全文获取类型
收费全文 | 107297篇 |
免费 | 10330篇 |
国内免费 | 6494篇 |
专业分类
电工技术 | 4412篇 |
技术理论 | 4篇 |
综合类 | 8286篇 |
化学工业 | 13653篇 |
金属工艺 | 8501篇 |
机械仪表 | 8251篇 |
建筑科学 | 6514篇 |
矿业工程 | 6208篇 |
能源动力 | 3668篇 |
轻工业 | 9860篇 |
水利工程 | 2429篇 |
石油天然气 | 8913篇 |
武器工业 | 1605篇 |
无线电 | 10787篇 |
一般工业技术 | 9955篇 |
冶金工业 | 5316篇 |
原子能技术 | 2495篇 |
自动化技术 | 13264篇 |
出版年
2024年 | 428篇 |
2023年 | 1534篇 |
2022年 | 2784篇 |
2021年 | 3489篇 |
2020年 | 3552篇 |
2019年 | 2909篇 |
2018年 | 2750篇 |
2017年 | 3406篇 |
2016年 | 3614篇 |
2015年 | 3920篇 |
2014年 | 6145篇 |
2013年 | 6408篇 |
2012年 | 7627篇 |
2011年 | 8234篇 |
2010年 | 5853篇 |
2009年 | 5901篇 |
2008年 | 5529篇 |
2007年 | 6986篇 |
2006年 | 6506篇 |
2005年 | 5577篇 |
2004年 | 4954篇 |
2003年 | 4230篇 |
2002年 | 3491篇 |
2001年 | 2962篇 |
2000年 | 2633篇 |
1999年 | 2087篇 |
1998年 | 1780篇 |
1997年 | 1597篇 |
1996年 | 1343篇 |
1995年 | 1088篇 |
1994年 | 992篇 |
1993年 | 713篇 |
1992年 | 584篇 |
1991年 | 482篇 |
1990年 | 399篇 |
1989年 | 356篇 |
1988年 | 237篇 |
1987年 | 155篇 |
1986年 | 123篇 |
1985年 | 146篇 |
1984年 | 88篇 |
1983年 | 98篇 |
1982年 | 108篇 |
1981年 | 79篇 |
1980年 | 49篇 |
1979年 | 55篇 |
1978年 | 24篇 |
1977年 | 29篇 |
1976年 | 19篇 |
1959年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
This paper mainly focuses on the influence of three kinds of media: air, air-10%PA (Nylon) and air-10% POM (polyoxymethylene) on low-voltage circuit breaker arcs. A threedimensional (3-D) model of arc motioa under the effect of external magnetic field is built based on magnetohydrodynamics (MHD) equations. By adopting the commercial computational fluid dynamics (CFD) package based on the control-volume method, the above MHD equations are solved. For the media of air-10%PA and air-10%POM, the distributions of stationary temperature and electrical potential and the transient motion processes are compared with those of air arc. The research shows that both air-10%PA and air -10% POM can cool the arc plasma and the former is more effective. Both of them can increase the stationary voltage as well. Moreover, the presence of the two mixtures can accelerate the arc motion toward the quenching area and ensures the arc quenched in time. 相似文献
82.
The surface of polyethyleneterephthalate (PET) nonwoven fabric was modified by He/O2 atmospheric pressure plasma treatment, varying plasma exposure time. The plasma treated PET surfaces have been analyzed to investigate the chemical nature and morphology of surface by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The change of wettability was measured depending on plasma exposure time. XPS results indicated the presence of oxygen‐based functional groups on the PET nonwoven fabric surface after plasma treatment and oxygen content increased as exposure time increased. The mean roughness increased after 30 s exposure and further increase in exposure to 60 s led to decrease of the roughness and then again increase. The root mean square roughness followed the similar trend to mean roughness. The average difference in height, Rz, increased after plasma exposure for 30 s, while it slightly decreased after 60 s exposure. Despite of redeposition, the Rz of 90 s exposed sample increased more than two times compared with those of 30 and 60 s exposed. Wettability increased progressively up to 10 times after 90 s exposure compared with the untreated. It is attributed to the increases of hydrophilicity and surface roughness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
83.
The in situ measurement of dynamic changes in viscosity induced by illumination has been performed on a range of photosensitive urethane dimethacrylates (UDMA) evaluating the response at three different illuminations intensities (1, 2, and 5 W cm?2) and at three different diluent concentrations (15, 30, and 50%), using 1,6‐hexanediol dimethacrylate (HDDMA). The initial viscosity value ranged between 1 and 10 Pa s for the mixtures with final viscosities approaching 1 × 107 Pa s after illumination. The initial rise in viscosity was analyzed using an exponential model with an exponent ranging from 1.0 to 2.5 with time under exposure. Higher conversion rates were observed with both higher intensity and lower HDDMA content. The analytical approach taken here could aid in developing more sophisticated models that consider simultaneous flow and cure advancement in other thermosets. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
84.
冯保罗 《有色金属材料与工程》2003,24(2):84-88,91
钟罩室退火护采用微压氢气作为保护气体,炉内压力的监控是保证安全生产不可忽视的必要手段,该文针对该公司选用的国产钟罩式退火护作了简要介绍,对国产钟罩式退火炉压力监控系统作了分析,指出了存在的缺陷,提出了改进措施。 相似文献
85.
Intelligent multisensor surveillance systems consist of several types of sensors, which are installed on fixed and mobile devices. These components provide a huge quantity of information that has to be contrasted, correlated and integrated in order to recognize and react on special situations. These systems work in highly dynamic environments, with severe security and robustness requirements. All these characteristics imply the need for distributed solutions. In these solutions, scattered components can decide and act with some degree of autonomy (for instance, if they become isolated), or cooperate and coordinate for a complete tracking of special situations. In order to cope with these requirements and to better structure the solution, we have decided to design surveillance system control as a multiagent system. This is done by applying an agent-orientated methodology, which is assessed with concrete scenarios. 相似文献
86.
This study examined the interrelationships among economic pressure, maternal depression, social support, and marital conflict in a sample of 239 mothers in Romania. Data were collected through a school-based survey. Findings indicated that higher levels of economic pressure were associated with higher levels of marital conflict. Economic pressure was also associated with higher marital conflict indirectly through increased maternal depression and lowered social support. The present results were similar to those obtained in studies conducted among U.S. samples. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
87.
用常规电阻率测井资料确定水淹层的剩余油饱和度 总被引:7,自引:0,他引:7
油田综合含水越来越高,利用电阻率测井资料确定地层的剩余油饱和度变得非常困难。针对这一问题,提出了确定地层水民阻率和含油饱和度的方法。(1)利用已知的地怪水分析资料,采用井下自然电位刻度,井间对经和双自然电位一方法来示准地层水混合电阻率,然后利用相邻井相同地层的电阻率对比方法求含水饱和度。(2)利用电阻率的横向探测特性,避开阿尔奇公式中m、a选择上的困难,采用横向法计算水淹层目前的含水饱和度。利用以 相似文献
88.
Plasmapropertiesoflaser-ablatedSttargetinairWangXiang-Tai(王象泰);ManBao-Yuan(满宝元);WangGong-Tang(王公堂);FanXi-Jun(樊锡君);WangJun(王军)... 相似文献
89.
90.
This paper presents a novel process for the fabrication of pultruded polyurethane (PU) composites. The effects of the processing parameters on the mechanical properties (flexural strength and flexural modulus, etc.) and thermal properties (HDT) of the fibre reinforced PU composites by pultrusion have been studied. The processing parameters investigated include pulling rate (in-line speed), die temperature, filler type and content, and post-cure time and temperature. Results show that the composites possessed various optimum pulling rates at different die temperatures. On the basis of the DSC diagram, the swelling ratio, the mechanical properties and the thermal properties of composites, the optimum die temperature can be determined. It is found that the mechanical and thermal properties increase with filler content for various types of filler. The mechanical and thermal properties increase at a suitable post-cure temperature and time. Furthermore, the properties which decreased due to the degradation of composite materials for a long post-cure time will be discussed. 相似文献