全文获取类型
收费全文 | 72292篇 |
免费 | 5989篇 |
国内免费 | 3110篇 |
专业分类
电工技术 | 2611篇 |
技术理论 | 5篇 |
综合类 | 5314篇 |
化学工业 | 15870篇 |
金属工艺 | 7086篇 |
机械仪表 | 4948篇 |
建筑科学 | 4606篇 |
矿业工程 | 2725篇 |
能源动力 | 1771篇 |
轻工业 | 6650篇 |
水利工程 | 1255篇 |
石油天然气 | 3237篇 |
武器工业 | 590篇 |
无线电 | 3312篇 |
一般工业技术 | 6573篇 |
冶金工业 | 6048篇 |
原子能技术 | 443篇 |
自动化技术 | 8347篇 |
出版年
2024年 | 253篇 |
2023年 | 790篇 |
2022年 | 1575篇 |
2021年 | 1981篇 |
2020年 | 2172篇 |
2019年 | 1649篇 |
2018年 | 1431篇 |
2017年 | 1865篇 |
2016年 | 2265篇 |
2015年 | 2430篇 |
2014年 | 4402篇 |
2013年 | 4622篇 |
2012年 | 5326篇 |
2011年 | 5595篇 |
2010年 | 4050篇 |
2009年 | 4147篇 |
2008年 | 3592篇 |
2007年 | 4658篇 |
2006年 | 4474篇 |
2005年 | 3864篇 |
2004年 | 3338篇 |
2003年 | 2960篇 |
2002年 | 2566篇 |
2001年 | 2195篇 |
2000年 | 1819篇 |
1999年 | 1510篇 |
1998年 | 1158篇 |
1997年 | 903篇 |
1996年 | 844篇 |
1995年 | 653篇 |
1994年 | 554篇 |
1993年 | 354篇 |
1992年 | 318篇 |
1991年 | 251篇 |
1990年 | 168篇 |
1989年 | 140篇 |
1988年 | 109篇 |
1987年 | 64篇 |
1986年 | 55篇 |
1985年 | 37篇 |
1984年 | 40篇 |
1983年 | 32篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 25篇 |
1979年 | 13篇 |
1977年 | 14篇 |
1961年 | 7篇 |
1959年 | 8篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 551 毫秒
181.
This article discusses the phenomenon of youth violence from a psychology of gender perspective. Although other factors are discussed--including gun availability, violence-related media influence, family and caretaker factors, and effects of teasing and bullying--the intention is to highlight new thinking on the potential relationship between boys' traditional masculine socialization experiences and violence. In this new perspective, traditional masculine socialization estranges and isolates many boys from their genuine inner lives and vital connections to others, which is theorized to heighten their risk of engaging in acts of violence. The authors identify school and community programs that may be helpful in counteracting damaging socialization experiences and supporting boys' healthier emotional and psychological development. Finally, the article discusses approaches that psychologists and other mental health professionals can use to help address this vital issue. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
182.
Yong Ma Yong‐zhen Peng Xiao‐lian Wang Shu‐ying Wang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(10):1118-1124
The laboratory scale anaerobic–anoxic–aerobic (A2O) process fed with synthetic brewage wastewater was designed to investigate the effects of changing feed C/P ratio on the performance of biological nutrient removal (BNR) processes. In the experiment, the influent chemical oxygen demand (COD) concentration was kept at approximately 300 mg L?1 while the total phosphorus concentration was varied to obtain the desired C/P ratio. Results showed that when the C/P ratio was lower than 32, phosphorus removal efficiency increased as C/P ratio increased linearly, while when the C/P ratio was higher than 32, the P removal efficiency was maintained at 90–98%, and effluent P concentration was lower than 0.5 mg L?1. However, regardless of the C/P ratio, excellent COD removal (90% or higher) and good total nitrogen removal (75–84%) were maintained throughout the experiments. It was also found that very good linear correlation was obtained between COD uptake per unit P released in the anaerobic zone and C/P ratio. In addition, the P content in the wasted activated sludge increased with the decrease in the C/P ratio. Based on the results, it was recommended that the wastewater C/P ratio and its effects be incorporated into BNR design and operational procedures, appropriate C/P ratios were used to achieve the effluent treatment goals. Copyright © 2005 Society of Chemical Industry 相似文献
183.
Predictive Maintenance can provide an increase in safety, quality and availability in industrial plants. However, the setting up of a Predictive Maintenance Programme is a strategic decision that until now has lacked analysis of questions related to its setting up, management and control. In this paper, an evaluation system is proposed that carries out the decision making in relation to the feasibility of the setting up. The evaluation system uses a combination of tools belonging to operational research such as: Analytic Hierarchy Process, decision rules and Bayesian tools. This system is a help tool available to the managers of Predictive Maintenance Programmes which can both increase the number of Predictive Maintenance Programmes set up and avoid the failure of these programmes. The Evaluation System has been tested in a petrochemical plant and in a food industry. 相似文献
184.
Hiroshi Ohta Tomoyuki Hirota Abdur Rahim 《The International Journal of Advanced Manufacturing Technology》2007,33(1-2):36-41
This paper analyzes a multi-product production / inventory system where demands for each item arrive according to a Poisson
process and the production time for each product has an Erlang distribution. The paper proposes an optimality condition that
specifies whether each product should be produced make-to-stock or make-to-order. In the event a product should be produced
make-to-stock, an approach for computing the optimal base-stock level is proposed. Numerical examples are given for illustrative
purpose. 相似文献
185.
本文分析了山西在推进煤炭流通市场化过程中面临的机遇及现行体制弊端,提出建立更加适合市场经济的煤焦流通体制的若干建议。 相似文献
186.
Yaxin Tang 《Materials and Manufacturing Processes》2002,17(6):789-796
An experimental apparatus was designed and built for the hybrid process of laser enhanced electrochemical machining (ECM). Comparison experiments had been done between solely ECM and laser enhanced ECM. The machining performance of hybrid process was investigated and compared with solely ECM. The principle of the hybrid process was exposed by analyzing the microstructure of machining surface. The results show that the hybrid process has advantages in machining accuracy, surface quality, and machining efficiency. 相似文献
187.
188.
189.
利用氧分子对金属钌化合物的荧光具有猝灭作用的特性,构造出基于荧光猝灭原理的光纤氧传感器。就用于水中溶解氧在线监测的光纤光谱仪的搭建、传感器探头的设制及传感膜的制作过程进行探索,并对传感器的响应性能进行考察。结果表明以联吡啶钌等作为荧光指示剂以溶胶-凝胶法制备的传感膜对溶解氧的响应具有良好的可逆性,稳定性,较快的响应时间和较长的使用寿命。与标准法相对照,用本仪器系统测定了不同盐度的人工海水中的溶解氧浓度,两种方法在不同浓度水平下的溶解氧测定值均无显著性差异。本法的日内和日间RSD在1.7%~5.0%之间。 相似文献
190.
讨论了现代企业的过程观经及企业过程的构成,提出了企业生产经营全过程的作业管理思想,并对全过程作业管理的基本内容进行了探讨,分析了企业过程重组和优化的驱动因素、目标和实现途径,最后概述了全过程作业管理的支撑技术。 相似文献