexity indicates that the implementation of the algorithm is practical. The illustrative studies that compare the performance of 1:1, unlimited sharing, and QoS-based backup sharing algorithms indicate that QoS-based sharing achieves comparable performance as unlimited sharing, which is much better than the 1:1 backup scheme in terms of connection blocking probability, average number of connections in the network for a given offered load, and network resource utilization. 相似文献
147.
Stakeholder involvement is essential to the development of a total maximum daily load (TMDL) and its implementation plan. A tool, beyond a simulation model, is needed to support the decision making process that requires negotiation and compromise among stakeholders. The decision support system (DSS) described herein has a TMDL module to calculate various combinations of point and nonpoint loads that can meet the water quality criteria. Its Consensus module allows stakeholders to formulate, evaluate, modify, and vote for alternatives. The DSS displays bar charts for pollution loads from various subwatersheds and attributes the nonpoint loads to land uses. The water quality consequence of the pollution loads is output in maps, which shows sections meeting criteria in green and those not in red. The DSS requires a front end effort of site specific adaptation and model calibration. An Internet-based stakeholder process was developed to allow more concerned citizens to participate in management decisions. 相似文献
148.
王飞 《理化检验(物理分册)》2003,39(12):636-638,650
为分析研究某特钢厂用户投诉的原因及存在的问题,统计了其两年间的弹簧钢棒线材用户质量投诉,从缺陷类型及生产过程控制进行了分析,重点对多起断裂原因不明的投诉进行了深入的失效研究。结果表明,弹簧钢生产厂在设备工艺、过程控制和管理中存在很多不足,加上用户的使用工艺、材料的内外质量和规格等综合因素导致了材料的断裂失效。 相似文献
149.
Don Kelleher 《Information Systems Journal》1995,5(2):137-157
Abstract. An Information Systems Methodology is usually presented as a sequential set of tasks — planning, analysis, design and construction — resulting in a new business application. This classical 'forward-engineering' approach must be adapted to changing business needs — business process redesign, quality management, process and systems templates, advanced technologies, application packages, the reuse of existing information systems resources, and rapid delivery cycles. Using the most general concept of a Business Programme, this paper describes a methodological approach incorporating these modern themes that is qualitatively and quantitatively different from the classical model. It provides a framework for the integration of otherwise independent methodologies, and shows how an entire programme can be formulated, planned and executed. An example is provided, and the approach is justified. 相似文献
150.
The engineering and management of human safety is an important societal objective that includes extensive efforts by governments, both legislative and administrative, to enhance the health and safety of the public. Although the achievement of safety goals depend primarily on individuals and organizations responsible for safety, much support is drawn from expertise in diverse scientific and engineering disciplines. The activities range from structural safety (dams, tunnels, bridges to tall buildings) to safe operation of hazardous industrial installations (energy generation facilities, LNG terminals, petrochemical plants) to transportation systems (airline, rail, car safety) to technologies designed to minimize adverse impacts on the environment. All these activities are crucially concerned with risk: with the likelihood and the probable effects of various measures on life and health. We have developed a unified rationale and a clear basis for effective strategic management of risk across diverse sectors. Safety is an important objective in society but it is not the only one. The allocation of society's resources devoted to safety must be continually appraised in light of competing needs, because there is a limit on the resources that can be expended to extend life. The paper presents the Life Quality Index (LQI) as a tool for the assessment of risk reduction initiatives that would support the public interest and enhance safety and quality of life. The paper provides an intuitive reformulation of the LQI as equivalent to a valid utility function that is consistent with the principles of rational decision analysis. The LQI is further refined to consider the issues of discounting of life years, competing background risks, and population age and mortality distribution. The LQI is applied to quantify the societal willingness-to-pay, which is an acceptable level of public expenditure in exchange for a reduction in the risk of death that results in improved life-quality. 相似文献