全文获取类型
收费全文 | 251281篇 |
免费 | 23837篇 |
国内免费 | 11940篇 |
专业分类
电工技术 | 15981篇 |
技术理论 | 35篇 |
综合类 | 24407篇 |
化学工业 | 33522篇 |
金属工艺 | 11371篇 |
机械仪表 | 12759篇 |
建筑科学 | 32745篇 |
矿业工程 | 14372篇 |
能源动力 | 11396篇 |
轻工业 | 17453篇 |
水利工程 | 11139篇 |
石油天然气 | 12956篇 |
武器工业 | 3375篇 |
无线电 | 17124篇 |
一般工业技术 | 20410篇 |
冶金工业 | 14780篇 |
原子能技术 | 2255篇 |
自动化技术 | 30978篇 |
出版年
2024年 | 1197篇 |
2023年 | 3735篇 |
2022年 | 6689篇 |
2021年 | 8643篇 |
2020年 | 8594篇 |
2019年 | 6671篇 |
2018年 | 6261篇 |
2017年 | 7754篇 |
2016年 | 9123篇 |
2015年 | 9621篇 |
2014年 | 17103篇 |
2013年 | 15363篇 |
2012年 | 18083篇 |
2011年 | 20127篇 |
2010年 | 14816篇 |
2009年 | 15081篇 |
2008年 | 13715篇 |
2007年 | 16526篇 |
2006年 | 14923篇 |
2005年 | 12867篇 |
2004年 | 10668篇 |
2003年 | 9198篇 |
2002年 | 7586篇 |
2001年 | 6215篇 |
2000年 | 5365篇 |
1999年 | 4252篇 |
1998年 | 3042篇 |
1997年 | 2647篇 |
1996年 | 2223篇 |
1995年 | 1809篇 |
1994年 | 1585篇 |
1993年 | 1139篇 |
1992年 | 923篇 |
1991年 | 645篇 |
1990年 | 555篇 |
1989年 | 496篇 |
1988年 | 287篇 |
1987年 | 216篇 |
1986年 | 187篇 |
1985年 | 221篇 |
1984年 | 161篇 |
1983年 | 136篇 |
1982年 | 106篇 |
1981年 | 103篇 |
1980年 | 97篇 |
1979年 | 52篇 |
1978年 | 30篇 |
1977年 | 24篇 |
1959年 | 28篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Gabriel Wainer 《Software》2002,32(13):1261-1306
The features of a toolkit for modeling and simulation based on the DEVS formalism are presented. The tool is built as a set of independent software pieces running on different platforms. Not only are the main characteristics of the environment presented, a focus on its use is also considered by inclusion of application examples for a variety of problems. Many models can be defined in an automated fashion, simplifying the construction of new models and easing their verification. The use of this formal approach has allowed the development of safe and cost‐effective simulations, significantly reducing development time. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
52.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
53.
54.
关于长江重大问题的思考 总被引:2,自引:0,他引:2
长江流域横跨我国华东、华中、西南三大经济区,地理位置优越,水资源得天独厚,是我国最重要的经济区域之一。新中国成立后,党和政府高度重视长江治理开发工作,组建了流域机构,开展了流域综合利用规划,初步建立了长江防洪、灌溉、水力发电、航运、水土保持和水资源保护体系,在保护 相似文献
55.
建立了挠性胶管阻尼耗能的简化模型。以此为基础分析了挠性胶管的阻尼耗能的一般规律,并得出了一些新的结论。 相似文献
56.
A nuclear microprobe with high spatial resolution and high analytical sensitivity was applied to analyze trace elements,especially lead,in vehicle exhaust of Shanghai city.The result shows that the chemical composition and its corresponding x-ray relative intensity are different among different vehicle exhausts.There are many kinds of metal elements in particles of vehicle exhaust.most are harmful to people,such as Ti,Cr,Mn,Pb,etc.We found that the lead concentration was 6820μg/g and the bromine concentration was 5300μg/g in the exhaust from Santana using leaded gasoline(SULG).which is higher than any other kinds of vehicle exhausts.We have also detected the minimum lead in the particles of unleaded gasoline and its content varies from one to another.Its mean concentration was 450μg/g and the highest reached 6210μg/g.The unleaded gasoline‘s Pb existed in the whole particle while the leaded gasoline‘s enriched in the surface of the particle and was more harmful to the human beings. 相似文献
57.
On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates. 相似文献
58.
一级开发大柳树高坝原始库容比二级开发小观音高坝多 4 0亿m3 ,库容大带来的好处体现在 5~ 7月可多向下游增供水量 ,缓解下游河道断流 ;延长泄放清水时间 ;增加发电效益 ;满足宁蒙河段防凌要求 ;增加汛期集中泄水 ,减缓下游河道淤积萎缩 ;满足南水北调西线工程水量调节要求等。为了更好优化配置黄河水资源 ,从全局和长远利益考虑 ,应采用一级开发方案 ,修建大柳树高坝大库 相似文献
59.
标准物质在分析测试中的重要地位及发展前景 总被引:2,自引:0,他引:2
标准物质在分析测试领域中无论在定值,方法的研究,误差确定等方面都有着重要地位。标准物质的质量保证及正确使用也应引起我们重视。随着科学技术迅速发展标准物质有着广阔发展前景。 相似文献
60.