全文获取类型
收费全文 | 117498篇 |
免费 | 5479篇 |
国内免费 | 7125篇 |
专业分类
电工技术 | 4890篇 |
技术理论 | 5篇 |
综合类 | 9823篇 |
化学工业 | 18199篇 |
金属工艺 | 16397篇 |
机械仪表 | 3958篇 |
建筑科学 | 6456篇 |
矿业工程 | 1581篇 |
能源动力 | 3337篇 |
轻工业 | 6215篇 |
水利工程 | 2184篇 |
石油天然气 | 7236篇 |
武器工业 | 828篇 |
无线电 | 7025篇 |
一般工业技术 | 18088篇 |
冶金工业 | 3907篇 |
原子能技术 | 2534篇 |
自动化技术 | 17439篇 |
出版年
2024年 | 155篇 |
2023年 | 696篇 |
2022年 | 1120篇 |
2021年 | 1568篇 |
2020年 | 1982篇 |
2019年 | 1896篇 |
2018年 | 1841篇 |
2017年 | 2166篇 |
2016年 | 2616篇 |
2015年 | 3214篇 |
2014年 | 5419篇 |
2013年 | 6497篇 |
2012年 | 5862篇 |
2011年 | 6710篇 |
2010年 | 5420篇 |
2009年 | 7019篇 |
2008年 | 6533篇 |
2007年 | 7220篇 |
2006年 | 6806篇 |
2005年 | 5663篇 |
2004年 | 5088篇 |
2003年 | 4786篇 |
2002年 | 4695篇 |
2001年 | 3566篇 |
2000年 | 3824篇 |
1999年 | 3506篇 |
1998年 | 2914篇 |
1997年 | 2773篇 |
1996年 | 2821篇 |
1995年 | 2947篇 |
1994年 | 2638篇 |
1993年 | 1632篇 |
1992年 | 1636篇 |
1991年 | 1116篇 |
1990年 | 821篇 |
1989年 | 737篇 |
1988年 | 684篇 |
1987年 | 398篇 |
1986年 | 246篇 |
1985年 | 392篇 |
1984年 | 428篇 |
1983年 | 453篇 |
1982年 | 357篇 |
1981年 | 413篇 |
1980年 | 288篇 |
1979年 | 120篇 |
1978年 | 120篇 |
1977年 | 70篇 |
1975年 | 58篇 |
1974年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
从目前电力系统的发展来看,不论是华北电网还是晋、蒙电网都存在着调峰能力不足的问题。为更好地利用黄河托龙段的水能资源,改善下游河道的水流条件,为地方经济建设提供清洁可靠的能源,建设龙口水利枢纽工程已经提到日程上来。龙口水利枢纽工程开发任务为发电、对万家寨电站进行反调节、兼有滞洪削峰等综合利用。根据电力系统的需求、泥沙淤积情况、动能经济指标和反调节等要求,综合考虑,选定正常蓄水位898m,装机容量420MW。龙口水利枢纽工程的建设符合国家关于调整能源结构,优先开发水电和加强基础设施建设,拉动经济增长的部署。 相似文献
154.
155.
运动会新闻发布系统的设计与实现 总被引:2,自引:0,他引:2
针对运动会比赛期间随时需要方便、快捷、高效地更新大量新闻的需求 ,研制和开发一套运动会新闻发布系统。利用微软最新推出的asp .net动态网页开发工具 ,采用web分布式三层设计模型设计实现了一套操作简单、功能完善、具有通用性的运动会新闻发布系统 相似文献
156.
157.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
158.
An efficient algorithm is presented for numerically evaluating a self-consistent field theoretic (SCFT) model of block copolymer structure. This algorithm is implemented on a distributed memory parallel cluster in order to solve the SCFT equations on large computational grids. Simulation results are presented for a two-component molten mixture of a symmetric ABA triblock copolymer with an A homopolymer. These results illustrate a case in which simulating a large system is required to resolve features with a wide range of length scales. 相似文献
159.
We demonstrate that alkali-halide salts, particularly potassium bromide, can reduce the photothermal emission (PTE) from single walled carbon nanotubes (SWNT). PTE is a prominent spectral feature in Raman spectroscopy when a near infrared laser is used to analyze a dark colored sample. We subsequently show that trapping salts inside SWNT and coating SWNT with the salt has a more pronounced impact on not only reducing PTE, but also enhancing the intensity of the Raman spectral features. The effect, which we have called nanotube enhanced Raman spectroscopy (NERS), has differences and similarities to the widely studied surface enhanced Raman spectroscopy (SERS). 相似文献
160.
Behavior of Magnesium‐Alloys for Automotive Applications under Mechanical and Environmental Loading: Influence of Passivating Films and Mechanisms of Local Breakdown To assure an efficient design of components under cyclic loading, all available data concerning fatigue have to be observed. Therefore the influences of manufacturing on the material condition, the mechanical loads and environmental effects have to be analysed. Magnesium‐alloys are of special interest for lightweight applications because of their excellent strength‐density ratio. The corrosion resistance of magnesium‐alloys depends on the same factors that are critical to other metals. The alloys have a good stability to atmospheric exposure and a good resistance to attack by alkali, chromic and hydrofluoric acids. However, because of the electrochemical activity of magnesium, the relative importance of some factors is greatly amplified. The nature and composition of passive films formed on magnesium‐alloys depend on the prevailing conditions, viz. alloy‐composition, passivation potential, pH, electrolyte composition and temperature. Passive films may be damaged by local breakdown. Because of this, magnesium‐alloys suffer a degradation of their properties when exposed to an aqueous environment. The main topic of the present investigations is the verification of mechanisms of the local breakdown of the protecting film. At least two mechanisms are possible for this localization: mechanical breakdown by slip steps and electrochemical breakdown (for e.g. by the effects of chloride ions). Corrosion and passivation of different high purity alloys have been studied in different solutions (neutral, alkaline with specific anions and cations) using electrochemical techniques. The diecasted alloys were tested as produced and machined. The results clarified that depending on alloy/material and surface condition/corrosion environment different mechanisms for electrochemical breakdown of the protecting films are possible. Hence fatigue life under environmental loading is influenced by surface and testing conditions. 相似文献