全文获取类型
收费全文 | 308922篇 |
免费 | 30157篇 |
国内免费 | 15750篇 |
专业分类
电工技术 | 21897篇 |
技术理论 | 33篇 |
综合类 | 31853篇 |
化学工业 | 36718篇 |
金属工艺 | 17249篇 |
机械仪表 | 21062篇 |
建筑科学 | 37280篇 |
矿业工程 | 17792篇 |
能源动力 | 13843篇 |
轻工业 | 17754篇 |
水利工程 | 14196篇 |
石油天然气 | 16954篇 |
武器工业 | 6133篇 |
无线电 | 21239篇 |
一般工业技术 | 24304篇 |
冶金工业 | 14162篇 |
原子能技术 | 3031篇 |
自动化技术 | 39329篇 |
出版年
2024年 | 1450篇 |
2023年 | 4217篇 |
2022年 | 8115篇 |
2021年 | 10083篇 |
2020年 | 10185篇 |
2019年 | 7589篇 |
2018年 | 7380篇 |
2017年 | 9404篇 |
2016年 | 11386篇 |
2015年 | 12347篇 |
2014年 | 21013篇 |
2013年 | 19147篇 |
2012年 | 22935篇 |
2011年 | 25391篇 |
2010年 | 18594篇 |
2009年 | 18719篇 |
2008年 | 17345篇 |
2007年 | 21234篇 |
2006年 | 18954篇 |
2005年 | 16182篇 |
2004年 | 13554篇 |
2003年 | 11501篇 |
2002年 | 9283篇 |
2001年 | 7658篇 |
2000年 | 6399篇 |
1999年 | 5050篇 |
1998年 | 3694篇 |
1997年 | 3140篇 |
1996年 | 2651篇 |
1995年 | 2162篇 |
1994年 | 1830篇 |
1993年 | 1282篇 |
1992年 | 1032篇 |
1991年 | 756篇 |
1990年 | 647篇 |
1989年 | 575篇 |
1988年 | 340篇 |
1987年 | 244篇 |
1986年 | 221篇 |
1985年 | 222篇 |
1984年 | 165篇 |
1983年 | 138篇 |
1982年 | 84篇 |
1981年 | 87篇 |
1980年 | 100篇 |
1979年 | 56篇 |
1978年 | 27篇 |
1977年 | 31篇 |
1959年 | 45篇 |
1951年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
53.
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
54.
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
55.
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
56.
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
57.
采用被动式工艺生产冷轧带肋钢筋须经过减径、成型两台轧机连续轧制.要求钢材的秒流量相等,否则将造成断线停产或线材在拉丝机卷筒上打滑,致使卷筒严重磨损.用双层卷筒拉丝机提供动力生产冷轧带肋钢筋时,线材直径与卷筒直径的匹配是在一个小的调整范围,通过轧机拉力控制在一定范围变化,可保证成品尺寸符合公差要求而不产生打滑,从而避免了卷筒严重磨损. 相似文献
58.
59.
罗立祝 《机械工业高教研究》2008,(2):106-110
从高校招生的演变历史看,中国在1978年以前对工农阶层子女实行高校入学优惠政策主要源于国家对这一阶层的特殊偏好而实行平均主义分配政策所致。国家通过报考资格政策、优先录取政策和免试推荐入学政策人为地大幅度提高了工农阶层子女在高校大学生中所占的比例。从公平视角看,这项政策不仅违背了公平原则,而且降低了人才选拔的质量。 相似文献
60.
In the paper, a model typical for contact situations of automotive brakes is established based on the method of movable cellular automata. The processes taking place at local contacts in an automotive brake system are analysed. Based on microscopic and micro-analytical observations, the following contact situations were simulated: (i) a couple of ferritic steel against pearlitic steel, both covered by an oxide layer mixed with graphite nanoparticles and (ii) the same situation but without oxide layers. The results of calculated mean coefficients of friction of the oxide-on-oxide contact correspond well to expected values for a real braking system, whereas steel-on-steel contact are twice as high. This allows one to make some conclusions; for example, oxide formation will take place more quickly than friction layer elimination, and finally this is responsible for the stabilisation of the coefficient of friction. 相似文献