全文获取类型
收费全文 | 53842篇 |
免费 | 7035篇 |
国内免费 | 3556篇 |
专业分类
电工技术 | 10763篇 |
技术理论 | 1篇 |
综合类 | 5532篇 |
化学工业 | 7056篇 |
金属工艺 | 1621篇 |
机械仪表 | 2445篇 |
建筑科学 | 4755篇 |
矿业工程 | 1891篇 |
能源动力 | 2243篇 |
轻工业 | 4218篇 |
水利工程 | 2230篇 |
石油天然气 | 3173篇 |
武器工业 | 526篇 |
无线电 | 4433篇 |
一般工业技术 | 4306篇 |
冶金工业 | 2229篇 |
原子能技术 | 1093篇 |
自动化技术 | 5918篇 |
出版年
2024年 | 165篇 |
2023年 | 756篇 |
2022年 | 1545篇 |
2021年 | 1889篇 |
2020年 | 2119篇 |
2019年 | 1831篇 |
2018年 | 1757篇 |
2017年 | 2125篇 |
2016年 | 2202篇 |
2015年 | 2376篇 |
2014年 | 3550篇 |
2013年 | 3835篇 |
2012年 | 4118篇 |
2011年 | 4312篇 |
2010年 | 3052篇 |
2009年 | 3216篇 |
2008年 | 3008篇 |
2007年 | 3493篇 |
2006年 | 3151篇 |
2005年 | 2510篇 |
2004年 | 2234篇 |
2003年 | 1866篇 |
2002年 | 1579篇 |
2001年 | 1296篇 |
2000年 | 1089篇 |
1999年 | 948篇 |
1998年 | 762篇 |
1997年 | 604篇 |
1996年 | 509篇 |
1995年 | 476篇 |
1994年 | 455篇 |
1993年 | 296篇 |
1992年 | 243篇 |
1991年 | 213篇 |
1990年 | 186篇 |
1989年 | 154篇 |
1988年 | 122篇 |
1987年 | 83篇 |
1986年 | 62篇 |
1985年 | 57篇 |
1984年 | 39篇 |
1983年 | 28篇 |
1982年 | 35篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1959年 | 11篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 859 毫秒
61.
62.
Based on the concept of complete stress–strain diagrams, we propose a new model describing the law of stress distribution in the prefracture zone in plastic materials in view of the type of the stressed state. 相似文献
63.
Analysis of non-stationary electrochemical oscillations emerges utilization of the techniques allowing an observation of time evolution of their parameters such as instantaneous frequency, amplitude or frequency band. An algorithm of extraction of these parameters can be based on one of linear or quadratic time-frequency representations of oscillations record. In this paper, the authors present representatives of such transformations (Choi-Williams and Cone-shaped) originating from one of the most popular joint time-frequency energy distribution—Wigner-Ville distribution. Short introduction to the mathematics of the topic discussed is provided, then the authors present an example of application in the analysis of current oscillations of copper dissolution process. 相似文献
64.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
65.
Accidents in different complex sociotechnical systems are rarely compared using the same theoretical framework for risk management. We conducted a comparative analysis of two Canadian public health disasters involving drinking water distribution systems, the North Battleford Cryptosporidium parvum outbreak in April 2001 and the Walkerton E. coli outbreak in May 2000. Both accidents resulted from a complex interaction between all levels of a complex sociotechnical system. However, the low-level physical and individual factors differed in the two cases, whereas, the high-level governmental and regulatory factors tended to be the same. These findings may have implications for the design of public policies to minimize risk in complex sociotechnical systems. 相似文献
66.
给出了覆盖层厚度对巷道周围应力分布的影响及巷道间相互作用的计算机仿真,用三维有限元法分析了在不同覆盖层厚度下巷道周围的应力分布和两个巷道之间不同距离下的相互作用。数值模拟表明了巷道周围应力分布和应力集中系数随覆盖层厚度增加的变化规律,找到了两巷道之间的距离的临界值,当两巷道间距离大于该临界值时,它们之间的相互作用消失。 相似文献
67.
68.
Oleuropein Inhibits LDL Oxidation Induced by Cooking Oil Frying By-products and Platelet Aggregation Induced by Platelet-Activating Factor 总被引:1,自引:0,他引:1
Oleuropein, a polyphenolic glucoside, constituent of olive fruit and oil, has been previously shown to exhibit, in vitro, potent properties as a biological antioxidant. In the present paper, two new properties are demonstrated in vitro as well, concerning its vascular protection activity, against the atheromatic lesion formation and its blood antithrombotic effect. Firstly, it was found that the oxidation of low-density lipoproteins (LDL), induced by different quantities of total polar materials (TPM), was inhibited by 10 μ M (final concentration) of oleuropein, revealing approx. 50% protection. Secondly, platelet-rich human plasma aggregation, induced by either the platelet-activating factor or adenosine diphospate or arachidonic acid, was inhibited by oleuropein. The 10 μ M (final concentration) of oleuropein was proven to be the most effective among the tested concentrations against LDL oxidation, while an IC50=0.41 mM was calculated for its inhibitory activity against platelet aggregation induced by 0.7 μ M platelet-activating factor. 相似文献
69.
Li Yu-cheng He Ming Dept.of Civil Engineering Dalian Univ.of Technology Dalian P.R.China 《水动力学研究与进展(B辑)》1993,(4)
Based on model test,the statistical distribution of extreme values of wave-current in-line forces acting on vertical circular cylinder is analyzed in this paper.It is shownthat the results calculated by the simplified method,proposed by authors,agree well with the testdata;Weibull distribution is also adoptable in the region of high KC number, and the shapeparameter a and scale parameter β are related well with KC number respectively. 相似文献
70.