全文获取类型
收费全文 | 239285篇 |
免费 | 21044篇 |
国内免费 | 14723篇 |
专业分类
电工技术 | 34217篇 |
技术理论 | 7篇 |
综合类 | 21275篇 |
化学工业 | 20008篇 |
金属工艺 | 14092篇 |
机械仪表 | 20106篇 |
建筑科学 | 20588篇 |
矿业工程 | 8583篇 |
能源动力 | 8729篇 |
轻工业 | 8657篇 |
水利工程 | 6754篇 |
石油天然气 | 8929篇 |
武器工业 | 3275篇 |
无线电 | 18721篇 |
一般工业技术 | 15442篇 |
冶金工业 | 11896篇 |
原子能技术 | 2468篇 |
自动化技术 | 51305篇 |
出版年
2024年 | 661篇 |
2023年 | 2794篇 |
2022年 | 4848篇 |
2021年 | 6025篇 |
2020年 | 6872篇 |
2019年 | 5423篇 |
2018年 | 4930篇 |
2017年 | 7080篇 |
2016年 | 7781篇 |
2015年 | 8477篇 |
2014年 | 15479篇 |
2013年 | 14050篇 |
2012年 | 17391篇 |
2011年 | 18740篇 |
2010年 | 13827篇 |
2009年 | 14311篇 |
2008年 | 13867篇 |
2007年 | 17261篇 |
2006年 | 15585篇 |
2005年 | 13427篇 |
2004年 | 11323篇 |
2003年 | 9980篇 |
2002年 | 8091篇 |
2001年 | 6824篇 |
2000年 | 5805篇 |
1999年 | 4653篇 |
1998年 | 3611篇 |
1997年 | 3198篇 |
1996年 | 2595篇 |
1995年 | 2078篇 |
1994年 | 1769篇 |
1993年 | 1260篇 |
1992年 | 1070篇 |
1991年 | 844篇 |
1990年 | 638篇 |
1989年 | 511篇 |
1988年 | 382篇 |
1987年 | 224篇 |
1986年 | 190篇 |
1985年 | 173篇 |
1984年 | 211篇 |
1983年 | 160篇 |
1982年 | 139篇 |
1981年 | 95篇 |
1980年 | 77篇 |
1979年 | 79篇 |
1978年 | 49篇 |
1977年 | 53篇 |
1975年 | 14篇 |
1959年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
PC2425破碎机是较为常用的锤式破碎机规格之一,主要用于石灰石的破碎,台时产量800~1 000 t,出料粒度≤70 mm,筛余5%,配套4 500~5 000 t水泥生产线。PC2425破碎机篦条为易损件,由于物料的冲击会导致篦条变形,但其原有的弓形架与篦条型式,更换时很难将篦条从弓形架中抽出,导致更换非常不便。此次改造,用户最初适量降低破碎机的出料粒度,以提高生料磨的产量及降低生料粉磨的电耗,虽然通过调整篦条与锤头的间距及篦条间隙可以达到降低出料粒度的要求。但是为了彻底解决篦条更换困难问题,重新设计了篦架结构。 相似文献
32.
33.
This paper proposes a method for the coordinated control of power factor by means of a multiagent approach. The proposed multiagent system consists of two types of agent: single feeder agent (F_AG) and bus agent (B_AG). In the proposed system, an F_AG plays as an important role, which decides the power factors of all distributed generators by executing the load flow calculations repeatedly. The voltage control strategies are implemented as the class definition of Java into the system. In order to verify the performance of the proposed method, it has been applied to a typical distribution model system. The simulation results show that the system is able to control very violent fluctuation of the demands and the photovoltaic (PV) generations. 相似文献
34.
铁素体钢在低温条件下存在明显的韧脆转变现象。为防止脆断事故的发生,需要确定铁素体钢制压力容器的最低使用温度。针对ASME中的A^D四条冲击豁免曲线,对应地选取了4种材料,基于材料实际的屈服强度和参考温度,按照ASME中豁免曲线的计算方法,计算得到4种材料的最低设计金属温度曲线,并与对应的A^D曲线对比,定量地分析ASME中豁免曲线的保守性。结果表明,ASME中的豁免曲线相对于材料自身的最低设计金属温度曲线保守性较大;韧性相近的材料被划分到不同的豁免曲线,使得韧性富裕量差异较大,对于某些材料,其断裂韧性被低估。 相似文献
35.
Puneet Parmar Nicolas Lopez-Villalobos John T. Tobin Eoin Murphy Frank Buckley Shane V. Crowley Alan L. Kelly Laurence Shalloo 《International Journal of Food Science & Technology》2021,56(5):2415-2422
The objective of this study was to determine the effect of temperature on whole milk density measured at four different temperatures: 5, 10, 15, and 20 °C. A total of ninety-three individual milk samples were collected from morning milking of thirty-two Holstein Friesian dairy cows, of national average genetic merit, once every two weeks over a period of 4 weeks and were assessed by Fourier transform infrared spectroscopy for milk composition analysis. Density of the milk was evaluated using two different analytical methods: a portable density meter DMA35 and a standard desktop model DMA4500M (Anton Paar GmbH, UK). Milk density was analysed with a linear mixed model with the fixed effects of sampling period, temperature and analysis method; triple interaction of sampling period x analysis method x temperature; and the random effect of cow to account for repeated measures. The effect of temperature on milk density (ρ) was also evaluated including temperature (t) as covariate with linear and quadratic effects within each analytic method. The regression equation describing the curvature and density–temperature relationship for the DMA35 instrument was ρ = 1.0338−0.00017T−0.0000122T2 (R2 = 0.64), while it was ρ = 1.0334 + 0.000057T−0.00001T2 (R2 = 0.61) for DMA4500 instrument. The mean density determined with DMA4500 at 5 °C was 1.0334 g cm−3, with corresponding figures of 1.0330, 1.0320 and 1.0305 g cm−3 at 10, 15 and 20 °C, respectively. The milk density values obtained in this study at specific temperatures will help to address any bias in weight–volume calculations and thus may also improve the financial and operational control for the dairy processors in Ireland and internationally. 相似文献
36.
针对臂式斗轮取料机运行中抖动现象,进行了故障分析和排除,并对其液压原理和元件选型进行了优化及改进,为相关液压系统的故障分析和设计选型提供参考。 相似文献
37.
针对南方客户在使用我司客车一段时间后,车身涂层不同程度出现了起泡的质量问题,进行了现场查看,发现起泡位置在车身左右侧蒙皮,且发生在涂层最底层。初步分析原因是热镀锌板+阴极电泳漆 +原子灰三者之间配套存在问题,通过热镀锌板 +阴极电泳漆 +原子灰三者之间的耐高温 80 ℃配套试验,以及室外曝晒试验,得出镀锌板表面是否钝化、电泳漆膜致密程度和原子灰苯乙烯含量是造成涂层底层起泡的主要原因。为了控制涂层起泡问题,重新修订了我司原子灰、镀锌板、电泳漆的技术标准以及部分工艺文件。 相似文献
38.
AbstractDifferent drying methods (spray drying (SD), vacuum drying (VD), microwave vacuum drying (MVD), and infrared vacuum drying (IFVD)) were applied in order to compare the hygroscopicity behavior of chicken powders. The hygroscopicity curves and glass transition temperature were used to evaluate the influence of ambient humidity and temperature on moisture absorption of powders. The results showed that the chicken powder dried by MVD had the lowest moisture absorption, followed by IFVD, VD, and SD. The hygroscopicity of SD chicken powders was different from other three kinds of chicken powders due to the physical properties of particles and the changes of protein secondary structure as detected by the Fourier transform-infrared spectrometer. For the three vacuum drying methods, the difference of protein secondary structure was the main reason of differences in hygroscopicity. Although MVD chicken powders were slightly inferior to SD chicken powders in taste, MVD chicken powders were the best in terms of smell and color as suggested by instrumental sensory parameter evaluations. It was found that MVD had a positive effect on reducing moisture absorption and maintaining sensory quality of chicken powders. 相似文献
39.
40.